The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: flatdeck on 24.09. 2007 22:26

Title: Auto-Advance Magneto question
Post by: flatdeck on 24.09. 2007 22:26
Hi, My 1949 A7 Star Twin has an auto-advance magneto, whether it was original or not I don't know. Last night's game was to get the timing right before trying to balance the carbs. So took off the crankcase cover, took the plugs out and turned the crank over ... I found that holding the auto-advance in the advance position was just a case of pushing the weights apart. When letting go I expected the springs to pull the weights back in quite strongly ... what actually happened was that I let go and the weights stayed where they were. Seems to me that it never gets retarded, which would explain why it is such a PITA to start. The good news is the points seem to be just about right ... So the questions are: should the auto-advance snap back to the retarded position when you let go of the weights? and is the likely cause going to be very tired springs? Have to say the springs don't even look man enough for the job ...  Is there anything else that in there that causes the return to retard?
Dave T
Title: Re: Auto-Advance Magneto question
Post by: Brian on 25.09. 2007 05:36
Hi Flatdeck, the weights should return when you let go of them. There is something wrong with yours. They shouldnt "snap'' back but should return easily. As you say your ignition wont be retarded at start up and will probably be at full advance at idle, both situations you want to avoid. These things are quite prone to wear so may well need much more than a couple of new springs. C@D autos in England have the springs, I just bought two sets myself. If you need a new or reconditioned unit the only ones I know about are at SRM in England. There is probably other sources to get one from and maybe someone else on the forum can suggest who to try. To set the timing I have a small piece of wood cut in a wedge that I use to hold the unit at full advance. Hope this is of some help, good luck.
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 25.09. 2007 06:11
Hi Brian,
Thanks for that. Is it only the springs though that actively try to return the weights? I read somewhere that if the full advance stops are worn away then it could go too far and stick. I don't think mine is as bad as that because it does return smoothly when done manually. If I replace the springs and that does not work I'll be starting to take it apart from that end to investigate, clean and lube it. There is also alot of debate about the pros and cons of replacing it all with something electronic.
Title: Re: Auto-Advance Magneto question
Post by: Brian on 25.09. 2007 07:32
Hi Dave, its just the springs that return the weights. Its the small pins that the weights and the small pieces that the springs connect to that usually wear. I believe there are some forms of electronic set ups available but I am a big fan of magneto's. The first thing I do when I buy a bike is get the magneto rewound, I've been riding these things most of my life and have not had one fail yet. I have had a few generators stop working though and if you have electronic ignition you need a charged battery. I think of it like this, if your engine is a bit worn it may use a bit of oil and rattle a bit, if your carby is worn it may run a bit rough but will still run, if your magneto is crook your bike will be hard to start or may not start at all, as soon as it gets hot it may well stop and not start. So I consider the magneto the most important part. If your advance unit is beyond repair for some reason you could replace it or maybe look for a manual advance set up.   Cheers, Brian.
Title: Re: Auto-Advance Magneto question
Post by: fido on 25.09. 2007 07:59
I would also recommend getting a manual advance magneto and plain pinion without the auto advance. Other sporty models like the A7SS had manual advance so it would make sense on the Star Twin. If you take the springs off the weights should flop about easily, if there is resistance to movement you will probably find the pivots have rusted.
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 25.09. 2007 21:57
Had both ends apart last night to understand how it all fits together. Cleaned it all up. One tooth of the fibre gear missing. Cleaned and oiled the cam ring. Put it all back together. Tested that the advance unit returned on the spring ... and it did ! Turned the engine on the crank and tested it a few times. Seems to be working. Balancing the carbs next ... Thanks guys.
Title: Re: Auto-Advance Magneto question
Post by: groily on 25.09. 2007 23:23
Hi Flatdeck,

If you've got a tooth missing then you need to take some action pdq obviously! Fibre pinions without the ATD in the middle are available, I think, from SRM to replace the original without having to buy the whole shooting match. If you think you've fixed the ATD with new springs and/or a bit of attention to the weights and the pivot pins, then that's great and well done - wear on the pins is a pain as it can make the weights move in a cock-eyed plane compared to the face of the pinion itself, and they can get stuck or sticky. Getting an ATD out of its fibre pinion strait-jacket ain't that easy though - needs a press on the collar and it can take several tons in some cases to do it. Big hammer not recommended and vice on bench will only occasionally do it.

