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BSA M20 Voltage Regulator - what is the correct type? Lucas MCR1 or MCR2

I've been looking through a bunch of older threads. What is the correct voltage regulator for a 1944 BSA M20?

It looks like there were two used during 1939-1945 BSA wartime production, the Lucas MCR1 and the MCR2, which look like they only differ from the height of the lid? The MCR1 being short and the MCR2 being taller. Both have mounting tabs on the ends. Are they marked specifically by a model or date code for the wartime years?

And from what I have read, the replicas currently being made in India fail after a short while and many suggest replacing the internals with a solid state regulator, inside of the older style housing.

email (option): questmasters(at)hotmail(dot)com

Re: BSA M20 Voltage Regulator - what is the correct type? Lucas MCR1 or MCR2

The MCR1 is the correct one for use with the short 45W dynamo, and was replaced post war by the MCR2 for the longer 60W dynamo. The MCR2 is taller and the sideways measurements are slightly different also, although the base mountings are pretty well identical.

You can use an MCR2 with a 45W dynamo (as often seen) But I don't think you can use an MCR1 with a 60W dynamo.

I have several times fitted a solid state regulator inside a duff, gutted MCR1. I just solder the four wires to their respective posts and the bullet connections can be made as though nothing has happened.

I've found these to be by far the best. http://dynamoregulators.com/dvr2.php

Ron

email (option): ronpier@talk21.com

Re: BSA M20 Voltage Regulator - what is the correct type? Lucas MCR1 or MCR2

Lucas CVC (Compensated Voltage Control) units are actually dated on the internal frame and there were several small internal changes during the war years which were reflected in altered suffixes to the type code shown on the cover which were dated too - there were also codes stamped to show a spare part unit, or a spare lid, supplied loose - but you're getting into serious rivet-counter country here. If you don't have access to the major UK jumbles and an inclination to spend days wandering round looking for the correct date, then you'll probably have to be content with simply an MCR1.

MCR1s were considered a little problematical back in the day and the MCR2 had an improved resistor (which accounts for the bulge on the back of the cover). They can be found in working order and are quite reliable, unlike the earlier version. This leaves the restorer with the choice of a correct silhouette hiding a modern regulator or a visually post-war box functioning mechanically.

Here you can see an 8 40 date (August 1940) :-

DSC05812

and a cover dated 7 42

MCR1-Lid-33020-A-7-42

Military workshops would have mixed and matched reconditioned units anyway. An earlier date on a later motorcycle would be quite possible.

Re: BSA M20 Voltage Regulator - what is the correct type? Lucas MCR1 or MCR2

Thank you!

email (option): questmasters(at)hotmail(dot)com

Re: BSA M20 Voltage Regulator - what is the correct type? Lucas MCR1 or MCR2

You can use a MC1 with a 60W generator, but setting it up properly is a problem.
Perte Scott Motorcycles set mine up using his lathe to run the genny.
The difference between not working and melting the solder was less than 1/8th of turn of the cut out so doing it on a vibrating bouncing motorcycle would not be easy.
Having sad that it has worked faultlessly for nigh on 20 years and I did a lot of night riding in those 20 years.

It now runs a DVR II which I bought a long time ago for when the MC1 karked it.

email (option): bsansw1@tpg.com.au

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