The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: chilblayth on 10.04. 2012 00:36

Title: magneto pinions
Post by: chilblayth on 10.04. 2012 00:36
are the metal mag pinions better than the fibre ones ?   a friend has offered to make me one in metal after i showed him the fibre one !  he says as its obviously not stressed/under load , aluminium would do ! 
whats everybodys opinion ?  *conf*
Title: Re: magneto pinions
Post by: beezermacc on 10.04. 2012 07:41
Components made out of fibre are referred to by engineers as 'sacrificial' as they are intended to break, if something else goes wrong, preventing damage spreading across the engine. In Gold Stars which use a magdyno the dynamo could seize so the fibre gear in the mag drive would strip, protecting the magneto. This thinking seems to have been transferred to the A10 though it is hard to see what could seize in a K2F magneto. Basically it's just good engineering practice. The fibre wheels do wear out eventually but new ones are cheap and relatively easy to replace (four rivets and a hammer - job done!). There are some billet aluminium gears available (SRM?) relatively cheaply so it's hardly worth tooling up to make your own.
Title: Re: magneto pinions
Post by: Dynamo Regulators Mike on 10.04. 2012 10:00
I would say the original fibre ones are as good as alloy. Quieter running is a bonus. Tufnol is a good material for this purpose, but different brands have very different properties, and it would be no surprise if manufacturers advice is not strictly followed with some pattern ones.
In the Lucas magdyno the fail-safe in the event of the dynamo seizing is not so much the fibre gears shedding teeth as the star spring and disc clutch slipping. In fact in a well used and neglected unit this clutch will slip as it warms up leading to low charge on a run, but a decent charge showing on the ammeter just after starting.
Title: Re: magneto pinions
Post by: Triton Thrasher on 10.04. 2012 17:55
Is the fibre pinion supposed to stop the LT earthing through the pinion?
Title: Re: magneto pinions
Post by: bsa-bill on 10.04. 2012 18:40
Quote
Is the fibre pinion supposed to stop the LT earthing through the pinion?

I had that thought TT but then it occurred to me don't the sporting models have steel pinions
Title: Re: magneto pinions
Post by: Triton Thrasher on 10.04. 2012 20:08
I've used a solid alloy pinion on a Triumph, without any bother.

And I have had a fibre wheel revert to its natural state (porridge) while riding.
Title: Re: magneto pinions
Post by: beezermacc on 10.04. 2012 22:51
Quote
Is the fibre pinion supposed to stop the LT earthing through the pinion?

I had that thought TT but then it occurred to me don't the sporting models have steel pinions
Nortons have an all-steel ATD unit, chain driven.
Title: Re: magneto pinions
Post by: Beezageezauk on 11.04. 2012 10:03
The fibre wheels do wear out eventually but new ones are cheap and relatively easy to replace (four rivets and a hammer - job done!).

Great info beezermacc but is there anything special about the rivets and do you know a supplier in the UK?

Cheers.

Beezageezauk.
Title: Re: magneto pinions
Post by: LJ. on 11.04. 2012 18:56
Quote
rivets and do you know a supplier in the UK?

Ray... I have an assortment of rivets in the shed, let me know what size you want so I can check if I have any for you.
Title: Re: magneto pinions
Post by: Beezageezauk on 11.04. 2012 19:52
Cheers Lawrence,

Thanks for the offer but I won't know the size until I start drilling the old rivets out.  As I have a couple of damaged units that need repairing,  I'm thinking that if I already had the rivets in the shed I could drill the old ones out, swap a good pinion for a knackered one and then re-rivet at the same time.   This would save me from having yet another half finished job on the bench.

If I don't find a supplier I'll try drilling a rivet out at the weekend and check the size.

Beezageezauk.

Title: Re: magneto pinions
Post by: beezermacc on 11.04. 2012 21:27
The fibre wheels do wear out eventually but new ones are cheap and relatively easy to replace (four rivets and a hammer - job done!).
Great info beezermacc but is there anything special about the rivets and do you know a supplier in the UK?
Cheers.
Beezageezauk.
I use round head rivets which I modify to create the shallow taper required. Repairing the manual A/R gear is easy because its just a metal/fibre/metal sandwich. Repairing the ATD is a bit more tricky as the collar has to be removed. It's a bit difficult getting the collar off without butchering the whole unit. I'll do a refurb on one today and post some pics on my site. I sell the whole kit (wheel, rivets and ATD springs for less than £10). They're in my catalogue, part no.s PMM156 and PMM151, download atwww.priorymagnetos.co.uk (http://www.priorymagnetos.co.uk)
Title: Re: magneto pinions
Post by: Beezageezauk on 12.04. 2012 09:12



[/quote]  I'll do a refurb on one today and post some pics on my site. I sell the whole kit (wheel, rivets and ATD springs for less than £10).
[/quote]

Thanks for the info.  I'll be in touch offline and order a complete kit.

Beezageezauk.
Title: Re: magneto pinions
Post by: beezermacc on 12.04. 2012 14:48
For all those who are interested, I've loaded the instructions up to my site. Follow the 'Do it yourself' link!
https://sites.google.com/site/priorymagnetos/atd-units (https://sites.google.com/site/priorymagnetos/atd-units)