Here is the compression gauge I recommend: www.howtomotorcyclerepair.com/compressiongauge GJ pass/fail thread: www.garagejournal.com/forum/showthread.php?t=27192
Even those thread adapters will add volume to the cylinder so don’t use a thread adapter on anything hand held like a blower, chainsaw, grass trimmer, etc. an adapter will drop the compression in half. It’s crazy how big a difference it makes.
I was tripping out. I just bought a used ski so I picked this up to check compression and I was getting about 70psi. Was driving me insane!! Thank you!
For best results with Harbor Freight tester. 1) Remove from box and throw tester in trash. To save time just throw $29 in trash. Then buy a quality tester.
i have a $29 compression tester on amazon and it has the schrader valve at the end by the spark plug. even if I get 8 or 10 uses out of it i dont care lol
I have the same problem. I thought my engine was bad, but before I come up replacing my engine, I check if the gauge has some problem. I started checking review of this product then I found you. I really appreciate for this information and saving my engine from replacing it.
I've been having a misfire on cylinder #1 on my 96 Volvo 850. I bought one of these gauges and it showed 50psi below where it should be. I went into depression thinking I have to rebuild the engine!!! I checked the other cylinders and it showed the same on all jugs. I couldn't understand, since the car doesn't burn oil or smoke and otherwise runs great. This high pressure Turbo couldn't even get out of my driveway with a compression reading so low. Your video is a life saver. I can't believe how they can mass produce this product without testing it first! I will send you a donation once I get my job back after this Corona hysteria is over.
Agree. I have an old 6 plus years harbor freight tester and just bought a new one. The old one has the valve at the end of the hose, while the new one only has the valve at the gauge. The new one reads 60 psi on my two outboards, while my old tester reads 110-120 psi. I exchanged the new one for another one and it reads the same 60 psi. I will be returning it tomorrow.
i just bought a compression tester on amazon and it also has the schrader valve at the end of the hose by the spark plug hole. havent used it yet but in either it should work just fine
This video is spot on. I had 92 psi when I should be having 177 at the minimum. I hooked up a different gauge to the stock harbor freight hose and I was losing all compression and not getting a reading because of the hose. I tried autozone and they don’t have the proper fittings for small engines, so I returned that. I’m going to buy a otc one soon and retest. Thanks for the video
Holy crap. I just checked my quadracer 250 and was thinking about spending $700 to rebuild the entire engine. This gauge told me 90psi. I’m hoping it’s actually a lot more than that. Maybe my issue lies somewhere else. Awesome video. Thank you
Thanks for this. I did some rough math and you can compensate for the volume of air in the hose. Its about 20" long, and maybe 1/8" hole. Math math says that is about 4CC of volume (ball park) My car (1.6L Mazda Miata), with 9.4:1 compression, is 42.5 CC minimum volume. So in my case, the hose volume made the pressure read about 9% low. The error will be worse on small engines, and engines with high compression.
Ad a Schrader valve in the end of the hose and it will work thats the only problem with the harbor freight compression tester I fixed mine that way cost my 5 bucks to fix it
All I know is that I used a gauge from Harbor Freight and O'Reilly's and both of them sucked . Dug out my old Snap On and it still works after 30+ years .
This Harbor Freight Compression Test Kit is garbage!!! The video is 100% correct and does a great job of explaining why the gauge readings are incorrect. I used it on a 4 stroke 2 cylinder motorcycle engine that I just completely rebuilt with all new parts - pistons, rings, bearings and valve job etc etc. The compression test with the harbor Freight Test Kit was was 115 lbs. which was way low for a newly rebuilt engine. I was bummed! I used it on another newly rebuilt motorcycle engine and it was also low. After the second test I started to figure something else was wrong. I found several items on the web describing low compression readings with the Harbor Freight Gauge. I purchased a new gauge made in America by a well known company. Surprise Surprise! My reading on the engine was not 115 lbs but 175 lbs! Thank you for spreading the word!
You should probably mention "Pittsburgh" in your title. Harbor Freight also sells one under the Maddox name which has good reviews. Amazon sells the Pittsburgh version under a boatload of different brand names for as little as $10.99 if you want to try and put a Schrader valve in the hose.
The flaw is the Schrader valve is at the end of the hose.. Mine is at the end of the hose. You take the two medal hold to the hole adapters they are shorter and read the correct pressure. They are also closer to the gauge and the volume inside is smaller.
I just did a top end on my bike because of this guage. It still read a little over 90psi with new top end!! I bought a different one and it reads 175 psi now.
I see, make sense but... Then again the space in the hose will have to be filled up regardless of the valve's location, to get the most accurate reading the gauge would have to be at the exact point of the valve's evacuation port. But obviously I'd kinda hard to do, so I believe that the good quality testers are calibrated to compensate for that extra air and the cheap ones don't, and I believe that's why transducers are really accurate because essentially their sensing part is close to the valve's evacuation side.
Actually, if the valve is near the head, when you crank the engine multiple times, the pressure will build and hold in the gauge and hose so that. after 10-20 cycles the hose is at same pressure as the head until you depress the valve and release the pressure.
Just bought a used sled, pulled out the hf comp tester while doing maintenance. Wtf??? 90 psi. I've had low readings on other engines in the past with this tester and was already thanking the tester was junk. Thank you for confirming my suspicions 👌
Possibly more to do with the hose being too narrow to see the peak pressure at the gauge end of the hose where the valve is. Since the peak pressure is only present for a very brief moment during TDC dwell the narrow hose is having a damping effect on the peak value at the gauge end where the valve is, hence the very low averaged reading. The proper one with valve at the plug end can see the full peak. That said, primary purpose of the compression gauge is readings are taken as relative to the readings of other cylinders to compare so absolute accuracy is not as critical as repeat-ability. But you are right that is a dodgy gauge and better buying one with a valve at the plug end.
ooooohhhh now i get it. I agree, but never thought about it. Thank you and I should have seen this. IF and I do not know IF the device has a 1 way valve at cylinder end, then reading is good. I do not see a 1 way valve to hold pressure.
holy shit. i luckily moved this gauge over to my pressure washer that works fine, same 30psi, my little scooter i was working on same psi 30. after a moped forum told me check the gauge i did it,sure enough gauge dont work on small engines
That's so weird! I got a chinese kit that looks just like the Harbor Freight kit, it's just in a red box and the coating has a copper/golden shine. It got a "one-direction" valve at the end, where you fit the adapter, works fine enough for hobby use
thats exactly the one i bought. its an 8 pc compression test kit. red box. came with 2 rubber metal attachments in case you dont have the right thread. should work good for small engine repairs 👍
You are 100% correct, but as it turns out there are two versions of the tester the newer one that I bought did not have a valve and my car measured around 125 psi (new motor) the a friend of mine found an older (harbor freight again) tester which had the valve at the edge and my engine showed on average 190 psi (which seems correct).
