LCGB Forums

panyone had a problem with flywheel woodruff key shearing off, have just replaced one and while setting timing the new one has sheared. any ideas would be appreciated

Usually caused by flywheel nut not tight enough. There is no strength in the woodruff key, it is merely a guide to position the flywheel on the crank. The "strength" is in the nut forcing the flywheel onto the crank taper. Lapping the crank taper and flywheel is often advised, although i've never done this myself.

Good advice^

Is this on an SX flywheel?

If so, it is justification of the reason why Innocenti upgraded the taper on the GP/DL crank.

Lap the flywheel to the taper.

is it an LI/SX flywheel & crank

Already mentioned, the function of the woodruff key is purely locational.

IMO lapping in of tapers is essential, but an easily overlooked problem can be inadequate keyway depths, thus causing the tapers never to engage. The key can easily have some shaved off via filing the flat, but the better solution is to file the keyway deeper in the flywheel hub if that is the item @ fault, as it ensures interchangeability & corrects the faulty part.

There can also be other issues causing the failure of the engagement of tapers & one is due to the crankshaft threads &/or nuts not being as OEM & locking up. Another annoying mis-machining issue that has caught me out the with two new items is with remade large taper flywheel hubs that have bores too large & drive up the crankshaft taper too far, allowing the nut/washer combination to lock on the shoulder. As those hubs were supplied by SR, my suspicions are that there may be many more hubs out there exactly the same. The solution to such a problem involves stepped washers or tubular spacers but that is not ideal as they are unlikely to be as hard as OEM items so any torque supplied is absorbed by the softer materials.

Lastly(!) & IMO rarely, the hub actually starts to split, usually along the keyway slot. Worth checking though.....

If anybody removing a correctly lapped in flywheel finds it all too easy to 'crack' the taper fit, then any, or all of the aforementioned issues may be the cause.

+1