Automatic Advance Unit

[AngleseyAJS]

Good afternoon,

I have a 1955 AJS 18s with a Lucas SR1 Magneto fitted.

I've slowly working through everything to get it back on the road after a layup before I bought it.

It starts on the button and runs quite well but there has been a couple of niggles. After looking through the forum and reading a lot of posts I decided to check the Automatic Advance Unit.

Granted I don't know much about them but I think it's absolutely knackered! I've never seen anything so worn . I'll post a picture

[AngleseyAJS]

Sorry I pressed post too soon!

It's so worn it's almost coming apart.

I've looked on line and it seems they are around £300 with the vat.

My thinking is that if I buy a new unit and fit it on and the Magneto goes wrong in 6 months I'm going to need to spend on that too , would I be better off getting a reconditioned Magneto that comes with a standard manual advance/retard device fitted and do away with the automatic unit?

What would you advise?

What would fit?

I've had a look and come up with a Lucas N1 4 but I don't know if it will fit.

Id appreciate your help and thoughts

Many thanks Chris

[Groily]

One man's 'knackered' is another man's 'loads o' life left', so it's a bit of a relative thing!

Knackered to me means:
* the two main parts of the ATD, the outer and inner, have a lot of slop and wiggle between them, caused by wear / rust on the central pillar through the middle
* the bob weights don't slide easily in and out because the plate across which they move is deeply gouged or because everything is bent
* the pins and holes on the weights are seriously oval
* springs are stretched or broken.

Wear on the main spindle is a pain, but it will still work.
Sticking in operation is bad as it affects performance on the road, starting if it won't retard, etc.
Worn pins and holes might be part of the stickiness, but they are all a bit tired by now and you'll be lucky to find a 2nd hand one that isn't. If it operates OK and the springs are OK, it should function, for the moment anyway.

To see exactly what is in one of these babies, have a look here, on the Priory Magnetos web site:

The parts shown are 'pinion driven' not sprocket but the principles and most bits are the same or very close).
Priory have some parts available usually, but don't I think they overhaul the units from AMC singles as they're Beesa / Triumph focused. Worth a call though - pricing is keen from there for recon units.
Or look here as well for more explanation of how they work:
https://www.brightsparkmagnetos.com/faq ... 20work.htm

and see also the concurrent thread here for more on the subject:
viewtopic.php?t=30671

You're not alone, and there are solutions.

Buying and maybe rebuilding a manual N14 (which will fit) is unlikely to be a cheaper option than working with what you have . . .

[AngleseyAJS]

One man's 'knackered' is another man's 'loads o' life left', so it's a bit of a relative thing!

Knackered to me means:
* the two main parts of the ATD, the outer and inner, have a lot of slop and wiggle between them, caused by wear / rust on the central pillar through the middle
* the bob weights don't slide easily in and out because the plate across which they move is deeply gouged or because everything is bent
* the pins and holes on the weights are seriously oval
* springs are stretched or broken.

Wear on the main spindle is a pain, but it will still work.
Sticking in operation is bad as it affects performance on the road, starting if it won't retard, etc.
Worn pins and holes might be part of the stickiness, but they are all a bit tired by now and you'll be lucky to find a 2nd hand one that isn't. If it operates OK and the springs are OK, it should function, for the moment anyway.

To see exactly what is in one of these babies, have a look here, on the Priory Magnetos web site:

The parts shown are 'pinion driven' not sprocket but the principles and most bits are the same or very close).
Priory have some parts available usually, but don't I think they overhaul the units from AMC singles as they're Beesa / Triumph focused. Worth a call though - pricing is keen from there for recon units.
Or look here as well for more explanation of how they work:
https://www.brightsparkmagnetos.com/faq ... 20work.htm

and see also the concurrent thread here for more on the subject:
viewtopic.php?t=30671

You're not alone, and there are solutions.

Buying and maybe rebuilding a manual N14 (which will fit) is unlikely to be a cheaper option than working with what you have . . .

Thanks Groily,
Looking at it closely it's worn in all pivot points and very worn in the central shaft and even being super optimistic I just can't see if being repairable. I completely agree that a second hand unit is not really worth bothering with as the chance's of finding a good one is almost impossible.

Funnily enough I have been in contact with Priory this morning. He doesn't repair or replace AAUs for AMCs but he can supply a fully reconditioned and guaranteed N1.4 for £300.
Don't get me wrong I don't want to spend £300 particularly but I'd rather have a new mag and do away with the AAU that just a new unit.

Will the N1 fit on without any modification or will I need a different mounting plate?

