What’s best? (Magneto fibre or alloy gear)

[bl**dydrivers]

Original Lucas manual advance fiber gear or new Lucas manual advance allow gear?

Recently found and purchased a complete manual advance K2F Magneto with fiber gear and in good condition.

adm edit: title changed to reflect topic content.

[muskrat]

G'day bd.
The fiber pinion was a safety thing. If something locked up the teeth would shred and save the otherthing. The alloys are good but make a bit (not a lot) more noise.
Cheers

[Triton Thrasher]

I’ve never heard a noise from a magneto drive pinion.

Why would it matter anyway?

[worntorn]

We used to use alloy big idlers in Vincents in the 70s. Some supplier back then thought they would be a good gear and many owners gave them a try
Over time they would shed flakes of aluminium from their teeth and pretty much destroy the engine.
We're back to original steel gears now, problem solved.
Whether an alloy gear on a magneto drive would be under enough stress to ever do this, I don't know. And of course there are hundreds of alloys.
The brown tufnol ( linen) item for the mag drive seems to be trouble free for a long time.

One of my bikes had a white plastic mag gear in place when I bought it.
The mag had been removed and replaced with a distributor, so there was virtually no load on the gear.
Nonetheless, the teeth were all shifted from their original position. The driving gear was slightly narrower so you could see the imprint of its teeth in the plastic gear. The plastic gear must have become very " plastic" at some point in time and allowed the teeth to go mushy.
I replaced the mushy plastic one with a tufnol item. 55,000 miles and it looks fine.

Glen

[Swarfcut]

Hi BD
   Before the interest in old bikes we have now, replacement fibre gears and ATD units were either non existent or extremely expensive. Back in the early 1980's, some plain alloy gears became available for manual mags, so I adapted one and rebuilt my ATD unit.
 However, the unit would not fit because the alloy teeth were very slightly the wrong profile. So, cheapskate that I am, I filed each tooth until the unit fitted and turned, cam wheel just marking the alloy teeth. After many attempts to get the clearance right, I got it all back together, and it ran well, nice and quietly. After a trip round the block, I took off the timing cover to find the teeth had said hello to each other, the hard cam gear had neatly machined the alloy teeth, and the resulting slivers of alloy were stuck mainly round the magneto end of the case, with others  piled under the cam wheel. Cleaned it all out, sump plate, oil tank.  Heart in mouth, touch wood, and its been fine. Side by side the wheel teeth profile looked fine, so another example of almost fit but not quite fit pattern parts.

 Back then there was no choice, and you had to make do. These days availability is better than when the bikes were new.

 Stick to fibre, it is a relatively cheap link, designed to fail in the event of some mechanical lock up. The alloy and fibre wheels will all  shed material a little as they bed in, but the fibre is relatively harmless, unlike the alloy.

 

 

 Swarfy.

[bl**dydrivers]

Thank you all for responding! Good job I asked and will stick to the fiber gear.

[Triton Thrasher]

A fibre gear caused a breakdown.

An alloy replacement didn’t.

[BSA_54A10]

The big problem with fiber gears is all of the owners who shove a screwdriver between the teeth when setting the engine timing in place of using a piston stop or at the worse a length of wire to prevent the gears from turning when tightening the magneto nut.
Thus every second tooth has a chunk missing from the front corner.

I can not remember just how many false reports I have read about fiber gears "crumbling to bits".
When pushed most did reveal that they only seemed to crumble on the outer edge.

[Tomcat]

On a club ride years ago an A10 shed some teeth from it's fibre gear, as it was near my place I loaned Old Mate my spare ATD. When we swapped them over we noticed that the magneto bearings had movement in them, so the breakage wasn't caused by the age of the gear.

[Butch (cb)]

Over time they would shed flakes of aluminium from their teeth and pretty much destroy the engine.

Get the same kind of issues swapping out timing chains on Guzzis for alloy gears.

[KeithJ]

Had a Tufnol gear shed its teeth years ago, so was just not age.  Teeth got in to places they should not and wrecked the engine.  I would not use them.  I've been running an alloy gear for years and all appears well.  Just replaced the manual A/R unit for an auto one and the fibre gears had no free movement on the teeth.  I was told that's how they are.  Opted for an alloy gear on my auto A/R and it has just a small amount of  free movement on the teeth.  Just my ha'porth.