Snolab

So my son and I did a basic comp test on my 69 - and here is what we got:
1- 170 2- 160
3- 162 4- 170
5- 160 6- 162
7- 170 8- 122 ??


So for you more knowledgeable guys what should I take away from this? I believe the car to have about 60k miles on it. Engine blows no smoke, sounds great, starts right up etc. Is it likely #8 cylinder has a bad ring? Just looking for how I should move forward. Need to pull engine as oil pan is badly dented and leaking pretty good. Thoughts?

MDchanic

Was the car warmed up?

Were all the spark plugs out?

Was the throttle wide open?

Did you do a second "wet" test on #8?

If all are "Yes," and #8 didn't change when wet, then do a leakdown test - could be a slightly burned valve, or just one iffy cylinder.

- Eric

Snolab

Eric,


Yes to all the questions except the redo wet test. We just did not know enough to do that and ran out of time. So are the other numbers within a reasonable range for this engine?


Tom

olds 307 and 403

Yes, those are acceptable numbers. It could be a leaky valve, which is the reason for the wet test. Inspect the spark plug on number 8, if there is oil or deposits will probably mean worn rings.

MDchanic

+1.

Overall numbers look fine.

A wet test, where you squirt in some oil (I always crank it around once or twice afterward, to eject any excess oil and prevent the dreaded hydro-lock) and then recheck the compression, will read higher if the problem is ring seal, as the oil will help seal the rings, but will not change if the problem is "upper," ie: leaky (burned) valves, head gasket leak, cracked head, etc.

- Eric

oldcutlass

Cylinders 3/5 may be pointing to a future head gasket issue, #8 may have an issue.