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justinpage426

mushroomed end of crank

15 posts in this topic

Was trying to get my flywheel off to replace my cam chain on my 01 yz426f and mushroomed the crank end. I filed off about 2 threads and it's not mushroomed anymore but the not will not go on still. What would be my best solution to fix it?

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you mushroomed it with a puller? 

 

you will need to doctor up the threads where you were filing to give the nut the opportunity to start. Unless you are saying its too short to even get the nut on with the flywheel in which case you are screwed.

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It's called a die. It cuts threads. One that large and metric won't be cheap. Do you feel sick yet?

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Use a standard file to reshape the end then use a thread file to repair the threads, be very careful if using a thread cutting die as its very easy to cross thread and make the problem worse.

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Use a standard file to reshape the end then use a thread file to repair the threads, be very careful if using a thread cutting die as its very easy to cross thread and make the problem worse.

 

I would go along these lines.  You can even use a standard file if you do it right.  If you don't know how to do it you might be best off finding someone who does.  You could ruin that crank if you take off anything more than you need to.

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It's called a die. It cuts threads. One that large and metric won't be cheap. Do you feel sick yet?

 

Most threads with large diameters are machine cut and without available dies.  Hand repairs are done with a file.

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also worth noting those threads are likely a class 3 thread meaning that if that portion is still mushroomed at all it will not fit in the nut.

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I always thread the nut on when using a puller so the threaded end of the crank doesn't bear the load.

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I always thread the nut on when using a puller so the threaded end of the crank doesn't bear the load.

 

If he had used the correct flywheel puller, there wouldn't room for a nut on the crank (see picture).  The hub of the flywheel is threaded M27 x 1.0 LH for this very purpose.  Attempting to use "steering wheel " type pullers that use a cross bar and a couple of bolts will virtually always fail or cause damage, as they do not apply the specific force necessary to remove the flywheel.  

 

Additionally, as a general practice when removing taper mounted parts like this, once the pressure screw has been run down to a point that feels like it should be tight enough (say 45 ft/lb or so) and the flywheel has not released, it's a good idea to stop turning the screw, pick up a steel hammer, and strike the top of the pressure screw sharply toward the crank.  The shock will usually dislodge the flywheel immediately without applying dangerously high pressure on the end of the shaft.  

 

I realize that none of that helps fix the damage done here, but it may help others avoid it.

 

To repair the damage here, clean up the thread with a standard "knife edge" file until you can reliably start a die on the shaft, then run it on to finish. 

puller.png

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I see that I missed the part about this being a flywheel puller.  I imagined a case splitter type tool with the flywheel removed.

 

I've had good luck with an impact driver on the flywheel puller.  A quick shot usually zips 'em right off but I don't know if that would have caused more or less damage in a situation like this.

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If you're talking about one of the hand-held drivers you strike with a hammer, I can promise you it would have caused less.  Air impacts are a bit riskier.  SImply running the torque up and giving it a good smack almost always works. 

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I did this on my ttr125. I was able to file down the part that was damaged. I then purchased a split die that i was able to start on the good part of the threads and back off to recut the damaged part.

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Made one of those once for an Arial Square 4.  It was an obscure British thread cut, and it took us a couple of months to find a die of any kind, much less a split one.  My boss almost freaked when I suggested breaking it instead of cutting, so that it would clamp back together at the correct size, but that's how we did it.  

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