TOPIC:

My 81 Gpz needed some attention, the primary starter clutch was slipping and I was planning to upgrade to forged wiseco 615cc pistons probably with a big valve cylinder head and base circle skim fast road cams.

Recently it develoed what sounded like a top end rattle which got a lort worse over the course of the next few hundred miles. What was a tired and slightly smoky engine got a lot worse....I knew I was on 99% by then.

This is the bike with slipping starter rattly motor and smokey exhuast.









much worse now -totally stufed.




This is what i found...




wrist pin fine



Bore not so happy, scored also on the other side









Piston boss badly cracked







.
I think i know what went wrong here. no probs, the engine was coming out and the block was coming off anyway. Call it routine maintenance.

Looks like the piston was flopping from side to side.
Steve

It sounded just like the wrist pin rattling in the top end, it got worse from just noticeable to really bad within a few hundred miles. The pin looks fine, half of one piston circilp was missing and the pin was floating far too much beyonfd the circlip groove . The worst damage to the top of the cylinder wall is quite localised.

I think it might be detonation damage. I was fooling around with a defective advancer and got some severe pinking open throttle on the highway. I wanted to feel the difference and knew the pistons were on their last leags.

Bummer, So you will probably go thru the bottom end too?

Probably not, all the shrapnel fellto the bottom of the sump. I might split it anyway, I can't remeber if I fitted a new primary chain or not. Bottom end all ok it seemed ok when I built it .