Compression worries

[turboman38]

Need opinions on what is good compression and what isn't. A friend and I did a compression test on my motor tonight. The motor has around 8000 miles on it after the rebuild. It's .030 over. There was nothing done to the heads on the rebuild. Not even valve guide seals. Stupid mistake but didn't have the money to get them done at the time. Here are the numbers from the test:

1 - 137
2 - 146
3 - 149
4 - 121
5 - 151
6 - 145

Average came out to be 141.5. The number 4 cylinder worries me. it's 13% below average. Do I need to be worried?

Any help is greatly appreciated!

 

[turbo buicks]

the specs listed on gnttype.org are 150 psi per cylinder w/no more than 15% variance. maybe you have a blown Head gasket. have you checked your coolant for bubbles or your oil to see if it looks like a a milkshake? could it also be blowby?

 

[WarpSpeed]

Overall, pretty good. 4# is off, however, how many times did you test it? Maybe the tester fitting wasn't all the way screwed in the sparkplug hole, or was leaking a little. Might shoot a little oil in that cylinder and see if the reading improves. If it does, that means something, I think, but I forget what. I don't think bad valve seals or guides will affect a compression test.

 

[turboman38]

Did the oil test and the number 4 cylinder came up to 136.

 

[alex]

If your reading went up with oil then its bad, dont want to
scare you, check with someone else but usually if you use oil and
# NOT going up then there is a good chance of bad valve guide seals.
Alex

 

[Jeff]

Just checked my '87 with 116K miles last month, 138-142 on all six cylinders.
I think something is wrong with your #4, if the oil helped it is most likely a ring issue on that cylinder and the oil helps seal the gap during the test.
Are you using much oil or seeing blow-by?
Jeff

 

[Chuck Leeper]

Low PSI??

Next test is a leakdown.. Listen for escaping air from the oil pan, intake and exh system.. That tells you which part of the engine is leaking and weak.
I wouldn't want to run an engine w/ more than 10% to a max of 15% and expect it to perform well..
Rebuild include a new cam?? If so, could be a lobe went south...

 

[turboman38]

Cam is new with the rebuild and It does not use any oil. I really don't want to rebuild it again.

 

[Chuck Leeper]

Rebuild again..

Guess then you can drive it til it blows and then maybe you will know where the problem was!!

 

[Two Lane]

Chuck...lol...lol

And then it won't be a problem anymore!
------------------------------------------------------------------

Seriously, it'd be cheaper to fix it now than later.

HTH