The Harbor Freight Quick Connect Compression Tester is flawed. The one-way valve for the tester is close to the gauge, not inside the end you connect to the spark plug hole. So when you compress the air, you're compressing the extra volume of air in the hose. Might not seem like much but throws the accuracy off as you see. Harbor Freight's other compression tester addresses this issue with a one-way valve in the brass fitting in the hose.
Just bought the same one. Working an f250 gas truck with a miss. Tested both good and misfire cylinders. Both came back at 60. Returning this junk tool tomorrow.
@@newenglandlife978 LOL! My shop compressor was et to 130 PSI and it's accurate! This crap tester read 65 PSI. It also read 65 PSI on my 8 month old Husqvarna T540 XP® II and it in fact reads 65 PSI on ANY other engine including my 2012 R1 and 07 ZX 10-R and they run 185 PSI when the shop tests them. LOL!!!!!!!! Just throw it in the trash.
pretty sure the harbor one reads at half psi because its also meant for heavy equipment, such has skid steers, tractors, semi trucks etc which i would think use higher psi (i could be wrong). where your amazon one is more so directed towards two stroke and four stroke machines would be my logical guess. the harbor one it still reads accurate, just at half psi compared to most common compression testers like the amazon one you bought. but yeah just easier if you get the amazon style one so your reading accurate right away and you dont have to worry.
Mine broke too after one day, have no idea if it even reads right my buddy wouldn’t even touch it when he got there 😂 pulled out his snap on one and tested my motor
Make sure the tester you buy has a Schrader valve at the very end that goes into the plug hole. This valve looks like one in a tire but it's not. It's very low pressure like 1.5 lbs. When it goes bad you have to buy special ones for compression testers.
I have that Harbor Freight compression tester and it consistently measures low, no matter which machine I put it on. You can buy compression testers that have the Schrader valve at the tip of the hose instead of and the end of it. I was suspicious of the last measurement I made with this tester, so I haven't yet bothered to take this machine apart. It's a well-known axion in physics that you cannot measure something without disturbing it, so we endeavor to disturb measurements as little as possible in order to get the most accurate measurements we can, recognizing that no measurement will ever be perfect. So I poured a fine liquid into the hose to see how much volume it takes up, poured it into a small measuring cup, and it was around 2.5 teaspoons, which amounts to about 12.3223 cc. The motorcycle I'm testing is 1000 cc and has four cylinders, so 250 cc per cylinder. Using the Gas Law, PV = nRT, assuming nRT is the same for both cases, we say that P1V1 = P2V2, or P1 = P2*V2/V1. If P1 and V1 are the undisturbed pressure and volume inside the cylinder, then P2 is the gauge pressure we'll read with our hose and additional volume, so V2 is simply V1 + Hose volume. In my case, P2 (gauge pressure) was around 100 psi, which I considered to be very low for this bike. But if we apply this fomula, V1 = 250 cc. V2 = 262.3223 cc, we get a ratio of around 105%, or an expected P1 = 105 psi. Which is still a bit low. But there is a 5% error in my reading. If the piston is smaller, the error will be larger, and if it's larger, then the error will be smaller. In the meantime, this bike seems to run just fine, especially when it should not be running below 150 psi, I suspect that the gauge itself is not working properly.
I tried my best to understand everything you wrote. From what I can understand it makes some sense to me. What is your profession? Physics? Have you ever looked into the double slit experiment? That is what this reminds me of with the act of measuring having an affect on the test
@@newenglandlife978 I'm familiar with the double-slit experiment, but this refers to the Heisenberg Uncertainty Principle, which applies more to quantum mechanics. However, having little or next to nothing to do with quantum mechanics, this problem has to do with ordinary mechanics, and perhaps more along the lines of thermodynamics. At any rate, no matter how small the impact, there will always be some disturbance in the measurement. In this case, this disturbance is pretty large - for my CBR1000, around 5 to 6%. For a 125cc bike, it would be closer to 10% error. In addition to the hose error, the gauge itself must bend inside the mechanism, since it is usually a tube that shrinks or expands with pressure. So here is a yet another source of error. My profession is retiree, but my degrees are physics, mathematics and a terminal degree (Ph.D.) in electrical engineering. My dissertation is online and centered around the study of quantum wires.
@@RobertMertensPhD This tester read 65 PSI on my 2012 Yamaha R1 which reads 185 PSI on my mechanic's tester. LOL. And it makes 170 RWHP on the Dyno so it is NOT 65 PSI!
The Harbor Freight Quick Connect Compression Tester is flawed. The one-way valve for the tester is close to the gauge, not inside the end you connect to the spark plug hole.
So when you compress the air, you're compressing the extra volume of air in the hose.
Might not seem like much but throws the accuracy off as you see.
