Compression test
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Mountain Pass
Joined: Dec 2024
Posts: 134
Likes: 6
Compression test
Hey guys, I got a 1967 f100 3 speed with a 352 engine
I ran a compression test and got 120 on 7 cylinders and 105 on one of them engine seems to run fine with no leaking. I get good vacuum. The test was done on a cool engine with no throttle at all.
any ideas how good/bad it is compare to specs?
Also, I just changed my speedometer cable and it seemed to work fine for a day and then stopped. There are no bends or anything like that. What can it be?
thanks!
I ran a compression test and got 120 on 7 cylinders and 105 on one of them engine seems to run fine with no leaking. I get good vacuum. The test was done on a cool engine with no throttle at all.
any ideas how good/bad it is compare to specs?
Also, I just changed my speedometer cable and it seemed to work fine for a day and then stopped. There are no bends or anything like that. What can it be?
thanks!
Tuned
Joined: Apr 2019
Posts: 294
Likes: 48
From: Southern Ontario
My 1967 Ford Truck Shop manual states for the 352 V8:
-Compression at sea level and at cranking speed - 160-200 psi
-Allowable variation between cylinders - 20 psi
This is obviously factory specs, and I'd be interested if anyone wants to chime in on what good numbers would be for a stock 352 that hasn't been rebuilt.
-Compression at sea level and at cranking speed - 160-200 psi
-Allowable variation between cylinders - 20 psi
This is obviously factory specs, and I'd be interested if anyone wants to chime in on what good numbers would be for a stock 352 that hasn't been rebuilt.
Logistics Pro
Joined: May 2015
Posts: 4,462
Likes: 951
From: Tri Cities, TN
You cannot get a valid number without blocking the throttle wide open because you are starving the cylinders for air with the throttle closed. The numbers you get will depend on your altitude and barometric pressure at the time you check it, plus whether the engine is warm or cold. As a general rule if they are all within 10 to 15% of each other you're fine.
Lead Driver
Joined: Jul 2017
Posts: 9,545
Likes: 1,156
From: San Jose, CA
Well there you go!
Engine sounds fine to me. What prompted you to do a compression test in the first place?
Since you’re in the mood, you might as well do the test again with the throttle held open. And on a semi warm engine, if you can do it after a run.
And as a secondary test, squirt a little oil in the cylinder before testing. See if the readings go up and buy how much. Seems like doing that would tell you if any of your low readings are ring related.
is the truck driven regularly?
Pull it out of the transmission or transfer case and check the gear. Make sure it hasn’t come unclipped, or gotten shredded somehow.
did you change the gear as well? Or reuse the old one?
Engine sounds fine to me. What prompted you to do a compression test in the first place?
Since you’re in the mood, you might as well do the test again with the throttle held open. And on a semi warm engine, if you can do it after a run.
And as a secondary test, squirt a little oil in the cylinder before testing. See if the readings go up and buy how much. Seems like doing that would tell you if any of your low readings are ring related.
is the truck driven regularly?
did you change the gear as well? Or reuse the old one?
Thread Starter
|
Mountain Pass
Joined: Dec 2024
Posts: 134
Likes: 6
Well there you go!
Engine sounds fine to me. What prompted you to do a compression test in the first place?
Since you’re in the mood, you might as well do the test again with the throttle held open. And on a semi warm engine, if you can do it after a run.
And as a secondary test, quirt, and oil in the cylinder before testing. See if the readings go up and buy how much. Seems like doing that would tell you if any of your low readings are ring related.
is the truck driven regularly?
Pull it out of the transmission or transfer case and check the gear. Make sure it hasn’t come unclipped, or gotten shredded somehow.
did you change the gear as well? Or reuse the old one?
Engine sounds fine to me. What prompted you to do a compression test in the first place?
Since you’re in the mood, you might as well do the test again with the throttle held open. And on a semi warm engine, if you can do it after a run.
And as a secondary test, quirt, and oil in the cylinder before testing. See if the readings go up and buy how much. Seems like doing that would tell you if any of your low readings are ring related.
is the truck driven regularly?
Pull it out of the transmission or transfer case and check the gear. Make sure it hasn’t come unclipped, or gotten shredded somehow.
did you change the gear as well? Or reuse the old one?
speedometer cable new- old gear …
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