Lambretta Flywheel Woodruff key sheared in half

[stokky]

Hi all,

just had this happen to me, never happened before, so just wondering if anyone else had it.

See photo below, Woodruff key sheared clean in half.

Bike is my Challenger 240, with an AF lightened flywheel.

Crank looks fine !!

Stupidly took all top end off before checking flywheel (DOH!).

Anyone interested, also a photo of barrel (transfers etc)

[Andy Pickering]

Yes many moons ago on a Honda 205 top end, not seen or heard of one shearing for a long time though..

Sent from my GT-I9300 using Tapatalk 2

[Adam_Winstone]

Woodruff key plays no part in holding the flywheel to the crank's taper, the only reason for the woodruff key is for providing a constant point of aliginment, which in turn allows for timing to be fixed. To shear a woodruff key the flywheel has had to move on the taper, which should not be able to happen! Reasons why it can are:

1. Flywheel nut not done up tight enough.

2. Taper of flywheel boss does not match taper of crank, which is why it is recommended that you lap the 2 together with gringing paste (NB: No grinding paste residue can be left on either as it can work its way into the mag's outer oilseal!).

3. The boss is faulty or the nut has been done up too tight and the boss is cracking along the woodruff key slot!

4. Can't think of a number 4!

Adam

[Boothy_the_makem]

Yes many moons ago on a Honda 205 top end, not seen or heard of one shearing for a long time though..

Sent from my GT-I9300 using Tapatalk 2

omg did yer have to say that lol

[Andy Pickering]

From memory the flywheel boss was nacked and had to change the flywheel..but it was about 1988/89 And I've had a few beers since then

Sent from my GT-I9300 using Tapatalk 2

[stokky]

hmm remember about 3 - 4 months ago messing with the timing on this bike as fitted a chiselspeed Mtech advance retard unit.

But not really done more than 5 miles since.

So hopefully I simply did not tighten nut up !!


Also the nut was actually loose, when I took off.


Oh well will soon see !!!!!

Will update outcome later on

Martin

[Bilko]

Happened to me. No. 1 on Adams list was the cause.

[Bilko]

double post

[Triken]

It happened to me too!! number 1 on Adams list.

[Special X]

Happened to me with a new AF light flywheel. Torqued up to 40 lb ft. The boss had stretched and become loose, which then caused the nut to be loose. Rayspeed had "never heard of this happening before" said it was wrongly fitted and refused to refund or exchange.

I would advise anyone with one of these flywheels to lap it to the crank with grinding paste, and re torque it after 500 miles as you would with a cylinder head.