Piston Diagnostic

[RM_Dude]

This is a Wiseco piston from a 1999 Suzuki RM125. It had probably 20 hours on it since being installed last fall. I followed the same heat/cool cycle for break in as I always do.

The bike was running great then suddenly I heard a pop followed by a small clicking noise from the engine. My first thought was that it broke a ring. The clicking noise stopped after a few seconds. I idled it back to the truck (from an MX track) and once I pulled the pipe I could see the chip on the piston while looking into the exhaust port. The cylinder is fine so I guess that chip made it's way out the exhaust before causing any trouble.

I have some images of the piston here:
http://www.rotinc.com/piston_pics/

Any ideas what would cause such a thing to happen?

 

[Jaybird]

How do the ports and the PV look?

 

[Glitch]

Looks like maybe it had a small encounter with your powervalve. You should check the powervalve to see if it is dented. Look at the head on your bike to see if it has any nicks in it also.
Also, you should consider yourself very lucky that the peice blew out and didnt ruin your cylinder.

 

[RM_Dude]

Sure enough, upon closer inspection I have found a broken exhaust valve but amazingly nothing else shows any damage at all. I can see very slight marks on the head where the fragment hit a few times before being ejected.

Suzuki gets $105 for that little valve no bigger than my thumb !! O well, I'll just be happy it didn't ruin the cylinder.

Thanks guys

 

[marcusgunby]

The RMs are renounded for doing this-have been since 89-seems a long time to have not sorted it out.

 

[Glitch]

Are the marks on the head big enough to cause hot spots you think?

 

[RM_Dude]

The marks on the head are just very light scratches, you can see something metal hit it and removed any deposits. Top of the piston has the same scuffs but I don't think they can be seen in the images.

Wish I knew of somewhere to get a replacement exhaust valve for less than $100. I do feel lucky to not have a trashed cylinder but I can't help but feel I'm getting the shaft from Suzuki for the valve.

 

[Fark]

maybe a machine shop can make them cheap. Or are they coated? :think: