Mon, 06/14/2010 - 14:19
Hello all. I ran into a mystery with a bike I purchased in 1983. I bought what I thought was a 1952 M72 long before they were common for $300. The bike has since sat in storage waiting for its turn on the restoration block. Back in the 1980's these bikes were very rare. At the time I found only one guy who even knew much about them and he lived in Berlin. The bike had a valid Ohio title and was listed as a 1942 BMW R71. The tags and BMW symbols had been nicked because the bike sat so long. Anyhow I digress. I began striping down the bike a month ago to start the restoration. I am familiar with both the Rusky and Chinese copies. This one seemed to be much more refined in a way. The castings were nicer, the welds neater. Since I have not had such an old M72, I chalked it up to age. There are a whole bunch of BMW parts on this bike. In fact there were so many that I began to think of all the extra cash these parts would generate. I cracked open the engine 3 days ago. And now I am at a loss. There are clear BMW casting marks on the crank, connecting rods, and many other parts. So now I am at a loss. Is this a M72 restored with BMW parts or an r71 with russian parts? The tank, electrics, and a few other parts are Russian. The heads look M72 but have OZ-74 casting marks. The engine case has the two circles where there should be the BMW emblems, but they have been ground down along with the serial number. Next to that are two Cyrillic characters and a 6 digit serial.
Now I have never owned an r71, so if anyone can offer any good ways of discerning what I have, I would appreciate the info. I have not stripped the frame yet, so I can not say if it has a number. My biggest question is that the original owner's son sold me the bike and said his dad brought it back from germany. I did not believe that because of the clear russian parts. No I am beginning to wonder.
So any info, or theories, or whatever would help. Thanks,
Dan
- 1349 reads
Mon, 06/14/2010 - 21:17
#2
I have considered that. Due
I have considered that. Due to the low serial number it seems to fit production numbers at IMZ 1940 and 43 thru 1945. I have only once found the serial record numbers for early M72 and they are apparently debatable. I have also spoke to several "experts" in Russia. They all agree that they have never seen a M72 older than 1949 or 50. Yet this is dubious to me because when I asked how to differentiate a war time production bike from one of the early 1950's variations they could not tell me.
I have no problem with the bike being an M72. I have plenty of other BMW's to placate my ego. I would however feel bad about parting out a rare bike whether Russian or BMW. I would not mind having a rare and early M72.
I have finished sandblasting the sidecar and frame this afternoon and it is for sure russian. I hope to start on the bike frame next. I should also mention that the front hub and all the brake shoes were also BMW.
Lastly let me run this by the group. I was told that a way of dating an M72 was knowing the differential ratio. The Bmw was geared more for speed. The first two years of production of the M72 had the same ratio as the R71. 1:3.89 It was changed in early 1944 to 1:4.62 where it stayed to 1956. Now I hate math, but is there an easy way to tell the ratio by looking at the differential?
Tue, 06/15/2010 - 01:39
#3
I don't know anything more
I don't know anything more about M72s than what Kurt found on Wikipedia. To figure out your final drive gear ratio, put a mark on the driveshaft and one on the tire, then turn the tire and keep track of how many turns the driveshaft makes. Keep turning until you have integers (no fractions) for the number of turns for each. That will tell you the tooth ratio, and if you divide the bigger number by the smaller one, you'll get a number like the ones you're quoting.
Tue, 06/15/2010 - 12:09
#4
That worked. Near as I can
That worked. Near as I can tell it matches the R71 specs. So now I have to just figure out if it is BMW or early Rusky. I have to say that over the years I have met so many BMW r71 people that have claimed to be able to distinguish an early M72 from an r71. I am beginning to think that is BS. I had two "experts" thus far and neither could tell. I am an R12 person myself and have always avoided the r71's. My pre-war r12 has numerous marks all over it. Surely some of these r71 experts must have compiled a list of casting marks identifying scars, or tattoos. I know that there are a few sites that are pretty detailed for the r12. I know that there was less than 4000 made, but surely there must be a real r71 guru out there. I speak German, so if anyone has any leads...
Thanks
Tue, 06/15/2010 - 13:07
#5
There are folks on this list
There are folks on this list who have contacts in Germany...hopefully they'll chime in. What about contacting Uli's Motorradladen, S. Meyer, Motorrad Stemler and see if they have any contacts?
From the resource links, I found the following:
http://www.bmw-veteranenclub.de/
http://dreher-oldtimerteile.de/cms/index.php
http://uk.groups.yahoo.com/group/KRADRIDER/
http://www.wehrmachtsgespann.de/
Another thing...go to the upper left search box and enter "M72" and look at the discussions that have already been posted. Maybe there's some info there.
Wed, 06/16/2010 - 04:25
#6
I do not know much about M72,
I do not know much about M72, but it sounds like you have at least some of an R71. If the heads have OZ74 stamped on them and have a casting number that starts with 271, they are for R71. The head mating surface of the cylinders will have a tiny BMW rondel (hard to see) stamped into it and the engine number may be stamped on the top surface of the cylinder where the valve adjustments are made. You would probably have to remove the little valve adjustment cover to see this.
If you are going to take the take the engine apart, the major castings will have casting numbers beginning with 260 or 261 (the block was first used on the 1937 R6).
The frame number for the prewar plungers is stamped in top of the driveshaft side plunger and should have the rondels before and after the 6 digit number. The early production frame numbers were shared among all models and the range is 505001-515164. The last production (±1941) had matching engine and frame numbers and for R71 were 703001-702200, R61 were 607001-607340, and R66 were 662001-662039.
