Restoring a 1973 BMW R75/5 Motorcycle

June 10, 2007

Monkey with a stick

Filed under: 1973, airhead, BMW motorcycle, motorcycle restoration, R75/5 — Penforhire @ 3:40 pm

Here’s the steering head.

The bearing tensioning mechanism is the slotted nut on top. Earlier /5’s used some extra-funky clamping system plus a nut.

Here’s the rear end mounted. Look at those shiny new bolt heads on the right of it! A stainless hardware kit was one of the optional things I bought but I think that was worth every penny since it came in bags marked with their locations (something I SHOULD have done with the original hardware).

I was worried about the wheel drive ring wear (see pic in a past post) but several sources suggest it works fine even over 50% wear and is only at risk when worn to a point! The mating wheel hub splines must be much harder because those are hardly worn at all.

Here’s the rear wheel hub guts.

I later beadblasted the rust on the axle. That took it off but the surface is still textured. When I first disassembled the wheels I remember remarking how there were too many pieces and it didn’t make any sense. Well, I studied Duane Ausherman’s article on wheel bearings (see the link to his site in my blogroll at the upper right of this page) and I began to understand. It helps to have the parts in hand to play with. It still seems like a funky way to get the job done.

I bought Ed Korn’s wheel bearing tool, a length of pipe, and I also did not “get” that until I monkeyed with the hub assembly. Here it is, on the left side, used to help measure the assembly’s tension when mounted or “preload.” This is supposed to be done with oiled-but-not-greased bearings.

The center of the hub, where my thumb is, is supposed to get snug between the bearings as the assembly is tightened. This is a simulation of what happens when the axle is tightened on the bike. The required tension on the stack before the center gets snug is adjustable and also subject to debate. Ed Korn says the “right” assembly has 4 lbs required to move the center hub sideways when the stack has 30-35 Ft-Lbs tightness. Duane says BMW is wrong when they claim it should just get snug with at 25 Ft-Lb on the assembly (I’m quoting here from memory so read his paper). He also does not trust this off-the-bike measurement. The alternative is a “shake the wheel” test, ideally assisted by a helper, to determine at what tension the wheel won’t wobble-to-the-touch on the bike. He says that is a very sensitive test. So what do you do if tension doesn’t match the recommendation?

BMW makes a series of spacers, what most people call the “wedding band.” It is roughly finger-ring shaped and sized so that’s a good moniker. A quick check at my local dealers confirms they are not a locally stocked item. Duane makes and sells a series of punched thin spacers to accomplish the same thing (added to an existing wedding band) and his system sounds more cost-effective. And lastly, you can lap two different components to loosen or tighten the assembly.

This is me lapping my rear wedding band (front and rear wheel assemblies are nearly identical) on some fine sandpaper on a sheet of glass. My rear assembly was obviously too loose, regardless of whose technique I used.

Duane warns that this is a sensitive operation and he’s not kidding. First time I must have lapped too much, maybe a whole mil or two, and the assembly got too tight (at too low a clamping force)! I had to lap the outer hub spacer to loosen it back up. Anyway, if you go this way use very fine (e.g. 600 grit) sandpaper. It is important to keep the surfaces parallel so be very systematic about it (e.g. lap three circles, rotate your grip, lap three more circles, …) and use a super-flat base (glass or a granite flat).

Oh yeah, why is this important? Read Duane’s paper for all the details but the bottom line is if the bearing race spins loosely in the hub you’re in trouble. A “spun” hub is usually replaced by a new hub. And since I just got my hubs re-laced and trued at outrageous cost I don’t want my hubs to die any time soon.

Similar to how I extracted the wheel assemblies, this is me preheating the hub with a hot work-light.

I had to add heat with a torch or it would take hours to get to temperature. You want water to sizzle on the hub, meaning 100 to 120 degrees C, before trying to load the bearing stack. I wasn’t taking any chances, because I know I’m a monkey, so I froze the hub stack and axle at the same time. The rear assembly slid right in with just a little tapping to make sure the bearings races were seated.

