What happened to my WR450

Can anybody tell me what happened to my bike. I recently checked my valve clearances, all valves were in spec except for the right side intake. It was way out, I shimed it with a 220 shim to put it back in spec, put the bike back together and had three great rides. The bike never ran better. Then the fourth ride the bike ran like crap, no acceleration, tons of backfiring, and the muffler got real hot, i mean like i could feel the heat off of it while sitting on the bike. Any how, checked the valves again and the same valve was way out of speck. Started tearing the engine apart and to my dismay the crank shaft is bent, visibly bent. How did this happen? There were no pieces of metal floating around down there, I didn't drop a shim down the engine. i'm working on a total rebuild now but how on earth did this happen?:thumbsup:

The crank shaft is bent, or one of the cam shafts?...SC

Im wondering the same thing, crankshaft???

Definetly the crankshaft. Pulled it out and it is bent! Not the camshafts

I don't see how this can affect valve backlash though, you must have more problems in the top end, like a valve mushrooming or somehting.

piston smacked the valve?

Maybe your decompression lever was making the valve seem out of spec. I am not sure about your specific bike and how it works. The decompression lever on my old XR400 would make it difficult to adjust one of the valves. Maybe the shim you put in caused that valve to stay open and damage your engine.

anytime you have to make a large adjustment at tune up, eather somthing is wrong with the machine or your doing somthing wrong,

befor any large adj. its critical to deturmin why

A 220 shim seems very large. Most of the WR's seem to have shims in 160 -180 range when new. Did you adjust because there was too large a gap or was there no gap. Valves normally get tighter because of wear to the seat or valve face causing the gap to get smaller. My guess is that your valve was held open by carbon, causing a large gap. This normally falls out next time you start the bike when you put in a 220 shim to close the gap, pushed the valve into the piston which bent your crankshaft. What size was the shim that you removed? A 220 shim is 0.50mm longer than a 170 shim, when you consider the normal valve clerance is between 0.10mm and 0.15mm for intake valves that is a huge change.

Well it seems I made a very costly mistake.... Guess I'll have to chalk that one up to experience. My bikes almost done and I can't wait to get back out there.

How could a incorrectly shimmed valve bend a crankshaft? As in the part that rotates around with the flywheel attached to one end and the main drive gear attached to the other? The valve would bend way before the crankshaft would if there was piston-valve contact.

pretty hard to bend a crank!! Did a crank bearing let go? Even in a worse case senario I would think that the rod would bend well before the crank. In fact I rebuilt a friends KX250F motor that grenaded. The piston hit a valve the valve broke off went into the cylinder bounced around a few times befor it got stuck between the piston and cylinder. It broke the rod in half and sent it onto the track through a huge hole. The cases were both damaged but the crank survived.

do you have a picture of the bent crank? what part is bent?

detenated right at tdc. are the signs of detenation in the conbushtion chamber?

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