You can always go for a manual system if you like - you'll need a cam ring with a notch for the cable end, and a mag end-housing that'll take the cable and adjuster gubbins (all usually available from several places) BUT -

- it's worth bearing in mind that an ATD system working properly is genuinely technically better than the manual system because with the ATD the spark is always delivered at the optimum point (of max flux) of the mag armature (a few degrees after 0 and 180 degrees of its slip ring's rotation) whereas if you go for manual you're asking the mag (other than at full advance) to generate sparks at sub-optimal moments. All very boring, but true.). That's why the bright (joke) chaps at Lucas dispensed with manual - and the point is made perfectly in relation to V twins, where the armature is asked to deliver sparks well outside the optimum range for a device that works best in equal intervals of 180 degrees. I don't know why some of the more 'sporting' parallel twins of the day retained manual advance-retard. It was not necessary and not a great plan in theory even if in practice it was OK. Maybe die-hards preferred to think they were in control of something that almost all of them would have left at full advance as soon as they had got the engine running. Control freakery and 'gimme more levers' sort of thing. Given that with a bent twig down the plug 'ole most of them wouldn't have got the basic ignition within 5 degrees of maker's, it's all nonsense.

My money would be on replacing the pinion and ATD in one unit, even though it's not a cheapie decision, cos that way you get peace of mind and a zillion hassle-free miles, easy starting, decent idling etc etc. I wouldn't go electronic myself, cos that's non-original and more importantly needs batteries and dynamos wot work. Mags are generally far more reliable than dynamos (and regulators, especially old mechanical ones). And if they'll start the thing at all, they'll give progressively better sparks as the revs rise, owing to the way they work.

Good luck!

Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 26.09. 2007 01:46
Groily... I am unhappy with the lost tooth but...  This AAU has not been apart since 1976 that I know of. When we checked the timing Monday night for the first time it was pretty much spot but I was concerned that the AAU was not returning to the retarded position (potentially causing the hard starting). Since the gear does not appear to be slipping I think I'll leave it as is for the moment. At least it is easily accessible. I am keeping a note of all the little "issues" I am finding with a view to dealing with them as parts/repair opportunities come to hand.  Cheers, Dave
Title: Re: Auto-Advance Magneto question
Post by: fido on 26.09. 2007 08:57
I prefer the manual advance as it gives you some form of adjustment for the ignition timing. The magnetos I've used all have some damage to the taper (yes, even the one I recently fitted which I had reconditioned) so they tend to go out of adjustment when I tighten the bolt. I don't have infinite patience for this job so it usually gets left once it's "near enough". With manual advance I try to err on the side of getting it slightly too advanced then find the optimum advance using the lever position i.e. get it pinking then retard it slightly. The published timing figures were only ever a guide anyway.
Title: Re: Auto-Advance Magneto question
Post by: groily on 26.09. 2007 17:22
Very fair point Fido - I know just what you mean and I have often relied on the same benefit of the manual lever, especially if I've had to do repairs in strange places. I've got one manual ignition non-BSA twin and the A10 with ATD.

A mate of mine who's much smarter than me has successfully modified a twin cylinder mag to give variable positioning of the cam ring - which is a very effective way of getting the same fine-tuning capacity the manual lever offers. The reason he did it was cos he wasn't satisfied that after a rewind the points were opening at exactly (like within a degree or 2 of) the right spots in relation to the position of the slip ring on the armature and this was the easiest way of ensuring that. The practical side-benefit is to deliver a neat fine-tuning capability within limits (those being the optimal spark position of the armature and slip ring, blah blah).

What he did was extract -carefully! - the little peg in the mag end housing that locates the cam ring (there's a tiny plug knocked into a small hole in what is in fact a small (BA I think) screw rather than the simple pin it looks like). But it does all come out. Then he drilled and tapped the housing for a bigger 5/16ths BSF or Cycle set screw with an eccentric machined on the end bit which goes into the notch and a slim locknut on the outside. He has got 10 or 12 (crankshaft) degrees of movement available, and it gets him over the point you make about not getting things spot on cos of lousy tapers etc. It also looks very neat. The original peg does have a small eccentric on it I think, which presumably the man at Lucas would have set in place to get the points to open at the position of maximum flux etc etc bore bore, but with the bigger one you get meaningful and useful adjustment.

