Threads stripped on clutch mandrel

ballinchestr

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Mar 6, 2014
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I lost all power to the rear wheel while riding today, the engine would just rev, and there was no resistance when the clutch was let out. I opened it up and tightened the flower nut, but then noticed that letting the lever out all the way and pulling it back in resulted in pushing the flower nut back out. I took the nut off and saw that the threads on the clutch mandrel were totally stripped, and can't provide any support for the flower nut. Letting the clutch out results in loosening of the nut.

To replace the mandrel, do I need to take apart the crankcase or is there a way to replace it without doing so? I'm currently at university and it would be really inconvenient to have to tear down the whole engine.
 

xseler

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Apr 14, 2013
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When I replaced mine, I didn't even remove the engine from the bike. I also tapped the pressure plate so I could use the larger 8-32 screw to keep the flower nut from 'slipping' past the original stop screw.



If you have limited access to tools or workspace, be sure to order the mandrel as an assembled unit. It does cost more, but it'll sure be a lot easier to re-assemble.


Best of luck in your repair!
 

crassius

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Sep 30, 2012
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I have often seen threads go bad in the flower nut, but never on the mandrel itself - be sure of where the problem is before ordering parts.
 

crassius

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Sep 30, 2012
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ah yes, easy to spot - I thought you meant the 6x1.0 rod that holds the flower nut
 

crassius

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it is easiest to use puller that comes with kit - fits sprocket & clutch hub at both ends of shaft - with shaft already damaged, one might hammer them off, but . . .
 

ballinchestr

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Mar 6, 2014
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So I got the old clutch shaft out. I don't have the puller that comes with the kit so I pried off the large clutch gear and popped out the shaft out the gear side. Now I have the old shaft with the sprocket and bearing attached. Does anyone know any tricks to get the sprocket and bearing off the shaft? I've thought of finding a bearing/pulley puller (the kind with two or three prongs) and using that, or putting the thing in a bench vise (If I can find one) and finagling it off by prying and or hammering. Any thoughts?
 

ballinchestr

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That's the plan. Where should I clamp the shaft assembly? Should I clamp the bearing first and hammer the shaft out of both the sprocket and bearing? Or should I somehow hammer out the sprocket first and then the bearing? It seems like it's gonna take a whole lot of hammering to get the shaft out of both at once.
 

crassius

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sprocket is wider than bearing, so open vise that wide and do it first, then bearing (being sure to support the inner race rather than outer)
 

crassius

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shouldn't take too much force - if you tend to be a bit clumsy with hammer, then you might want to use the puller that comes free with kit
 

ballinchestr

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I'll give it a shot, since I don't have a puller and cant really have one shipped in the time ill need it. About the bearing, how can I support the inner race if its covered up by the spring of the clutch shaft?

Okay so I got the thing all back together, and as soon as I tried riding it, the same thing happened. letting out the clutch resulted in the flower nut skipping threads and moving outwards. It's as if the flower nut is slightly too big for the 6mm rod that its supposed to go on. Both the flower nut and the shaft were brand new. the flower nut was noticeably loose when it was threaded onto the shaft, and had both side to side and back and forth play. What do I do?
 
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crassius

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on at least 1000 motors in for repair over the years, I've only seen stripped flower nut about three times - they were always on motors with circles rubbed into inside of outer cover which made me think maybe they had been jammed into the cover so hard it stripped them, but never saw any clear info about how it happened

suspect you're just not seeing something here, but you might try a washer, then two thin 6x1.0 nuts doubled on the rod
 

ballinchestr

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Mar 6, 2014
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Central MA
on at least 1000 motors in for repair over the years, I've only seen stripped flower nut about three times - they were always on motors with circles rubbed into inside of outer cover which made me think maybe they had been jammed into the cover so hard it stripped them, but never saw any clear info about how it happened

suspect you're just not seeing something here, but you might try a washer, then two thin 6x1.0 nuts doubled on the rod
Well both the flower nut and the rod were brand new, but the problem was between them, so I don't see how it could be a problem somewhere else within the bike. I think there wouldn't be enough room for two nuts and a washer on the shaft, because it barely protrudes out past the clutch plate.
 

crassius

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Sep 30, 2012
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sometimes when clutch fails to grab well (and maybe flower nut goes in so deep as to hit end of shaft) one has to hammer an outward dimple in the middle of the plate to get more pressure on it - in the case of rod not protruding, one might be able to form an inward dimple in the middle of the plate

however, it would be best to find out why this is happening
 

ballinchestr

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Mar 6, 2014
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Central MA
I've had that problem before, but this time, its a failure of the flower nut, as even though it's adjusted properly, and the clutch is grabbing the way it should, the flower nut moves away from the engine, skipping the threads of the rod its on.