I have a 69 coupe that has a 302 in it with compression readings of 115 psi +-5 on all of the cylinders. Does this sound a little low or is this what was normal for this year?

Thanks in advance!

Shawn

 

It does seem a little low for a late 60s engine, but,,,if you have a warm cam, this readingmay notbe out of line at all. As a general rule thewarmer the cam, the lower the compression.

If the cam is stock you may have some wear issues, a leak down test would be better to diagnose this though.

115 psi /14.7 lbs = 7.8 to 1 CR.... (ok close to that at sea level) under impossibly perfect conditions. a 10 to1 CR engine would develop 147 lbs of pressure undrer thes same impossible conditions.

So,,, maybe it is a little low and maybe not..... I hope this helps!!

Sorry, if you know what cam you are running I could probably make a better guess...

I have a feeling that Norm could answer this well.... Norm Peterson where are you!!

 

I am not sure what cam I am running. When I first ran the compression test my #2 cylinder was way down around 60psi. A little inspection revealed that a rocker arm was almost completely unbolted. Once I torqued it back into place it came back up to the others which was around 115 psi. It runs much better, obviously, so I am now questioning a total rebuild. The compression just seemed a little low.

Thanks for your advice!


Shawn

 

Certainly don't rebuild it on the basis of the compression test, there are too many variables that might make your compression readings more than just ok..

 

Yeah, I was going to rebuild because of the burning oil that was caused by the loose rocker arm. I thought for sure that the rings were going bad. That is why I am second guessing that thought since correcting that problem. I was actually pretty surprised that the all of the cylinders were as close together as they are in compression readings. The previous owner did not take good care of the car as I have found many bonehead rigging such as wires stripped,twisted, and left hanging in the engine compartment and under the dash.

Anyway, I am planning on tearing it down and replacing the gaskets so I am sure I will find out what makes her tick in the process.


Shawn

 

do your compression test again but before you do it squrta little oil in the cylinders first. if compression raises then you know your rings are bad

 

+1

The rule is youdon't want any cylinder to be more than 10% off from the rest. If you're +/- 5psi, I'd say you're in fairly good shape.

Did you do the test with the engine warm? The engine needs to warm up to get a proper reading, and the oil squirt trick will tell you the condition of the rings.

 

thanks guys, I reran the test today with the engine warmed for 20 minutes and got 135 +-5 on all cylinders. Last time I only let it warm up for about five minutes and it was very cold, so the engine may not have been warm enough.

Thanks for the incite!

 

Nice, I'd call it good