But Flatdeck, coming back to your dental problem! If one tooth has gone, there's been stress on the thing (specially if the tooth broke off due to the pinion slipping on the taper, which can happen) and I truly think it might not last tho' I truly hope it does. . . the adjacent teeth are likely to be weakened so even though the loss of one ain't enough to cause the timing to jump . . .

Least I'd do is carry a plain steel gear (w/out ATD) in the tool box, cos even if (agreed) it's easy to get at, there's no easy way home if it strips on the road. I've had it happen twice in my life with fibre pinions when i was a poverty-stricken student a zillion years ago. It's always raining, dark and miserable when they go. The battery's dying, the lights are flickering. And the pub's shut. I hate pushing and the sainted memsahib hereabouts hates coming out to rescue me! Good luck!

Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 26.09. 2007 21:52
Very interested in looking at the cam ring option for giving some fine-tuning. I am getting a lot of help from an ex-Rolls Royce engineer (my mate who's much smarter than me!) and I'm sure if he read your last post Groily he'd say "that'd work!". We have been shaking our heads wondering why it was designed so we have to take the crank cover off to adjust it. We are very close to getting this baby running well though. I see the price of a new fibre drive gear is about 8 quid but then I understand fitting it can a bit of a PITA ... It's all fun.
Title: Re: Auto-Advance Magneto question
Post by: LJ. on 26.09. 2007 22:32

Blimey! "an ex-Rolls Royce engineer" bit of an over kill for our BSAs isn't it?  *lol*
Title: Re: Auto-Advance Magneto question
Post by: Brian on 26.09. 2007 22:45
While we are all on this subject has anyone used or currently running a auto unit with a alloy gear. I am in the process of building up a auto unit and I have a new alloy gear that came with a bike I bought. I have good fibre gears to use  but was thinking about putting the alloy one in. I am not quite sure why BSA used the fibre gears, the singles [B33 etc] all use steel gears with no problems. SRM sell their ones with fibre gears so maybe there is a good reason to stay with fibre.
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 27.09. 2007 00:10
LJ, I would be screwing things up badly if I was left alone :-) The ex-Rolls Royce engineer won't let me use the wrong tools on anything ... having said that he has a hammer named "Excalibur" that he says he only uses for "gentle persuasion" *sarcastic*. He does have a hydraulic vice that does several tons so I could look at replacing the fibre drive gear (see Groily).
Title: Re: Auto-Advance Magneto question
Post by: groily on 27.09. 2007 06:12
Not sure why fibre gears came in, but they arrived when the switch was made to ATD from manual I think. Can't remember seeing a steel pinion wirh ATD in, but maybe they exist too? One theory is that the fibre pinion offers a failsafe in that if the mag seizes up the teeth on the fibre pinion strip rather than more expensive bits of the timing gear train busting. Sounds unlikely - BUT I have another very smart mate who did lose a fibre pinion just like that - the insulation in the mag melted on a very hot day here in France after a 150 mile local club run, turned to araldite inside as the bike cooled down (uniting the armature and the rest of it in a lump of goo), and when he tried to start the thing - whack - one busted pinion, which also slipped about 90 degrees on its taper. It unseized the goo too. The resultant back fire - yes there was still some HT activity in the thing - broke the kickstart quadrant and various other bits - a classic bad hair day!

An alloy pinion would probably be great if you were to live with fixed timing or go to a manual system. Fibre pinions are quite cheap - but you'd need that hydraulic vice on the collar of the ATD I suspect! Given the price of ATDs from SRM or wherever, it's probably the best and most cost-effective route to go though.


Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 10.10. 2007 01:44
Still struggling with getting this A7 to go. We have recently set the timing to points starting to open at TDC whilst fully-retarded (per Munro - Thanks Jeff) and it certainly sounded like it wanted to start (coughed and spluttered a bit). We have since tried advancing it about 2mm on the points each time and are now about 10mm from where we started. Still she is not starting. We are spraying Engine Start into the carbs, and tickling the floats till the fingertip is damp with petrol, so I don't think fuel is the problem. I'm fairly happy that we have tried a broad range of timing so I have to wonder whether we are getting sufficient spark. How do you tell? I see bright blue sparks when the plugs are out of the cylinders but does that necessarily translate to sparks in the cylinder? Can the compression that is generated suppress the spark in the cylinder enough to stop it igniting the fuel?
Title: Re: Auto-Advance Magneto question
Post by: Brian on 10.10. 2007 02:29
If you set the points to open when at TDC and fully retarded that should be close enough for it to run. You can check the spark by disconnecting the plug caps from the lead, leave the plugs in and hold the end of the plug lead about 1/4" from the spark plug cap. Kick the bike over and see if you have a spark. If you have tried spraying easy start in the carby and it didnt do anything then you have something wrong, it should at least fire a few times. Have you checked that you have the correct plug lead going to the correct cylinder? To do a simple check take both plugs out, hold you finger over one plug hole and turn the motor over until you feel pressure against your finger, then bring that piston up to TDC, you should have this cylinder on its firing stroke at this stage. Once you have done this follow the plug lead from this cyl back to the maggy, remove the pick up from the maggy and look in the hole [may have to use a mirror] you should be able to see the brass strip on the pick up ring. If there is no brass strip visible swap the plug leads over. Hope this helps, Brian.
Title: Re: Auto-Advance Magneto question
Post by: 1KCBC on 10.10. 2007 02:46
Try and try flatdeck,Brian gave you a good idea and for the compresstion,it should not suppress the spark.
Have a nice day. *work*
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 10.10. 2007 04:18
Hey, thanks Brian. Last night we sat looking at it for 10 mins doubting ourselves having adjusted the timing for the 4rth time and having been rewarded with a short splutter at best. We shall start at the beginning again and check we have TDC, that we understand which way is BTDC looking at the points, that we have a spark (thanks for the tip Brian) and that we have petrol in the cylinder. We didn't think the compression would be enough to snuff out the spark we were seeing.
p.s. What else would I be doing :-)?
Title: Re: Auto-Advance Magneto question
Post by: fido on 10.10. 2007 08:20
If an A7 or A10 won't start it is nearly always due to magneto trouble. Obviously things like spark plugs and valve clearances also need to be checked but is there any way you could borrow a different mag to try?
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 15.10. 2007 22:02
Hi guys, more testing last night. We are happy the timing is as it should be. Checked the brass strip was in view when piston at TDC and it is. We have fuel, timing and compression so we can only conclude that the spark is just too pathetic. We are getting a blue spark across the plug gap but if we disconnect the lead from the plug we are getting nothing jumping from the lead to anything. The plan is to replace the fibre drive gear (that has a tooth missing), hopefully removing a some play in the magneto drive, and then investigating whether electronic ignition is the way to go. Has anyone here replaced their magneto with CDI? Any info on this would be appeciated, especially on where the ignition gets its timing (I would prefer to get it from the crank if possible avoiding all the sloppiness in the mag drive. Cheers,
Title: Re: Auto-Advance Magneto question
Post by: G/F DAVE on 15.10. 2007 22:43
Hi, Flatdeck personally I would not bother with electronic ignition ,Best bet is to get your magneto checked & reconditioned & replace timing gear.As for setting ignition timing  I use an old oil pump worm drive with a bolt welded into centre to take a degree disc I screw this onto crankshaft & use a dial gauge into plug hole to find top dead centre then set disc to zero degrees useing a pointer attached to crankcase ,once set turn crankshaft backwards to remove slack in timing gear then turn clockwise to 34 degrees before top dead (GOLDFLASH)  if you have auto advance magneto pinion you need to make sure this is fully advanced with points just begining to break open once happy with position of points tighten centre nut on can then check for equal timing on both cylinders on degree disc .This should make for a smooth running motor.  Dave..
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 15.10. 2007 23:02
Hi, thanks Dave. I am finding out so much as I go along ... mainly that there are so many favoured ways of doing things! I would prefer using the existing technology but a couple of chaps have suggested EI improves the reliability for about the same price as a magneto check/rebuild. There are a couple of guys reasonably near me that rebuild mags so I might just take it off and get them to do it and see how we go. I have to buy a fibre drive gear and replace it anyway though because there is definitely play in that. Have to see how much is in the pocket money jar ...Cheers,
Title: Re: Auto-Advance Magneto question
Post by: Brian on 15.10. 2007 23:27
Hi Dave, sounds like your maggy is definitely dead. If it wont throw a spark when you still have the plugs in then its cactus. Personally I would rebuild the maggy. If you do give the maggy to someone to rebuild make sure they rewind it and replace the condensor, not just clean it up etc. I would only give the maggy to someone that has a good reputation. Good Luck, Brian.
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 16.10. 2007 04:07
Decided on where to spend the money. New fibre drive gear and a test and repair as necesasry on the magneto. There's a guy within 10 minutes drive from work that specialising in magneto rebuilding ... I'd call that providence / a clue :-). Whilst that is all happening I guess I'll do some polishing.
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 23.10. 2007 20:48
Update: Magneto went to the magneto specialist last night. A quick revealed small, weak and pathetic spark from one plug only. Remagnetised the mag with the result that it is a hopeless case and will neeed rewinding apparently. New fibre drive gear for the AAU in progress from the UK. I'm spending the next 4 weeks polishing and cleaning waiting for bits....
Title: Re: Auto-Advance Magneto question
Post by: snowbeard on 20.11. 2007 20:46
so here's a question spurred by groily's description of his "smart mate"

