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Musings on my 1951 R51/3... a ongoing story of trials and tribulations

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808Airhead
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Musings on my 1951 R51/3... a ongoing story of trials and tribulations

Post by 808Airhead »

Hello, fellow admirers of vintage BMW motorrad, I am writing this to share about the trials and tribulations I have experienced with purchasing, owning and giving new life to a machine I have always wanted and now is one of the favorite of my small collection. The bike I am speaking of is a 1951 R51/3,a very early bike, 701st one made, it has many one year only features/parts and has the early "metal shrouded" conical front forks, which I find so stylish, and beautiful, and is one of the first type of twin (after the R51/2) manufactured post war, and these early machines actually used body work and frame/ fork that were almost the same as the late 1930's machines made before war broke out.
These bikes are special since they have the old 30-40's styling,however with a "new generation" single cam motor, which is much easier and cheaper to rebuild and use as a rider. This story is about the pitfalls and perils I faced getting this machine up to the state that it is in now, a "first kick" reliable machine I can ride anywhere. I will update this story with additions over time to share with you "my" experience of renovating the bike that gave me the hardest time and kicked me in the nuts, but I learned a lot along the way. I do have a motto I share with anyone asking about purchasing or restoring these bikes "BE READY TO REBUILD THE WHOLE GODDAM THING". :lol:
1. The purchase..... I had, at the time, 3 vintage machines, 2 Earls fork and a gorgeous 1954 R67/2 ,this was one of the last of the plunger era bikes, with its full aluminum hubs, torpedo mufflers, rubber gaited forks,etc. I really enjoyed the riding experience as well as really classic, vintage styling of it, but pined for the even MORE classic early type with the 1/2 hubs/ metal shrouded forks/swallow tail mufflers/painted wheels etc. I always kept my eye opened for one,and missed out on a beautifully restored one by Todd Rasmussen, that hammered for 23k on a ebay auction I could have bought it,but hesitated on pulling the trigger, after that I swore I would not be so gun shy. About a year later another R51/3 came up, for sale in Virginia, by a gentleman named Barry Weurgler, he had a nice collection of older bikes and seemed to know his stuff about these bikes. He said, "yeah the bike is great,everything was rebuilt on it, and it is ready to ride.....READY TO RIDE!!! I was gonna go for it!
I won the auction at 17K,and from the pictures the bike looked very complete, and I was looking forward to getting my hands on it after it travelled across the country to LA, then to be shipped by boat the Honolulu,HI. The shipping was around $13-1500.00 IIRC ,so all in I had paid 18,500.00. The day arrived! I picked up the bike and looking at it up close, it was a "20 footer".......mint from 20 ft. away.......corroded spokes, hand brushed-painted wheels, 1/2 hubs faded paint..but these were aesthetic issues, so I was not too disappointed, but was hoping it was in a "little bit better" shape than it was. After getting it home and assessing it I fueled it up and got it started...it puffed out a big puff of blue smoke and with a lot of clanking noises internally, I got it running! I was excited for my first ride!! Well,I got it out on the road , it rode VERY STIFF, I thought it was the old,rock hard tires, and I had to shift it very soon,and when I hit 4th gear I was revving high at 40 mph! I shut it down....this bike was SETUP AS A SIDECAR MACHINE!! It had the sidecar springs which ride horribly as a solo bike,and the rear final drive, after clooking closely, had been restamped under the original ratio with a lower ratio that was installed from a Russian Ural gear set. Needless to say this bike was FAR from "ready to ride!" I was disappointed,but this is part of the vintage game, taking a leap of faith and buying sight unseen. I knew this was a machine that had a unknown past, but now I had to give it a new future....... this is just the beginning of the story... the tip of the iceberg as they say............keep checking back for more installments! Next is.....the "final drive and teardown" until next time......

