Head/Piston look sandblasted, what cause?

[Glitch]

Hey yall,
So this is off a 02 yz133, engine done by eric for mid/top porting. I ran it for the summer, not too much riding, maybe 15 times total, and one novice race at unadilla amateur. Compression had been slipping past couple rides, not too much but I was hoping to get acouple more rides out of it before winter and rebuild. Well took it out the other day, after sitting for 3 weeks and this happened after 15 minutes, could push the kick start with hand. Took it apart and it looked like the squish band area on head and around top edge of cylinder was sandblasted by large pieces of sand. There is also alittle bit of a sharp lip around the top edge of piston, also a tiny chunks took a tiny gouge out of an intake port, very small, but that chunk is now melted to top of piston. I didnt think it was lean at all, always had some smoke coming out of it, even pinned. Any ideas why it did this? so not to happen again. I do not have a carb mod which was suggested I think, and it does have the sst pipe on it. So I was thinking sending it back to have the 144 mod, and getting a fatty pipe and the carb mod... any comments welcome, and I do feel like an idiot for letting this happen...
Thanks, jim
sorry for bad pics, but from cell phone, only way to get pics onto internet.
also, the bike ran freaking amazing the whole time.

 

[Rich Rohrich]

That comes from detonation, which is a common problem with the SST pipes. They are prone to causing spark knock that leads to detonation if you don't tune for the pipe correctly.

So you need to run higher octane fuel or less ignition advance, or different jetting or a combination of all three.

 

[Glitch]

Ok, thanks. Do you think that the head can be fixed/ground down some if I send it to eric? Was thinking of gettting the 144 anyways. Then getting a fatty pipe, I heard that was recommended. Do you know of any threads or site that has info on getting that carb modification? or could you guys do that too?
Thankyou a lot for the post.
Jim

 

[Rich Rohrich]

Ok, thanks. Do you think that the head can be fixed/ground down some if I send it to eric? Was thinking of gettting the 144 anyways. Then getting a fatty pipe, I heard that was recommended. Do you know of any threads or site that has info on getting that carb modification? or could you guys do that too?
Thankyou a lot for the post.
Jim

If the head isn't torn up too bad it can usually be fixed. The SST isn't a bad pipe you just have to tune for it.


I'm not sure what carb mod you are referring to.

 

[wirefryer#85]

Rich is likely right, but make sure the Circlips are in there keeping the piston pin where it needs to be. I have a cylinder and NEW slug out in the shop that a circlip got loose in and detroyed about 4-500$ worth of work.

Don't forget to flush the lower end to get all the debris out.

Luck!

Tim