Do I need to replace my crankshaft? - BMW Luxury Touring Community
 
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post #1 of 6 Old Mar 28th, 2016, 9:16 pm Thread Starter
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Do I need to replace my crankshaft?

Hi All, just purchased my first Airhead. See pics below. Is there any way I can salvage this crankshaft? What if I file it down with a wire brush to smooth it out? Or do I 100% need to replace the crankshaft?

The alternator rotor and stator seized up resulting in the crankshaft tip stripping metal, as the alternator rotor would not turn...so it was the crankshaft tip churning against a rotor that would not move. Stripping metal off the crankshaft tip and the inside of the rotor.

I am definitely replacing the alternator.

Any way I can save the crankshaft? Does it have to be 100% smooth or EXACT original diameter? I'm hoping to be able to save it and just install the new alternator.
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post #2 of 6 Old Mar 28th, 2016, 9:32 pm
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Re: Do I need to replace my crankshaft?

Quote:
Originally Posted by dica9 View Post
Hi All, just purchased my first Airhead. See pics below. Is there any way I can salvage this crankshaft? What if I file it down with a wire brush to smooth it out? Or do I 100% need to replace the crankshaft?

The alternator rotor and stator seized up resulting in the crankshaft tip stripping metal, as the alternator rotor would not turn...so it was the crankshaft tip churning against a rotor that would not move. Stripping metal off the crankshaft tip and the inside of the rotor.

I am definitely replacing the alternator.

Any way I can save the crankshaft? Does it have to be 100% smooth or EXACT original diameter? I'm hoping to be able to save it and just install the new alternator.
dica9, that looks pretty rough. I don't currently own an airhead but the taper of the crankshaft needs to match the taper of the alternator when bolted on and be round and centered or from running in an eccentric circle would at best cause vibration and at worst, another catastrophic failure. I am not sure you could obtain the required taper for centered contact with a file and a wire brush wouldn't touch those burrs. My calibrated eyeball might not even try. You are probably in for a new crank unless someone has a better idea.

PS. if the metal on the crank is aluminum, then the damage to the underlying steel shaft mey not be that bad. You might try using a utility knife and see if ht will shave off without causing damage to the steel. That is the only idea i have.

Gordon
Sugar Hill, GA
2001 K1200LTI Champagne (current ride) Lazy Susan
1998 R1100RT Never should have sold it
1974 Yamaha TX 750 Twin. Omni Phase Balanced


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Last edited by bmwcoolk1200; Mar 28th, 2016 at 9:40 pm.
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post #3 of 6 Old Mar 28th, 2016, 9:56 pm Thread Starter
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Re: Do I need to replace my crankshaft?

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Originally Posted by bmwcoolk1200 View Post
dica9, that looks pretty rough. I don't currently own an airhead but the taper of the crankshaft needs to match the taper of the alternator when bolted on and be round and centered or from running in an eccentric circle would at best cause vibration and at worst, another catastrophic failure. I am not sure you could obtain the required taper for centered contact with a file and a wire brush wouldn't touch those burrs. My calibrated eyeball might not even try. You are probably in for a new crank unless someone has a better idea.

PS. if the metal on the crank is aluminum, then the damage to the underlying steel shaft mey not be that bad. You might try using a utility knife and see if ht will shave off without causing damage to the steel. That is the only idea i have.

Thanks for the quick response! I'll think it over. Looking for a few suggestions then decide what to do....what would happen if the crankshaft taper is not 100% smooth and I install a alternator over it? Seize up again?

How long does it take to replace the crankshaft? I did a good amount of research, willing to put in the time if I have to.
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post #4 of 6 Old Mar 28th, 2016, 10:10 pm
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Re: Do I need to replace my crankshaft?

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Originally Posted by dica9 View Post
Thanks for the quick response! I'll think it over. Looking for a few suggestions then decide what to do....what would happen if the crankshaft taper is not 100% smooth and I install a alternator over it? Seize up again?

How long does it take to replace the crankshaft? I did a good amount of research, willing to put in the time if I have to.
I don't know how long to replace the crank and it would surely need more parts than just that but the interface between the alternator and the crank needs to be pretty smooth. If the aluminum comes off and there is a good amount of usable undamaged shaft with no raised areas, it might work. Tiny gouges might be OK as long as there was no raised metal to offset the interface between the tapers.

I am speaking off the top of my head as i have not had to deal with this type of thing before myself but I did have a friend with a spun crank bearing from a car and it left material on the crank that did come off with no damage to the crank so he was able to reuse it. This could be a similar situation or it could just be a hunk of metal that needs replacing. Lets see what others say.

Good luck.

Gordon
Sugar Hill, GA
2001 K1200LTI Champagne (current ride) Lazy Susan
1998 R1100RT Never should have sold it
1974 Yamaha TX 750 Twin. Omni Phase Balanced


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post #5 of 6 Old Mar 31st, 2016, 7:15 pm
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Re: Do I need to replace my crankshaft?

I would clean up the shaft as best you can with some emery cloth. Pack something behind it to keep grit out of the engine. Once it is smoothed up coat with some anti size and install the new alternator rotor (actually a stator). It is not a rotating interface (well yours did when it went bad) so once you have secured the new rotor to the shaft it will not care what the surface is like. The only caveat is if it got out of round - then you may have a problem. It is a big job to replace the crank.

John
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2006 Bushtec Turbo+2 Spell
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Have ridden a Motorcycle in all 48
But lack DE, MA, RI and CT with the 2005 LT

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post #6 of 6 Old Apr 1st, 2016, 5:35 am
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Re: Do I need to replace my crankshaft?

Agree, I would also replace the crank seal.

Pete Murray
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2014 RT
1973 R75/5
2002 LT 171 K Gone
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