[Groily]

Well . . . a rebuilt N1, if you have doubts medium term about the SR1 AND are in for nasty ££ pain to replace the ATD with 'decent', is a good answer. You'd need a plain sprocket, plus cable and h'bar lever - Andrew Guttman might be able to do (but ? the sprocket), the Club would have all of it I think without checking.
N1 should go straight on afaik. Personally, I actually prefer N1s to SRs as they have more of a solid feel to them (I think), but they are an older design of course and 'not original' for '55-'57 if you care. Also, maintenance can be harder, but that shouldn't matter with a decent rewound rebuilt one of good provenance, that should last for ages.
Could get your money back in part if you resold the SR1 (there's always demand for them) - but maybe you'd want to keep it with the bike's bits.
So . . . From what you say, sounds like a good plan to get to happy quickly!

[Andy51]

Hi Chris, just to confirm what Groily said about mag interchangeability. My '54 G80 came with an N1 mag fitted with Lucas ATD. It ran well but I fitted an SR1 after a year or so for originality's sake. As an aside, I then found that the cylinder barrel was from an earlier year and the front fins were not cut away enough for this larger mag so had to remove barrel, get fins machined away, then had to repaint cylinder - a quick 'bolt-on' job took weeks, should have left the N1 on... moral of this story is think carefully before fitting non-standard parts! As another aside, my ATD from my AJS was worn, I scored a very reasonable one for a BSA from ebay (which has a gear wheel mounted), drilled out fixing bolts, removed gear wheel, and put the AMC one together with most of the BSA parts - cost 20 quid and a couple of evening's work. They are simple enough to work on but I recall having to use a puller at one point. Andy

[Groily]

I was wrong saying " '55-57' " for SR1 Andy - I'd forgotten the 500s got them a year earlier than the 350s. But no big deal in the context. From what you say it seems the N1 will go on anything, SR1 needs the fin treatment or the different cylinder if going on an older engine.

It's quite interesting that your N1 retained the ATD (unless it was one for a stationary engine with no manual AR). Probably for the want of a plain sprocket in the PO's hands, but it's not a bad plan actually.
There be a good few people who like to have both manual and auto advance, as it offers the ability to retard manually on hills under heavy load when the ATD is still at full advance; and it provides easier starting as manual retard isn't necessary for that so the spark stays at its strongest when you need it most. I've seen Beesa twins with the same dual system, and it's handy, especially with the tendency of alloy head A series twins with lumpy pistons to pink quite badly using 'book' settings for the timing. I have often wondered whether it would have been possible for Lucas to have developed a vacuum diaphragm system operating on the inlet manifold depression to provide some 'load sensitivity' on the timing, as per old car distributors . . . but 'wondering' is as far as I ever took that thought because implementation would be difficult. Impossible maybe!

The bits for the ATDs are all pretty much the same, so fitting a sprocket to a pinion-drive job is as you say a relatively OK job. Just need the right length rivets really, and yes, a puller to get the collar off the inner end of the central shaft. The BSA unit and the AMC single ones have the same 11°-13° arc of movement, so even that's 'correct', not that a degree or so would make much odds.

However, I think Chris will be happy to have avoided the cost and / or work involved with the knackered ATD unit and to have acquired decent sparks for the longer term at an affordable price!

[Andy51]

Hi, another thought on refurbing ATDs. My original plan was to tighten things up by bushing the pivot holes, but the pivot pins were worn badly out of round. I then thought I could knock up new pins on the Myford, but the old ones were a VERY tight fit in the bobweights and I managed to break one trying to press it out. Then I saw the BSA one on ebay at a very good price, and as it was in pretty good condition I went down the caniballisation route. I also had a couple of bits left which I gave to another member with similar peoblems. To refurb by bushing and/or new pins would not be practical unless you relish a real challenge for its own sake! Andy

[Groily]

Hi, another thought on refurbing ATDs . . . .To refurb by bushing and/or new pins would not be practical unless you relish a real challenge for its own sake! Andy

Ain't that the truth! Nasty nadgery job, very much best avoided, I agree!

[56G80S]

On the barrel fins front, when I bought the 1956 (reg 1957) G80S in the mid 1970's it had the SR1 and all was fine. I've found the SR1 to be a great piece of kit but after years of complete neglect, it failed.

A stationary engine enthusiast acquaintance sold me an SR1 for £25 so I wouldn't be without the G80S during the summer. It had been on his shelf for many years but with a clean of the points worked fine (even the original capacitor). On refitting the refurbished SR1 I thought fit a new chain. I couldn't adjust it, the barrel was in the way and I replaced the original chain. It seems that the PO had fitted the "wrong" barrel at some point. Angle grinder work later the refurbished - and I have to say fitted with an EasyCap - SR1 would adjust properly but I checked the chain wear and stuck with the old Renold chain as it seemed to have no wear at all!

Johnny B