Check out my lovely crack

[rich]

As the hybrid frame has now gone for coating I thought I'd make a start on the engine. Imagine my surprise when I removed the top end today to be greeted by a lovely great crack across the top and down the side of the r/h piston The bike has been laid up for a couple of years but was regularly being thrashed right up till it was sorned with no apparent loss of power or excessive rattling either. Any ideas what could have caused it? The bores are on 0.75 and from what i can see they are gen Yam pistons. There is also a crack on the skirt too. My guess is the head gasket was weeping coolant into the bore (hence the clear areas on top of the piston) and this may have caused it? Any thoughts? Enjoy the pics

[JonW]

ooof! nasty!

[rdstars]

Probably wrong here but when you say regularly thrashed, was it trashed from cold. Looks like it's tried to or got near a four corner seize. If it did the crank has pulled it down when it did causing the damage.

BUT I'm probably wrong.

[bigal1]

i would use differant 2 dtroke oil to there is a lot of build up on that piston

[Norbo]

One thing is for sure . you are bloody lucky you split the lump and didm't just fit and thrash .

[rich]

Yep, can't believe how lucky I was. If I hadn't stripped the motor, I wouldn't have been any the wiser and if that piston shattered it would have made a big mess! It must have been like it a while as there is a lot of carbon build up around the crack and the area around the rear crack has been polished by the edges of the inlet port. As for thrashing from cold, no not really. I normally give it a bit of time to warm up first. I still reckon it's stress fractures from coolant seeping in. I always use decent fully synth oil (TTS, Rock Oil synthesis 2 etc) and premix at 40:1 although I may increase this to 33:1 when it goes back together.

[47x]

wow!!! u are soooooo lucky.seeing as the corners are cleaner,yep i would say coolant seepage,see the difference in genuine and after-market parts!!!! although that maybe a 1 of.lucky

[billyboy]

am i right in thinking rich you used a single layer headgasket ? i did the same on my 2 valve engines ,getting worried now.

[hazey]

That could have been messy

[arrow]

You were really lucky you found that when you did.

[lcbob]

Very lucky there! Its probably non consolation but exactly the same happened to me on an RD200 bought new in 83. Run in, decent 2 stroke oil etc . Not as big a crack but at 6500 miles there it was

[voivod]

wee bit solder n a polish it will be ok