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R50S Restoration

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sblaylock
Posts: 183
Joined: Thu Jul 22, 2010 1:05 pm
Location: Victoria, BC. Canada

R50S Restoration

Post by sblaylock »

Hi,

I'm working on a '61 R50S and I have a couple of questions.

I was told the 20207 rear spherical roller bearing is not the way to go on R50S' and R69S' these days. These was a 20207 in there before and the crank needed to go out to be redone. I'm being told the 6207 M (C3) is the way to go now. Is this info correct?

Second, I'm trying to get some advice on the Camshaft and Crankshaft Timing Gear set. The case has -2, the Cam is -4 and the Crank is +1. The Crankshaft gear is badly pitted so it needs to be replaced. There were no measurements done when the engine was taken apart so I have no reference to go by. The Barrington Book mentions in these types of situations - no reference data, that going one size smaller gives good results. Does going with a -3 seem like a good idea? I read Mal went to one size smaller and said two smaller would probably have been a better choice. To add to the confusion, I have no idea the mileage of the bike.

Thanks,
Scott.

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jwonder
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Location: Long Island, New York
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Re: R50S Restoration

Post by jwonder »

sblaylock wrote:
Thu Nov 17, 2022 3:12 pm
I'm working on a '61 R50S and I have a couple of questions.

I was told the 20207 rear spherical roller bearing is not the way to go on R50S' and R69S' these days. These was a 20207 in there before and the crank needed to go out to be redone. I'm being told the 6207 M (C3) is the way to go now. Is this info correct?
The 6207 C3 bearing is the way to go, and many people suggest the brass cage M bearing. I have heard several people argue about the merits of the brass cage over the steel cage, and I use either brass or steel depending on what is on the shelf! for an R 69 S or an R 68 I would use the brass cage, for the others a steel cage should be just fine. Do not use the plastic cage bearings.
sblaylock wrote:
Thu Nov 17, 2022 3:12 pm
Second, I'm trying to get some advice on the Camshaft and Crankshaft Timing Gear set. The case has -2, the Cam is -4 and the Crank is +1. The Crankshaft gear is badly pitted so it needs to be replaced. There were no measurements done when the engine was taken apart so I have no reference to go by. The Barrington Book mentions in these types of situations - no reference data, that going one size smaller gives good results. Does going with a -3 seem like a good idea? I read Mal went to one size smaller and said two smaller would probably have been a better choice. To add to the confusion, I have no idea the mileage of the bike.
My R 50 S had bad gears as well and I purchased the matching gear set (-3 in my case) and they were perfect! My R 50 S had all the signs of being ridden hard so I replaced everything. I really don't believe that the block changes over time. If you think about the stresses on the block, I do not see that happening. I would like to see empirical evidence of that happening and not just someones opinion.

NOW, it is very possible that the factory did not put the perfect size in to start with and when someone rebuilt a motor the next size up or down was better. I could 100% believe that.

I built a jig to test the gear backlash (picture below) and thats what I used to test my R 50 S gears when I got them from Salis. He said I could return/swap them if I had not "installed" them so this jig works fine. This is much like what Jan at Salis uses!

Again, my case was marked -3, I purchased a -3 set and the fit was perfect! The motor runs fabulous with no noise!
Attachments
IMG_8025.JPG
James Wonder
Vice President, Vintage BMW Motorcycle Owners
2022 BMW Friend Of the Marque
Long Island, New York

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sblaylock
Posts: 183
Joined: Thu Jul 22, 2010 1:05 pm
Location: Victoria, BC. Canada

Re: R50S Restoration

Post by sblaylock »

Hi James,

Thanks for the info. I too was chatting with Jan at Salis and he was the one that recommended the 6207 M (C3). He was also the one that had said a -3 "may" work for my -2 case but there are no guarantees.

Correct me if I'm wrong, but the potential issue for going -2 set with a -2 case is at running temp the mesh could be too tight. With a -3 set in a -2 case the issue could be noisy at idle but fine at running temps.

Thanks for the photos. I was planning to build something to test the mesh without pressing the gears on as well.

Scott.

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jwonder
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Re: R50S Restoration

Post by jwonder »

Scott,

Jan knows his stuff, and going with the 6207 C3 M is never a bad thing.

As for the gears, I do not prescribe to the "the block changes dimension" argument, I just need to see real facts on that one. This means that if you go with what is stamped on the case, and BMW measured right during their production line run, and the aftermarket gears are correct, the gears should mesh fine. I think you get into more trouble when you start mixing, but I have not done enough motors (I have done 10) to be sure on that, so please take that as a small sample set. I would love someone who has done more motors than myself to empirically verify the block changes dimensions over time.

I build tools (sometimes poorly) for all types of operations. I will probably use this one 5 times (if I am lucky) in my lifetime! :-)
James Wonder
Vice President, Vintage BMW Motorcycle Owners
2022 BMW Friend Of the Marque
Long Island, New York

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sblaylock
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Joined: Thu Jul 22, 2010 1:05 pm
Location: Victoria, BC. Canada

Re: R50S Restoration

Post by sblaylock »

James,

Thanks for that. I was thinking the same thing with having a -2 case then get a -2 set, but Mal's excursion down that road and the Barrington quote made me question my thinking. Maybe I'll chat a bit more with Jan before I order the new set.

