Flower Nut Stripped Off During First Ride - Cracked Case Cover! Any ideas??

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derusnathan

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Milwaukee, WI
First post here, so if this should have been posted elsewhere please let me know.

I just recently completed my first build, (80cc on an older Trek MTB) and thanks to this forum and some helpful hints from small engine savvy friends, it started first try and ran like a dream. I did not go very far, just around my block, and did not take it to full throttle or anything like that. As I was making my way back into the alley to park the bike, there was a big Jerk and the engine died as the pedals seemed to lock up simultaneously. Trying to engage or disengage the clutch seemed to make no difference whether the rear wheel would turn, and upon closer inspection I could see a bulge under the sticker on my clutch cover.

I lifted the rear wheel off of the ground for the remainder of the walk back to my house and straight to the shop I went. After removing the clutch cover, the issue was immediately apparent. The flower nut somehow managed to strip off of the clutch mandrel and once loose managed to punch a nice crack into my clutch cover and then lock things up. Tons of metal shavings on the gears in there. The screw that is supposed to prevent the flower nut from spinning loose stayed in place.

Any Ideas on what could have caused this? Could it be operator error of some kind on my end?

My biggest fear is that I will need to crack the engine to repair this which I would do if I absolutely have to but id rather not. Any help is greatly appreciated!
 

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Will it rotate now? It should. If not you may be experiencing "chain jam". Pull the side cover off that has the bucking bar and see if the chain is jammed into the case. That very well could cause this.
 
Dogsoldier said:
Is it possible flower nut was loose and screw was not in notch to start with? Did you check this before starting engine?
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Thanks for the prompt response! Yes, I actually tightened it myself because I noticed that after I installed the clutch lever, when engaged fully, there was a metalic rubbing coming from inside the case, which I realized was the flower nut screw coming into contact with the case cover, so I ended up tightening the flower nut a bit to compensate and stop that from happening.
 
Gordy said:
Will it rotate now? It should. If not you may be experiencing "chain jam". Pull the side cover off that has the bucking bar and see if the chain is jammed into the case. That very well could cause this.
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It is rotating now, the issue was the flower nut being jammed inside after it stripped off and it was sort of wedged in the area where the crack you can see in the picture is.
 
derusnathan said:
It is rotating now, the issue was the flower nut being jammed inside after it stripped off and it was sort of wedged in the area where the crack you can see in the picture is.
Click to expand...
As long as the jolt didn't throw off the trueness of the crankshaft you should be able to fix it without splitting the case. Will the flower nut thread back on to that shaft, or are the threads ruined?
 
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