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1977 BMW R100RS Restore Project

Cause of Transmission Problem

Folks,

Here is a picture that tells the story of my transmission problem.

<a title="My Circlip (Left), Correct New One (Right)" href="https://www.flickr.com/photos/brook-reams/23502636068/in/album-72157685064960932/"><img src="https://farm5.staticflickr.com/4437/23502636068_9e4af99162_z.jpg" alt="My Circlip (Left), Correct New One (Right)" width="480" height="640" /></a>
My Circlip (Left), Correct New One (Right)

The new circlip I purchased from my dealer is not the correct size. I was not attentive enough and also failed to compare it to the old one to sanity check that the new one was correct. So, the lesson for all of us is "check your parts" because human beings work at BMW and they are capable of making unintentional mistakes, just like we do. :)

There are not many parts counter folks who really know airhead parts well enough to catch a mistake like that, particularly when a dealer has to order the parts from BMW which is the typical case for airhead parts. In that case the parts arrive in a sealed bag specifically for you. Most parts folks will call you to pick up the parts and are not going to verify what they received from BMW is what you ordered for two reasons; they likely don't know airhead parts well enough to make that determination, and they don't have the time.

As another example of unintentional parts mistakes, I ordered the upper and lower rear brake shoes and I received two brake shoes each in a bag with the correct part numbers. But the top shoe bag had a lower shoe in it and I didn't notice that until it was time to install them. No great harm, but its another example of why checking what you receive when you receive it at the parts counter is a really good idea.

At times like this, I recite Confucius' "By Three Methods Do We Gain Wisdom":

"By three methods we may learn wisdom:
First, by reflection, which is noblest;
Second, by imitation, which is easiest;
and third by experience, which is the bitterest."


I usually seem to end up learning by the third option :)

Onward ...

Best.
Brook Reams
 
1977 BMW R100RS 4,400 Mile Update

Folks,

After I finished rebuilding this bike, now called "Gonzo", I've ridden it about 4,400 miles in two months. I documented the issues, changes and updates I made starting with the first engine start and you can find that write-up here:

I still have some things to do, but it is running well at this point.

My thanks to those on on this list and others I participate in who helped answer my questions and provided advice during this year long project. Without that airhead support, I would not have been able to complete and ride this bike to the rally.

In particular, special thanks go to Tom Cutter for reasons that are very clear when you read my blog about my ride to the 40th R100RS anniversary rally.

Best.
Brook Reams.
 
40 vs 38mm

b-

I have both. While the bikes do run and perform a bit differently,........the difference just doesn't seem that great to me. I really wouldn't make it a factor in acquiring or riding one of these old beauties.

Good luck w- the '77.

Wm.
 
b-

I have both. While the bikes do run and perform a bit differently,........the difference just doesn't seem that great to me. I really wouldn't make it a factor in acquiring or riding one of these old beauties.

Good luck w- the '77.

Wm.

William,

I agree. I suspect if I rode multiple 40 mm header pipes 77 RS bikes I'd find sufficient differences in their performance that mine would fit in that range somewhere.

Best.
Brook Reams.
 
Quite the read on Brook's documentation of the rebuild in the Owners News. Here's links to Parts 1 and 2...can't wait for 3! Nice job, Brook!

Just hit "Close" to go to the first page.

http://content.digitalpub.blue-soho...ber2017/html/index.html?page=64&origin=reader

https://content.digitalpub.blue-soh...ber2017/html/index.html?page=44&origin=reader

Kurt,

Thank you. It was hard to step away for all the detailed documentation I had produced on this project and then try to condense my experience down into these three articles. Bill Wiegand, the editor of the MOA magazine, was very forgiving about article length delivered vs. length requested :).

Happy Holidays to you and yours.

Best.
Brook Reams.
 
Yeah, it hit me that this was by far the longest article I'd seen in a long time...other than a travel piece! :hide And then you had to do it in three articles! That should give people in the future something to ponder and drool over. :thumb
 
Apologies for a "ME TOO!" post but I just have to chime in with Kurt here.

First off Brook it was a real pleasure to meet you at the RS Anniversary gathering. We get the MOA rag a week or two later up in Canada and I just finished your latest article this morning. It is indeed awesome as is your website http://brook.reams.me/

Although I did not fully restore my Bro in Law's 92 RS or my 82 RS for the epic ride out east I did go through a lot of the same stuff you had to do. I also want to thank you for answering my questions during the steering head bearing replacements on both those bikes along with other questions. Your support and examples on your website were extremely helpful. I did take photos but nowhere near as many as you have! My bike was also repainted and by the time I got everything back, well, your memory plays tricks on you doesn't it?
Lucky me, your photos filled in some blanks.

Thanks for all you do for us home wrenchers Brook! You are a great contributor to the airhead community and a heck of a nice guy who truly does "endeavour to persevere". :thumb
 
Apologies for a "ME TOO!" post but I just have to chime in with Kurt here.