As it turns out I have another R50 motor coming in next month in boxes with again no pre disassembly measurements so any tools I spin up for the R50S will be handy for that one.

Thanks again,
Scott.

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sblaylock
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Location: Victoria, BC. Canada

Re: R50S Restoration

Post by sblaylock »

James,

Taking a closer look at your dummy shafts I couldn't help but notice "Canada" stamped on the 6207. Who knew we made bearings here in Canada... well I'm sure some people knew, but I had no idea.

If you put that in your R50S I'm assuming they are good quality?

Scott.
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6207_Canada.gif

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jwonder
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Re: R50S Restoration

Post by jwonder »

That was the bearing that came out. I used it for my tool. That was also the front cast iron carrier that came out with broken ears. I machined it down slightly to fit in the block.

Buy the -2 gearset and enjoy life!!! 😄😄
James Wonder
Vice President, Vintage BMW Motorcycle Owners
2022 BMW Friend Of the Marque
Long Island, New York

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malmac
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Joined: Sun Jun 29, 2014 2:10 am
Location: Toowoomba, Australia.

Re: R50S Restoration

Post by malmac »

Hi James

My case is stamped -0 and I had to go to -5 gears before I had the factory backlash (.015mm measured)

I am not saying my case is normal and I would listen to Jan at Salis before I took my individual case as the benchmark.

By the same token I am not doubting your experience, James which is much more than mine.
But it seems that I am able to give you evidence of just one example. Obviously the jury is still out and so they should be.

Mal
MAL_5435.jpg
mal - R69s
Toowoomba- Australia

Seek
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Re: R50S Restoration

Post by Seek »

At the moment I am in the same process with my R69. Which bearings to choose and which gears? On my crank the rear bearing could be slipped on and of the crank with bare hands easilly. So it really was way too loose. Indeed on measuring I found the bearing journal to be about 0.02 mm undersize. There was a 20207 bearing in there with a nylon cage, which hadn't cracked (yet).

I now have the crank bearing journal hardchromed and regrinded to spec at a German revision shop. I got some good endorsements for this shop. They recommend a NOS 20207 bearing from FAG. But this needs a careful matching of the bearing to the crank journal. Back in the day this was a factory job and it wouldn't have been done at a normal workshop. When neccessary the engine would have been sent back to Munich. That illustrates how critical this is.

The reason of the 20207 barrel bearing is the flexing of the crankshaft at high rpm's. Rabenbauer (another very experienced parts dealer, mechanic, producer of replacement parts) has done some tests with an engine on a test stand and concluded that the worst vibrations are around 6300 rpm. His advice is to use a 6207 C3 M bearing from FAG or SKF or similar high quality production, and not running the engine for extended periods at the critical rpm. So either stay below 6000 rpm or accelerate quickly to rpm's above 6500.

Rabenbauer also has written about the timing gears. https://www.rabenbauer.com/restauration ... 2&section= . Run it through google translate if you don't understand German. The idea is that the engine case grows over time, but at least 100 000 km. Many hot-cold cycles doesn't help either. So you would need a larger set, not smaller, if your engine has run a lot of miles.

I happen to live relatively close to Jan Withagen and I will have my engine case measured. He uses a set of dummy shafts for this procedure. Using the bearings will not result in an accurate measurement because of the inherent slop in roller bearings. I am very curious what the result will be.

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sblaylock
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Re: R50S Restoration

Post by sblaylock »

James has had multiple successes matching the gear set with the case number. Barrington seems to have success going one set smaller than the case number and Mal needed a significant reduction in set size to get the correct lash. Based on this, it seems there is no clear "rule of thumb" on what set to install if you don't have measurements prior to the disassembly. I don't have the luxury of bringing multiple sets in so I think I'll go with a -3 for the -2 case and hope for the best.

The Rabenbauer article says "Growing" the engine case is the increase in the distance between the camshaft and the crankshaft. However, I, maybe incorrectly, gathered from Duane's article The result of all of these shoves is that the case gets wider. As the case gets wider, it must get shorter to accommodate getting wider. The height of the case “shrinks” down a bit. I can absolutely relate to this as I see what has happened to my body over 35+ years of eating. In my 20s I was 6' tall and weighed 175 pounds. After multiple cycles - trips to the fridge followed by a trip to the bathroom, at 60 I'm 5' 10" and 200 pounds. After, as Duane calculated, 400 Million cycles, I too have gotten wider and shorter.

All kidding aside, my thought (understanding) was as the case got shorter the crankshaft and camshaft would get closer together not further apart as the Rabenbauer article mentions. Thinking of Duane's article, you would need to go in a negative direction in the gearset due to the shrinkage in height as my understanding is a smaller gearset -2 to -3, +4 to +3, 0 to -1... actually meant the circumference of the gear was truly smaller. Basically a Camshaft or Crankshaft Timing gear of +3 has a physical circumference bigger than say a -4.

Is my understanding correct?

Thanks,
Scott.

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