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festanley

Wanted - Switch and Tech Info for ZR6 Two Spark Magneto

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I have acquired a Bosch ZR-6 two spark magneto for a project I am working on. I need a switch for the magneto but don't know exactly what switch is correct. I also need information on how to wire the mag and ignition system.

Also any thoughts on a good mag rebuilder would be helpful

Alan

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Layden,

I am not sure. It is marked ZR6 two spark. I have attached some pictures so maybe that will help identify it.

Alan

mag.jpg

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Be sure to watch the spark plug gap or you will perforate the armature windings. As the 2 spark plugs are wired in series, you must keep their total gap to not more than a single plug, IE: no more than .017" each. Unfortunately one of the shortcommings of a 2 spark Bosch. The 1 position on the switch is usually for the set of sparkplugs over the intake valves on a T head engine ( leads coming from the knobs).

PICT0002.JPG

PICT0003.JPG

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Layden,

That is very useful information. Judging from what you have shown this mag is not set up to operate with a battery and coil. I assume that is the definition of a 2 spark dual magneto.

Do you have any suggestions on how I might go about bench testing this magneto? My expectation is that it will need to be rebuilt but I would like to check it out before sending it to a rebuilder.

Also do you know where I might find a switch? I would guess it is something that can be found in a good flea market.

Alan .

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Correct, this mag would need a second set of contact points mounted on it to be able to wire it for battery starting ( dual system). Dual in Bosch terminology refers to 2 sources of energy to make the spark, battery and shaft motion. 2 spark refers to 2 spark plugs per cylinder. Note that these are 2 different things, some Bosch frame models ( ZR, D, DR, etc.) could have come with no optional features ( called an independent magneto), one installed option, the other option, or both options ( there are 2 spark dual magnetos).

I do not recommend a "bench test" of antique magnetos. If the windings are in good shape and dry then yes it should give a spark but will have to come apart for cleaning and lube anyway as the grease is no doubt dried up. If the windings are good shape but wet ( moisture absorption is common), the test will ruin the insulation thus requiring a rewind of what was a good armature. The safest and in my opinion best thing is to bake the armature before test.

Good luck in your search for a proper switch, they are harder to find than the magneto.

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HI Alan,

at the moment there are 4 or 5 magneto switches on motors.ebay.com.

I'm not so sure which one you would need.

I'm looking for a 2 Spark Bosch as yours.

Where did you find it?

Good luck.

Michael

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:) Greetings I am looking for a coil for a ZR6 Bosch magneto out of a 1927 American LaFrance Type 75 water tower tractor. Any suggestions. Rodger

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Bosch type A dualcoil for sale at $475. Unrestored and obviously needs its face washed ( polished really). Click on my name and send an email if you have interest.

Thanks

bosch dualcoil a.JPG

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Layden-

Can you provide some close up detail pictures of the key for this? I have a friend who has a switch, but the key is missing.

Also, could someone explain the proper operating precedure for this switch? I see there is a battery setting and a magneto setting, as well as a run and start setting.

On his rig it has no distributor, just the dual (?) magneto

???

-Keith

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post-95544-143142773132_thumb.jpg

Be sure to watch the spark plug gap or you will perforate the armature windings. As the 2 spark plugs are wired in series, you must keep their total gap to not more than a single plug, IE: no more than .017" each. Unfortunately one of the shortcommings of a 2 spark Bosch. The 1 position on the switch is usually for the set of sparkplugs over the intake valves on a T head engine ( leads coming from the knobs).

PICT0002.JPG

PICT0003.JPG

This is an older thread, but we are having some issues with a ZR6 on our 1929 Ahrens Fox fire truck and info here is now timely.

What did you mean about the "sparks plugs are wired in series"? There are separate sets of leads for each of the two plug sets, which to me appears to be a parallel set up.

As to the question about switches, ours has a single wire connecting to a switch which earths out the magneto and kills the spark (same as any magneto) on both channels (you cant select one or the other). Any switch will do this job. The truck also has a coil and distributor ignition (yes, 3 plugs per cylinder) which has its own switch.

Our particular problem at the moment is that one channel of the magneto only fires on 3 of the 6 cylinders, and the other channel fires on the other 3.

post-95544-143142773123_thumb.jpg

Edited by Museum of Fire (see edit history)

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There is little to go wrong with a magneto. Sometimes just remagnetising the casing will solve a lot of problems.

I did have an interesting experience with one many years ago. The truck had been on a long trip, but had run faultlessly. We parked it up overnight, but when we went to start it the next morning the engine seized and wouldn't turn over. Went looking in all sorts of places to find the problem but nothing. In desperation we took off the magneto and the engine turned over. Turned out that the lacquer in the windings had heated up and softened, and then overnight cooled and hardened solid.

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You are one of the luckiest men on earth not having stripped the gear or twisted the shaft off of the mag!

You used up one of your lifetime mulligans.

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