Magneto: from manual to auto advance

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Magneto: from manual to auto advance

Postby sunnybob » Tue Jun 28, 2016 3:55 pm

Hello, I have a K2F magneto with manual advance on my 1958 model 20. It was converted to Thorspark electronic ignition and I'm wondering if I can go to auto advance. What should I change exactly and where can I buy the parts needed, please? I saw several auto advance for K2f but they are only for BSA, triumph or velocette. Which are the difference? Thank you.

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Re: Magneto: from manual to auto advance

Postby clive » Thu Jun 30, 2016 4:26 pm

no auto advance fitted to the AMC K2F there is no room in the timing side cover. surely there is some electronic auto advance that can be fitted to the electronic system you are running.
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Re: Magneto: from manual to auto advance

Postby sunnybob » Thu Jun 30, 2016 4:46 pm

Thank you for answer. I will ask Thorspark if they have something. Somebody told me I could swap the magneto with a Lucas 18D2 distributor but I can't find any for AMC. I suppose they were on Model 31 and G12... Am I right?

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Re: Magneto: from manual to auto advance

Postby Stuoyb » Thu Jun 30, 2016 4:52 pm

There are electronic ignitions that will fit inside the K2F shell.
AMC fitted distributors in conjunction with alternators not dynamos. Many twins from 1958 onwards had a distributor fitted.
You would have to modify the wiring to provide a switched power feed to the ignition unit

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Re: Magneto: from manual to auto advance

Postby sunnybob » Thu Jun 30, 2016 5:00 pm

Stuoyb wrote:There are electronic ignitions that will fit inside the K2F shell.
AMC fitted distributors in conjunction with alternators not dynamos. Many twins from 1958 onwards had a distributor fitted.
You would have to modify the wiring to provide a switched power feed to the ignition unit


My thorspark electronic ignition is in the K2F shell now. It use a Coil that is outside and is already powered by battery (they say the energy use is very small). So I suppose I could fit a distributor with auto avance as well. Or not? :?: And where can I find it?

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Re: Magneto: from manual to auto advance

Postby Stuoyb » Thu Jun 30, 2016 5:14 pm

You will only find a used distributor as there are no new ones available.
Try putting a "wanted" advert on the website which will also go in the Jampot magazine.

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Re: Magneto: from manual to auto advance

Postby Duncan » Thu Jun 30, 2016 6:05 pm

Roberto

It is possible to modify a Fiat 500 distributor to fit although they are getting rare now as well but I have a feeling there may be more of them in your part of the world, you will still need a drive gear and Lucas mounting platform although you could make something to suit:

DSCF2004r.jpg

DSCF2009r.jpg
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Re: Magneto: from manual to auto advance

Postby sunnybob » Thu Jun 30, 2016 6:59 pm

Duncan wrote:Roberto

It is possible to modify a Fiat 500 distributor to fit although they are getting rare now as well but I have a feeling there may be more of them in your part of the world, you will still need a drive gear and Lucas mounting platform although you could make something to suit:

DSCF2004r.jpg

DSCF2009r.jpg


Duncan wow! That's great! I suppose it is quite easy to find a 500 distributor here in Italy!!! Also the driving gear is available at club shop so the problem is the Lucas mounting platform!!
Did you made this one by yourself? Is it for sale?

@Stuoyb. I'm going to put an add now! Thank you for the suggestion!

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Re: Magneto: from manual to auto advance

Postby Duncan » Thu Jun 30, 2016 8:27 pm

Roberto

Sorry not for sale, it is fitted to my G12, I took the pictures about ten years ago when I picked it up from an auto jumble. I believe the platform is standard Lucas, keep an eye out on auction sites and see what turns, the Lucas distributors were fitted to several british twins so don't constrain yourself to just searching under AJS & Matchless. The drive shaft on the distributor need to be cut and drilled for a drive pin so make sure its not something you want to reuse on a Fiat first.

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Re: Magneto: from manual to auto advance

Postby Groily » Thu Jun 30, 2016 9:21 pm

It is in fact possible to get an ATD to fit under the timing cover of a standard AMC twin.

I hadn't realised (per Clive's post) that even the late twins never used an ATD - but just as an experiment I modified a spare camshaft pinion to take an ATD a while back, and it fitted and worked on my Mod 20 (narrow timing cover). There's enough steel on the gear to relieve the central portion, then machine out the middle for the ATD shaft and drill holes for the attachment of the ATD. A specialist, or a talented person with a fetish for gear-cutting, could probably knock up a rather better job and save a fair bit of weight at the same time - I've seen super gears in steel and alloy made for people who don't like the fibre ones typically used with many ATDs, and for eg B*As there are after-market metal options 'off the shelf'.
That would perhaps be an easier route than trying to fit a distributor from a Fiat, although less adventurous!

Easier still, the Thorspark literature says clearly that manual ignition control can be retained, so in the case where a conversion is being planned for a magneto that has a fixed camring, there would only be the need to get hold of a manual end-housing - not so hard to do that as there are plenty of them around. It's what many Thorspark users presumably have done?

Easiest of all, there is the not-actually-ridiculous option of running many of these machines on fixed timing. (How many of us apply retard every time the revs drop to tickover, or as engine load increases as revs drop, throttle open?) If the tickover speed is set a tad higher than usual to reduce lumpiness at prolonged idle, this can work well. On a 500 twin there's not a whole lot of risk to the kickstart leg either, as they start so extraordinarily easily. A couple of of my machines have run, or are running, on fixed timing mags. I like their greater precision for having fewer moving parts at the contact breaker end, the lack of cable-clutter round awkwardly-parked carburettors etc - and I tolerate the slight risk of footache when starting.

So, even absent the desire to invest in an electronic system that has a curve programmed in, to buy new bits of magneto, or to sort out a one-off ATD unit, a well-mannered machine will likely stay a well-mannered machine without going to any serious trouble. (But - and fair enough - I know some wouldn't agree, especially those who live in built-up areas.)

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