Yz125 cracked case on first start up

I bought the bike with the motor partly tore down with a bad top end. I have put in a new Wiseco crank, bearings, top end, nikasil coated cylinder, and clutch kit into this motor. This morning after work I put the plastics on the bike and kicked it over for the first time. Fired rite up on the first kick and had a very high idle that I was dialing in for about 2 minutes when all of a sudden it starts leaking and dies. At first the kick starter didn't want to budge like the motor was locked up, then I rolled it back into the garage drained the dripping trans fluid and coolant took the clutch cover off and the kick starter was turning the crank over without a problem.

here is a pic of the carnage

crackedcase.jpg

Hopefully I will get a chance to dig into the motor and do a a full autopsy the next couple of days. It was low 40's when I started it, could just the temp change from the high idle have caused the case to crack? If nothing else is damaged can I mate an outside case from a different case set, and if so what years are interchangeable

No way temp change did that. I've ridden bikes in 0F weather, and snowmobiles at -30F. Something came apart, something was left inside that got caught in the primary gears, etc. Autopsy time...

Remove the clutch basket and closely inspect things, definitely something came loose inside.

Wow! That really sucks. Did you notice any cracks in the case when you had it split? The only thing that comes to mind is it got damaged when you were pressing the crank in or something was cocked and the force of the engine running did it. My guess would be that bearing right there at the top of the split wasn't straight.

My guess is the nut came off the crank shaft. It looks like the sidecover and not the engine case it self. did you torque the nut to spec when you installed it?

My guess is the nut came off the crank shaft. It looks like the sidecover and not the engine case it self. did you torque the nut to spec when you installed it?

Yep, exactly what happened. It's completely my fault, the bike was a project I picked up over a year ago, started, and never finished until recently. I guess I just mocked up the clutch side and planned to torque everything to spec before I put it in :smirk:

What years are interchangeable for the outer case?

Thanks

It is an '02, I should have specified.

Edited by wondo

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