MatthewMCRepair I just went to HF yesterday (3/2/19) to replace my gauge with the one my friend has (which works) and as it turns out that was their old model (the one that worked). That model has been replaced by the one I have that doesn’t work (as you mention on this video). To summarize as of 3/2/19 harbor freight doesn’t have a properly working engine compression tester - thank you for your video, you saved me from a lot of frustration!
Yeah completely true! Have a Pittsburgh tester from harbor freight and my bike was smoking and for shits and giggles I hooked it up too my bike. It read 35 psi so I figured it needed a whole new top end I completely rebuilt it right it had amazing compression and it still read 35 and that's when I new it was junk.
ATTENTION: Here are results from compression tests I did a couple days ago with a brand new harbor freight gauge and a professional gauge. Harbor Freight: 131, 133, 132, 131, 134, 134 Professional Gauge: 169, 168, 130, 151, 160, 160 While it did cool down about 10 degrees before I tested it again with the legit tool, the Harbor freight tester was still completely oblivious to the fact that cylinders 3 and 4 were waaay down on compression. Ill be using the attachment included in the harbor freight tester to do a leak down test before I send that POS back lol.
Good vid. I bought the Harbor Freight one and took it back once I realized this. It was built totally wrong. The placement of the 2 cent valve made the whole thing completely useless!
has nothing to do with a leak down test,or any other test ,, this only applies to correct psi pressure held in the cylinder.what did you expect? a 200 dollar unit for 20 bucks? lol
my chainsaw reads 120 psi with the actron tester you recommended, the harbor freight gauge read 30 psi. that thing is complete junk. return it if you can. if you can't just throw it away and get the actron on amazon or get one from a matco tool truck or something.
Thanks for the heads-up.The Actron has a better desing certainly however I wouldn't personally recommend this brand. I have a fuel pressure tester from them and the internal valves, or o-rings failed after about 3 yrs. It hadn't been used much though, just occassionally on 3-5 cars at all.
You probably have an older version of the tester because mine has the valve at the end of the hose and the compression read between 185 to 190 on a Volkswagen engine.
Buy any reputable compression tester that has an assortment of adapters and the valve is at the gauge, not the the hose end. For example, OTC makes the specialty tools for Ford dealerships. They're the same as the HF gauge. Common sense tells us that we're measuring PRESSURE, not volume of the chamber. And NO gauge/hose setup stays pressurized. So you have to build pressure regardless. BTW, you forgot your affiliate link in the description.
I disagree. The valve has to be located at top of combustion chamber in order to get same PSI per service manuals. If you increase combustion chamber VOLUME, the PRESSURE will be less.
@@HTMR whether the valve is at the bottom of the hose or the gauge, you still have to pressurize both, in EVERY setup. So, no matter what, you will be adding that volume.
@@ToolsOutsideTheBox That is true, however, if given a swept volume of air (cylinder/piston), if you squeeze it into 2 different sized chambers, you will get a different PSI reading (compression ratio). The hose length between valve and gauge is simply how many kicks/crank time will it take to fill and stop climbing. I encourage you to buy both gauges like I did and test for yourself.
TheBCSledder This is an interesting issue and discussion. It’s a known scientific rule that PV=nRT, which means that pressure is impacted by volume. Pressure would equal nRT/V (moles, gas constant, temperature/ volume) respectively.. I believe there is some merit to this valve/hose issue brought up, but I also question why other compression testers (with similar designs) work? I guess I’m gonna have to get a quality “known” unit to compare with my Pittsburgh tester. Now, obviously I’m here because I already had doubts, so I will take the HF unit back and buy a more reputable tool. Thanks for the advice and theory. I would like a better explanation of what exactly the valve is.. ie which one and where etc.
I should have seen this before I purchased it and used it to test a chainsaw that I rebuilt the entire motor for because it was reading only 30psi. Surprising thing to me after the fact is that it continued to read 30 psi even after the rebuild. The thing runs great now with no apparent issue. I'm scratching my head why a chainsaw with 30 psi runs like a brand new saw. And here it is. The damn tester is a piece of garbage. Going to try and return it
Thanks for explaining this. I was wondering why my HF gauge is low by 25 psi. I bought it over a year ago wish I brought it back then. Now I'll guess its too late, Oh well.
Not true. The engine is only capable of "pumping" so much air. If you had that amount of air squeezed in 1 liter or 2 liters, wouldn't the pressure be different??? Don't believe me? Buy the HF & any proper gauge and test it yourself.
You have to get 100 psi to the gauge so it doesn't matter where that valve is placed. Your argument about volume would only relate to the hose length not valve placement.
@@bgarcia856 You are looking at the issue wrong. With the valve at the end of the hose, the engine is cumulatively preasurizing the line, building preasure inside the whole guage and hose assembly with every stroke of the piston. With the valve at the guage however, the preasure from each stroke of the piston which must fill the hose to reach the guage is being lost, meaning the piston must repressurize the line with each stroke, creating a lower preassure reading at the guage.
@@TheBCSledder so easier said. You're saying the displacement is already exhausting before it hits the valve? That would have to be a tiny displacement engine.
