Compression Test on an Engine
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- Опубліковано 11 бер 2017
- How to perform a compression test.
I like to have a lightly warm engine(a few minutes of running), but not a too hot to work on/around engine. Any difference over 20% between cylinders is a concern and you will generally have performance/running issues. Where as engines within 10% of each other are in good condition. If you are comparing the data for your engine to new factory compression specs, remember that there is a 3% per 1000ft in elevation drop(160 psi new rating will only be 136psi at 5000ft above sea level). You can remove all of the spark plugs to do the test and the engine will spin up faster, but I've seen no difference so I prefer to do one at a time.
The compression tester I use allows me to hook a standard air compressor line to to fill the cylinder with air for on engine valve work or cylinder leak detecting.
This is the tester I've used for the past 15+ years: amzn.to/2mXDmMo - Авто та транспорт
![How To Perform a Compression Test - [EASY]](http://i.ytimg.com/vi/3VmmL0YAO14/mqdefault.jpg)
![How To Perform a Compression Test - [EASY]](/img/tr.png)
been a mechanic over 30 years and that was a very nice clean quick way of showing a compression check. great way of showing how important it is to keep up with service history.
Thanks Stephen. -Moe
Never knew about that altitude deal. Good thing to know where you live. Really like those years/trucks that you have. Nicely presented video, again!
Thanks.
Nice video man. Appreciate you taking the time, and also letting everyone know not to freak out if it's a little low, especially when the trucks 20-30 years old.
So cool that you have those historical records!! Thanks for uploading.
Hey Thanks.
Good old mechanical check still rocks! It's good to know where you stand. You kept great records on that engine.
Thanks.
Great tip with the oil, and I just love the sound of that truck. 👍
Thanks.
Even with slightly lower compression in two holes, she'll probably last longer on the road than anything made new today! I had an old ranger that reminded me of your truck. She was a workhorse!
These old things just keep chugging along. I'm sure if it was a modern engine the computers would have self destructed by now.
Another great video my friend!
Thanks Paul.
Nice video simple but always appreciate someone else explaining their techniques and why!!! take care!
Thanks.
I always do a compression test on fully warm engines after all the plugs are removed because a warm engine will have different compression than a cold engine and having the plugs installed in the other cylinders can effect the pressure readings. If all the plugs are removed you eliminate that irregularity.
I hate burning myself so I do it on a slightly warmed engine and with only one plug removed at a time. The pressure reading doesn't matter as much as the comparison between the cylinders. I've pulled plugs and done one at a time and have never seen a difference. The only time it would make a difference is if the battery is junk.
@@sixtyfiveford no thats not true. If you have a head gasket leak between cylinders you can miss that only pulling one plug at a time. Its best to pull all the plugs then test.
@@jesseduke694 Two side by side cylinders are never going to be on the compression stroke at the exact same time. When will be it virtually zero PSI always while the other one is compressing.
@@sixtyfiveford your missing the point. The two cylinders dont have to be on the compression stroke at the same time. If you only pull one plug & have a leak between two cylinders the other cylinder has the plug in then they still build pressure giving you a reading witch in turn will be hiding the leak. However all the plugs out & the leak between two cylinders shows up becouse you don't build cylinder pressure becouse the other cylinder can't hold it with no plug in.
I agree with First Listro. You have the same mind set as me. Give good information, don't worry about the money rolling in and never acting like you've been bought by the system. Kudos on that note Moe! Also, excellent information as always. We're a lot alike. Have you ever used Blackstone Labs to do a motor oil analysis? Every time I do an oil change, I send off a sample to see how healthy the oil is and there fore, how healthy the engine is. They tell you Water content, fuel content, heavy metal content etc. Just an extra added measure for our older vehicles and gives us a better chance at catching a major problem early on. Cheers my Friend! Zip~ Just google Blackstone Labs and you should find them easily enough.
I've considered it, but figured it's not worth the more than doubling my oil change cost. I think the info would be fun to look at, as I spent the time to cut open every old oil filter and inspect the contaminants in the pleats, but nothing more. Of course this is my opinion and I've read a few articles on it. I have the sixtyfiveford lab.
When I was young and crazy I had a 68 camaro that was so worn out I had to put oil in the cylinders in the winter just to get enough compression to fire the motor. (Shot rings) Good video.
Great story. I had a chainsaw I used to do that with. Much quicker to do a chainsaw than a v8.
It's a great way to make a quick test of some of the internals. I guess the next best test is having an oil sample analyzed, but this is a simple test that's easy to do. Thanks Sixty-Five!!
I've never had it analyzed. I've considered it.
Great video as always, only thing you forgot is to always have the throttle and choke set wide open, the draw from the carb can adversely affect the reading.
