Magneto change

[mshaw]

Hi can any one tell me if I can fit a auto advance to a 1958 ajs model 30 I have two auto advance but the cogs are smaller than the one that is fitted to
my bike
my mag as no spark so I am changing to a BTH Mag that don't have manual advance
Mike shawmerlin13@aol.com

[clive]

I do not think any mag ignition AMC engined twins had auto advance, problem being there would not be enough room under the timing side cover for the unit.

[Reynard24]

As Clive says, I don’t think there is enough room under the standard timing cover to accommodate an auto advance unit but the later twins, with double capacity oil pumps, had a wider timing cover. If you can find one of these you might have enough room to fit it..

[Groily]

That's true and it's a very good point - BUT the question is, does a gear exist that would be suitable even if a wide timing case could be had? I haven't seen an ATD mounted on one of our steel pinions and as far as I can see from the Lucas lists (could be wrong of course) none was made.

Years ago I made an ATD version just as an experiment (using a spare camshaft pinion) but it required metal machining out of the outer face to create a comfortable recess to fit the ATD after drilling and tapping the necessary holes to attach it. Tough cast gears to modify on a small lathe, too.
A fair old palaver frankly if there is no such gear available off a shelf somewhere.

My advice to Mike is to try to find a manual (Lucas) magneto and get that sorted, or get a fixed cam ATD one modded to manual, but sadly there aren't any cheap and easy options. Whereas parts exist, new, to replace Lucas manual camring housings, I'm not sure if they do for BTH, I've never seen them anyway.

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As a matter of genuine interest, has anyone fitted a BTH KC2 to a 500 or 600cc twin by the way? The timing cover studs and the bottom nut and bolt will almost certainly be too short owing to the extra thickness of the flange on the BTH, but is there clearance for the engine side HT pick-up, given that they stick straight out at 90° to the body on them? Or the gearbox side for that matter?

[mshaw]

Hi guys thank for your replies and help and bill browns help I will try to find a new mag or get my mag repaired
thank again

Mike

[Groily]

And I just offered up a KC2 BTH with pick-up on to a 500cc assembled engine on the shelf here Mike - and the answer to my Q below is
No, a BTH won't go on. The front pick-up fould badly against the crankcase, more than could be fettled.
So it has to be Lucas, and we shall have to see what we can come up with.

[Tolly]

Hi folks, just caught up with this thread and like to add. When I bought my G11 it vibrated badly, I thought the timing was out. When I checked I had no manual advance lever and when I looked the mag had no advance mechanism within. I took off the timing cover to find just the normal drive gear so the timing was set. I can't remember where I obtained it from but I fitted an auto advanced gear. See image.

G11 Gear.jpg

[Groily]

That's a great picture Tolly and proves it can be done then. Really informative!
Be good to know the source of the pinion, I imagine a one-off probably - also did it need the later wider timing cover per previous comments?

Memory is a bit hazy on this, but if I recall correctly the experimental one I concocted using an old cam pinion would JUST go under the standard Matchless cover, having recessed the gear to take the ATD 'deep-set' but I don't think it went under the Ajay standard version.
Given the tight run of the advance/retard cable on some twins, and the advantages offered by an ATD in terms of magneto performance, it would be great if this option were more widely available!

[Tolly]

Hi Groily. Yes I did use the standard Matchless cover with no problem. If I remember rightly I took the original fixed gear off and luckely matched the dia up with the same number of teeth with this one, can't remember from where though. I was thinking with your knowledge and experience is there another Brit manufacturer who fitted the auto gear as standard, e.g. Ariel or BSA maybe? I have a feeling this just wasn't a one of.

[Greybeard]

My 52 BSA A10 has an auto advance unit fitted - Im guessing the Ariel Huntmaster does too. Might be worth following up re teeth number etc

Steve