R51/3 Ignition Coil rewound: How many Ohm at the resistance?

[schrader7032]

Is the R51/3 magneto coil the same style as the /2? Not sure, but... I had saved some notes when the question was raised about the /2 magneto. There are two windings, a low and higher resistance one. The low resistance one is in the range of a couple of ohms at most (connects frame ground and moveable side of points). The high resistance winding is around 17K ohms (connects the left and right plug).

Kurt in S.A.

[Allan.Atherton]

The Magneto coil needs a rewound. The workshop is able to do it, but needs to know the resistance, as the wire is to thin to be counted...
You are in Israel? It sounds like your workshop has general experience in rewinding motors and coils, but has not wound a vintage BMW coil before. The coil has a complicated winding pattern, the job is very difficult and specialized, and it is best left to experienced people who are in the business of rewinding these particular coils. There are only two such sources I know of, one in Florida, and Huggett in Switzerland. I have heard of one attempt by a general rewind shop to rewind a /2 coil, and it was not successful.

Why not play it safe and buy the coil from Huggett. My Huggett rewound coil has worked for the past 7 years and 12,000 miles.
http://www.bmwbike.com
12 13 8 004 104 Ignition coil, "NORIS", R51/3 - R69S (hand wound) 210.00 Swiss Francs

[Micha]

Hi Allan, Thanks for the idea. I know Mr. Huggett that runs a very good and reliable business, but at the time I'm very short with money, so I'm looking for alternatives. Pls see new topic.

[Allan.Atherton]

... The Magneto coil needs a rewound. The workshop is able to do it, but needs to know the resistance, as the wire is to thin to be counted....
Here's a story by the late Jerry Cook about another shop that felt they could rewind a /2 coil. Perhaps it will help your shop.

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Jerry Cook, November 3, 2000
http://clubs.yahoo.com/clubs/vintagebmwmotorcycles

"I get to play in a BMW repair shop. My friend Lap Nguyen has been doing BMW repairs for 25plus years. ANYWAY.......... He gets a lot of /2 and /5 business. We were looking at a bad coil and wondered if it could be rewound locally. Well since there is a Motor rewinding shop next door to Laps place QUALITYMOTORCYCLE.com we asked them if they would try to rewind one for fun. We furnished a case of Heineken and started. They wound it straight just like a “NORMAL" coil. We put it on a bike or the coil tester and it lasted for about one spark. Coil windings were blown open. The wire is the finest gauge I have ever seen. Angel Hair!!!!
We took another bad coil and decided to take it apart. (Too much spare time EH?) What we found was that on the secondary they had wound 50 turns, then they moved over 1/4 - 1/2 inch and did some more turns then moved to another place. And If I remember correctly there were two separate coil windings. Both doing a relatively small number of turns and then moving to another area. They figured it was done to eliminate arcing or different charge polarities canceling each other.
Anyway it was too much trouble to even think about setting up their stiff to wind like that. And basically they do big commercial motors that usually need a lift to move them around.
But Kevin at the motor shop wrote down all the winding patterns on a notebook. I think it was 3-4 pages worth. He is the only one that can make sense out of it.
Anyway....... The Coil is definitely not a "Simple" thing when we are talking about the BMW /2 coil."
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[EuroIron]

My favorite electronics professor ran a consulting firm that deal mostly with AC power........ lots of transformers and the like

he told me often that winding transformers (what an ignition coil is) involved just as much luck and black magic as it did science

[Allan.Atherton]

Another description of the coil that would be of interest to a rewind shop first attempting this job:
---------------------------------

From Ron Cichowski, /2 Group, 2 Nov 2006

The coil is a bit more complex internally than I figured it would be. Starting from the outside is an impregnated wrap that covers the coil from end to end. This wrap protects the coil and holds both terminal blocks in place. Under the exterior wrap ahere are TWO separate coil segments (left & right)! They are separated by almost 1/4" at the center of the coil and are at least 1/8" away from each end flange. You can literally unwrap half the coil without disturbing the other half. The two coils are connected via a small metal strip at their inner ends. Their outer ends are connected to their respective wire terminals. The wire is fine and probably measures less than .012" in dameter. IT IS MULTIPLE SINGLE LAYER WINDINGS FLAT AND EVEN WITH NO OVERLAP.There is an insulating layer between each winding layer! I had assumed they would built up a winding like a transformer in multiple layers, WRONG. This device must have taken more than a few minutes to produce correctly.

Under the fine wire secondary windings is the primary. It is wound with the diameter wire you see mated to the points wire. This is a neatly done full width multiple layer winding that wraps around the iron core and probably adds 60% to its diameter.

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[Bruce Frey]

I have no /2 experience, but I know some guys have a rigged up a coil (so a battery is needed) as a backup for a failed mag coil. I think Alonzo Walker has a write up on how to do it. Just another option.

I don't have the link, but I'll bet Allan has it archived.

Caio,
Bruce

[Allan.Atherton]

I do have a long document on it, consisting of articles written by Walker, Hamlet, Cook and Harms on how they did it. But it's not on the web. If anybody wants it by email, send one to my VBMWMO address here and I guess it will be redirected to my real address.

At one point I had bought the required coil (cheap but hard to find), but didn't want to mess with adding it as a back up, and sold it.

[VBMWMO]

Hello. The Magneto coil needs a rewound. The workshop is able to do it, but needs to know the resistance, as the wire is to thin to be counted.
It is stamped: 40 125 / 1.
Any help is appreciated!
Best – Micha.

[Rodolfo850]

Allan..hello

Did you still have this document?? I would like to read it!!

Please send to my email ..rcastillo244@gmail.com

Regards

Rodolfo