2. The final drive.............my first duty to get this machine ridable was to replace the sidecar gears with solo gearing. This machine had a final drive assembly that was, thankfully, in great shape,it is unusual since the cover has a strange "lug/protuberance" on the cover with a depression in the middle, after talking to some people, I am assuming this was made by the factory to attach a rear friction damper (similar to the one for the front fork) that was never put into production, so more than likely the final drive is not original (assuming it was a later modification) or maybe this was a early experiment?
Moving on, upon inspection the free play seemed tight and the differential smooth. The ring & pinion were of very nice quality,and I assumed they were original BMW manufacture, but afterwards found that the ratio stamped on the case indicated these were Russian made gears. I now had to find the solo gears,I searched high and low and waited but could not find any on ebay, etc. It was incredible to find out later that BMW had these manufactured for their "mobile tradition" phase they went through a few years back. I priced out the gear set,they were $880.00 in the states, I found them direct from Motorrad Stemler for $400.00 dollars ,which I was quite pleased with! I also ordered new ring and pinion bearings not to mention gaskets. I saw on ebay "SM motor company had a VERY reasonably priced rear drive spline assembly for $250.00.
After acquiring the proper shim set,etc. I proceeded with the rebuild, I soda blasted the rear drive case and started to "git ur dun". The final drive spline assembky was a very nicely manufactured piece, I think "KML motorrad" in Turkey makes these, they actually make very nice parts,and this one was excellent, everything fit right,bolt holes for ring gear lined up perfectly,etc... so it was a very fortunate circumstance to be able to get these quality parts for a 70 year old bike! It must be SO much easier today with the internet and parts being remanufactured, than it must have been in the 20th century.
After doing the locking wire on the ring gear bolts it was time to grease the spline drive and stick all the losse roller bearings in grease, install the assembly and shim the gears and check contact pattern. Vech helped me a lot when he mentioned the "lipstick trick" so my wife gave me lipstick and I applied it to the ring and pinion and after a few different shims I came to a perfect contact pattern. Next was to shim for free play, that is where I did some head scratching......BMW farms these parts out to bid and I do not know "who" manufactured these ring gears, but they were slightly "off".....around the circumference, when rotated, at different points in the rotation the freeplay varied!!! Must have been some, "not so precision" manufacturing, but what could I do? I got my best clearance possible and when you hold the driveshaft and rock the rear wheel, there is slightly more freeplay some points than others, but there is no noise or anything unusual, it works perfectly for thousands of miles now and I do not notice any greater movement/play at rear wheel.
When I had the rear end apart I inspected the plunger suspension shafts and bushings in the frame, and these were in very good shape so I polished the metal shafts and lubricated the rear end and put new solo rear springs in and proceeded to take her for a spin. I had it running as good as I could with a quick oil change/valve adjustment, carb synch,and away we go! Getting it in gear I got it up to speed, and I was able to finally drive at a decent speed without the engine screaming....and it did feel odd with the solo rear spring and front sidecar springs still in,but it tracked well and shifted well....however the engine pissed oil all over the rear shelf and coming back it was hard to start and very low compression............... "ready to ride"......famous last words.... :lol: This will eventually lead to the teardown of my "ready to ride" engine :lol: this will be my next installment and the longest, most painful endeavour of this entire saga. "Ahui hou" (until we see each other again)
3. This was supposed to be the beginning of my engine rebuild woes I encountered,however I changed my mind and wanted to pontificate on the chassis/wheels/bodywork. While the engine was out I decided to assess the bodywork for this early 1951 bike. Incredibly the front fender and gas tank were both original paint,they had the marks of time and were initialed by the stripers. You can easily tell original paint on these machines from a respray,no matter how "original" they try to make it look. These were a production machine so the paint was thin and the stripes were never perfectly consistent in paint thickness/depth/you can see how they were hand drawn, vs. modern stripers are very good and make it perfect and take their time, the originals were done with attention to quality, but in a hasty fashion. The gas tank was in incredibly good shape, however it is not "correct", a correct one would have the sideways opening glovebox and the fuel tap on the right hand side. These are rare,and if this one was not in such perfect original shape, I would attempt to replace it with the correct one, however the perfect condition of this tank makes up for the fact it is not correct.
The rear fender was older, original paint but had a couple small wrinkles but a very good basis for some work and a respray. It was a fortunate twist of fate that I found one of the last BMW "mobile tradition" new manufacture rear fenders, at the time they had, a few years earlier, started making all kinds of parts for these,including bodywork, painted and striped. I bought this "new factory BMW" fender for a little over 1k IIRC ,and sold the original to Brock Downey on here *(he's a great guy!). The fender was perfect,very high quality, fit perfect and it had the "too perfect" paint job,it has thicker paint,perfect stripes on it, looks beautiful and thankfully does not outshine the original paint parts too obviously. Body work= check....chassis work next. Having replaced the rear sidecar springs for solo, I proceeded to rebuild the forks, these are the metal shrouded, conical forks, a carry over from the 1930's and R51/2 machines, I think they are gorgeous and one of the attractive styling cues of this era BMW twin.
The forks were thankfully in decent shape, I stripped them down and was pleased to see the fork clamps / triple clamps were in great shape with no cracks. The forks have the original, very simple inner fork dampers, basically a "square nut in a round tube" where fork fluid was restricted from flowing by the square nut,very rudimentary,these only offered rebound dampening, and the compression dampening seems to be from "air"...yes, air. The forks have, on top, 2 aluminum TRIM caps,and they are vented, there are also 2 small holes on the top fork caps, upon compression you can hear "air" rushing and hissing out of the top of the forks,this air pressure IMO, was the "compression dampening force". I have never read/heard of this mentioned, but IMO this is part of the design, quite genius. After checking all of the components, I replaced all the gaskets and seals as well as headstock bearings and reassembled the lot,and they do not leak and have been working great for thousands of miles. Whenever replacing the front wheel on these early machines, I take care to leave the lower pinch clamp on the left fork leg loose and bounce the front up and down vigorously to "seat" or settle the forks before tightening the pinch clamp and locking in the front axle. If you do not do this sometimes the forks are not parallel and can have some stiction when moving. I encountered this and from now on I always do that little drill to keep the forks parallel at the front wheel axle.
After the forks were finished the wheels came next, the original wheels were, unfortunately, drilled out for bigger spokes/spoke ends. I purchased 2 new reproduction "painted black with silver stripe" wheels from S. Meyer in Germany,these are nice reproductions, however in some small spots I see a little bubbling underneath, as if there is already corrosion under the paint! At this point I had powder coated the thankfully, great condition hubs, and had new stainless steel spokes so I just looked away from my imperfect brand new wheels and built the wheels myself, which was a great experience. With the Barrington manual guiding me, I laced them up, trued them, and they are absolutely gorgeous and run true. New bearings and seals were installed and am pleased with my choice of SS spokes, they look just as good today as they did years ago.>>>>>> more to come. Below are some pics,the one with the complete bike ar as I picked her up off the dock.
Attachments
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Last edited by 808Airhead on Fri Sep 23, 2022 6:39 pm, edited 9 times in total.
Thomas M.
R69S - R60/2 - R67/2 - R51/3 - R69

