250-500cc WR250 Post Mortem

Well if you read my other post on my WR250 failure yesterday, I tore down the top end today (see pic). So the rear skirt is cracked, pieces of metal everywhere. The cylinder actually doesn't look too bad and MIGHT be reuseable with a honing, but it will need close inspection and measurement. I just read the Piston Problem Troubleshooting guide from Eric Gorr's site and this excerpt is EXACTLY the symptoms that occured before my bike died.

"A cracked piston skirt happens when a piston is allowed to run too much piston to cylinder wall clearance, or when its simple worn out. Cracks appear on the intake side of the piston, and the engine makes a rattling noise, especially at idle. If the piston runs too long sometimes the skirt can break off and cause catastrophic engine damage".

It just seems weird that the bike ran pretty well shortly before all this happened. I will still look for other possible causes. In addition, I will split the cases and do the crank too. No sense in investing in the top end even if I believed the bottom was cleaned out and within spec.

The up side of this is you will probably have it like new for less than $400 rather than $2000- $3000 if it was a 4t.

how many miles you think?

Remarkably, everything inside appears to be the original piston, and the bike is a 99". Can't tell miles, but I'm sure lots of hours since 99", and 2 owners before me. If this failed just due to wearing out, the moral of the story is its much cheaper to replace the piston and rings every so often, even if the bike still runs pretty good!

Where's the missing piece?

I picked up a bunch of large and small chunks out of the exhaust and some were laying right on top of the crank. However, I'm going to split the cases, clean everything, and send the crank out for a rebuild.