if you get the magento drive gear cinched down tight and realize that you're off by just a little on the timing, couldn't one simply move the cam ring in the end plate to adjust timing as well? or is that not a good idea for one reason or another?

I have a strange confabulation of a mag, it has the manual advance static fibre gear, but the auto advance static cam ring and end plate.  but with either correct system, moving the camring should be acceptable, no?

I'll qualify this question wiht the information that I don't understand how the field collapse and slip ring, etc all interact, sounds like if you took the cam ring too far it might not open in conjunction with the slip ring brass/pickup coincidence?
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 20.11. 2007 21:09
The camring has a keyway that locks it in place stopping it from moving unintentionally .... I haven't investigated inside the magneto at all ... so can't comment
Title: Re: Auto-Advance Magneto question
Post by: snowbeard on 21.11. 2007 06:13
I see that in mine, but my cam ring notch is at least 1/4 " away from it! 

it must be a testament to these bikes that mine ran at all!! wobbly armature, no advance, camring off kilter!   

or the PO, maybe he wasn't entirely crazy...

I hope to hear how yours runs so well when you get your mag back! *smile*
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 21.11. 2007 20:14
Apparently I can't expect the mag back till Xmas  *sad2*. I am a bit disappointed to say the least having been told 4 wks a month ago. Oh well, lots of cleaning to do ....
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 27.12. 2007 09:39
YIPPEE! Magneto returned Friday before Christmas. New fibre drive gear too big for the casing ??? Bizarre ... definitely the right gear. So some delicate filing inside the case and now the gear has clearance all round it. Fit the magneto and retime her and what do you know .... she runs! Got to do some carb tuning next time so she idles but it sure does sound great. Word of thanks to all those who posted on this thread. Hope I've leant some stuff that I can pass on some time.
Title: Re: Auto-Advance Magneto question
Post by: LJ. on 27.12. 2007 10:08

