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Well it looks like my roadside failure was as a result of the rotor coming loose & sheering off the woodruff(?) key, so a few questions:-
1. what size key do I need to refit?
2. Do I need special tool whilst torquing up?
3. What is the torque setting?
Thanks & looking forward to getting back on the road.

That's unlucky-but remember it isn't just the key and nut that holds the rotor secure-the taper is the important bit. The key is a fairly common size but the dimensions escape me for now, I'll try to find it. In the meantime you need to take a good look at the taper in your flywheel and on the crank. With a bit of luck you could lap it in, using fine grinding paste (remove the remains of the old key first) to recover it. Hopefully it wasn't loose and fretting for too long before the key gave way?
For torque settings and possibly key dimensions you need to get a manual and parts book. The manual is available online here (somewhere!)

meant to add-yes, you need to hold the flywheel from turning against the torque when you tighten the nut.

Dickyboy wrote: ↑22 Jul 2025 21:19 Well it looks like my roadside failure was as a result of the rotor coming loose & sheering off the woodruff(?) key, so a few questions:-
1. what size key do I need to refit?
2. Do I need special tool whilst torquing up?
3. What is the torque setting?
Thanks & looking forward to getting back on the road.

Good luck - hope it's not too much of a pain.........

@ Steve Brown - thanks for the advice re the taper & I'll take a butchers at the manual to see if it makes sense to me.

Hi Dickboy.

I recently re-fitted my rotor after fitting a new cambelt. The 'Blue Book' recommends a torque setting of 6.5Kg/m which equates to 47.021 Ft/Lbs.

As Steve said, it is very important that both the external and internal tapers are scrupulously clean and undamaged.

You will need a holder to steady the rotor while you torque up the nut. My rotor has three holes but I think earlier ones had two.

Attached is an image showing the dimensions of the holder, and a picture of the tool I cobbled up which looks a bit rubbish but which worked a treat.

Thanks Morini Jen - will see what I can sort out, seems to think the club may have tools to borrow?

In case of emergancy (on the road ...) put in the 6th gear and step on the rear break to hold the flywheel

I made one out of some wood (about 12 x 2cm) drilled in the centre to allow a socket to pass, then suitable M8 bolts at the right point to fit. Cheap as chips. That taper must be sound as already said. Of utmost importance.
By the way check your lower pulley has no movement. A friend’s did have.
Does key 3mm wide x 5 mm high x6.5 long sound right?

I think this may be of interest:

https://www.mdinaitalia.co.uk/SKU040029020.html

MickeyMoto wrote: ↑23 Jul 2025 16:07 I think this may be of interest:

https://www.mdinaitalia.co.uk/SKU040029020.html

Thanks, if all else fails I have some other parts I was planning to order from them in the autumn when I refurb the forks.

Does key 3mm wide x 5 mm high x6.5 long sound right?

Thanks I'll check, off to an engineering place this am so should be able to pick one up.

4 x 5 R 6.5 according to the manual, the 3 x 5 R 6.5 is for the camshaft...

If I have read the parts book correctly.

Word of warning, surprisingly the 500 and 3 1/2 woodruff keys are different sizes. Details in the respective parts books. The 3 1/2 size is widely available, the 500 less so. I ended up lapping an oversize one to fit. Can't check details of correct size, or what I ordered atm as I'm away from home. Can update late next week.

Good luck!

Good point, Robin.

I think the size will be in the parts book.

Most important - make sure that the key isn't too tall when installed!
The key should 'stick out' of its slot on the crank much less than the depth of the slot on the flywheel. It's ONLY job is to locate the flywheel in the correct position (so tdc and strobe marks are correct) and that is all. The taper does all the work.
Far too many people think that woodruff keys are there to provide a positive means of providing drive which they aren't designed for.
Rant over,
George

Very true.