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Re: Musings on my 1951 R51/3... a ongoing story of trials and tribulations

Post by Slash2 »

Fun reading so far.. thanks for sharing!

I’ve never bought a bike “sight unseen” that didn’t come with a few surprises.
Western Pennsylvanian - Airhead Extraordinaire

808Airhead
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Re: Musings on my 1951 R51/3... a ongoing story of trials and tribulations

Post by 808Airhead »

Slash2, thanks for the kind words, glad you are enjoying it. With your collection, you could write an Encyclopedia!!!! Aloha!
Thomas M.
R69S - R60/2 - R67/2 - R51/3 - R69

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Re: Musings on my 1951 R51/3... a ongoing story of trials and tribulations

Post by tboooe »

Following! Love these kinds of threads. Looking forward to learning something, I need all the help I can get!
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Tommy
1967 R69s + a bunch of Ducatis

DragoTheHun
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Re: Musings on my 1951 R51/3... a ongoing story of trials and tribulations

Post by DragoTheHun »

I enjoyed your article and appreciate the finer detail that identifies the earliest bikes from the rest. Like the top rear sidecar connection hole that takes a 12mm (not 13mm) bolt, like the numbers are on the left side of the bike, the fuel tank is a right sided fuel tap, and the toolbox lid opens left to right, the front guard brace is painted etc etc... like the pre war bikes. I was not as fortunate as you in finding a complete bike, mine was made into a chopper in the early 1970's then laid up outside in the weather for years and years because the kick start ratchet got stripped so the only way to start it was to jump start it down a hill. By the time I got it from a deceased estate on eBay the engine was siezed in one cylinder, the gearbox was full of water and every fin and oriface on the engine had wasp nests in it. All of the drivetrain aluminium was heavilly corroded. Attached is a pic of what it looked like when I bought it. The only items I kept were the frame loop, all the running gear including the rear wheel hub (which was cactus anyway). At least it was a matching numbers project!, So these past 11 years I have collected parts for this bike from Germany, Poland, Ukraine, Latvia, Argentina, Greece, Turkey, China (dare I admit it!), Australia of course, Slovenia, Italy and Russia. The most difficult / expensive were the front forks and the correct wheel hubs and brake drums. The M72 hubs are OK but the splines are not exactly the same and the German ones, and the brake drums dont have the two ribs around the outside like the german ones have. I had to hot rivet russian drums onto german hubs then shrink fit the two separate external ribs savaged off worn german drums onto the russian drums. Ive managed to get the correct headlight bucket that has the single round green neutral light below the speedo so my bike is period correct, other than using a dual leading shoe front brake .... but Ive gone further and made it look more pre war because all I could buy at the time was a repro front guard for an R52 which has number plate brackets, and the front brace doesn't go up over the nose, it gets riveted from underneanth. Also my handlebars are 1" with reverse leavers, and my Hi/Lo beam switch is bowden cable operated from the handlebar down into the headlight shell where the switch is. This gives the bike a more pre war feel. Its going to be my daily rider and set up the way I want it - not a concourse Queen of course but together with the dark blue paint at least I will be able to spot my bike when the the classic Beemers are all lined up at the rallyies! I might add that Im an old age pensioner and have to do everything on a budget! My second pic is of my bike almost finished in dark blue 2 pack paint
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just need to paint the fuel tank now
just need to paint the fuel tank now
as purchased
as purchased

808Airhead
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Re: Musings on my 1951 R51/3... a ongoing story of trials and tribulations

Post by 808Airhead »

Your machine looks absolutely stunning, it will be a joy when you finish it! Your story is a labor of love and you are almost at the finish line! Post pictures when it’s done. You have inspired me to finish this thread ….. the engine is a LONG nightmare story!! 😂🤙🏽
Thomas M.
R69S - R60/2 - R67/2 - R51/3 - R69

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Re: Musings on my 1951 R51/3... a ongoing story of trials and tribulations

Post by malmac »

My friend bought an R51/3 which was apparently a runner. Well we have been working on the engine on and off for the last year and a lot of things have required attention.

Your article has been most interesting and I look forward to hearing about the engine work.

Cheers

mal
mal - R69s
Toowoomba- Australia

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