First off Brook it was a real pleasure to meet you at the RS Anniversary gathering. We get the MOA rag a week or two later up in Canada and I just finished your latest article this morning. It is indeed awesome as is your website http://brook.reams.me/

Although I did not fully restore my Bro in Law's 92 RS or my 82 RS for the epic ride out east I did go through a lot of the same stuff you had to do. I also want to thank you for answering my questions during the steering head bearing replacements on both those bikes along with other questions. Your support and examples on your website were extremely helpful. I did take photos but nowhere near as many as you have! My bike was also repainted and by the time I got everything back, well, your memory plays tricks on you doesn't it?
Lucky me, your photos filled in some blanks.

Thanks for all you do for us home wrenchers Brook! You are a great contributor to the airhead community and a heck of a nice guy who truly does "endeavour to persevere". :thumb

Hi There,

I was envious of your nice ride from BC and back . That sounded like a nice trip. My return was quite uneventful compared to getting there :)

BTW, I'm also very envious of your "1881 R100RS" bike that you show in your profile, as that one is definitely a collectors item and must have been designed by Han's grandfather. Now we know where he got his inspiration. :)

Best.
Brook.
 
Oooops. Fixed that. I'm still not sure if my RS is 81 or 82. It's an August 81 build but was registered as an 82 when it came to me. I know the cutoff is normally November but this one might have been a lollygagger. One of the very few I've seen with a factory kick starter. The ride home was a bit of a race against winter. I rode from Toronto Ontario to Vancouver BC in 5 riding days. That's 4,641kms or 2,883 miles. The last two days were over 1100 kms per day. I beat the snow but not the rain or the cold.

I'd do it again tomorrow though... I might even go back in '19 when Todd plans to do the G/S rally. That will take more planning since it's an open bike unlike the RS with that great all weather fairing. Hoping Todd can move the date up to August or something a bit earlier in the season. Sure was a great time there. Having Hans Muth's signature on my bike now was a real treat. Such an interesting guy and what a legacy he has put together. Amazing.

I might be the only guy in Canada with one of these !

20171019_144256.jpg
 
Enjoyed seeing your articles in the ON's R100RS. I had several friends who bought the '77 R100RS as new bikes. They had great insight into what a great bike that it was/is. My late buddy Art Grisanti was one of those. Rode with him many times when he was riding that bike. After he passed another buddy got the bike. I got the opportunity to help freshen up the bike. One of my best memories is doing the heads on the bike. I also set the heads up in a milling machine and opened the exhaust ports from 38mm to 40mm. Yep, it's one great bike. Good job on your bike. Barry
 
Enjoyed seeing your articles in the ON's R100RS. I had several friends who bought the '77 R100RS as new bikes. They had great insight into what a great bike that it was/is. My late buddy Art Grisanti was one of those. Rode with him many times when he was riding that bike. After he passed another buddy got the bike. I got the opportunity to help freshen up the bike. One of my best memories is doing the heads on the bike. I also set the heads up in a milling machine and opened the exhaust ports from 38mm to 40mm. Yep, it's one great bike. Good job on your bike. Barry

Barry,

Thank you. It was a fun bike to ride to the east coast and back.

Best.
Brook.
 
Brook - I really enjoyed your articles and it was great to see how you started your story here on the forum. :thumb

Ian
 
Brook - I really enjoyed your articles and it was great to see how you started your story here on the forum. :thumb

Ian

Hi Ian,

Thank you. I rode Gonzo Sunday to a restaurant for our Colorado ABC annual planning meeting. A fellow crossed the street as I was parking wanting to know more about my "really unique looking bike."

At many gas stops on the ride to PA and back, someone would come up to ask me about the bike and comment about how it looked, "... not like the ones you see every where these days".

Hans' statement still speaks to people.

Best.
Brook.
 
Brook -

I know I'm resurrecting something pretty old, but I just ran across this discussion you were having on the Airheads Airlist. I'm so far behind in reading those digests, I couldn't respond at the time. I posted this also on the Vintage website.

At one point, you were questioning the masses how to orient the fork tubes with respect to the holes in the tubes. At first you thought just putting them pointing back towards the bike would be the way to go. Tom Cutter offered up a way to find the high spots in the tubes rolling around a flat surface and using that to your advantage when it came time for assembly. That would reduce stiction.

I was wondering what did you finally do?

My reason for bringing this up is from a structural stress standpoint. I wished I could have commented at the time, but I wasn't actively reading the digest emails at the time. My input would have been to put the holes either pointing at each other or directly opposite meaning pointing out the sides. The reason is that the tubes are undergoing flexing fore-aft. As the tires hit imperfections, as you get on the brakes, the tendency is to bend the tubes fore and aft. Think of the bike on the centerstand with the front wheel off the ground...then grab the sides of the axle with each hand and push the axle parallel to the ground. This is the type of bending going on.

For a tube bending this way, the maximum bending stresses are going to be either along the front surface or the trailing surface. At the mid point of the tube, or in this case, the side of the tube, the bending stress is zero. Typically, the front side will go into tension while the exact opposite side will essentially be compression of the same value, just negative from the front side.

