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Hello all. Just ran a compression test on a 1954 chevy 235. Never heard it run till today when I got it idling smooth. However, I found my compression test results to be interesting. Shop manual calls for 130 psi or better per cylinder and states that all cylinders should read alike within 5 to 10 psi (just throwing that out there for reference). Here are my results:

Cylinder 1 - 135 psi Cylinder 2 - 130 psi Cylinder 3 - 150 psi Cylinder 4 - 110 psi Cylinder 5 - 145 psi Cylinder 6 - 130 psi

I added oil directly into cylinder number 4 via the spark plug hole and retested, getting then 180 psi. The manual calls that a sign of lost pressure at the piston or rings.

The engine mileage is unknown to me. Additionally, this is my first time taking a crack at diagnosing internal engine conditions using compression results. Any and all info on what you make of the results would be great. I figure a visit to the machine shop might be in order.

Thank you!

How long has the engine not run? Think I would try running some top cleaner and something that would clean up the rings before pulling the trigger on rebuilding anything. It will b a very short time before someone tells you to do a leak down test too. The compression test has gotten you into the ball park on the engine condition the leak down will most likely be more precise.

Is this engine in a drivable vehicle? If so, I’d drive it a while before jumping to any conclusions about that compression test.

And if it’s not in a drivable vehicle, I’d try to rig up a way to run it for some extended periods and retest compression and/or leak down.

You might just have some sticky rings that need to be loosened up. Heat and pressure under running conditions is a great way to do that. There’s also a procedure I’ve used with a crankcase filled with oil and then overfilled with a quart or so of diesel. Running 20 minutes of thereabouts at a high idle and no load.

How long this engine has sat without a start up is completely unknown.

Thank you for the ideas! Today I will rig up a temporary way to run the engine for extended periods. I will perform your overfilled crankcase procedure as well. Perhaps ACDelco GM engine cylinder/combustion chamber cleaner will find its way into the engine as well. After a while of running and flushing the cooling system I will perform another compression test alongside performing a leak down. Lets see if I can't get to it before the rain falls.

Ill come back with an update

Side note - I've heard Valvoline VR1 Racing oil is preferred for our old blocks due to their zinc additives. Would anyone have anything to say for or against that oil choice? Thank you!

There is an additive called zddp I think
Adds zinc to newer types of oil. Lot cheaper than $10 per quart.

* Use like a cheap 30 weight for the diesel flush. I can’t remember if I added 1 or 2 quarts for the overfill. HRL can chime in. I stole the idea from him.

* VR1 is probably the best choice you have for oil. I would avoid ZDDP additives. You’re just playing blind chemist doing that.

* Although I don’t have before/after compression results to prove it, I think adding a PCV valve aided in reviving my engine to a healthier condition. Used to have a lot of blow by, now very little. I think relieving crankcase pressure helped rings initially seal better, and they eventually found a more permanent seal after some run time. My 235 sat for 30+ years and had some miles on it before then. It runs great now.

Very interesting comment regarding the PCV valve… did you throw it onto the vent tube like others out there have?

Never did pass chemistry class so VR1 sounds great to me, ha

Or use Classic Car Motor Oil if ZDDP is important to you. 1600ppm versus 1400ppm in VR-1.

https://inrccca.org/product/classic-car-motor-oil/

Alrighty - made my mock up running rig and ran for a solid handful of intervals. My initial readings (which I listed in the first post) were taken while the engine was cold. Online I read that a hot test was more ideal, so I did that on my new test. My readings were roughly 20 psi lower than my first test, but the pattern was the same as the first test. Below is a link of the engine running which I uploaded to YouTube just because. After a water jacket flush using water, the results were muddy water (maybe some oil). All of these results combined are making me think head gasket. Seeing as I will not run this engine an extreme amount I am not going to change the gasket YET. I will put it into the truck when it's ready and then I can make the change down the line.

Leak down test will be done tomorrow.

Cheers


Youtube video of engine running

Compression test:
Measure with a micrometer
Mark with chalk
Cut with an ax

Basically, a big waste of time and effort. Go directly to the leakdown test- - - -do not pass GO- - - -Do not spend $200.00. Get some accurate results instead of a guesstimate about what's happening!
Jerry