I sold my '95 Bonne to a friend of mine and he said while his son was driving it, there was a noise from the engine and then it started missing. He pulled all the plugs and on the #3 cyl. the electrode was completly gone. When we tore into it, we found there was a burned area near the side of the cyl. and a hole burned through the piston.

Anyone ever saw this?

My old Buick Somerset did it twice. I decided it did it for reasons not likely on a Bonneville (valve that pulled air off the exhaust manifolds when it was cold never closed after it warmed up so the engine pulled in super hot air).

But a Bonneville didn't have that... so I don't know what would cause it besides maybe a really lean condition and WOT.

Did he run regular fuel in it? Need premium for a boosted car.

Non-premium and a bad fuel injector (or bad valve) could easily do that.

A little more extreme application, but this was 87 octane in a premium only motor:



So what fuel was it?

Well after doing some head scratching, I think I know what may have caused this. When my buddy, who I sold the car to started working on it,he bought a new set of spark plugs, and he told me when he pulled the ones out for the comp.check, he noticed they were shorter, I.E. the wrong plugs. When he pulled the head off he noticed the (wrong) plugs barely extended past the end of the threads. So We're thinking this caused a hot spot in the cylinder due to the plugs firing too hot, or irratic firing or both? I imagine he was using regular gas, that'* what I used in it when I had it, but I don't think that what caused this, although it could have been a combination of things.

Doe'* anyone know where I can get a set of stock size rings for the one piston we'll be replacing?

That'* what did it.

Supercharged engine + 87/89 octane + WOT = Boom.

Simple equation.

AUTOZONE PT# 2M4764 HASTINGS

I don't mean to sidetrack this topic, but the owner'* manual for my '93 SSEi says:
"If the octane is less than 91, you may get a heavy knocking noise when you drive. (In an emergency, you may be able to use lower octane--as low as 87--if heavy knocking does not occur)."

FWIW, I personally know people who use regular or mid-grade fuel in their supercharged cars because of today'* high cost of gas, and nobody has noticed any problems.

Are you saying that "Boom" will occur?

In time, yes. Every knock your engine produces is slowly damaging your pistons. If you have KR, it means the engine already sensed the knock, and retarded the timing to protect itself. But the knock has already happened.

It'* a reaction more than a protection.