Great news there Dave thanks for keeping us updated on your mags progress. Now that the mag is sorted it can just about be forgotten, you wont have any more trouble with that. Let us know how things go with the carb.
Title: Re: Auto-Advance Magneto question
Post by: groily on 27.12. 2007 18:11
Many congrats! Funny how some of these new parts don't quite fit the space - well done with the pinion. Sounds as if you're almost there . . . if she starts and revs and sounds good, can't be far to go now. If the jets are right, if the throttle slide has the right cut-out and is not too floppy in the bore, if the pilot air screw is there and the slow running throttle-stop ditto, and the screw-on cap at the top does up firmly (and if there's no choke slide fitted, the hole for the cable is bunged up to keep extra air out) you should have it ticking over like a clock. And even if it's a bit temperamental, so what? It'll be great blipping the throttle to keep her alive! Groily
Title: Re: Auto-Advance Magneto question
Post by: groily on 06.04. 2008 18:19
And now I'm going to find out for myself exactly what the mag pinion/ATD options are, as today, in the snow (April for gawd's sake), after 275 trouble-free kilometres in the worst weather I can remember since the last time it was the worst weather I could remember . . . freezing cold, soaked to the proverbials from top to bottom . . . wham bang, stripped pinion, miles from any****where, natch. And where was my mobile dog'n bone . . . at home where I'd forgotten it. Roadside removal of timing cover proved what looking up the other end of the mag had indicated . . . and no way home. Luckily a suspicious passing native lent me his mobile - well, took a Euro off me - and the memsahib was prepared to mount a rescue operation. Shame about the 2 dogs that came with her and ran wild in the countryside - but if anyone wants to know this unlikely fact: you can get a whole A10, with both wheels still attached, bars turned down, tank off for safety's sake, in the back of a . . . . Renault Scenic. Plus wife (all squashed up at an unnatural angle in passenger seat, plus 2 dogs of medium build). Have to like the parfum of petrol and oil that comes with this idiocy, but . . . gets you home. Twill take longer to clean her car than it will to replace the pinion, is the only downside. This is all, however, a good thing - I can only get an AMC twin in a Renault Scenic if I take a wheel out. Full marks to Small Heath for thinking of this aspect of 1990s design in 1950 something. Groily
Title: Re: Auto-Advance Magneto question
Post by: bsa-bill on 06.04. 2008 20:39
Why is the pinion stripping cogs - that question needs to be answered before any other action takes place.
Something just goes not seem right here

All the best - Bill
Title: Re: Auto-Advance Magneto question
Post by: groily on 06.04. 2008 22:06
Don't know yet Bill . . . maybe some play in the drive-end mag bearing, maybe some other fault in the gear train, all will be revealed tomorrow I hope when the bits are on the bench and I can see the camshaft pinion properly. Have to say it won't be the first time a fibre gear has shed its teeth in my possession - the first A10 I ever had, a million years ago, did the same thing (same as the fibre dynamo gear, once at least, in every magdyno I ever owned when I was an Ariel single person). I recall others in the dim and distant past with the same experience, too. I do think it's i) a case of age and ii) a known point of weakness (hence length and long-lasting nature of this thread, the notion of alloy or steel pinions and manual A/R as opposed to ATD), and I think it can happen when there's nothing else wrong. New pinions, with or without ATDs, are quite hot sellers. When I had the gear train apart a few months and a few thousand miles ago, all was perfectly acceptable (in terms of slack and backlash in the whole train, even the idler pinion shaft, and the mag itself) - but the mag pinion looked good too, or I'd have replaced it then in light of previous experience. No funny noises then, and no warning of sudden loss of ignition timing when teeth went walkies today. But you wouldn't expect to hear much as steel munches fibre I suppose, until it's well-munched and you lose the timing. It's clear what has happened (just knew it had the moment it went sick and stopped - lovely backfires), possibly less clear as to why. And any way up, a lousy day for roadside maintenance here in Northern Yrup . . . I'm still cold hours later, and I'm better insulated than a high tension mains cable . . . Groily
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 07.04. 2008 05:10
Groily, you may find this useful, Dave
Classic Solutions (North East) Limited

Unit 10C
Tanfield Lea North Industrial Estate
County Durham
+44 (0) 1207 299 020
+44 (0) 773 766 5570

Fibre drive gear for BSA A10/A7 auto advance unit.