Different in what gas they measure, but a Refrigeration manifold with gauges and hoses has no Schrader valve and they measure accurately if you bleed the hose at the gauge
@@HTMR - There is a book with that name - it is funny as hell - on amazon I believe - definitely worth a look - Of course I am lefty - have a gudun - It tells crazy things like the king who built castle staircases with the opposite twist so he could fight with a sword in his left hand
@@HTMR Different side of the brain controls thought - whole different way of looking at things - I am sure you already know this - and thanks about that Schroeder valve thing - kept me from buying it
The POS cost me fortune! I was wondering why I am having such low results when my outboard motor is running great. Thought the motor was shot. Sold it cheap
Late to the party on this, but as stated the valve has nothing to do with compression. It just releases pressure for tool removal. In either case the whole line is open. If it wasn't the line couldn't be evacuated unless through the threads. Imagine this, a small electric pool toy pump that can only generate 5psi will do it with any size (volume) blow up item. Yes the larger ones will take longer. The gauge is prob the culprit. (Or the quick connect is leaking) Simply put, a high quality gauge will outperform a low quality one. Put your Snapon gauge on the HF hose and see! If one hose is longer, it might be a single psi lower, but that's it I do like the valve close to the end though, so it doesn't trip when swinging around in the test.
I'm afraid your wrong. Go look up a compression ratio formula. What happens when you add more head volume? Because that is what you are doing with a improper gauge.
So if you know the reading's at half of what it should be just calculate that mistake in your test. Like I do with my torque wrench. Improvise. Adapt. Overcome
So there is nothing wrong with the gauge itself. RIGHT? You can easily tap the fitting for a schrader valve. It's just a schrader valve. Very simple. Just saying. Also I've checked the Harbor Freight gauge against my old Snap on gauge. The gauges read exactly the same. It's just a simple schrader valve guys. I think I just bought a pack of 5 from Walmart for a couple of dollars...
If the compression tester measures psi not volume right? If that is true then it won’t matter as long as the tube is pressurized the same as the cylinder. So maybe give it more time to fill the tune completely.
i just chek with this presure item my xtz 750 kilidre nuber one 75 psi and kilidre nuber 2 105 psi in the manual normal is 135 psi i thing the intrument not ok can start engine with 75 psi????? my motor working ok and start...
same problem drove me nuts up till i found this video thanks for sharing this couldnt get more than a 40lb reading on 4 machines one i really wanted and didnt buy because of this gauge lol
The one thing you failed to talk about was with small engines, you won't get accurate readings unless you have the throttle open on the carb. Unlike a car, motorcycles and outboards generally have a single intake manifold for each carb. If you have the throttle closed, you won't be sucking in as much air to compress. Take a look at the difference. People commenting that they get low readings should try it also. I have seen a difference of 40 PSI from checking compression with open and closed throttle. The schrader valve location has little to do with this.
I bought a harbor freight gauge and it was reading 90psi on a brand new top end and went to my buddies house and used his snap on gauge and it said 165 psi. I took that shit back lol
Had just rebuilt my cr250 put this gauge on and read 105 compression. I chanced it on not sending the cylinder off ended checking it with craftsman gauge. Read 195! Happy i double checked this gauge is junk!
HF items are good only if you can modify them. They are far cheaper than competition, so the reason we buy them. Don't buy if you can't modify. And I guess you should be able to modify yours, changing the location of scherder or at least calibrate your current one, with a decent one and then make another video that might have a lot more to learn. Any ways, thanks for pointing to this flaw.
See here's the thing, I just redid the top end (actually completely redid bike) on an old KX80 and its been at 55PSI with my new Harbor Freight compression tester since the day I finished it. In fact it's holding 55PSI as we speak as I speak for the past 10 minutes plus. I thought you were correct because I've heard other people say these testers are whacked. And you guys are right this tester has got to be whack. But you can't be right about where that release valve is I don't know whether it is a schrader valve or not. Because it doesn't matter how many times you kick it, if I had a limited number of kicks yes I would see your point as to volume playing into the equation, As I may kick it as many times as I like it's just going to build pressure I mean if the bike holds 220 PSI or 55PSI haha that is saying mine does it doesn't matter I can kick it as many times as I want it will build PSI until it stops building PSI. So volume no matter try again.
@@HTMR dude even said that the one u linked had release valve at same end. In that size hose you have to go 100' to lose 50 psi and that's with a constant regulated pressure from another source. I'm the source of the pressure and I can continually kick it to build whatever pressure I want; it has a plug in it and I kick until I received the pressure that it will hold before leaking or rupturing. If I could only kick it 5 times I'd be regulated, which I am not, therefore I could kick it until I receive the pressure that it will hold.
And thought this may help... You guys are making one major error: 10 -1 compression would be 14.7 psi (atmspheric0 plus 10 X 14.7 or 147 plus 14.7=152. NO small engine has this compression ratio because it would be very difficult to pull start it. Most of the smaller horsepower engines use less than 90 PSI. And, for my figure of .034, I used 3.1416 for pi and then rounded up from 0338 to 034. But embellishing what I said in my original reply: The gauges we buy to test are accurate probably in the 2-5% range and are usually graduated in 2 PSI increments. Any difference the hose length would make is well below the level of inaccuracy we would achieve between reading errors and gauge error. And, to test any engine for compression ratio. we think we have a problem: Thus, Compression ratio will either be high or low. We don't care about splitting hairs over a pound.
I had same problem with this HF 62622 tester. It read 70 PSI on my outboard engine. I used an old craftsman compression tester without a house on it and it reads 125 PSI. I returned the 62622 Pittsburg compression tester to Harbor Freight and exchanged it for another and got the exact same reading of 70 psi. I took this one back and they won't refund my money back to my credit card. They said that they could only give me a gift card. I can't use their gift card to purchase a good compression tester somewhere else. WTF. It ain't my fault.
Great video,,Matt I unfortunately watched this video too late.,I kinda had a feeling it was off 10 kicks on my cr and it only built 100 psi... absolutely seemed low
Hard to purchase at harbor freight based on reviews. Harbor freight ABSOLUTELY deep sixes reviews they don't like. They have rejected many of my two and three star reviews. Ever notice that all of their products have 4.2 ⭐ reviews?
Thank you! My new 1990 Mustang 5.0 engine has 600 miles on it. The Harbor Freight compression tester showed 120psi only. I'll return it tomorrow. Engine runs strong and if my engine would only have only 120psi compression in it than it would be like an engine with 3000000 miles on it.
Same problem here. I bought the HB compression tester and had a similar experience. This was the $26 kit which does not have the valve on the hose end. It read max pressure of 120psi. I rented the autozone gauge and got about 140 across all cylinders with less than 2% variance.
AZ Model was 27138. I ultimately purchased a nice Craftsman gauge from sears for about $70. It gave me about the same reading as the AZ gauge, average was about 140ish across the board.
