Help-Investigate Root Cause-Blown Piston

Hey Gang, I need some help identifying the cause of a detroyed piston. I wrode my new to me 2002 WR 426 last weekend for 30 min. and the motor just locked up. I couldn't kick it past TDC. When I tore it apart I found that a relatively small piece of the piston blew off, and left molten aluminum stuck to everything... head, valves, piston, cylinder. The piece came off on the outside diameter of the piston just above the rings. The rings appear intact and the piston was not seized to the cylinder , once I removed the head and debris the piston moves freely in the cylinder. I am thinking that it must have overheated because there is molten metal stuck all over. Is it the oil flow, the coolant flow, piston, something else. I have never heard of or seen anything like it. Fluid levels were OK and the bike supposedly only has 60 hrs or so. :thumbsup:

I tried to attach pictures as they would help greatly to explain, but they are saved on my PC and it is asking for my URL, and I'm not sure how to attach(direction on this would help).

Thanks for your help!

You need a photobucket or flikr account to facilitate attaching pictures with clarity.

I have attached the pics below for reference.



Looks like a fatigue failure of the ring land. Lots of hours or lots of bouncing off the rev limiter...


Caused by too low an octane fuel, too much ignition advance, too much compression or too lean.


Caused by too low an octane fuel, too much ignition advance, too much compression or too lean.

Yep! Any chance the previous owner ran regular in the bike? That damage likely took place over a long period.

It's 2008.

The bike is a 2002.

Do the math.

It was tired and blew up.

I vote for lean condition, that piston look awful clean for a 2002.

Or foreign material entered the cylinder.

Check your carb to see is the plate inserted in front of the slide is in one piece. There has been reports of part of the slide or part of the plate breaks off and gets sucked into the engine. If any foreign material of such size end up on top of the piston it will surely break off the top of the piston, just as your picture shows.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now