Part No: CS50277 Price: 8.51 pounds

Title: Re: Auto-Advance Magneto question
Post by: groily on 07.04. 2008 11:05
Thanks Flatdeck - I saw that and have duly added to 'Favourites'. Sadly, cause of the problem, I think, is very excessive wear on the centre bush of the ATD device - makes Richard's rod wobble look like nothing, and over a much shorter length. 8 teeth ground down to the point of missing the camshaft gear teeth (which are just fine) as are the rest of the train. Clearly there'll be some grunge in the system, but I suspect the teeth ground over a period - there are no lumps of much anywhere I can see without serious additional dismantling . . . so it'll have to be an oil change and general clean-up and fingers crossed. SRM are awaiting an order of new ATD units complete with pinion this week, so I've ordered one to come with a K2FC mag I already have with them for the full works. Not cheap compared to the bare pinion (144 quid I think) but it'll last. Mate with a Velo had the same prob recently with the pinion for either a mag or dynamo (not sure what drives what in Velocettes myself). I shall attempt - see previous comments in this thread as to do-ability - to strip the ATD without damaging it and use a morsel of phosphor bronze or something to make a new bush, then fit to new bare pinion to have as a spare (that I'll never probably need now!). Problem is getting the collar off the back (mag-side) of the thing without a press, so might have to wait till I have access to one. . . . Groily
Title: Re: Auto-Advance Magneto question
Post by: RichardL on 07.04. 2008 11:43
Sorry to hear of your ill-fated pinion and frozen ride. I am, though, a little confused as to why you were out in that weather. One might say that it was a sign of love for riding, or, punishment. You might know a better source, but I just found www.weatheronline.fe. Surprisingly, this weekend was beautiful and 60F+ here in Chicago, but I was in Los Angeles for most of it visiting my "dear old mum." 96 is old, right? Doesn't really matter, I wasn't going to riding, as you know.

Hearing of your purchase from SRM, and given flatdeck's link, and given that you may already know about these guys, it may be moot to mention I am curious what caused the bushing wear. Just time and miles? I guess we should assume that the mag is spinning freely or you would have mentioned it.

Happy reassembling!


Title: Re: Auto-Advance Magneto question
Post by: groily on 07.04. 2008 17:40
Ah well, the joys of club life Richard - we always go out for an organised run the first Sunday of the month, come what may! But yesterday was a tough one, starting well over 65 miles from home and ending about 60 miles from home, after a 50 mile trundle round - well, roughly, I've gone all kilometric lately!

Re the pinion. Yep, wear is the main culprit here. Got it apart this afternoon without a press, and apart from the springs and the bobweights, it's scrap and not worth trying to fix. The central shaft is pitted and horrible, as is the 'bushing' - really just a hole in the middle of the thing. Not enough meat to do a really good job with a bushing, although I suppose one could remake most of it from scratch etc etc - but loads of work, not all of it easy.
Shame, but I'll be pleased to have a new one and know that that particular point of failure won't strike again.

As to dismantling the thing, if anyone's keen to be similarly mad (SRM will, given time, recon one's own unit for less ££ than a new one), it's a Q of 'get the collar off the magneto-facing side'. Somehow. This allows you to pull the 2 halves apart. The rivets that hold the ATD in the pinion can then be tapped out from the mag-side - they can't from the other side. With them out, the big washers that hold the fibre pinion in a solid sandwich are free and the pinion can be pulled from the inner half of the ATD to which it's very firmly attached - light taps with small hammer using suitable sized socket spanner as distance piece. The central fixing hollow bolt comes out of the outer half of the ATD on a coarse LH thread which might or might not be a left handed 9/16 ww, mine's too messed up to tell for sure. Apply pulling pressure to the bolt head - pair of self-locking pliers or similar, and turn clockwise.
If the state of the thing had been better, I'd have bought Fido's £8 pinion and done it myself, but life's never that pleasingly simple it seems! And I'd have been wondering why the teeth got so messed up. At least I can see why, per Bill's query. Ah well, end of day and time to go and get clean. Groily
Title: Re: Auto-Advance Magneto question
Post by: groily on 08.04. 2008 00:45
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 . . .
Title: Re: Auto-Advance Magneto question
Post by: LJ. on 08.04. 2008 10:00

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...  *yeah*
Title: Re: Auto-Advance Magneto question
Post by: groily on 14.04. 2008 21:23
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
Title: Re: Auto-Advance Magneto question
Post by: flatdeck on 17.04. 2008 03:30
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.
Title: Re: Auto-Advance Magneto question
Post by: groily on 25.04. 2008 23:46
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
Title: Re: Auto-Advance Magneto question
Post by: groily on 27.04. 2008 13:29
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!
Title: Re: Auto-Advance Magneto question
Post by: bsa-bill on 27.04. 2008 15:56
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 *smile*

all the best - Bill
Title: Re: Auto-Advance Magneto question
Post by: groily on 27.04. 2008 18:46
Ah well, Bill, comes back to never throwing anything away. I find dead lawn mowers have lots of useful stuff in them!