@@hf1cadenas well that's good. just purchased a good looking Toro Personal Pace mower that probably had gas left in it too long. but i am gonna use my new 8 pc compression tester on it for the first use 👌 excited to see if its accurate at all
Just remember that compression has to be tested with engine hot as a cold engine will skew your results. Let the engine warm up to normal operating temp then test and be sure the butterfly valve at the carb is wide open as well for maximum air ingestion. Wear gloves unless you want burnt knuckles.
Thanks for confirming my suspicions. Couldn’t find my tester so picked up this one. No better than 75 psi on three different engines. One cylinder was half that, so gauge is still useful to me for finding weak cylinder.
Tbh while your probably right, 99% of the time compression isn’t going to be down over all the cylinders and most of the time your just trying to find a problem. I’m using this right now and just making sure that all the cylinders measure the same or within 10psi of each other. So in my case I’m looking for precision over accuracy.
Yeah well you need to know if there will be enough compression for it to even run. Also, all compression specs in service manual base it off a tool with Schrader valve.
The gauge you have in the link is not the same one in your video and some one asked where the Schrader valve was and they said it's in the bottom of the gauge not the end of the hose like yours so apparently they changed the design on it so you might want to remove the link since it's not what your advertising for them.
that whole "space in the hose before the schrader valve" is a flawed theory. On your compression tester the air needs to travel the length of your hose also before it reaches the gauge so what's the difference?
The volume of air that the tester hose can handle is so minimal. You would never notice a difference. You definitely have a defective gauge or something.
Thanks for confirming my suspicions. Sitting here beating my head against the wall (look up insanity), not understanding why my reading isn’t making sense. Usually you can fair okay with HF, just amazed this tool is this useless.
SO THATS WHY MY LEAF BLOWER AND PUSH MOWER (WHICH RUN) ONLY READ 25 PSI. FML. Wish I saw this vid earlier. Returning this POS tommorow. Not to mention the reason I bought it was for another non running leaf blower, which I tore apart thinking had low compression, but only had a faulty carb. WTF.
I'd like to know where to buy the compression tester you recommend. My cheap tablet doesn't show pop ups so I don't know where to buy it. Could you please put the information in your description?
Quick question: How about the length of the thread on the tester? Jeff from Slavens says that if using a 3/4" spark plug (Type E), the thread length of the compression tester should be equal to the spark plug itself. The shitty tester from HF (that I just bought, of course!) and yours seem to have a shorter threading; not as long as a spark plug. Is that difference, despite minimal, enough to not give the proper reading?
I used the HF Compression tester the other day and got a reading of 75. I was loosing my mind knowing the motor only has 5k miles on it. granted its an 83. I used the older HF Model compression tester, so maybe thats the problem, trying to get the motor started. I will deff get a new one from somewhere else and test it again. Great video thank you!
@@HTMR math is not needed! The gauge reads what it reads and it doesn't care where the valve is! Either way the hose has to also be filled before it reaches the gauge! If you took the valve out the reading would be the same! It just stops the air from escaping! PSI is the same, the volume of air is also the same no matter where that valve is! It's no more than a check valve I'm not arguing I'm just saying! Think of a tire! If read my air pressure on a regular tire and it reads xxx then I put one of those long valve extensions on like a semi truck has on the inside tire the psi is going to be the same even though the valve is now relocated in a longer stem tube!
Here is the compression gauge I recommend: www.howtomotorcyclerepair.com/compressiongauge
GJ pass/fail thread: www.garagejournal.com/forum/showthread.php?t=27192
The one you linked is exactly same design. One shrader valve at top into gauge only.
Just got same one and it's either not the same or Amazon sending their "similar" product.
Even those thread adapters will add volume to the cylinder so don’t use a thread adapter on anything hand held like a blower, chainsaw, grass trimmer, etc. an adapter will drop the compression in half. It’s crazy how big a difference it makes.
I was tripping out. I just bought a used ski so I picked this up to check compression and I was getting about 70psi.
Was driving me insane!! Thank you!
Literally the same here. Both my skis were showing 80 psi, but they ran fine. I was almost gonna start tearing them apart to rebuild them.
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For best results with Harbor Freight tester. 1) Remove from box and throw tester in trash. To save time just throw $29 in trash. Then buy a quality tester.
i have a $29 compression tester on amazon and it has the schrader valve at the end by the spark plug. even if I get 8 or 10 uses out of it i dont care lol
i may buy a matco next though
I have the same problem. I thought my engine was bad, but before I come up replacing my engine, I check if the gauge has some problem. I started checking review of this product then I found you. I really appreciate for this information and saving my engine from replacing it.
I've been having a misfire on cylinder #1 on my 96 Volvo 850. I bought one of these gauges and it showed 50psi below where it should be. I went into depression thinking I have to rebuild the engine!!! I checked the other cylinders and it showed the same on all jugs. I couldn't understand, since the car doesn't burn oil or smoke and otherwise runs great. This high pressure Turbo couldn't even get out of my driveway with a compression reading so low. Your video is a life saver. I can't believe how they can mass produce this product without testing it first! I will send you a donation once I get my job back after this Corona hysteria is over.
Agree. I have an old 6 plus years harbor freight tester and just bought a new one. The old one has the valve at the end of the hose, while the new one only has the valve at the gauge. The new one reads 60 psi on my two outboards, while my old tester reads 110-120 psi. I exchanged the new one for another one and it reads the same 60 psi. I will be returning it tomorrow.
Good info thanks.
I have a harbor freight compression tester and the Schrader valve is right at the end of the hose.
Mine does not.
i just bought a compression tester on amazon and it also has the schrader valve at the end of the hose by the spark plug hole. havent used it yet but in either it should work just fine
This video is spot on. I had 92 psi when I should be having 177 at the minimum. I hooked up a different gauge to the stock harbor freight hose and I was losing all compression and not getting a reading because of the hose. I tried autozone and they don’t have the proper fittings for small engines, so I returned that. I’m going to buy a otc one soon and retest. Thanks for the video
Buy this one: www.howtomotorcyclerepair.com/compressiongauge
Holy crap. I just checked my quadracer 250 and was thinking about spending $700 to rebuild the entire engine. This gauge told me 90psi. I’m hoping it’s actually a lot more than that. Maybe my issue lies somewhere else. Awesome video. Thank you
Thanks for this.
