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MZ-B magneto and alternator for the /2 BMW twins.

by Duane Ausherman and many others, thanks


This page is about the BMW motorcycle models R51/3, R67, R67/2, R657/3, R68, R50, R60, R69, R50/2, R60/2, R50S, R69S, R50/US, R60/US, R69US. 

A full description of the install is being prepared now and should be out in early 2005. 

This page is only to supplement the existing information on the Mz unit.  This page isn't intended to be any permanent thing, only until Joel gets his own web site up and running. 

Replacement for the Bosch magneto

The unit is made in the Czech Republic and is very high quality.  It can be purchased in two versions, one to replace both the generator and magneto, or just the magneto alone.  It is imported into the USA by Joel Rapose and his email is jrapose@thegrid.net Joel has a service to install and test the system on your bike, ask for current rates.  He also has spare parts and is willing to assist with advice on installation. 

I will post photos as soon as good quality ones are available. 

The web site for the makers is http://www.dynamo.mz-b.de/bmw/bmwmain.htm 


A collection of emails

The MZ-B system does not use the battery for ignition.  The alternator that you get with the MZ-B system has two windings on it.   One winding for the battery charging / lighting and the second winding is for running the ignition system.  It will run just fine without a battery in the bike.

Slight modification to my statement below.  The electronics in the electronic advance module does require 12 volts from the battery charging side of the alternator.  Very little current, however.  The spark energy does not come from the battery.  It comes from a second, separate, winding inside the alternator as I stated below. 

NOTE! If you do run the MZ-B system without a battery, DO NOT allow the battery terminals to short! The MZ-B system uses a permanent magnet field, unlike the /2 generator or alternator.  Hence it will produce voltage if it's spinning.  Best would be to put a electrolytic capacitor in place of the battery.  100 uF or more, rated for 25 to 50 volts. 



 Yes, it is a translation problem.  But it's not with the translation from some other language to our own.  It's with our tendency to modify our own language through common useage.  We confuse ourselves in the process.   It's like this.  There are several kinds electrical generators in general use.  They fall into two basic categories, those that generate direct current and those that generate alternating current. 

 We tend to shorten things in common use, therefore an "alternating current generator" becomes an "alternator".  We then use the word "generator" when referring to the more 'old fashioned' direct current generator.   The type of generator used in the MZ-B system is a permanent magnet alternating current generator, commonly called an alternator.  It consists of a magnetized rotor which spins , and a stator with field windings, which remains stationary.  

 Nortons, Triumphs, and BSA's from the mid-sixties through the eighties use a similar system manufactured by Lucas.  The only significant difference being that in the Lucas system the rotor spins inside the stator, whereas the MZ-B system is the reverse of that .   The alternating current produced is converted to direct current by a rectifier in the Lucas system, and a zener diode is used for voltage regulation. 

 A capacitor is available as an alternative to the battery for those who wanted to use it.  With the capacitor correctly installed no battery is needed to run and you still retain full use of the lights.   It works quite well but there are some minor drawbacks; at least in the Lucas system. 
 A.  The engine won't start if the lights are on, and... 
 B.  The lights tend to flicker at low rpms, getting very dim at idle.   

 I can't think of any reason a capacitor such a Wolter suggests wouldn't work with the MZ-B system.  But if a capacitor is used to replace the battery, you might experience the same drawbacks as with the Lucas system.  But hopefully not, as the electronic voltage regulator might do a beter job than the Lucas rectifier and zener diode. 

Herb Mann



1.  This System replaces the original Magneto and 6 volt DC generator

2.  The new 12 volt Alternator is a 2 in 1 unit.  it has windings for the lighting circuits and a second set of windings for the Ignition circuits.   The two systems are independent. 

3 The new system replaces the points with a Magnet and sensor like a Hall Effect unit. 

4.  The new system is delivered with a coil unit and ignition control.  Regulator/Rectifier and spark plug wires

Jerry Cook


I don't think I am so fond of the idea of running without a battery...it seems plasable but not on MY bike.... 

What I would like to try is to install a damper on a R50 or R60 like the R69S has.... 

The MZ-B alternator is so much shorter than the old generator that I think it would work without changing the cover. 

By using the alternator tool nut as a mounting base for the damper it mounts great...  and I think there is clearance. 

I have dampers on both my R69S bikes using rubber and new disks from Vech and they work super...I check them every 500 miles or so, but have yet to see any wear or rubber deteroation. 

Joel Rapose


Ron - Yes, MZ-B also sells an ignition-only system, if you already have a 12v conversion (or an original 12v system).  I have this system, though I haven't installed it yet.  It will take some extra work to mount it, as my existing Motorrad Elektrik alternator conversion takes up the space under the tank that the MZ-B system needs.  I think I'll be able to get everything under there, but I will have to make a new mounting plate.  Next winter... 

Paul Evans


Visual directions, short version of the parts on the engine

This is the bare case after you remove the BMW magneto and generator

This is the bare case after you remove the BMW magneto and generator. 

MZ Ignition sensor plate mounted

MZ Ignition sensor plate mounted

The MZ stator mounted with the ignition wire hooked up.

The MZ stator mounted with the ignition wire hooked up. 

Proper grounding position for the stator.

Proper grounding position for the stator. 

MZ ignition rotor installed.

MZ ignition rotor installed. 

The is the all of the MZ components mounted under the front engine cover.

The is the all of the MZ components mounted under the front engine cover.

A close up of the MZ alternator rotor.

A close up of the MZ alternator rotor.

This shows the only timing mark of.   See it lined up with the MZ sensor?

This shows the only timing mark of.   See it lined up with the MZ sensor?

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This page was last edited: 04/02/2006 - copyright Duane Ausherman
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