Overheated this weekend - 0 compression in 5 and 7

[pridekit]

One other piece of good news, my buddy was able to clean up my pedal position sensor/throttlemate assembly and it is now working wayyyyy better. It was binding up through its range of motion due to a lot of crud building up around the shaft, plastic bushing, and some other moving parts. Now it's super smooth and snaps right back to 0 if you don't have a cable hooked up to it (before it wouldn't even move with out you forcing it). That saved me $250


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[CJD]

I love new motor parts!

Strange about the #3 compression. If it was good before the head came off, then it seems it would have to be head related...or maybe the bad lifter was affecting it...

I'm especially glad to hear the compression was good on 5 and 7. That means the rings are good. You should see a world of difference next time you take the boat out.

[pridekit]

It was low prior to the whole overheat scenario, I thought it may have just been a bad reading from a cheap compression gauge. I'm not ruling the lifters out though, I'm going to buy a new set and see if it helps. If that does nothing then I'm going to try a wet compression test.

[wotan2525]

Wiped lifters means oil starvation. I'm not optimistic about the long-term for this engine. The good news? You'll be pretty damn good at wrenching on it by the time you're done with this!

[pridekit]

It would mean oil starvation to the valves and rockers, which are now replaced. My understanding is the valves/rockers are the last thing to get oiled in the GM 350, and the lifters are what provide the oil to that (and only that). I'm trying to wrap my head around the way the pistons get oil, it can't come through the valves because that would cause detonation. I'm struggling to find a good diagram of how the 350 provides oil there (everyone seems to talk about the crank and valves, no one mentions the pistons )

[wotan2525]

It would mean oil starvation to the valves and rockers, which are now replaced. My understanding is the valves/rockers are the last thing to get oiled in the GM 350, and the lifters are what provide the oil to that (and only that). I'm trying to wrap my head around the way the pistons get oil, it can't come through the valves because that would cause detonation. I'm struggling to find a good diagram of how the 350 provides oil there (everyone seems to talk about the crank and valves, no one mentions the pistons )

The pistons are oiled from the crank bearings. Oil from those is flung off and into the bottom of the pistons and on to the piston skirt.

[pridekit]

I wish I could see through the block and watch that process. It doesn't seem like there would be much oil actually getting to the piston.


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[CJD]

It's enough. The SBC was the mainline engine at GM for over 40 years, so it works very well. If you get into heavy super charging, then it becomes necessary to add more oil to the cylinder walls.

If a couple squirts of oil in the plug hole raises the compression, then you know it's a ring problem.

[pridekit]

I took a part the manifold on the bad side. One side of the gasket looked a bit funky. Other than that it just looked orange and a bit bubbly in there.









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[pridekit]

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