I did some rough math and you can compensate for the volume of air in the hose. Its about 20" long, and maybe 1/8" hole. Math math says that is about 4CC of volume (ball park)
My car (1.6L Mazda Miata), with 9.4:1 compression, is 42.5 CC minimum volume. So in my case, the hose volume made the pressure read about 9% low.
The error will be worse on small engines, and engines with high compression.
Holy math , your a pretty smart fella
Ad a Schrader valve in the end of the hose and it will work thats the only problem with the harbor freight compression tester I fixed mine that way cost my 5 bucks to fix it
All I know is that I used a gauge from Harbor Freight and O'Reilly's and both of them sucked .
Dug out my old Snap On and it still works after 30+ years .
This Harbor Freight Compression Test Kit is garbage!!! The video is 100% correct and does a great job of explaining why the gauge readings are incorrect.
I used it on a 4 stroke 2 cylinder motorcycle engine that I just completely rebuilt with all new parts - pistons, rings, bearings and valve job etc etc. The compression test with the harbor Freight Test Kit was was 115 lbs. which was way low for a newly rebuilt engine. I was bummed! I used it on another newly rebuilt motorcycle engine and it was also low.
After the second test I started to figure something else was wrong. I found several items on the web describing low compression readings with the Harbor Freight Gauge.
I purchased a new gauge made in America by a well known company. Surprise Surprise! My reading on the engine was not 115 lbs but 175 lbs!
Thank you for spreading the word!
I almost rebuilt my sled because of a brand new out of box hf comp tester. Borrowed an otc tester and was 40psi difference lol
You should probably mention "Pittsburgh" in your title. Harbor Freight also sells one under the Maddox name which has good reviews. Amazon sells the Pittsburgh version under a boatload of different brand names for as little as $10.99 if you want to try and put a Schrader valve in the hose.
I made a huge mistake before watching this and bought a compression tester from harbor freight
The flaw is the Schrader valve is at the end of the hose.. Mine is at the end of the hose. You take the two medal hold to the hole adapters they are shorter and read the correct pressure. They are also closer to the gauge and the volume inside is smaller.
I just did a top end on my bike because of this guage. It still read a little over 90psi with new top end!! I bought a different one and it reads 175 psi now.
I see, make sense but... Then again the space in the hose will have to be filled up regardless of the valve's location, to get the most accurate reading the gauge would have to be at the exact point of the valve's evacuation port. But obviously I'd kinda hard to do, so I believe that the good quality testers are calibrated to compensate for that extra air and the cheap ones don't, and I believe that's why transducers are really accurate because essentially their sensing part is close to the valve's evacuation side.
Actually, if the valve is near the head, when you crank the engine multiple times, the pressure will build and hold in the gauge and hose so that. after 10-20 cycles the hose is at same pressure as the head until you depress the valve and release the pressure.
Just bought a used sled, pulled out the hf comp tester while doing maintenance. Wtf??? 90 psi. I've had low readings on other engines in the past with this tester and was already thanking the tester was junk. Thank you for confirming my suspicions 👌
I just tested my 1990 Suzuki rm125 engine with this tester and it read 30psi yet the engine ran fine. I wish I saw this before I bought it.
Possibly more to do with the hose being too narrow to see the peak pressure at the gauge end of the hose where the valve is.
Since the peak pressure is only present for a very brief moment during TDC dwell the narrow hose is having a damping effect on the peak value at the gauge end where the valve is, hence the very low averaged reading.
The proper one with valve at the plug end can see the full peak.
That said, primary purpose of the compression gauge is readings are taken as relative to the readings of other cylinders to compare so absolute accuracy is not as critical as repeat-ability.
But you are right that is a dodgy gauge and better buying one with a valve at the plug end.
ooooohhhh now i get it. I agree, but never thought about it. Thank you and I should have seen this. IF and I do not know IF the device has a 1 way valve at cylinder end, then reading is good. I do not see a 1 way valve to hold pressure.
1:24 For some reason the sound of the marker reminds me of Bob Ross doing a painting.
Yes! Returning mine today. I knew it was the gauge because all my readings were exactly the same - 60.
holy shit. i luckily moved this gauge over to my pressure washer that works fine, same 30psi, my little scooter i was working on same psi 30. after a moped forum told me check the gauge i did it,sure enough gauge dont work on small engines
That's so weird! I got a chinese kit that looks just like the Harbor Freight kit, it's just in a red box and the coating has a copper/golden shine. It got a "one-direction" valve at the end, where you fit the adapter, works fine enough for hobby use
thats exactly the one i bought. its an 8 pc compression test kit. red box. came with 2 rubber metal attachments in case you dont have the right thread. should work good for small engine repairs 👍
I got 30 psi on my snowblower and 70 psi on all 3 of our snowmobiles, one with a top end rebuild just this year. What a waste of money
Thank you!!! This was driving me crazy. My engine seem to run strong but 50% like you said.
You are 100% correct, but as it turns out there are two versions of the tester the newer one that I bought did not have a valve and my car measured around 125 psi (new motor) the a friend of mine found an older (harbor freight again) tester which had the valve at the edge and my engine showed on average 190 psi (which seems correct).
Good to know.
MatthewMCRepair I just went to HF yesterday (3/2/19) to replace my gauge with the one my friend has (which works) and as it turns out that was their old model (the one that worked). That model has been replaced by the one I have that doesn’t work (as you mention on this video).
To summarize as of 3/2/19 harbor freight doesn’t have a properly working engine compression tester - thank you for your video, you saved me from a lot of frustration!
Yeah completely true! Have a Pittsburgh tester from harbor freight and my bike was smoking and for shits and giggles I hooked it up too my bike. It read 35 psi so I figured it needed a whole new top end I completely rebuilt it right it had amazing compression and it still read 35 and that's when I new it was junk.
ATTENTION:
Here are results from compression tests I did a couple days ago with a brand new harbor freight gauge and a professional gauge.
Harbor Freight: 131, 133, 132, 131, 134, 134
Professional Gauge: 169, 168, 130, 151, 160, 160
While it did cool down about 10 degrees before I tested it again with the legit tool, the Harbor freight tester was still completely oblivious to the fact that cylinders 3 and 4 were waaay down on compression. Ill be using the attachment included in the harbor freight tester to do a leak down test before I send that POS back lol.
