5.7l compression question

[aktrucker]

Late 70's Volvo/GM 350, 260HP; 280 V/P S/P outdrive; 21' Bayliner Skagitt Sunbridge

After running thru many problems, I finally got around to checking my compression......here is what I found:

1-152 2-150
3-140 4-155
5-145 6-150
7-160 8-170

My question is this: I have read that more than a 20# difference is indication of a bad head gasket.....but with my compression this high is that still a possibility. And why is it the #7/8 cylinders appear to be holding better compression?

 

[Bt Doctur]

Re: 5.7l compression question

I see nothing to worry about with those numbers. may be from a slight difference in the bore size, ring seating, cross hatch,piston size, break-in procedure.

 

[aktrucker]

Re: 5.7l compression question

I got those with the engine cold, and no extra oil added. I don't have a carb right now, but once it gets here I was thinking od doing another test with the engine warm.........not sure what diff it could make but after I sent my carb off I read that the compress test should be done on a warm engine.

 

[Bondo]

Re: 5.7l compression question

Ayuh,... Those are Good #s,....

A few years ago, I had like 195 or so on my aft cylinders,...
Turned out the risers were leakin',... water don't compress...

Not sayin' that applies to you though,... There'd be Other signs as well...

 

[JustJason]

Re: 5.7l compression question

What you read on 99% on websites and the truth are 2 different things. Here is the correct answer straight from GM.

The lowest cylinder can be no lower than 70% of the highest cylinder. And all cylinders must be at least 100 PSI. No 1 cylinder can be lower than 100psi.

Your compression numbers are fine.

 

[aktrucker]

Re: 5.7l compression question

Ayuh,... Those are Good #s,....

A few years ago, I had like 195 or so on my aft cylinders,...
Turned out the risers were leakin',... water don't compress...

Not sayin' that applies to you though,... There'd be Other signs as well...

I don't think that is my problem....my boat is stored on the trailer, not the harbor......I have bigger problems though. I wish I had just bought a new Edelbrock instead of the POS rebuilt I got..........

 

[fossill]

Re: 5.7l compression question

My question is this: I have read that more than a 20# difference is indication of a bad head gasket.....but with my compression this high is that still a possibility. And why is it the #7/8 cylinders appear to be holding better compression?[/QUOTE]


Positive diagnosis of a bad head gasket is made by doing a cylinder leakdown test.