Author Topic: Magneto woes  (Read 1513 times)

Online beezermacc

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Re: Magneto woes
« Reply #15 on: 05.04. 2017 12:21 »
Dont worry too much about a difference in points gap. Lucas put a tolerence of 3 thou...

The main thing is that the timing is the same on both lobes. 1 degree out at the mag is 2 degrees out at the crank.

I bought a complete K2F from Priory just over 2 years ago - the points gaps were the same and the timig spot on between cylinders. No easy to achieve that.

Thanks for the kind remarks. The imbalance of points gap is, as you say, not that critical. Nearly all data refers to points gaps of 010" - 012" (012- 015 on later ones) because anything less than 10 thou gets into the territory of potential arcing across the points. An excessive gap causes 'hammering' of the points faces which can either dent or crack the contact tips, and causes excessive wear on the cam and points heel. I can usually get the gap imbalance down to less than 002" and the timing imbalance down to less than 1 degree. Unfortunately, particularly on manual magnetos, the cam ring housings are worn so it is necessary to tolerate a little inconsistency or pay for a new cam housing and cam ring (don't go there!£!£ ouch!£!£).
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Online groily

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Re: Magneto woes
« Reply #16 on: 05.04. 2017 18:34 »
And while we're doing a bit of agreeing entirely  . . . I'd like to agree entirely with Beezermacc.
It can take longer to get the firing interval near-right, with a sensible within limits poiints gap both sides, than it takes to do almost anything else. For all the reasons stated.
It is quite distressing sometimes to see how far out the interval is on some (usually manual) mags which look otherwise quite good and otherwise 'work well'. Now and then it is sadly necessary to go the ££ouch, ££ouch route although I'm sure we all try not to have to.
The good part is when the thing responds to corrective treatment and functions properly. And, mirabile dictu, you get a decent tickover, reduced pinging on things like SRs with lumpy pistons 'cos  the timing is right both sides, your plugs look a lot better, the bike is smoother by miles, and life is suddenly good again.
Bill

Online RichardL

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Re: Magneto woes
« Reply #17 on: 05.04. 2017 19:57 »
While our magneto gurus are on hand, I think I'll ask the question: How old are my mag windings, really? I think the armature is original from the manufacture date in '55. Therefore, calendar age is about 62 or 63.  Don't know how many miles it did before I got the non-running bike in '73, but it hadn't been running from, say, the middle of '71. Let's guess 10,000 miles. Then, the rebuild in the '70s was completed at the end of '78 and did, maybe, 300 miles before wrecked at the end of '79. Then, sat inside and outside until '03 followed by a rebuild that got it on the road in '07. Has done about 6500 miles from then to the present. So, that amounts to an estimate of 27 years on the road and 16,300 miles. Right now, the bike starts on the first or second kick from cold and third or fourth kick from semi-warm (most of the time for both). Of course, it now has an EasyCap. I guess part of this question is whether age, alone, is an issue in the windings, or is it strictly mileage?

Thanks for your thoughts.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online RichardL

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Re: Magneto woes
« Reply #18 on: 05.04. 2017 20:05 »
...and, yes, you two must be called magneto gurus whether you like it or not. Not ruling out anyone else here to whom the moniker might apply.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online groily

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Re: Magneto woes
« Reply #19 on: 05.04. 2017 21:56 »
Well, it's a lot better than a few other things I get called when, just let's say, oil unaccountably gets on car seats, steering wheels or all over some bit of kitchen apparatus Richard!

To your question, I guess I'd say you are quite lucky to have an original winding that is still good. The original shellac insulation material does deteriorate over time - so it's not just a mileage thing. Modern materials aren't the same and don't suffer in the same way. (Having said which, how many 'modern' rewinds have done a half-century??)

Far be it from me to say you're on borrowed time, but I wouldn't risk a trundle through uninhabited deserts where the only signs of previous incursion are bleached bones leavened with traces of long-dried vulture droppings. A well-looked after and low mileage coil can last, as yours proves, but the majority are past their best by now. The same goes for other makes, so it's not just a 'Lucas' thing.

Someone will now say that their one-family-owned something-or-other has never been looked at in 100 years. There's probably one out there somewhere!
Bill

Online RichardL

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Re: Magneto woes
« Reply #20 on: 05.04. 2017 23:13 »
Great answers, both.

Thanks for the imagry, Groily. I now can't help but envision myself (or parts of me) strewm among that field of skeletal detritus. Note to self: Keep phone charged and stay within coverage.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online beezermacc

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Re: Magneto woes
« Reply #21 on: 05.04. 2017 23:22 »
To add to Groily's remarks.... One very good thing about magnetos is they usually give warning before failing. Typically, capacitor failure makes the bike difficult to start when hot; this is often accompanied by sluggish running and all sorts of weird occasional misfires but the 'hard to start when hot' is the giveaway. Coil breakdown, either breaks in the wire (usually where the secondary is attached to the primary or arcing in the slip ring) or insulation failure, usually starts with the occasional misfire which gets progressively worse until the bike is unrideable. Other things can go wrong, like ingress of oil or some sort of mechanical failure in the points, but these can often be temporarily fixed at the side of the road. Lots of customers tell me their magneto has been 'playing up for some time', very rarely does anybody say their magneto gave up without any warning. It always amazes me how long people will tolerate a troublesome magneto, knowing that it completely spoils the ride, yet a good magneto is affordable (IMO) and transforms the ride. Our club enjoys some quite ambitious runs and there are usually three or four A10's amongst us - during the past three years we have ridden around Brittany, to the MotoGP in Le Mans, The Assen TT, the Rockers' Reunion at Brighton (twice) and a 'Coast to Coast' run in the UK plus lots of other local runs. We always take a spare magneto with us, but, as yet, we have never needed it!


Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Online RichardL

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Re: Magneto woes
« Reply #22 on: 05.04. 2017 23:29 »
I'm so envious of those rides. I'd love to have a chance to chance the need for that spare magneto.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online groily

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Re: Magneto woes
« Reply #23 on: 06.04. 2017 06:19 »
A good ride in prospect for me this year (which I'm sure one or two people here have done in the past?) is the Vuelta a Cantabria in Spain.
I'll be taking a spare mag, yes - and indeed a whole spare bike too (by white van) - just in case!
The A won't be one of them on this occasion as I'll be riding with friends with more modern Italian classics. I don't think 35-odd bhp would play too well ('cos I'd break it due to want of self-control). So it will be '60s AMC or Norton, to have the extra 10-15 horses.
Never know, there might even be the odd person over from the US Richard, I'll report back if there is anyone.
http://www.mcpiston.com/vuelta%20a%20cantabria.html
Bill

Offline BSA500

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Re: Magneto woes
« Reply #24 on: 13.04. 2017 20:55 »
Well magneto woes no more thanks to Priory Magneto's. Runs lovely now a little welding and setting tyre pressures and away we go.

Online beezermacc

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Re: Magneto woes
« Reply #25 on: 14.04. 2017 21:14 »
Very pleased to hear the mag is now doing the job. Thanks for the mention here.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Offline BSA500

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Re: Magneto woes
« Reply #26 on: 16.04. 2017 19:48 »
No problem you always do a good job and with the dynamo's as well. I hate timing it up I always have to have at least two attempts before getting it right  *smile*