1929 BSA Engine shaft timing pinion key

[robbsa]

 :(so, in moving house and moving all my parts around, i seem to have caused myself a massive headache by not being able to find my engine shaft timing pinion key (part 15-40). Its a comon part across most models of this year (mine is an L29 350 SV). If anyone can help, i'm slightly panicking!

Even if it is provide me with the correct dimensions of the key (however i should be able to measure the slot and work this out) so i can find out about having one fabricating. I would hazard a guess that this will not be easy to fabricate myself as it will need to be hardened steel and ground. However, I have access to grinding facilities so if anyone has done this before i would like to know.

Its a simple woodruff key. thinking about it i can probably buy one from a gears manufacturer.

[33d6]

Not to worry. Woodruff keys are made to standard sizes and any decent engineering supplies shop should be able to supply them over the counter. They are often fractionally oversize to allow for final fitting. A few strokes of a fine file is usually sufficient. They aren't made of anything exotic. Hardening & grinding is not required. They rely on accurate fitting to to do their job.
They are so cheap I normally buy a number of them because Murphys Law rules in my workshop. If I have one I'll drop it and spend ages hunting for it. If I have half a dozen theres never a problem.
As you say, BSA used the same size Woodruff key across the range so a small supply of them won't hurt.
Cheers

[cardan]

Just a word of warning re making your own key - which is a simple thing to do. I recently acquired a bike (said to be full restored and "running beautifully") which in fact was in a spot of bother. One of the issues was that the flywheel nut had come loose and fallen off, leaving the flywheel/clutch loose on the taper but trapped between the motor and gearbox. Unfortunately the key was made of stern stuff, and instead of shearing off it not only broke the flywheel into three pieces but also badly chewed out the keyway and ruined the mainshaft. (I ran the bike on the stand for about 2 minutes and have yet to get a ride on it!)

Anway, the key is not there to transmit power. It should be made from key steel which is pretty pliable stuff so that it will shear off is the driven part comes loose on the taper. (Having said that, maybe an engineer can tell me why the key is required at all!)

Cheers

Leon

[robbsa]

Ah, thanks guys. that makes sense, hadn't considered it being sacrificial. great stuff, i'm glad I'm not the only one to loose thing. Thankfully it looks like that was all that was missing.

[Rex]

I wouldn't consider it to be "sacrificial" in any shape of form. It's ordinary "soft" MS because not being subject to wear, it doesn't need to hardened. It would actually be detrimental were it to be hardened, as a good fitter would file to a perfect fit (rather like kick start and pedal crank cotter pins where only the ignorant bodgers just welt them in) and hardening would prevent that.

They're there to prevent a shock loading breaking the taper and/or for critical positioning.

[robbsa]

woodruff key obtained, skimmed and fitted. Thanks guys.

Rob

[Goldy]

Keys are there to transmit torque even components that are press fit cannot be guaranteed not to slip so a key is used. The slot in the shaft is known as the key seat and the slot in the driven component is called the key way. The key should be a sliding fit on the sides and have clearance on the top. A key is not sacrificial, there is a completely different set up where a small pin is fitted which will fail if too much torque is applied and this is known as a shear pin.

[robbsa]

thanks Goldy, appreciate any knowledge anytime.

cheers,

Rob