Hey yall been a while since the last time I checked in!

Working on my 75 Gt80 today, it runs currently but stalls after warming up and it puts on quite the smoke show. At first I thought to adjust my premix, or to set the carb to run leaner, although neither of these worked.

I pulled the top today and noticed a lot of residue of what looks like crankcase oil.

I did a dry and wet compression test, cold because I can't get the engine warmed up properly. I got a consistent 75psi for the dry test, and consistent 90psi for the wet test.

Is this enough of a difference in compression to assume that the issue is that my piston rings are worn and letting crank oil into the head?

Thanks in advance for any help! Always appreciate the feedback I get here

Crank is lubed by premix. Sounds like you have a bad crank seal on the transmission side and are sucking in oil there. Depending on how long you've run it, you might be able to tell that the transmission oil level is dropping.

Assuming this is the issue, how big of a job is changing crank seals? Would this mean splitting the case? I have never done this before although I have replaced my selector rod oil seal once.

Cases don't have to be split but you do have to remove the clutch cover, crank gear, and possibly the clutch on one side and the flywheel and stator on the other.

Service manual in the Tech Library can give you an idea of what's needed.