Thanks. I mention it briefly at the beginning. 1:26
@@sixtyfiveford Doesn’t that flood it?
Short and concise! Love it!
Thanks, I'm glad you liked it.
Hello 65Ford guru! fairly new subscriber. I am going back and viewing your older videos as well. Question??????? Do you have a video on the air compressor line to cylinder procedure please? Thank you. Cheers from Motown/Dearborn.
Are you talking about a leak down test? I do not.
That's a good thing to check. You take pretty good care of your stuff if you're doing compression tests every year or 2.
I try to do it when I change spark plugs as there is very little extra effort involved.
Very good job, thanks. I learned a lot.
Thanks for the video!
Great video I enjoyed it. Lots of good info!
Thanks for watching.
Good Video! Could you do something related to the power steering box on the F100. It would be nice to know how much play is to be expected. Don't suppose you have ever reconditioned one? Thanks,
I've actually pulled a few apart. Most of the time I find most of the play in the steering wheel is in the the tie rod joints. But I've adjusted the screw/nut on the top with a little success. I have never got super tight steering like a modern car, but better.
Engine restore additive surprisingly does increase compression readings.
I don't doubt it does, but stuff like this always seams short lived.
Good explanation
Good info Moe from one Ford truck fan to another
Thanks Man.
Good idea to check compression every couple years! That's a nice truck!
Thanks Will. -Moe
very nice job and thanks for sharing.
Thanks.
Good tips and reminders Moe.
Thanks George.
Giddy Yup! Nice video, and had fun watching your hands get dirtier and dirtier. LOL. How is your oil pressure on the modified Cleveland? My 400 has some to be desired while idling, but it is getting long in the tooth and still has stock pump.
Oil pressure hasn't been great since I put it in 15+years ago, but it just keeps chugging along. It'll drop pretty low/non existent when hot at a low idle. I got this 351M free(traded for a C4 trans I got for free) from a guy who pulled it from a 70's LTD and left it in his back yard for who knows how long. I had a 351M-400 in it before(still have it, never checked bore/stroke) that lost a rod bolt and the rod came off that this replaced. I would like to rebuild it to a 400 as I had a 78 Bronco with the 400 and it had gobbs more power.
Good video, love old Ford trucks!
Thanks Judd. So do I.
Your right. I have the tester but rarely use it.
I like having a timeline.
i have a 1993 ford f150. hade to replace the computer now when it gets warm it bogs down.
Thats not bad really, predictable drop due to piston ring/bore wear.
What level would you do fresh rings at, 100 psi perhaps?, or are you not too bothered as long as its still usable.
At my elevation I could probably go down to 85-90psi(6 bar) before she was worn completely out.
Is your carb tuned for this altitude ?
It is.
Do you take all the spark plugs out before you do a compression check? I do, and the motor cranks easily so it turns faster for higher compression. i found my car was kind of stalling trying to crank, and i figured 3 cylinders later itmight be a little weak. so i removed all the spark plugs to make it easier. what would be do you know the right reading? and what way do you do it? Do you do it this way, too?
I pull one plug at a time. I've done it both ways and always end with identical results. A good battery should crank the engine very well.
I never realized if your at high altitude it gives lower readings. I normally like to see around 180.
Wow can't say I've ever seen my gauge go to 180. That would read around 155 here at 4500-5000feet.
sixtyfiveford A Ford mini van I just worked on had 225 psi.
I'm guessing it had a pretty high compression ratio for these new flex fuels.
How bigs the light bar on your 78 I just bought a 52inch I might put on mine. We have a very similar taste in trucks I have a 78 250 snow fighter and a 65 ford late 64 build tho so old style cab and grille I put on a superduty frame shortened 5 inches it's getting a healthy 429/460 asap
It is a 50" if I recall. Nice trucks.
where is a good place to buy one and what would you pay for one? always great videos moe , keep them coming!!!!!!!!!!!
I have a Sears branded (Actron CP7827) tester that has tested over a hundred engines. I paid around 30 bucks and it hasn't let me down in the past 15years. I put a link to it in the video description.
Thanks Moe, I hope you never retire from this for a long time because your like a doctor on demand, Thanks i'm going to sears to pick one up and if its tested by you , that's all i need to know , Thanks again!!
i have a 92 trans am, fuel injected, i think i heard you say that you have to remove all the plugs and wires to do a compression text on a fuel injected, did i hear that right?
You don't have to remove them all at the same time, but you can. You need to remove the main coil wire so the engine doesn't start, but then you can just remove one plug/wire at a time.
You need to pull out all your plugs before you start the test and make sure the engines been warmed up ... And 10 pounds variance is just fine, 15 is marginal and 20 is where you start noticing some slight rough running. 30 year veteran auto shop owner speaking...
