NPC! Engine problem Options

[ripper911]

I am here to draw upon the wealth of mechanical knowledge on this forum to help diagnose my brothers chevelle. I don't know much about that type of engine.

I believe the engine is a 400ci that has been destroked to 377ci.
It recently started flattening the spark plug gaps. He doesn't think the rods have stretched because they are supposedly high quality. It doesn't sound like the crankshaft is moving around or anything.

He's a mechanic, neither he, his boss, nor anybody else he's asked has been able to figure it out.

[Bulldog9]

Plugs are likely too long.

Even if they are the stock plug, a modified setup may require a shorter plug. Things may have been fine for a while but carbon buildup on the piston may raise the height just enough to now make contact. I would measure the threaded portion of the head, then the threaded area of the plug. If the plugs have been in for a while and the plug is too long, even long enough to protrude in the combustion chamber the lower threads will be discolored. That is an easy check.

One other thing to think about, the plugs for most SBC engines DIDDNT come with a crush ring or jacket. Back in the day we would add a copper crush ring to the plug when we were worried about this. I'm sure they are still available.

I'd add a gasket then run some serious cleaner at high concentration, then change oil and see how things go.