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Peter D. Nettesheim
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OK you vintage experts. Here is a quiz for those of you that love the pre-war BMW's. As this Forum is dedicated to these early models, I have no resistence to asking this very specific question. I am also doing so to help any others who struggle with some of the same problems I have run into. The first to answer the question correctly wins a "Mobile Tradition Team " shirt that was used at last years Vermont rally. I have a few left in a variety of sizes. You pay the few dollars shipment. BMWNA pays for the shirt. Here we go.......

What is the name of the material Bosch and BMW recommend to be used to make the strap that holds the magneto onto the R42,47,52,63,57,12,11,17......
and why is this strap not made of steel?

You need to answer both parts to win and please be advised that the material has a very specific name, not just like "a mixture of brass and something else".

The clock is ticking. Any answers from you pros??? And I do mean pros.

Peter D. Nettesheim
bmwmuseum@hotmail.com

Barry Robin
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San Francisco, Ca.
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hi peter-

gee, as far as i know, the strap is made of brass-or actally, bronze-with a mild steel bottom pin and buckle.

it has to made of a non-conducting material where it touches the magnets, such as brass, as it contacts the generator...and steel would ground it out-not to mention eventually depolorise the magets themselves...

need me to be closer with my answer?

cheers,
-barry robin

Peter D. Nettesheim
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the material has a very specific name like, brass or nickel or gold. the question is what is this one word name?

Barry Robin
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well, you got me peter! damned if i know (and it had better not be the german for non-conductive red bronze strapping!); i'm curious now myself...someone better correctly answer soon to put me out of my misery.

and the answer better not involve an adjective...Smile

-b

Peter D. Nettesheim
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the name of the material is the same in english as german.

Peter D. Nettesheim
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the name of the material is the same in english as german.

bmwmyplace
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Australia
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Hi Just come back from a trip up country, I have read all the references that i have ie bosch manual and BMW hand book and all they refer to is "strap" when I looked it some time ago it appeared as Robin said to be of a Brass apperance so it seems to me to be a copper alloy metal in particular phosphore bronze , possessing great hardness, elasticity, and toughness, obtained by melting copper with tin phosphide. It contains one or two per cent of phosphorus and from five to fifteen per cent of tin.

thats my guess but then I dont have the reference library that you are blessed with .... Peter G Big Grin

Barry Robin
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VBMWMO #52
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phosphore bronze-exactly peter! that's the same as what's commonly referred to as "red bronze". if that's not what he's looking for it looks like we're out of luck again...
-barry

Peter D. Nettesheim
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OK, We are getting all the proper discriptions and the compound make-up is actually very close to what you mentioned. The actual percentages are 80% and 20% but you still don't have 80% what? and 20% what? Plus, you have not answered the question with the one word answer I am looking for. What is the name????!!!. I'll give a hint, its a six letter word and again, its the same in english as it is in German.
The shirt I am giving away is real nice..............
Now I'm going to add a bonus. I will include one of thoise spiral small notebooks that you see being sold on E-bay that gives the history of BMW. If someone doesn't get it soon I'll have to add an original R100RS brochure or something like that.
Any answers???
Peter D. Nettesheim

Darryl.Richman
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Surf City, USA (Santa Cruz, CA)
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My friend Sascha, from Karlsruhe, answers as follows:

The material is tombak (also spelled tombac by some). The purpose is to have a nonferrous material that won't siphon off the magnetic strength of the exposed permanent magnets. A steel band, for example, would become magnetized and reduce the magnetic field in the coil of the magneto.

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Darryl.Richman
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Surf City, USA (Santa Cruz, CA)
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A quiz with a prize!

Just to establish Sascha's bona fides, here's a picture of him at the Windmill Trophy rally in Osthofen, Germany, a couple years ago:

That's his grandfather's 1920 Victoria KR I, which he inherited and restored.

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Barry Robin
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VBMWMO #52
San Francisco, Ca.
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hey, i think you got it there, darryl! as soon as i sae the word the dim light bulb went on...

oh well- at least i got the second question about the nonferrous material verus the magnetic exposed magnets!

darn! and that notebook was looking really tasty.

-b

Peter D. Nettesheim
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Yes! Yes! Yes!!!!! The name is Tombac and Bosch is specific about this material for the application. Since anybody can now look up the compenents, I will give it to you as 80% copper and 20% Zinc. It is non ferrous to conform to Bosch requirements that the magnets of the magneto not have ferrous material against them. I needed to know this when I was faced with replacing one.
Darryl, give me Saschas address so I can send him the shirt (to bad you gave away your source and too bad he is so far away, the shipping is going to be more than the shirt!).
As the mediator and officer, you had to know you were not eligible to win, right??.

Is everybody ready for another quiz???

Peter D. Nettesheim
bmwmuseum@hotmail.com

Darryl.Richman
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Surf City, USA (Santa Cruz, CA)
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A quiz with a prize!

Peter, I didn't have a clue about the name of the material, so I wasn't participating. But I was Skyping with Sascha this morning and mentioned it, so he told me what it was. Besides, I figured everyone had had a couple days at it...

I will PM you with Sascha's address.

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schrader7032
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San Antonio, TX
Joined: 10/27/2006
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A quiz with a prize!

Wikipedia says more like 90/10...if it can be trusted...

http://en.wikipedia.org/wiki/Tombac

Next quiz??

Kurt in S.A.

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bmwmyplace
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Australia
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Well we must really like in a backwater here, I have been around for a few years now and never heard of Tombac , well you learn something every day , I wonder if Dreher and his friends in Polland have gone to the trouble of making their replacement straps out of Tambac.... probably not

Speaking of Poland has anyone ever bought timing gears for flat tankers from Leszek, I have ordered a set for my R42 as mine worry me with the amount of clatter, Im really not game to ride it any distance as it is , way to precious to my mind. Peter G any comments please.

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