I warm the engine, not hot just warm as I hate burning myself intentionally. I made a personal decision to only pull one plug mainly because I hate the idea of the other open cylinders pulling in dirt from an open spark plug hole and a vibrating engine. From my experience it makes no difference on pulling all the plugs or leaving them. It may take 1-2 more rotations of the engine to push the pressure, but any good battery can power through this. I did the #6 cylinder 2nd and the entire engine after and when I came back with a weaker battery still got and identical 115psi on #6. I appreciate your input.
so, with the oil. if number goes up its the rings. if it stays the same or goes down means valves ??????
Yes, any amount that the compression increases with oil is how much you're loosing through the rings. The rest is what your valves are loosing.
I saw your gauge hold the pressure after you stop cranking, I wonder why mine don't stay, and loose the pressure slowly... do you have an idea?
There's a little Schrader valve in the end that screws into the spark plug hole. It looks like the exact same thing inside of a tire valve core.
ive never done one .. ..I paid for a sparkplug change in 2006 and in 2010 the motor on my 4.7 headgaskets blew.. typical mopar 4.7 and when I pulled the plugs to get the coolant out of the hydrolocked motor I noticed the plugs were original's ... the dealer screwed me of over 100$
That'll make your day.
if you disable the engine by removing leads it is best to ground them on a bolt or something attached to the block. particularly on older coils if the spark has nowhere to go it can short between the primary and secondary coil and then the coil is dead :-( I've seen a lot of coils killed this way at tafe on stationary engines by students ;-)
That's good to know.
Looks like there is still a lot of life in the old girl yet! What size motor did you say it had?
It has a 351M. I put so few miles on it every year, it'll keep going for a long time.
its cool to see how much they dropped over the years
It's neat to have a timeline.
I Didn't know the oil tip to compression testing, I was thinking before you did it I wonder how you tell if it was valves, Seats etc or Rings and you showed us , Thankyou
Now a question for you
I have a Toyota Hi-Ace 2.8 litre Diesel Van ( I Live in Western Australia) Do you need to do a compression test on them ( Being Diesel) I replaced the Glow plugs about 1 year back and it was a bloody Pain in the A$$
esp as the engine is under the passenger and driver seats and I have noticed that a diesel Or mine anyway has a critical powers level it needs to start if it drops below that voltage it wont heat up the glow plugs and even turn over the engine ( But I could take out the battery so to speak and start any petrol without an issue using the same battery with no extra charging
so if you need to check compression how would you do it ESP with the Glow plug issues
the engine has done 325,000KM's ( 1996 model) I have owned the van for approx 14 years and put less than 40,000kms on it I do less than 5000kms a year
change the oil every 5000kms (Synthetic from last change onwards )
gearbox & Diff oils every 10,000kms
new air Cleaner if needed every 5000kms
Tony
Moondyne .Joe Sounds more like a starter motor issue than a compression issue. note- You will need a Diesel type compression gauge to do the test. But I would check your starter first considering your battery won't turn your van over but will start your petrol car. Because Diesel engines have such a high compression ratio the starter motor does work alot harder. But a voltmeter on the battery and crank over the engine your battery should recover back to 12 volts in around 15-20 seconds. I am from Queensland Cheers Mark.
Moondyne .Joe most likely the starter or the wiring/relay, could also still be the battery, petrols are a lot easier to crank, average petrol compression ratio is roughly 9/10:1 (modern slightly higher) whereas even old simple diesels pre fancy electronics are around 16:1. if you had lost any large amount of compression it would actually be easier to crank, harder to start but easier to spin :-) fellow sandgroper btw, nice to see another one out in the wild :-D
tapper88
Starter is fine once the car starts ( as in first time I fire it up on any day) the car will start all the time usualy within less than 1/2 a rotation of the engine the battery from day one always seemed to do that and even the original battery when I brought the van did It just seems to have a certain voltage it likes to start with and once that volage is below a certain amount ( no I havent as yet put a meter on it to find what that is) it just cranks slower and slower till no crank at all as long as I let the glow plugs warm up ( the red light goes out then about 10 seconds later a Click is heard) it starts fine winter can be a pain so I always carry some areostart with me I Live up in Toodyay ( Hence the name of Moondyne Joe Grin) so we do get some Cold winters here Starter has never given me any problems as I have said , Maybe it has got good compression nd just , Like me has its own personality (:
Tony
Mark Thomas
Hi Mark I don't think that their is anything wrong with the starter , and i Do have a powerbank if needed to add a bit of extra Zing to startups and as I said to Tapper88 on the day , once it has started it is excellent to start each and every time , Usually within 1/2 a rotation of the engine crank
Tony
Moondyne .Joe . Hi Tony, if it starts that well sometimes I very much doubt it will be a compression problem. Starter motors can have intermittent problems all depends on condition of brushes and the bendex etc. Also could be a bad battery cable or earth lead. If it has a big resistance when cranking it will take power away from other components on the engine like glow plugs, relays, engine shut off solenoid etc. Next time it gets hard to start try cycling the key a few times to make sure the glow plugs are hot. remember to wait each time for the relay to click. I am a Mechanic I have been doing this for over 25 years it is a bit hard to diagnose the problem with out seeing it. Any other questions don't hesitate to send me another message. Hope you sort it out mate. Cheers Mark.
