vespa shearing woodruff keys


i've sheared two crankshaft woodruff keys in the past month. the magneto comes loose and i see that the woodruff key is shorn in half.

these are the only times this has happened. both times this has happened i've been riding pillion.


malossi 64cc

TOP 12mm crank

malossi multivar variator with 4 and 8 gram weights

malossi 9:1 gears, malossi belt

i've fixed it both times and it's fine now, but am not sure what caused this.

when reassembling the magneto, i see that the flywheel spins freely, though loosely. but when i tighten down the variator it's tight and fine.

actually, last time this happened, i noticed that the variator nut was loose. maybe it is as simple as that.

but anyone else have this happen? what a bitch it is to drop the engine and pull everything apart just to replace the little crescent shaped metal piece.

Re: vespa shearing woodruff keys

Shorn woodruff keys are an indicator that the flywheel is not seating properly on the taper, or is coming off taper. The loose nut would cause this for sure. Basically, the key is not meant to hold the flywheel in position. It is there for initial positioning only, and after than the taper holds things in place. I would tap the flywheel onto the taper with a mallet and a piece of handlebar or something. You might also look into loctite 660 keyway repair if you need it.

Re: vespa shearing woodruff keys

yea, as i posted it i realized it was probably just as simple as the variator nut coming loose. loctite is a good idea. thanks james.

Re: vespa shearing woodruff keys

A american size woodruff could be a problem

Re: vespa shearing woodruff keys

also make sure you have the correct shims in place,

and your cluch plate D-shaped hole is intact.

Re: vespa shearing woodruff keys

got the og vespa woodruff key (with angled cuts), so couldn't be that.

have the spring washer and the clutch plate D hole is pretty tight. the woodruff hole looked to be ok...not super tight, but pretty good. i'll come back to this if it happens again.

gonna loctite for now.

Re: vespa shearing woodruff keys

My flywheel doesn't really lock on to the taper of the top crank like it did to the stock crank. I don't know if the taper is slightly off or the shaft is too smooth / not smooth enough. Seems to be OK with the variator (clutch on a single speed) cranked down so, keep that bitch tight and get the lock washer from zippy if you need to. As far as woodruff keys, check any replacement for proper fit. a lot of the replacements are wider than stock. for these wide ones you need to sand or file them down a little or it is super hard to get them back out.

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