[Wayne C.]

Hello ever one. I'm new to the cougar world. I came across three cougars a couple of months ago, one of them being a 68 GT 390 with a rust free body. The other two I will use for parts.

Now for my question. I just completed a rebuild of the 390 motor and the compression readings are between 150-155 on all the cylinders except #8 which is 125. What do you guys think would be the cause for the lower reading on #8. The motor has not been fired up yet, just cold cranking compression with all plugs out, no carburetor installed.

Thanks for any info/opinions you might have.
Wayne

 

[Bad69cat]

Hi Wayne - Welcome! What did you do head/valve wise? Could be you have a valve leaking by a bit...? Some variability isn't to unusual though.....

 

[1970fastcat]

Unless you can think of something that wasn't done, or wasn't done right, I wouldn't be concerned with it. Wait until the engine is running and the rings get seated good. You will have better compression readings then.

 

[Wayne C.]

Thanks for your reply. I will be firing it up on an engine stand this week. Hopefully the low one will come up close to the rest.
Wayne