Fitting the MZ-B 12Volt alternator to R67/2 and R51/3 models (and early R60’s? etc)

 By Stephen Henry

Owners of the R67/2 and R51/3 wanting to replace their 6 volt charging system, but retain the existing magneto, will face an additional challenge to owners of later model bikes in fitting the MZ-B alternator.  Unlike the photo Fig 1. below of an R69S timing case, borrowed from Duane’s web site, the earlier timing case does not have conveniently located ventilation channels to run the cable for the alternator. If the cable is run through the gap, between the alternator and magneto you will be unable to refit the original magneto without making some modification.

   Fig 1.

Option 1. It may be possible to cut the outer insulation off the alternator cable to feed the wires through the gap but the thought of fraying the inner wire insulation, on all those sharp edges, and having a short circuit to earth is not an attractive solution.

Option 2. Cutting a segment completely out of the MZ-B supplied alternator mounting ring may allow you to feed the alternator cable through.  One day I will remember/see why I did not solve the issue this way.

Option 3. My approach was to remove some material from the alternator mounting ring (Fig 2. shows the back of the mounting ring supplied by MZ-B) and a small portion of the timing cover casting from the area circled area in the photo of the timing cover, refer Fig 3.

 Fig 2.   Fig 3.

When working out where to remove material from the timing cover I had the advantage of having it off the bike so was able to see where the casting was thickest.  Fig 4. shows what the case looks like after competing the grinding of the timing cover casting.  I would strongly recommend that you do not attempt to grind a channel in an equivalent position to the ventilation channels shown in Fig1.

Fig 4.

Fig 5. shows the alternator cable exiting between the MZ-B alternator and the original magneto after grinding a channel in the casing and the alternator backing plate.

 Fig 5.

To remove material from the alternator backing plate a round file was employed.

Fig 6. Material was removed from the timing case using an electric drill and a $1 drill bit grinding stone shown below.

Fig 6.

Comments

1. Would I fit a MZ-B alternator to another bike? Yup.
2. Owners replacing both the existing magneto and charging system with MZ-B replacement parts may not have to modify the timing case to get it all to fit. They may however have to grind off some material where the wiring and new coil ignition leads enter the top casing.
3. For people replacing the magneto ignition - The MZ-B website states there is insufficient space to hide the MZ-B ignition coils in the petrol tank cavity for R51 and R67 models. The coils will have to be attached elsewhere, unless you are really creative the bike is going to end up looking “non standard”.
4. I have fitted the voltage regulator in the frame where it is hidden by the tank and right out of the way, refer Fig 6.  Time will tell if there is excessive heat build up and subsequent regulator failure due to insufficient airflow in that location.
5. It seems to be possible to grind the timing case while it is in situ on the bike, I would recommend removing the magneto and alternator first.

 Fig 6.  

Stating the obvious

1.      If you do not feel comfortable with modifying the timing case casting on your bike, do not do it.

2.      Wear safety glasses when grinding the timing case casting

3.       Keep the removal of material from the casting to a minimum, refit the alternator and magneto frequently to see if the alternator cable feeds through the gap

4.      Mask off area’s on the bike where you do not want aluminum (proper spelling, aluminium) flakes ending up when grinding the timing case. It is amazing how the aluminum flakes fly around.