Compression ck numbers

So i did a compression gk on my '72 Skylark 350-4 stock motor with a/c componets removed and smog removed.

I did as per '72 Buick service manual and suggestions from Cliff. I check everything twice.

The numbers I got are:
1=178
2=178
3=175
4=178
5=178
6=186
7=180
8=185

According to the service manual I fell that the compression is good and the rings, pistons and valves are in preaty good shape.

I have not had the time to install my rebuilt distributor or power time it yet.

I'm thinking the smoke I'm getting when I start it up in the morning is becouse of the valve stem seals and the the simi rough idle is becouse the Qjet is a from a '73 buick century and isn't turned for my car.

Once again, I have no coolant loss and no smoke when I driving during the day and the car acelerates good with no stumble.

I do go though about a quart and a half of oil every 1,000 miles. I see no drips on my driveway.

I started a nother thread asking how to change the vale seals and got some really good suggestions and how to. I think I'll tackle that next, or maybe the power timing.

I'm I thinking right?

Thanks,
Brad

 

If you are not running PCV you might be burning oil as a result of excessive crankcase pressure. Also check for oil in your coolant, but if those are all the problems you see then I'd bet you're right about the valve seals vaporizing.

EDIT: Reading a little closer, when you start the car in the morning it is absolutely the valve seals.

 

A compression test will not tell you much about the oil control rings. be design, they are not supposed to hold compression, only to scrape the oil off the cylinder walls and channel that oil to the inside of the piston.

 

Yes, as with valves. You need to do a leak down test. But compression numbers are very good for a 72.

 

Thank you guys, I've just learned some new stuff today. I'll check into a leak down test!
Thanks again!

 

I was thinking that too. 170 180 are quite high for a 72. I wouldn't be surprised if there were shallow dish pistons in there

If I remember I was seeing like 135 after a rering.

 

I check every cylinder twice just to make sure my readings were correct. I don't know the complete history of car. I bought it from my brother and he had it for about nine years. He said he never did anything to the motor. Or maybe someone rebuilt it befor it got to my brother. I know the Qjet is not the original and neither is the distributor.

There's 80,000 miles on the odometer which maybe it has 180,00 miles on it and some one rebuilt the motor...

I'm gonna pick up a leak down test kit just suggest by Alec298. It'll be nice to know a little more about the motor.

 

OOOOR, it could be a bad compression gauge, OOOR carbon build up on piston tops, OOOOOR, a smaller than stock cam.
I would try another gauge, the gauge I had for years would always read 90 psi, so I bought a Snap On gauge, my psi numbers went to 178/189
That was on the engine I pulled out last year.

 

I wonder if I could hook it up to a compressor with a know PSI to ck if the gage is correct?

 

Leak down test shows more in my opinion. I also say if the readings are correct I think it’s now a 9.5:1 engine to get those numbers.

 

A puff of smoke on start up is usually the valve seals.
You can chuck some air into the cylinder at TDC and simply listen where any pressure escapes from.
Don't leave anything attached to the crank.

 

You can't really say that with a compression test because it is more of a measurement of the dynamic compression, not so much the static.

If it had 9.5:1 dynamic compression it would need to run on race gas for sure.

More than likely if it is an untouched factory low end it probably had an RV cam swapped in it at some point.

 

It could also be a strangely degreed cam to get the high compression test... my guess it’s a high compression engine... it’s a guess that’s all... agree or disagree or guess yourself

 

Yes and that would still be the dynamic compression if the cam is making the compression test read higher.

An engine with a 11:1 static compression ratio can have a PSI compression test reading in the 140s if in the cam was big enough with enough overlap to bleed off low RPM compression.

 

how can the compression be 140 with the valves closed and the piston is coming up to TDC. Less time to build compression since the cam is bleeding off with the overlap? Mine hits 190 and my overlap is 230-245.

The leak down test is the way to go then you know if the thing is holding or not, the last time I did this I had numbers in the 90-95% range. Leak at about 7%

 

Ahhh Gotcha makes sense.

 

Man you guys know your stuff! I've hit a very busy time in my life so I have to put the leak down test off for two or three weeks. I also want to check to see if the compression gage I'm using is good. After reading what you guys have been saying I want to double check everything. the car runs strong but have my doubts if it's been built up.

I know that about 7 or 8 years ago they installed a T/A high performance oil pump and I think timing cover but i haven't heard of anything else.

Attached is a photo of the motor before I repainted it.

Thanks,

Brad

 

Thanks 8ad-f85, do I need to remove the valve covers to hear the leak or ca I leave them on?

Brad

 

You can leave the valve covers on.
If an intake valve is leaking, you'll hear it thru the carb
If an exhaust valve is leaking, you'll hear it thru the exhaust manifolds/headers
A leakdown test wont really tell you if a valve seal is worn.