The Maddox harbor freight Deluxe compression worked spot on for me
Good vid. I bought the Harbor Freight one and took it back once I realized this. It was built totally wrong. The placement of the 2 cent valve made the whole thing completely useless!
Yup!
has nothing to do with a leak down test,or any other test ,, this only applies to correct psi pressure held in the cylinder.what did you expect? a 200 dollar unit for 20 bucks? lol
my chainsaw reads 120 psi with the actron tester you recommended, the harbor freight gauge read 30 psi. that thing is complete junk. return it if you can. if you can't just throw it away and get the actron on amazon or get one from a matco tool truck or something.
Thanks for the heads-up.The Actron has a better desing certainly however I wouldn't personally recommend this brand. I have a fuel pressure tester from them and the internal valves, or o-rings failed after about 3 yrs. It hadn't been used much though, just occassionally on 3-5 cars at all.
My tester is still going strong. Thanks for the heads up.
You probably have an older version of the tester because mine has the valve at the end of the hose and the compression read between 185 to 190 on a Volkswagen engine.
Glad they fixed it.
Buy any reputable compression tester that has an assortment of adapters and the valve is at the gauge, not the the hose end. For example, OTC makes the specialty tools for Ford dealerships. They're the same as the HF gauge.
Common sense tells us that we're measuring PRESSURE, not volume of the chamber.
And NO gauge/hose setup stays pressurized. So you have to build pressure regardless.
BTW, you forgot your affiliate link in the description.
I disagree. The valve has to be located at top of combustion chamber in order to get same PSI per service manuals. If you increase combustion chamber VOLUME, the PRESSURE will be less.
@@HTMR whether the valve is at the bottom of the hose or the gauge, you still have to pressurize both, in EVERY setup. So, no matter what, you will be adding that volume.
@@ToolsOutsideTheBox That is true, however, if given a swept volume of air (cylinder/piston), if you squeeze it into 2 different sized chambers, you will get a different PSI reading (compression ratio). The hose length between valve and gauge is simply how many kicks/crank time will it take to fill and stop climbing. I encourage you to buy both gauges like I did and test for yourself.
Volume effects pressure so your argument is invalid.
TheBCSledder This is an interesting issue and discussion. It’s a known scientific rule that PV=nRT, which means that pressure is impacted by volume. Pressure would equal nRT/V (moles, gas constant, temperature/ volume) respectively.. I believe there is some merit to this valve/hose issue brought up, but I also question why other compression testers (with similar designs) work? I guess I’m gonna have to get a quality “known” unit to compare with my Pittsburgh tester. Now, obviously I’m here because I already had doubts, so I will take the HF unit back and buy a more reputable tool. Thanks for the advice and theory. I would like a better explanation of what exactly the valve is.. ie which one and where etc.
I should have seen this before I purchased it and used it to test a chainsaw that I rebuilt the entire motor for because it was reading only 30psi. Surprising thing to me after the fact is that it continued to read 30 psi even after the rebuild. The thing runs great now with no apparent issue. I'm scratching my head why a chainsaw with 30 psi runs like a brand new saw. And here it is. The damn tester is a piece of garbage. Going to try and return it
Works for me .
Thanks for explaining this. I was wondering why my HF gauge is low by 25 psi. I bought it over a year ago wish I brought it back then. Now I'll guess its too late, Oh well.
No problem. The bigger the engine displacement, the less it will be off.
I add to this claim, I was getting 120 psi on a high compression motor that should be near 200. Got a quality guage and got 195 psi on same motor.
Regardless of where the one way valve is you need to pressurize the whole length of the hose! One or two more cranks and you get a correct reading.
Not true. The engine is only capable of "pumping" so much air. If you had that amount of air squeezed in 1 liter or 2 liters, wouldn't the pressure be different???
Don't believe me? Buy the HF & any proper gauge and test it yourself.
If the valve is at the gauge, the air still needs to flow thru the tube to get there.
You have to get 100 psi to the gauge so it doesn't matter where that valve is placed. Your argument about volume would only relate to the hose length not valve placement.
@@bgarcia856 You are looking at the issue wrong. With the valve at the end of the hose, the engine is cumulatively preasurizing the line, building preasure inside the whole guage and hose assembly with every stroke of the piston. With the valve at the guage however, the preasure from each stroke of the piston which must fill the hose to reach the guage is being lost, meaning the piston must repressurize the line with each stroke, creating a lower preassure reading at the guage.
@@TheBCSledder so easier said. You're saying the displacement is already exhausting before it hits the valve? That would have to be a tiny displacement engine.
The newest version of harbor freights kit comes with the Valves where there supposed to be located.
Good to know thanks.
Holy shit you were right went to AZ picked one up wayyyy different results not to mention harbor freight charges a restocking fee for the garbage
Different in what gas they measure, but a Refrigeration manifold with gauges and hoses has no Schrader valve and they measure accurately if you bleed the hose at the gauge
The natural born superiority of the left hander - well done
Yup :)
@@HTMR - There is a book with that name - it is funny as hell - on amazon I believe - definitely worth a look - Of course I am lefty - have a gudun - It tells crazy things like the king who built castle staircases with the opposite twist so he could fight with a sword in his left hand
@@tonyswhirl I see that book, I'll have to check it out LOL.
@@HTMR Different side of the brain controls thought - whole different way of looking at things - I am sure you already know this - and thanks about that Schroeder valve thing - kept me from buying it
@@tonyswhirl Yup lefties are different. I'm an engineer and most of my colleagues are lefties as well.
The POS cost me fortune! I was wondering why I am having such low results when my outboard motor is running great. Thought the motor was shot. Sold it cheap
That sucks.
@@HTMR so if it was running great, why sell it?
Late to the party on this, but as stated the valve has nothing to do with compression. It just releases pressure for tool removal. In either case the whole line is open. If it wasn't the line couldn't be evacuated unless through the threads. Imagine this, a small electric pool toy pump that can only generate 5psi will do it with any size (volume) blow up item. Yes the larger ones will take longer.
The gauge is prob the culprit. (Or the quick connect is leaking) Simply put, a high quality gauge will outperform a low quality one. Put your Snapon gauge on the HF hose and see! If one hose is longer, it might be a single psi lower, but that's it
I do like the valve close to the end though, so it doesn't trip when swinging around in the test.
