BTH magneto advance/retard unit

[tractorman]

Hi, I've heard it said that the BTH advance/retard units can be likend to  hand grenades, and have wrecked many engines. Has anybody actually experienced or witnessed this , or is this an old wives tale. They seem nicely constructed and easier to work on then the Lucas units and BTH have a good reputation for building magnetos

[Welsh Wizard]

Back in the 60's the BTH was a prized possession on any bike, now if the bike needs a mag as long as you can get a good one, as they are so hard to get in really good condition. Never heard that they were engine destroyers.

[R]

Race engines totally prefer slack wire advance units.

Magnetos that need the wire pulled tight to get full advance can vibrate back to retarded timing. Which may be OK/ just a nuisance on a touring bike, but in the heat of combat in a race, the rider may not notice, and this can harm or destroy engines...

The advance-retard bit is often a bolt-on part, so can be configured to suit whatever it is used on. Note that this may not fit onto some engines. This would be applicable to most magnetos, not just BTH ?

Opethiselps.

[tractorman]

thanks guys. I think I should have elaborated my question.  It is the automatic devise [ADT]  in the timing cover, driving the magneto I was refering to as being dangerous and liable to fly apart, not the manual devise moving the cam ring. I have raced with BTH magnetos and have a high regard for them, but all my racing engines had fixed steel drive pinions and fixed cam rings.

[R]

Never actually sighted a BTH auto advance unit - what do they look like ?
Anyone got a picture ?

The Lucas version for Norts Turnips etc seem pretty tough, although the springs can get weak and the pivots all wear something terrible - only with big miles though...

[tractorman]

picture attached.
between the 5 sets of steel retainers are approx. 1/2" brass rollers

[Gromit]

There's a bloke who advertises in the VMCC mag ... did a marvellous rebuild job on my Prince of Darkness auto advance on me Norton 650ss came back like new and the springs actually retard it back at standstill !! miracle as they didn't always do it from new I am told

Thoroughly recommended so if it needs some work to make it like new give him a ring

Roy Price is his name ...01480 473225

Regards Gromit