Author Topic: Magneto: Auto or manual A/R?  (Read 1162 times)

Offline a101960

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Magneto: Auto or manual A/R?
« on: 17.12. 2015 09:36 »
The time has come I think to have my magneto overhauled. I have thought about having it converted to manual A/R at the same time. Any thoughts on wether this is a worthwhile thing to do, or should I stay with auto A/R?
John

Online Klaus

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Re: Magneto: Auto or manual A/R?
« Reply #1 on: 17.12. 2015 10:23 »
l have both on the bikes, the manual A/R and the automatic unit. Both have their advantages, by manual timing you can tune for best acceleration by driving. The automatic A/R plug and dont care about, but often the fibregear is worn and so you have some play at the gears. There are alloy gears for them available, which are recommented to fit.

cheers Klaus


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Online groily

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Re: Magneto: Auto or manual A/R?
« Reply #2 on: 17.12. 2015 15:11 »
Alloy gears are good, I agree, and an ATD can be mounted on one if you can find a gear - they seem to have got scarce recently. Got a couple from SRM a while ago, but they had none last time I looked.
Frankly, given that you'd need to change the cb end housing, probably/maybe replace the bearing while you're on, get a cable and associated bits (the routing of which might give you a headache around the carburettor float chamber depending on your exact fitment), and modify or replace the cam ring, I'd stick with the ATD, although like Klaus I run both types. (Brand new end housings, cb covers and camrings can be had - but you'd be looking at a good few beer vouchers on top of the cost of a straight refurb.)
The great advantage of the ATD is that the internal timing of the mag stays at its strongest at all times because the drive is what's being varied, not the relationship between the armature/magnet and when the points open. The disadvantage is that they can get a bit tired, the gears can strip (always in the dark when it's raining), and they can also be quite expensive to fix.
Bill

Online Klaus

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Re: Magneto: Auto or manual A/R?
« Reply #3 on: 17.12. 2015 15:26 »
Here are both alloy gears for a real good price.

http://www.degroot-bsa.nl/index.php?route=product/product&path=46_158&product_id=2950

http://www.degroot-bsa.nl/index.php?route=product/product&path=46_158&product_id=2631

l have converted to alloy as the fiber lost his teeths 2 miles form home *eek*


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Online groily

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Re: Magneto: Auto or manual A/R?
« Reply #4 on: 17.12. 2015 18:28 »
Thanks for the information Klaus -  and what's more, drilled already for the ATD. Nice!
Bill

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Re: Magneto: Auto or manual A/R?
« Reply #5 on: 17.12. 2015 18:33 »
Aluminium drive gears also available here....................

https://sites.google.com/site/priorymagnetos/magneto-atd-spares
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Offline Viking

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Offline v8ivor

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Re: Magneto: Auto or manual A/R?
« Reply #7 on: 27.12. 2015 15:29 »
I have just fitted a fibre geared ATD to a Manuel A/R mag ( Because that's all I have ) And fixed the the cam on the mag, but I can feel no end play on the mag and the ATD does not spring back to the retard position freely ( It does as soon as I start to turn the engine over by hand )I am just wondering if the manuel gear and the atd gears are interchangeable ? Does any one know ?
Thank you,
Ivor.

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Re: Magneto: Auto or manual A/R?
« Reply #8 on: 27.12. 2015 18:58 »
G'day Ivor. That will happen if it's in a position where the magnets are working against it.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

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Re: Magneto: Auto or manual A/R?
« Reply #9 on: 27.12. 2015 19:29 »
I have just fitted a fibre geared ATD to a Manuel A/R mag ( Because that's all I have ) And fixed the the cam on the mag, but I can feel no end play on the mag and the ATD does not spring back to the retard position freely ( It does as soon as I start to turn the engine over by hand )I am just wondering if the manuel gear and the atd gears are interchangeable ? Does any one know ?
Thank you,
Ivor.

I get lots of customers phoning me about that 'problem'. Adding to Musky's explanation which is absolutely correct, there are a number of issues in the magneto which prevent the ATD snapping shut if you twist it by hand. The magnets of course, but also all the friction points (points heel, brushes, earth brush). There are also friction points in the ATD, particularly the sleeves which are in contact all the time. As you have observed, if you turn the engine over gently you should find the ATD will close completely. The ATD is a fairly crude device which needs to close as the engine comes to rest so that next time you start the bike it is fully retarded; provided it does that and opens up gradually as engine speed increases it is probably OK.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Offline v8ivor

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Re: Magneto: Auto or manual A/R?
« Reply #10 on: 27.12. 2015 19:41 »
Oh, Thank you yet again chaps, I was worried in case the manual mag and the auto gear was not compatible. Mind you, I had to remove a little alloy from the corner of the mag to create some clearance from the crankcases because the correct mag has a slab side at the front I was told.
Ivor. 

Offline worntorn

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Re: Magneto: Auto or manual A/R?
« Reply #11 on: 28.12. 2015 16:26 »
Do the alloy gears ever shed bits of metal? This is a problem we have with Vincents. For awhile there were alloy gears available for replacement of the steel big idler and a lot of race minded owners used them for the lightness of the gear. They destroyed a lot of engines.
Maybe the alloy gear on the BSA may doesn't have enough torque on it to ever do this?
The alloy Vincent gear didn't lose entire teeth, but bits alloy would flake off and go thru bearings, oil pump etc and fairly quickly destroy the engine.
The mag gears that stood up best were made of Tufnol, a linen product ( made from flax)  After the problems with the alloy big idlers, no one tried alloy on the mag gear, but lots of various nylon or other plastic gears were offered as an "upgraded" replacement. All of the plastic gears eventually failed miserably and destroyed some engines along the way as well. Most often they just lost their teeth and left you at the side of the road.
Some had engine damage caused by teeth partially melting with heat which created very strange ignition timing.

Now we have come full circle and are back to using the same Tufnol mag gear that Vincents used from 1934 on. They seem to last forever.

Just wonder if there is any parallel here with the BSA experience? Are the alloy mag gears an old , old product or a relatively new thing?

Glen

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Re: Magneto: Auto or manual A/R?
« Reply #12 on: 28.12. 2015 17:39 »
Hi Glen,
My thoughts are that the Vincent gear is in the centre of the drive train,
It has to drive the cams and onwards to the magneto.
If I understand correctly these also were a "select" fit so one size does not fit all without problems ???
Theres a Comet awaiting my time to fit a new idler + original AA unit and an original BTH magneto (the magneto needs a bit of modifying to fit *work*  )

The BSA magneto gear is at the end of the geartrain so only needs to drive the magneto
I have not had or heard of any issues with the BSA alloy gears
A lot of the fibre magneto gear problems can result from stressing the gear teeth when tightening the magneto nut

Johns 2 cents worth  *smile*
1961 Super Rocket
1963 RGS (ongoing)

Offline worntorn

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Re: Magneto: Auto or manual A/R?
« Reply #13 on: 28.12. 2015 18:17 »
Hi John

The Vincent big idler is on an adjustable boss so it can slide up or down to make the fit to the cam wheels. The crankshaft timing pinion that sits below the big idler and drives it comes in a multitude of sizes in order to take up the difference, if that makes sense.
The big idler is doing a lot more work than the mag gear on the BSA, so that may be where the problems come from.

Glen

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Re: Magneto: Auto or manual A/R?
« Reply #14 on: 29.12. 2015 00:47 »
Hi Glen.
Thanks, Before I get to work on thje Comet I will read the big black book *eek*

Cheers
John
1961 Super Rocket
1963 RGS (ongoing)