Compression leaking into the intake is a thought I had awhile ago. It runs good aside from some occasional low power issues which I attribute to some air intrusion I had been fighting. But once I kill the engine when it’s hot, it’ll let little hisses out almost like pressure is relieving so this is why I considered the compression leaking. I put studs, new head gaskets, as well an intake gasket on this engine when I got it. It was in solid shape. I’m going to do a compression test like IHC1740 said and pull valve covers to see what I can find and I’ll return with what I get.
That's crankcase gasses.
No it's not normal. The pushrods get their oil through the lifters. If, for some reason, one or more of your lifters aren't getting enough oil into them, that could possibly explain why you're getting combustion back through the intake. If a lifter for an exhaust valve doesn't have enough oil pressure to hold it open, then it's not letting all or at least some of the burned gasses out of the exhaust valve. When your intake valve opens, some of the combustion left overs can come back out of the cylinder through the intake valve. The piston has compressed what is still left in the cylinder so it has more pressure than the incoming fresh air. That means that the compressed mixture in the cylinder will leave by the only available opening. The intake valve.
We’ll this thing has a few bit of oil leaks, I’m going to start patching them up while I wait for the compression adapter to arrive and just chip away at this thing until it’s good to go.
That’s a good point I hadn’t considered. I’m going to clean the rods and order new lifters just to save myself the stress.
