Auto-Advance Magneto question

[groily]

Ah, good question Richard and not touchy at all. Had I ground to a halt an hour earlier in the course of our club run, no problem . . . trailer follows us round to pick up the pieces and get them back to, at least, neutral ground (as in someone's garage). . . thing was, I'd done all the organised bit, had a great run round, and was on my own on the homeward run . . . parted company with a couple of similarly frost-bitten people about 20 minutes before coming to a halt. Had there been a few others around, the old camaraderie thing would have kicked in and we'd have ended up celebrating the joys of breaking down in some bar, with a trailer on the way to collect the oily remains . . .  Perversely, I don't mind the odd breakdown too much, although I suppose I ought to subscribe to some recovery service to avoid reliance on Her Indoors. I do carry a lot of tools, inner tube, pump, fuses, bulbs, cables etc in an effort to cover the likely hassles but sometimes there's nothing to be done - luckily rarely. In 7 years of trundling round hereabouts I've only had to trouble Herself twice, although I can't say I haven't struggled home late once or twice after having to do running repairs . . .  All part of the fun, I guess . . .

[LJ.]

Spot on Groily! aint that just what classic motorcycling's all about? The 'will it or won't it'? and when it does... The warming satisfaction of it having done so... 

[groily]

There's nothing like a few days reflection when things go wrong . . . I wasn't happy at the thought of shelling out a lot of english money to buy a new ATD and fibre pinion for the beast . . . and I'm not going to.

For a fraction of the cost I've found a 2nd hand manual advance and retard end housing for a K2F, I've modified (as in drilled and tapped a couple of new 2BA holes) in the mag body to take account of the different locations of the fixing screws on a manual as opposed to fixed-cam-ring mag, made a wotsit to engage with the slot in the manual cam ring, dug an old handlebar lever out of box of bits, re-worked an old throttle cable, and have got an inexpensive aluminium fixed pinion on its way. So should be up and running soon.
 
Now I know I have said a few times that the ATD is a better proposition, given that the advance and retard doesn't affect the optimum sparking position of the armature, but heck, the lever is fully advanced most of the time - at which point the mag ought to be at its most efficient. So goodbye to edible pinion, welcome all metal gear train, and quite a few ££ saved.

Having made those choices and done those things, thoughts returned to the ATD device which I described as scrap and which was staring balefully at me on the bench. However, amazing what can be done with a bit of dead sit-on lawn mower rear axle shaft . . . when it's a finish-ground bit of 3/4 inch stock, it's obviously crying out to be machined up to make a new centre shaft for a knackered ATD . . . With a gentle ream - more a touch than a scrape - of the 'other half' of the ATD to make good the bushing, it's as good as new with the various important bits pressed or brazed on, a new self-extracting home-made sleeve nut, and it just awaits the arrival of a 2nd aluminium pinion which I'll machine up to fit and have as a spare if I feel like swapping mag parts round again or get bored with the cable.
 
Very pleasing, 'warming satisfaction' LJ!, or will be when I have some pinions to play with. As the registration document - it's probably a liar - says that the beast was once a Super Rocket, the manual ignition is, I suppose, 'original'. Suppose I'll have to find an alloy head next, if this silliness carries on . . . . Groily

[flatdeck]

Hi,
When I had the fibre drive gear replaced I sent the whole ATD + new drive gear to John at British Spares, Silverstream, Wellington, New Zealand. The new fibre drive gear was fitted and the springs replaced and the whole thing cleaned and checked and couriered back to me for the equivalent of about 30 quid .... v happy.
Dave

[groily]

Well, new pinion in alloy installed (35 pounds or so from SRM) and back on the road. Very happy. ATD to Manual mag mods done and OK and so far so good. A/R cable routing not as comfortable as I'd like owing to carb and drip tray getting somewhat in the way (?whether there are other versions of the K2F manual end housing that would suit an A10 better), but works OK for now after some trouble finding a suitably strong spring for the cable at the mag end. Am nearly there with machining up a 2nd alloy pinion to go on remade ATD unit, fingers crossed it all goes together and works as planned . . .. if it does it will be tougher than original, if it doesn't, it'll sit there as a monument to my incompetence and another 35 quid wasted. Groily

[groily]

For anyone who likes this sort of stuff, here's a pic of the remade ATD. Now with re-worked alloy pinion and a new centre shaft made from a bit of 3/4" finish-ground steel stock (ex-lawn-mower rear axle). Self-extractor works by shouldered sleeve 'nut' coming up against a shoulder inside the shaft. It engages after the nut's been undone 2 full turns on the armature. The 'nut' is in fact a 2 piece item, with a head brazed on from the 'outside'. That's the penalty for being too idle to replicate the left-hand thread arrangement. The taper in the end of the shaft is the original one, cut off and turned down, then press-fitted into the new shaft . . . idleness again, as short internal tapers on critical applications can be a pain to get perfect. The outer bit of the ATD itself is also press-fitted over the outboard end of the shaft. Rest of it is the original, and the 'bushing' was pretty OK after a good clean up. No wiggle at all, literally nil, identical overall dimensions, goes on and extracts from an old armature very nicely, retains original dished washer with locating-peg holes and horseshoe retainer under the head of the nut, and cost 35 quid rather than the 144-odd for a new one. Irony is that having gone for manual advance and retard, it'll sit on the shelf until the next time something goes pear-shaped. But just wanted to see whether the conversion and repair was a feasible proposition, which it is, as long as time has no value!

[bsa- bill]

well done , looks like a nice fix.
I had mine done on an exchange basis, cost about £60 so your still well in pocket, course I did not have a spare Lawn mower lying around

all the best - Bill

[groily]

Ah well, Bill, comes back to never throwing anything away. I find dead lawn mowers have lots of useful stuff in them!