Harbor Freight's other compression tester addresses this issue with a one-way valve in the brass fitting in the hose.
Just bought the same one. Working an f250 gas truck with a miss. Tested both good and misfire cylinders. Both came back at 60. Returning this junk tool tomorrow.
I still use mine. I just double the reading
@@newenglandlife978 LOL! My shop compressor was et to 130 PSI and it's accurate! This crap tester read 65 PSI. It also read 65 PSI on my 8 month old Husqvarna T540 XP® II and it in fact reads 65 PSI on ANY other engine including my 2012 R1 and 07 ZX 10-R and they run 185 PSI when the shop tests them. LOL!!!!!!!! Just throw it in the trash.
pretty sure the harbor one reads at half psi because its also meant for heavy equipment, such has skid steers, tractors, semi trucks etc which i would think use higher psi (i could be wrong). where your amazon one is more so directed towards two stroke and four stroke machines would be my logical guess. the harbor one it still reads accurate, just at half psi compared to most common compression testers like the amazon one you bought. but yeah just easier if you get the amazon style one so your reading accurate right away and you dont have to worry.
I came here because everything I tested with one that I borrowed from a friend came back 50 psi, I was very confused!
Scary
strange i have that compression tester and tested it against my neighbors snap on guess what its pretty much the same maybe you got a bad one
@@frankgrimes1385 maybe. I have a few more. It still works but I just have to double it.
Mine broke too after one day, have no idea if it even reads right my buddy wouldn’t even touch it when he got there 😂 pulled out his snap on one and tested my motor
Make sure the tester you buy has a Schrader valve at the very end that goes into the plug hole. This valve looks like one in a tire but it's not. It's very low pressure like 1.5 lbs. When it goes bad you have to buy special ones for compression testers.
I have that Harbor Freight compression tester and it consistently measures low, no matter which machine I put it on. You can buy compression testers that have the Schrader valve at the tip of the hose instead of and the end of it. I was suspicious of the last measurement I made with this tester, so I haven't yet bothered to take this machine apart.
It's a well-known axion in physics that you cannot measure something without disturbing it, so we endeavor to disturb measurements as little as possible in order to get the most accurate measurements we can, recognizing that no measurement will ever be perfect.
So I poured a fine liquid into the hose to see how much volume it takes up, poured it into a small measuring cup, and it was around 2.5 teaspoons, which amounts to about 12.3223 cc. The motorcycle I'm testing is 1000 cc and has four cylinders, so 250 cc per cylinder. Using the Gas Law, PV = nRT, assuming nRT is the same for both cases, we say that P1V1 = P2V2, or P1 = P2*V2/V1. If P1 and V1 are the undisturbed pressure and volume inside the cylinder, then P2 is the gauge pressure we'll read with our hose and additional volume, so V2 is simply V1 + Hose volume.
In my case, P2 (gauge pressure) was around 100 psi, which I considered to be very low for this bike. But if we apply this fomula, V1 = 250 cc. V2 = 262.3223 cc, we get a ratio of around 105%, or an expected P1 = 105 psi.
Which is still a bit low. But there is a 5% error in my reading.
If the piston is smaller, the error will be larger, and if it's larger, then the error will be smaller.
In the meantime, this bike seems to run just fine, especially when it should not be running below 150 psi, I suspect that the gauge itself is not working properly.
I tried my best to understand everything you wrote. From what I can understand it makes some sense to me. What is your profession? Physics? Have you ever looked into the double slit experiment? That is what this reminds me of with the act of measuring having an affect on the test
@@newenglandlife978 I'm familiar with the double-slit experiment, but this refers to the Heisenberg Uncertainty Principle, which applies more to quantum mechanics. However, having little or next to nothing to do with quantum mechanics, this problem has to do with ordinary mechanics, and perhaps more along the lines of thermodynamics. At any rate, no matter how small the impact, there will always be some disturbance in the measurement. In this case, this disturbance is pretty large - for my CBR1000, around 5 to 6%. For a 125cc bike, it would be closer to 10% error. In addition to the hose error, the gauge itself must bend inside the mechanism, since it is usually a tube that shrinks or expands with pressure. So here is a yet another source of error.
My profession is retiree, but my degrees are physics, mathematics and a terminal degree (Ph.D.) in electrical engineering. My dissertation is online and centered around the study of quantum wires.
@@RobertMertensPhD This tester read 65 PSI on my 2012 Yamaha R1 which reads 185 PSI on my mechanic's tester. LOL. And it makes 170 RWHP on the Dyno so it is NOT 65 PSI!
If this vid hits a million views we'll give away the crocs!
Same thing here then they charge u 20 percent to bring back
i have winter CROCS with fur in it...CROCS ROCK !!!
La gallina te quiere ayudar 😂
@@rolysmota6703 ese gallina gracias al cielo ya no está.