I'm afraid your wrong. Go look up a compression ratio formula. What happens when you add more head volume? Because that is what you are doing with a improper gauge.
So if you know the reading's at half of what it should be just calculate that mistake in your test. Like I do with my torque wrench. Improvise. Adapt. Overcome
Rather return it and buy the right tool.
So there is nothing wrong with the gauge itself. RIGHT? You can easily tap the fitting for a schrader valve. It's just a schrader valve. Very simple. Just saying. Also I've checked the Harbor Freight gauge against my old Snap on gauge. The gauges read exactly the same. It's just a simple schrader valve guys. I think I just bought a pack of 5 from Walmart for a couple of dollars...
If the compression tester measures psi not volume right? If that is true then it won’t matter as long as the tube is pressurized the same as the cylinder. So maybe give it more time to fill the tune completely.
i just chek with this presure item my xtz 750 kilidre nuber one 75 psi and kilidre nuber 2 105 psi in the manual normal is 135 psi i thing the intrument not ok can start engine with 75 psi????? my motor working ok and start...
I had same problem he read 60 psi and the engine has 120 with snap on rented in auto zone,no recomend spend money in that thing
Were the link for the 1 you got off Amazon please
Im going to be buying the maddox version :-)
same problem drove me nuts up till i found this video thanks for sharing this couldnt get more than a 40lb reading on 4 machines one i really wanted and didnt buy because of this gauge lol
Electric start or kick? Good battery and crankover for 10ish seconds = good reading.
The one thing you failed to talk about was with small engines, you won't get accurate readings unless you have the throttle open on the carb. Unlike a car, motorcycles and outboards generally have a single intake manifold for each carb. If you have the throttle closed, you won't be sucking in as much air to compress. Take a look at the difference. People commenting that they get low readings should try it also. I have seen a difference of 40 PSI from checking compression with open and closed throttle. The schrader valve location has little to do with this.
Compression test should always be performed WOT.
I bought a harbor freight gauge and it was reading 90psi on a brand new top end and went to my buddies house and used his snap on gauge and it said 165 psi. I took that shit back lol
Had just rebuilt my cr250 put this gauge on and read 105 compression. I chanced it on not sending the cylinder off ended checking it with craftsman gauge. Read 195! Happy i double checked this gauge is junk!
HF items are good only if you can modify them. They are far cheaper than competition, so the reason we buy them. Don't buy if you can't modify. And I guess you should be able to modify yours, changing the location of scherder or at least calibrate your current one, with a decent one and then make another video that might have a lot more to learn. Any ways, thanks for pointing to this flaw.
See here's the thing, I just redid the top end (actually completely redid bike) on an old KX80 and its been at 55PSI with my new Harbor Freight compression tester since the day I finished it. In fact it's holding 55PSI as we speak as I speak for the past 10 minutes plus. I thought you were correct because I've heard other people say these testers are whacked. And you guys are right this tester has got to be whack. But you can't be right about where that release valve is I don't know whether it is a schrader valve or not. Because it doesn't matter how many times you kick it, if I had a limited number of kicks yes I would see your point as to volume playing into the equation, As I may kick it as many times as I like it's just going to build pressure I mean if the bike holds 220 PSI or 55PSI haha that is saying mine does it doesn't matter I can kick it as many times as I want it will build PSI until it stops building PSI. So volume no matter try again.
I'm sorry but you are wrong. Volume does matter. Buy a correct gauge and see for yourself.
@@HTMR dude even said that the one u linked had release valve at same end. In that size hose you have to go 100' to lose 50 psi and that's with a constant regulated pressure from another source. I'm the source of the pressure and I can continually kick it to build whatever pressure I want; it has a plug in it and I kick until I received the pressure that it will hold before leaking or rupturing. If I could only kick it 5 times I'd be regulated, which I am not, therefore I could kick it until I receive the pressure that it will hold.
And thought this may help...
You guys are making one major error: 10 -1 compression would be 14.7 psi (atmspheric0 plus 10 X 14.7 or 147 plus 14.7=152. NO small engine has this compression ratio because it would be very difficult to pull start it. Most of the smaller horsepower engines use less than 90 PSI.
And, for my figure of .034, I used 3.1416 for pi and then rounded up from 0338 to 034.
But embellishing what I said in my original reply: The gauges we buy to test are accurate probably in the 2-5% range and are usually graduated in 2 PSI increments. Any difference the hose length would make is well below the level of inaccuracy we would achieve between reading errors and gauge error.
And, to test any engine for compression ratio. we think we have a problem: Thus, Compression ratio will either be high or low. We don't care about splitting hairs over a pound.
i bought the actron on your recommendation. Good info on that schrader valve. returned my pittsburg. had to pay a goddamn 6 dollar restock fee : (
Restock fee? Did you tell them it is defective?
@@HTMR ya they didn't care
@@HTMR my actron got here today, my chainsaw tested at 120 psi. the harbor freight gauge read 30 psi. that thing is total junk
Ya its junk the Pittsburgh gauge reads low on everything even excellent running engines it reads way below 100 psi.
I had same problem with this HF 62622 tester. It read 70 PSI on my outboard engine. I used an old craftsman compression tester without a house on it and it reads 125 PSI. I returned the 62622 Pittsburg compression tester to Harbor Freight and exchanged it for another and got the exact same reading of 70 psi. I took this one back and they won't refund my money back to my credit card. They said that they could only give me a gift card. I can't use their gift card to purchase a good compression tester somewhere else. WTF. It ain't my fault.
Tell them it is broken.
Great video,,Matt I unfortunately watched this video too late.,I kinda had a feeling it was off 10 kicks on my cr and it only built 100 psi... absolutely seemed low
B@$!© B®0 done exactly same on my rm only getting 110 max thought it couldn’t be right as the bike strong cr500 ha
all you need to know is in the first 9 seconds of this video !
But my new whiteboard is badass, gotta check it out.
oh yes! I had watched the entire video
Everyone should check out ichibans channel they know how to check psi
@@HTMR not really.
Thanks for saving me the trouble
Hard to purchase at harbor freight based on reviews. Harbor freight ABSOLUTELY deep sixes reviews they don't like. They have rejected many of my two and three star reviews. Ever notice that all of their products have 4.2 ⭐ reviews?