Good tips. My car motor is mounted in such a way that half the spark plugs can't be accessed without removing half of the motor. The engineers designed it so that the motor is crammed in sideways.
Dasdfjkl what kind is it?
It's a 15 year old Santa Fe.
Darn front wheel drive V6 vehicles. Always a pain to work on.
I have a carburettor engine with a mechanical fuel pump, are you suppose to clamp the fuel line down or will it be ok to carry on the compression test with just disconnecting the coil?
You will be just fine running the compression test without doing anything to the fuel line. You should have the gas pedal depressed all the way though for maximum air flow into the engine.
@@sixtyfiveford thank you, I did the compression test when I cranked the engine the gauge went up and then lost pressure, back to zero. I did the others and the same thing happened. Do you reckon its a faulty compression tester?
@@ashikdossajee7533 If you compression tester goes up and then looses pressure it has a faulty schrader valve. This is a little one way valve that is supposed to hold the accumulated pressure in the gauge until you release it manually.
@@sixtyfiveford thanks for your help ill try again with another compression tester 👍
Just be careful who loan your gauges out to. Mine have disappeared. If is something I don't use often then I forget who borrowed it. Usually it is a relative. The hand held rubber tip are okay for small engines if have someone pull the rope starter.
Yeah, it's always annoying when they grow legs. I have a rubber tip one that gets brought out for the odd size mini spark plugs.
How many miles on the jalopy
You don't keep track once they get old.
Cool
Thanks.
Time for some Restore Engine additive. It works!
She has a long life left without doing anything.
What engine is that? I hope for your sake it's not the 351M/400.
It's the 351M. Not powerhouses like the 351W or FE but they just keep chugging along. I got this 351M for free out of a guys backyard. It had been pulled from a 70's Ford LTD and sat for who knows how long with who knows how many miles. I replaced the original 351M that lost a rod cap bolt on the freeway and it has been chugging along for the past 15 years.
sixtyfiveford Hi Moe. Those old 351 engines are a great engine. We use to get a version of it over here in Australia in our Fairlane/LTD I bought a LTD for $500 and put the 351 and running gear in my Falcon. It had a alloy intake and a 850 double pumper on it with a late model electronic distributor and a fmx auto behind it. The thing used go really well. Great videos mate . You done a awesome job on your boat looks cool with color scheme. I can't wait for the next video. keep it up mate. Cheers Mark.
OH NO! Not an M! We used to buy Gran Torino Elites for a few hundred bucks back in the early 80's just to have spare "M"'s for my buddy's 78' F250 4x4 (we would change those dogs as much as a pair of socks) -luckily it had the NP 435 w/creeper 1st so we just had to find a 460 bell housing when we finally dropped in a 460 out of a Merc wagon. He still has that truck.;-)
Explorer model with the bedside tool box?
78 F150 Ranger Lariat.
was the tool box an option across all models you think?
deme7063 Online articles claim all options were available to every model.
It looks great for it's age.
Video makes here look a lot nicer than she is. She's rough and that's why I bought her years ago. I wanted a truck that I didn't care got a ding or dent went I took her off road. Best 900 bucks I ever spent.
Don't think an engine could vapor lock with one teaspoon of oil and the spark plug out of a cylinder
Treating that old girl right! :) Great video Moe thanks for sharing.
Thanks Luke.
good man thats the way, spray soap water on your testing fitting from time to time👍
That's a good tip to eliminate any leaky fitting readings.
You never did say how to tell the diff between worn rings or valves? You just said pour oil into cylinder and so you did, but never heard you say anything about what the differences would be from valves to rings? Please verify.
Compression goes up a decent amount with oil added=worn rings
Compression stays about the same with oil added=valves.
@@sixtyfiveford Thanks man.
Pretty good in general for the ol'girl
Thanks. Just having fun.
Not anything you can do except rebuild.
Yep. Good to know you still have life in them though.
complicated, that's why I prefer diesel....
Because diesels don't have compression....
good methods, stupid low cylinder
Thanks. Even the weak one has some miles left in her.
yeah, but if someone had OCD it would screw with them bad, lol. Not a real issue, just a thought.
frist listo I agree thanx ehhh
Thanks Man.