87 GN Blowing compression out the oil cap!

[86cutlass400hp]

I have a 87 Grand National that is bored .40 over , put about 20,000 miles ion it since rebuild. It is blowing compression out of the oil cap spewing oil everywhere. I pulled the heads off the car tonight thinking it was going to be headgaskets, but the head gaskets are fine and cannot see any cracks in the head and the pistons and cylinder walls look fine. I know i should of done a compression test, but I did not thinking it was going to be something obvious. Can any one tell me if they ran into this problem before or give me any suggestions. I want my GN BaCK on the road!!

Thanks
Tim

 

[TurboBuRick]

You should have dug deeper before your tore it down.
Was it blowing oil all the time or just under boost?

 

[86cutlass400hp]

it does it all the time. Idleing and driving. I didnt drive it after it happened.

 

[TurboBuRick]

If it's doing it while idling then it has to be a issue with the rings. How did the spark plugs look? How do the pistons look. Any of them look worse than others? Carbon or oil build up?

 

[Jerryl]

Blown HG into the lifter valley.

 

[DailyDrifter]

Rings

 

[84BuickGNYorkPA]

"Rings" + 1
Compression is going by the rings and into the crankcase, blowing the dipstick up about 1" and causing the valve cover vents to get soaked with oil and drip onto the exhaust manifold or headers. Ask me how I know this.. Maybe you are lucky and only have bad rings...
By the way how did the car run at .040 over? Pretty darn good I bet!

Chuck

 

[1 QWIK 6]

I will go with the head gasket into the lifter galley. Had the same thing happen to me.

 

[Otto J]

What pistons did you use on the rebuild,Id be hard pressed to think rings.But if the head gasket is definetly perfect into the lifter valley.
You may have cracked a piston.
Got any pics of the head gaskets you can post?

 

[Turbo1dr]

Do a search on "catch cans". A lot of members went that route instead of rebuilding their engine.