The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Josh Cox on 04.10. 2009 02:31

Title: Disassembly of Auto Advance Unit ?.
Post by: Josh Cox on 04.10. 2009 02:31
Hi,

am about to diassemble my auto advance and install new cog purchased from Draganfly, has anyone done this before, any tricks ?.

as here: http://www.draganfly.co.uk/shop/pd-2060969223.htm?defaultVariants={EOL}&categoryId=0
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: LJ. on 04.10. 2009 08:58
I seem to recall that Groily has, as he certainly mentioned in great detail of some chopping about with the auto advance sometime ago.
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: bsa-bill on 04.10. 2009 09:41
interesting - that looks like an alloy cog, mine is fibre

All the best - Bill
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: Josh Cox on 04.10. 2009 10:52
My old one is fibre, the new one appears to be alloy, stay tuned.
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: A10Boy on 04.10. 2009 16:42
I would be interested to know if the center bolt/nut can be taken out and replaced, does anyone know?
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: bsa-bill on 04.10. 2009 17:00
Mine came out when I was fitting it, seemed like you just had to continue unscrewing it.
Also had some difficulty getting it to tighten up until I twigged it had not srewed in far enough - needs to be slack.
Would be worth taking one to bits to see what goes on - how does it pull the pinion off the taper by contnued screwing out if screwing out also free the nut ???

All the best - Bill
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: groily on 04.10. 2009 17:06
The centre bolt should come out OK. Keep winding! It's really just a question of getting the steel collar off the inner side to get the main spindle out (it's on quite tight usually, or should be), then unriveting the pinion from the metal sandwich it's in, and installing the lot on the new gear, re-riveting, pressing collar back on, etc. Also worth getting new springs for the weights.  Assuming all bits are serviceable, they're not so bad to muck about with. Following the death of my fibre one, I installed the ATD unit in an alloy gear. But worth looking closely at all parts for slop, wear, straightness, loose pivot posts for the weights, tired self-extract thread etc. How that works is easier to figure by looking at it than to describe - but it's obvious when you have one on the bench.
Because in the meantime I'd put a manual mag on my A (with a plain alloy pinion), the modified ATD is still in the bits box waiting for the next time - and for some new springs for the weights.
I think the alloy gear is marginally noisier than the fibre one was, but otherwise I reckon it has to be a better option. Think I said somewhere before that I know of 4 stripped fibre pinions just in the last year or two, on 4 different marques - and it's a PITA breakdown to suffer. It was of course snowing when mine stripped. There's no reason not to use a metal pinion AFAIK - my AMC twins use steel.
Good luck!

Title: Re: Disassembly of Auto Advance Unit ?.
Post by: Triton Thrasher on 05.10. 2009 09:45
I would be interested to know if the center bolt/nut can be taken out and replaced, does anyone know?

The outside of the bolt has a left-handed screw thread, which should wind out through the yoke-thing if you pull the bolt out and turn it (the bolt) clockwise at the same time.
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: A10Boy on 05.10. 2009 11:19
Thanks for that info.
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: Josh Cox on 07.10. 2009 14:41
Gents,

Thanks for the help, have got the old one apart, wating for the new parts.

Tried heating the collar off, no joy, ground it away and wedged it off with a screw driver, the pictures tell the rest of the story, gee I am very glad I pulled the unit to pieces.

One of the idle stops are broken off my current unit, the other stop was about to break, that would have been an expensive event if it happened whilst running
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: RichardL on 07.10. 2009 15:30
Josh,

Are the plate and horseshoe washer intentioanally missing from the picture of the old assembled audo-advance unit?

I apologize if this is obvious, but I believe you should test the tooth and diameter fit of the aftermarket aluminum mag pinion before committing to any rivet swadging.  Not that I have I have heard of any problems with the part, but a test seems good a good idea, to me, at least.

Richard L.
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: Josh Cox on 07.10. 2009 15:43
Washer and horse shoe not in the pictures.
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: groily on 07.10. 2009 16:02
Reckon that's as near dead as you'll find. Glad for you that the stop didn't fly off and cause major angst, must have been close.
Not sure what the best sources for bits are. SRM do an exchange service or maybe even a new one - but they ain't cheap at 140 pounds or so if memory serves. Maybe someone here knows a better source of recon/new units? 'Cos that's probably the simplest option in this case judging by the pix.
Alternative is a manual mag end, cam ring, cable + gubbins and plain gear - but that ain't a cheap solution either. Nor, probably, original.
My plain alloy gears came from SRM (not cheaply) and were sold specifically for the job - per Richard's very good point about gear fit. A mate of mine gave me a long lecture at the weekend about the correct tooling required for making involute teeth - there's only one correct cutting tool apparently for any given gear, and his professional opinion was that making pinions on millers with dividing heads was a bad plan as the sliding mesh can't be 100%. Having said that, another mate with a Speed Twin made his own alloy gear (same reason!) by liberating some plate and some tooling at work, and it seems to be fine. Guess alloy is a lot more forgiving than steel, and I believe the problem is accentuated when the driven and the driving gear are different sizes, as that's when the 'involute' bit really starts to matter. Way way outside my farmyard skill set anyway, just thought I'd mention it.
Good luck with it though and thanks for the photos - all too familiar!
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: Josh Cox on 08.10. 2009 01:33
Good morning Groily,

Above I have put a link to the Draganfly product, am waiting for it to arrive.

I am going to go out on and limb and say, "its not Rocket Science", but if the other stop came off whilst running,,,,,,,,,,ouch.
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: groily on 08.10. 2009 12:46
Must say hadn't checked Draganfly for ATDs Josh as I always thought they were for Ariels and my B. Just goes to show. They are great to deal with and I've even got their catalogue somewhere in the shed which probably answers the question!
Agree it's not rocket science - but the collar can be a bit contrary.
You'll be running again in no time obviously . . .
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: rocket man on 10.10. 2009 11:11
i have a question why did they make them fiber was is to make them less nosey
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: flashblack on 10.10. 2009 11:43
I always thought it was to protect the mag in case the engine locked up. Years ago my drive chain snapped and locked everything up and stripped the fibre teeth off!

Richie
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: groily on 10.10. 2009 22:24
Reckon Flashback's theory is the most-often-stated one . . . but how many manual mags used fibre-drive? Haven't met a plastic sprocket or chain yet. So the built-in 'first point of failure' argument does not work for me. And yet, so many manufacturers went with the fibre option for twins. BSA, Triumph, Velocette, Vincent even. I have no real idea why. Norton twins managed with chains and steel like any good sado-masochist, so did Royal Enfield, AMC ran steel pinions on twins. Nobody apparently told them they shouldn't. Fibre's quieter, almost for sure, but that's about it. And when there are up to six pinions in the train for any bog standard twin camshaft motor, what's the difference in practical terms? Maybe it was Mr Lucas who proposed it, as I imagine he sent the ATDs ready assembled to the factories. All I can say is I wish he hadn't.
And another thing - Magdyno pinions for the dynamo . . . yuk.
Title: Re: Disassembly of Auto Advance Unit ?.
Post by: Brian on 10.10. 2009 22:38
It doesnt make much sense, BSA used fibre on the twins but steel on the singles ????

I have a alloy one in my 61' A10 and its no noisier or anything. The reason they used fibre I think is one of those things that come under the heading of    "it seemed like a good idea at the time"