is it safe to braze on my scooter's crankshaft?

Question

My woodruff key was sheared off, and the hole it sits in is widened enough to prevent a new one from being installed properly.  I just want to know, or at least be reassured that a brazing would hold.  If you don't already know what a woodruff key is, it's a small piece of metal that holds the flywheel tight to the crankshaft.  

I'd imagine this should be able to withstand the speeds the thing spins at, only because it would be ideal that there be no play to begin with, so the metal being somewhat soft isn't a big deal.

Jon · Accepted Answer

I've seen em tack welded before, but they dont last, and are never really straight when you weld them. Brazing it wont hold.

mr_d150 · Answer

Is your ignition timed off a magnet on the flywheel? Then you're stuck with repairing the keyway or buying a new crankshaft.

Braze will hold fine IF you re-machine the keyway properly and torque the flywheel on properly (btw, improper torquing was why it failed)

The brass, if properly bonded to the crank, becomes part of the crank actually melting into the pores of the steel, but you've also got the bore of the flywheel covering the brass to further retain it.

As a Journeyman Millwright, I've seen keyways on 300 ton capacity smack presses brazed up and then run for another ten years ... and that brass takes a whole lot more punishment than your little Woodruff key will cause.

fyi: in the early 70's, a race car chassis manufacturer made a complete F-1 chassis and brazed it together and it tested stronger than the same frame done with inert gas welding.

Max Cruise · Answer

I'm a Machinist.  This happens to large shafts where I work.
I have a few suggestions.  
One.  Re-machine the key for a larger Woodruff key and mill the larger Woodruff key that sits above the shaft to fit the flywheel slot.  We call this a step key.
Two.  Machine a new Woodruff keyway 90 degrees to 120 degrees to existing keyway.  
Three.  Braze up the old keyway.  File smooth.  Re-machine the Woodruff keyway.  This would be my least favorite choice.  You are inducing heat into the crankshaft.  Brass needs to be heated to around 1300 degrees F.
Four.  This would take a bit of research to see if this is workable.  Fill the old slot with JB Weld.  Let cure.  File smooth.  Re-machine Woodruff keyway.
There you go.  Several choices.
If it were mine, I would go with option one or two.  Both will cost come money unless you find a Machinist willing to tackle the project for say a 12 pack of his favorite beverage.
Good Luck

friedach · Answer

the heat will de-magnetize your flywheel & soften the shaft.   braizing will NOT hold it-you NEED a new crank web pressed on.  Sorry but it's the ONLY way.  Welding will prob wreck the bearings.

mn · Answer

best fix is make the hole bigger.. fit larger Key..  plus there's hardly any heat involved..

that machinist you spoke to should be able to do it..  would be fixed properly..

Candid Chris · Answer

When did Tonka start making toy motorcycles?

You'd be better off trying 'Super-glue'.

Daniel B · Answer

Wont last

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is it safe to braze on my scooter's crankshaft?

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