BMW R5/R6 and R51/R71 frames underwent several upgrades over their production (and many were retrofitted, too) and that may help identify the frame. I am attaching copies the two pertinent "Assembly Instructions" dealing with the frame reinforcements. The early plunger frames were not very robust. If your frame does not have all of these reinforecments, I think it is likely that it is BMW as I understand that Russian versions were fully reinforced.
My R71 frame has none of the reinforecments and required a lot of straightening and repair work to the fix previous "repairs".
Bruce
Wed, 06/16/2010 - 12:36
#7
R71 and M72
.
Lastly let me run this by the group. I was told that a way of dating an M72 was knowing the differential ratio. The Bmw was geared more for speed. The first two years of production of the M72 had the same ratio as the R71. 1:3.89 It was changed in early 1944 to 1:4.62 where it stayed to 1956. Now I hate math, but is there an easy way to tell the ratio by looking at the differential?
The number of teeth in the rear gears should be stamped on the top of drive casting near the front, although there is no guarantee that is what is inside. In a prewar plunger bike, you could expect to find one of the following:
8/37 = 1:4.62 R51/R61 sidecar
8/35 = 1:4.38 R66 Sidecar
9/35 = 1:3.89 R71 sidecar, R51/61 solo
10/36 = 1:3.6 R66/71 solo
As Kurt suggested, counting revolutions should get you close.
My civilian 1935 R12 engine has a several little "proof mark" type numbers in the kickstart side (no OZ 74 or military stamps). My R71 has only the engine number and OZ74 stamp.
Bruce
Wed, 06/16/2010 - 19:03
#8
Thanks for the info.
I began
Thanks for the info.
I began sandblasting the frame and has a very faint 511305 flanked by two circles which may have once been rondels. Connecting rods have r71 and small rondels. Pistons underside have what appears to be the piston size? with small cast rondels. Crank has numbers but no clear casting marks. Final drive housing has a rondel. There are a few numbers on the inside of the case but nothing that I can see as a possible rondel. I think the heads are from another model, they look different from the russian type. Could earlier heads have been used from an older model?
The seat is from an r75. The handle bar controls have fruh and spat which has cyrillic crudely overstamped on it. It had the original bosch distributor in it but with russian parts in it. The front cover also has a clear rondel.
Other than that the rest of the parts are russian or not easily recognized. I should add that the frame was clearly at one time gray. No other part I have stripped was this color.
So I guess I need to figure out what to do with it. I had the budget for an M72 restoration not a BMW.
Thu, 06/17/2010 - 07:38
#9
It looks like your bike has
It looks like your bike has more German than Russian blood!
AFAIK, there is only one series of R71 heads. I have seen modified R12 heads on R71/M71. The R12 heads have studs, so the studs were removed and the heads drilled out to accept headbolts. There should be a casting number on the heads which should identify what it is from. I doubt any Russian heads would have OZ74. Are the bores 78mm? If they are 70mm, the cylinders and heads are from an R6/61.
Can you post some pix of your heads and pistons? It is interesting to see a "Russianized" BMW. Usually the goal is to make a Russian bike look German.
Make sure you have good photographic records of all the BMW rondels and casting numbers. When I was looking for my R71 a fellow asked my why I wanted an R71 because even if it is real, no one will believe it.
Bruce
Fri, 06/18/2010 - 00:12
#10
Well the thing now is to do
Well the thing now is to do more research. I did a title search knowing I risked loosing the bike if it were hot or invalidating the current title. The original was issued in 1946 and it is for this bike. That tells me that this bike came here right after the war. That pretty well makes it the earliest russian / german hybrid. I have confirmed that the carbs and various other parts that are russian were produced pre-war. That alone makes russian collectors drool. Nearly all the early M72 bikes were destroyed captured or sent to China. Apparently they are so rare that they only exist in museums.
I managed to contact the original owner's son and he sent a number of pictures of his father on this bike in Europe. I am sure it is this bike because it had an odd steel faring similar to the old fiberglass ones that the 60's and 70's hondas had. It had custom made brackets which are still on the trees. It appears from the picture that the only cosmetic repair was the tank. Unfortunately the bike did have the slimmer BMW tank on it. It was badly dented during shipping and disposed of in favour of this russian style tank. That too fits with my paint archaeology. The story of this bike must have been very interesting. Either this was an early russian Molotov pact bike, or an r71 which was repaired with soviet parts. In any case it represents clear German use of captured soviet parts because either they captured the whole bike or its donor bike. I have the original German plate. I hope to be able to strip it carefully as to preserve any original markings.
I have not had this much intrigue since I restored my Kuebelwagon! I think the best course of action is to put it back together as it is. I will document the bike with pictures and post them here.
My understanding of these bikes, especially those around the war, is pretty limited. I thought I read something on one of these forums by either Bruce or Darryl outlining how things ending up in Russian and finally Chinese hands, but I can't seem to recall where I read this.
Is there a possibility that the reason there are so many BMW parts on this Russian bike is that it was one of the first bikes they built where there were significant OEM spare parts around. I can see where they might start assembling bikes with what they had and then as the OEM parts ran out, they began to substitute their own copies of the parts.
That may not wash with the situation or with history, but that's something that popped into my head.
Edit: I remember now where I read the information...it was on the BMWMOA forum. They referenced this wikipedia article. See the 3rd paragraph under History.
http://en.wikipedia.org/wiki/IMZ-Ural
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2