The hole in the tube creates a stress concentration...typically circular holes cause a factor of 3 rise in stress at the very edge of the hole. If there should be an imperfection there, the local stresses become three times higher and a crack can form and eventually grow.

For this reason, you do not want the holes to be on the front or the back. They should be either pointing at each other or pointing away from each other to the side.

I would loved to have had that input to the discussion but missed my opportunity.

Thanks...
 
Brook -

I know I'm resurrecting something pretty old, but I just ran across this discussion you were having on the Airheads Airlist. I'm so far behind in reading those digests, I couldn't respond at the time. I posted this also on the Vintage website.

At one point, you were questioning the masses how to orient the fork tubes with respect to the holes in the tubes. At first you thought just putting them pointing back towards the bike would be the way to go. Tom Cutter offered up a way to find the high spots in the tubes rolling around a flat surface and using that to your advantage when it came time for assembly. That would reduce stiction.

I was wondering what did you finally do?

My reason for bringing this up is from a structural stress standpoint. I wished I could have commented at the time, but I wasn't actively reading the digest emails at the time. My input would have been to put the holes either pointing at each other or directly opposite meaning pointing out the sides. The reason is that the tubes are undergoing flexing fore-aft. As the tires hit imperfections, as you get on the brakes, the tendency is to bend the tubes fore and aft. Think of the bike on the centerstand with the front wheel off the ground...then grab the sides of the axle with each hand and push the axle parallel to the ground. This is the type of bending going on.

For a tube bending this way, the maximum bending stresses are going to be either along the front surface or the trailing surface. At the mid point of the tube, or in this case, the side of the tube, the bending stress is zero. Typically, the front side will go into tension while the exact opposite side will essentially be compression of the same value, just negative from the front side.

The hole in the tube creates a stress concentration...typically circular holes cause a factor of 3 rise in stress at the very edge of the hole. If there should be an imperfection there, the local stresses become three times higher and a crack can form and eventually grow.

For this reason, you do not want the holes to be on the front or the back. They should be either pointing at each other or pointing away from each other to the side.

I would loved to have had that input to the discussion but missed my opportunity.

Thanks...

Hi Kurt,

I agree with the stress analysis (ex Mechanical Engineer). But, the more important aspect to manage is fork stiction. So, the slight bends in the tubes need to be aligned to get minimum stiction. If the factory installed the tubes as you suggest, all is good as the slight bend will correlate with the orientation for minimum stress concentration at the holes.

I've not done a stress analysis of the tubes, but they are thick wall tubes. I strongly suspect the BMW engineers specified the wall thickness to be sufficient to prevent stress fractures at the edges of the holes under the highest stress expected. IIRC, holes minimize stresses compared to slots, so the form factor is the most conservative.

[As anecdotal input, I hit the rear end of car on my R75/6 at about 3-4 mph. I rode the bike with bent forks for another 30,000 miles before I addressed the problem with new fork tubes when I rebuilt the bike. There were no fractures around the holes. They saw pretty high bending stress and but it didn't cause any fracturing at the holes. That said, I again don't recall how the holes were oriented.]

I honestly don't remember where the holes ended up, and after checking my pictures, I don't have any showing that detail (no matter how many I take, there's always something I wish I had photographed :)

Thanks for posting your informed input. The more the better. :)
 
Brook -

In all likelihood, you're probably right that the BMW engineers had a handle on the situation. Doubt we would ever see any analysis this detailed...that said, I can't say that I've heard/seen much about what any motorcycle designer does in terms of stress analysis, finite element analysis, testing, etc.

Location of the holes can minimize any issues regarding crack formation and BMW would have the luxury of putting it in the best possible location on the assembly line. Once the bike has lived many miles, the choice might be different.

As for crack formation and growth, it is dependent on a variety of factors: quality of the hole; stress levels; cycles at various stress levels. If the edges of the hole are smoothed and even better yet, application of a compressive stress at the edge of the hole can stop or delay the formation of a crack. Each material has an inherent material property of incremental crack growth versus stress...the lower the stress, the less chance a crack will grow; the higher the stress, the faster the crack will grow. Of course, the stress levels and the number of stress cycles over time will determine how fast a crack can grow.

Another unusual phenomenon that can happen is crack growth retardation. Each material has a different response. In the cases of an overload, the area that is just in front of the crack goes into compression and makes a crack difficult to propagate through. Once the crack grows through the plastic zone, crack growth rate returns to normal.

Hard to say but you could have induced a retardation situation when you had the frackass with R75/6. But it's only a concern if there was a metal imperfection, and the stresses in the material were high enough and occurred often enough to promote crack growth.

When I had the tubes out in my /7, I didn't go through nearly the same level of scrutiny that you did. All I remember doing was just remounting with the hole facing each other. I didn't have an stiction that I remember, so I guess everything must have worked out!
 
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