Do you happen to know what compression tester would work best on small engines like weed eaters and lawnmower?
Buy this one: www.howtomotorcyclerepair.com/compressiongauge
Thank you! My new 1990 Mustang 5.0 engine has 600 miles on it. The Harbor Freight compression tester showed 120psi only. I'll return it tomorrow.
Engine runs strong and if my engine would only have only 120psi compression in it than it would be like an engine with 3000000 miles on it.
Same problem here. I bought the HB compression tester and had a similar experience. This was the $26 kit which does not have the valve on the hose end. It read max pressure of 120psi. I rented the autozone gauge and got about 140 across all cylinders with less than 2% variance.
@@hf1cadenas nice what brand was the one from autozone? you know?
AZ Model was 27138. I ultimately purchased a nice Craftsman gauge from sears for about $70. It gave me about the same reading as the AZ gauge, average was about 140ish across the board.
@@hf1cadenas well that's good. just purchased a good looking Toro Personal Pace mower that probably had gas left in it too long. but i am gonna use my new 8 pc compression tester on it for the first use 👌 excited to see if its accurate at all
Just remember that compression has to be tested with engine hot as a cold engine will skew your results. Let the engine warm up to normal operating temp then test and be sure the butterfly valve at the carb is wide open as well for maximum air ingestion. Wear gloves unless you want burnt knuckles.
Do you have a video on how you make a compression tester together with a leak down tester like both testers built into one tester?
www.howtomotorcyclerepair.com/how-to-leak-down-test-diy-build/
What is the inside diameter of the HF hose that you're claiming to have so much more volume capacity versus the other brand?
Thanks for confirming my suspicions. Couldn’t find my tester so picked up this one. No better than 75 psi on three different engines. One cylinder was half that, so gauge is still useful to me for finding weak cylinder.
ua-cam.com/video/jbRsJbbYY1A/v-deo.html&ab_channel=IainFrew
ua-cam.com/video/EO1C4cZuV80/v-deo.html&ab_channel=srcarr52
So now that you know that just double the value that easy
So which compression tester do you recommend?!
Here is the compression gauge I recommend: www.howtomotorcyclerepair.com/compressiongauge
Tbh while your probably right, 99% of the time compression isn’t going to be down over all the cylinders and most of the time your just trying to find a problem. I’m using this right now and just making sure that all the cylinders measure the same or within 10psi of each other. So in my case I’m looking for precision over accuracy.
Yeah well you need to know if there will be enough compression for it to even run. Also, all compression specs in service manual base it off a tool with Schrader valve.
Thanks I thought my outboard motor was no good
I ordered the same gauge it was 10 dollars cheaper on eBay
The gauge you have in the link is not the same one in your video and some one asked where the Schrader valve was and they said it's in the bottom of the gauge not the end of the hose like yours so apparently they changed the design on it so you might want to remove the link since it's not what your advertising for them.
Yes, but old ones are still out there giving bad readings.
I returned my Harbor Freight compression gauge for the same problem. I guess it works on larger cylinders?
The larger the displacement, the less error it will have.
that whole "space in the hose before the schrader valve" is a flawed theory. On your compression tester the air needs to travel the length of your hose also before it reaches the gauge so what's the difference?
The hose adds volume to head. Go look at engine compression formula.
The volume of air that the tester hose can handle is so minimal. You would never notice a difference. You definitely have a defective gauge or something.
Nope, the smaller the engine (50cc) the larger the error. For a car, yes, barely make a difference
Thanks for confirming my suspicions.
Sitting here beating my head against the wall (look up insanity), not understanding why my reading isn’t making sense.
Usually you can fair okay with HF, just amazed this tool is this useless.
SO THATS WHY MY LEAF BLOWER AND PUSH MOWER (WHICH RUN) ONLY READ 25 PSI. FML. Wish I saw this vid earlier. Returning this POS tommorow. Not to mention the reason I bought it was for another non running leaf blower, which I tore apart thinking had low compression, but only had a faulty carb. WTF.
Thank You!
What is the name brand of the one at Harbor Freight? Is it the Pittsburgh?
Yes.
Man you are so dead on ... I just brought one back to HF ....it was off by 30 lbs
I'd like to know where to buy the compression tester you recommend. My cheap tablet doesn't show pop ups so I don't know where to buy it. Could you please put the information in your description?
Buy this one www.howtomotorcyclerepair.com/compressiongauge
Quick question: How about the length of the thread on the tester? Jeff from Slavens says that if using a 3/4" spark plug (Type E), the thread length of the compression tester should be equal to the spark plug itself. The shitty tester from HF (that I just bought, of course!) and yours seem to have a shorter threading; not as long as a spark plug. Is that difference, despite minimal, enough to not give the proper reading?
Ideally, yes, however this tester accommodates short plugs as well.
I used the HF Compression tester the other day and got a reading of 75. I was loosing my mind knowing the motor only has 5k miles on it. granted its an 83. I used the older HF Model compression tester, so maybe thats the problem, trying to get the motor started. I will deff get a new one from somewhere else and test it again. Great video thank you!
OTC 5606
Muy buen video, gracias!
Can you suggest a good compression tester Matt?
www.howtomotorcyclerepair.com/compressiongauge
you can’t put a shrader valve in the correct end?
Maybe, but why not just buy the correct one.
the location of the valve does'nt mater
Take a look at the math to calculate compression ratio and prove me wrong then.
@@HTMR math is not needed! The gauge reads what it reads and it doesn't care where the valve is! Either way the hose has to also be filled before it reaches the gauge! If you took the valve out the reading would be the same! It just stops the air from escaping! PSI is the same, the volume of air is also the same no matter where that valve is! It's no more than a check valve I'm not arguing I'm just saying! Think of a tire! If read my air pressure on a regular tire and it reads xxx then I put one of those long valve extensions on like a semi truck has on the inside tire the psi is going to be the same even though the valve is now relocated in a longer stem tube!
Does this happen with the evertough brand from o Reilly? Bought one for $50 and it said 65 psi, tested another, 65 lbs?
I don't know
Is this gauge wet testing capabilities also?
Sure why not.
So thats what's wrong with my howasaki.
The hose is to long