I just have to post this. My 86 XT 600 is an awesome bike - hands down the best Enduro I've owned. I've figured out the carb trouble, suspension woes and minor squabbles. But there was this racket coming from the rear tire area that was making me nuts. I re-aligned the tire, checked bearings, chain, rear sprocket, spokes but still had a 'chain-slap' noise that wasnt going away until.... I geared down to third to turn right, made the turn, got on the throttle when BANG and parts went flying. My rear locked up until the chain snapped, I went into a speed slide, bike died but I held onto it, coasting to the curb. Behind me lay strewn about was pieces of plastic and metal. The front sprocket snapped in half at about 60k. Along with it the chain is KIA, chain guard, chain guide and sprocket cover. $250.00 Can.

The noise was from the sprocket bending because of the cracks and making the chain whip.
The reason it snapped is evident in the pictures. Yes that is failed weld. Who welds a sprocket onto a tranny shaft??
This is a classic case of 'buyer beware' and things you do when drinking too much . I ve saved the sprocket, will put it in a sock and nail the dumb SOB in the head with it. I could've been killed had this happened on the freeway.
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