Piston Crack

[Campbell]

I had a piston that was down on compression versus the others so I pulled the head and found a head gasket that wasn't right (distorted shape around the cylinder).. that was obvious enough. As long as I had it opened up I pulled the piston: the compression ring moved freely but the #2 ring, was pinched in place and didn't move freely at all. At the pinch point is a crack that runs straight down from the #1 ring slot to the #2 ring slot. A couple of dumb questions, would this impact compression? I assume you shouldn't use any piston that has a crack? since this is the first time I have come across this I really don't understand the technical aspects of it. thanks

[Conover]

Pictures?

Is that an 8V?
8V's are non interferance, so if it was an impact you either dropped a valve or something got loose in the combution chamber, like some foriegn object.

Maybe that cylinder was leaned out, fuel injector O-rings leaking? loose spark plug? Pictures of the piston might help.

[Campbell]

Yes I have battled a run lean condition, and this cylinder had been the leanest according to the plug condition. Thanks

[green golf]

also check your timing. too much can make it detonate causing ring lands to break. i run 28 deg. advance on my a2

[Greg Amy]

Replace it, and thanks your lucky stars the over-lean condition resulted in only a cracked piston and loss of compression. I've totalled lunched VW engines due to detonation, and it tweren't pretty...

[joeg]

eh..while you are replacing the piston, you might want to take a good look around for other issues. If you have experienced detonation severe enough to crack a piston, that means reconditioning rods, all new pistons, perhaps a line hone, etc.