I didn’t get so lucky with the front hub. The first time I tried to insert the cold stack I left the outer grease seal on the stack and that was a mistake. Well, it was mistake #2. Mistake #1 was swapping the seals from left to right. They’re not the same size. Even if they were the same size it might still have gotten hung up on the far lip that holds the far bearing race in place. As it was, no way was that seal getting through there. It was off-center and hung up on that lip. I didn’t see that at the time so I pounded on the stack blindly. I could tell it was not seating correctly and eventually (after my bicep cramped from pounding with a hammer) I gave up. Good news bad news. The good news was I managed to extract everything before the hub cooled and I would be truly screwed. The bad news is I managed to mangle one bearing and cut the OTHER grease seal. Hey more good news, I had a spare bearing since I mis-managed my parts ordering. The grease seal can be replaced later with minimal hassle-factor.

Okay, so I found that problem. Felt a bit foolish for swapping ends and more foolish for leaving any chance of a hang-up. That far grease seal can be loaded from the far side after everything else is loaded. D’oh! So, back to the heat and cold. Hmm, now the first bearing race will not even enter the hub more than a little bit? Son of a …! Pound it out from the reverse side. Cool it all down, feel around, hmm, I don’t feel any distortion at the entry. Heat and cool again. Make sure I’m good-and-sizzling-hot. Check the first bearing race for damage (nope, feels fine). Go for the third try and… damn, still won’t go past the hub opening! At this point I’m stumped. I feel like a monkey with a stick. I need professional help.

Okay, given a night to sleep on it I’m not giving up yet. I found a ridge I must have formed in the hub when I knocked out the stuck assembly the first time. It is so even I must have thought it belongs there. It does not. The tricky thing will be to sand down this ridge without expanding the bearing race seat significantly. Otherwise the don’t-do-this-at-home solution will be to glue the outer race in place. Told you not to listen to me! We’ll see how it goes maybe next weekend.

Hey check this out. Bead blasting is not as fast as it sounds. There is a fair bit of time in getting these parts cleaned with my table-top unit. However it is really nice to be able to clean up parts as I go, as opposed to bagging and tagging everything for an outside service. Here are some valve covers, before and after bead blasting.

Hmm, more good news bad news. They sure cleaned up nicely but the dark finish was hiding a drop my dad must have had before he put on that engine protection bar. It is a flat spot. I don’t see any cracking so I’ll give it a go on the bike. At least valve covers are easy to change later if I have to.

Well, having one wheel finished means I can play with my new balancer from Marc Parnes (see

This rig is good. It is the bare essentials, note the jack stands I’m using to support it. The custom inner sleeves were a perfect fit to the bearings. The outer bearing friction is so light it pendulums when the spin slows down enough. That’s the slow part of the job, waiting for the wheel of fortune to stop spinning. The rear wheel required two 1/4 Oz stick-on weights on the rim, not bad. At that point I needed something like 1 gram to exactly balance, in the noise, so to speak. The idea is to get it close enough so every time you spin it stops at a random location, no repeating heavy spot at the bottom.

I changed one spring on the rear drum brakes. They are a pain to mount, so much spring tension. Then I slathered the hub drive splines with Honda Moly 60 grease (well regarded for this application). Then I mounted the rear wheel to the rear drive and put the axle in place.

Well, more monkey-with-a-stick action now. The rear brake lever seems to operate in reverse! I must have loaded the brake shoes flipped upside-down. You can’t mis-load them left-to-right because there is a cylinder on one side and matching semi-circles on the shoes. The “spreader” on the other side must be working backwards and I know it is not the lever itself because I marked the assembly with a punch when I took it apart, to keep perfect alignment. Grrr. No, it is not the end of the world but the rear brake shoes are a grunting-hard couple of pieces to mount. Give me a banana.

I’m on a streak. I called Bob’s BMW to see if I could schedule my head and cylinder restoration. Those of you who read their catalog, you know where it says you should send stuff like this to them in Winter because they get busy in the Spring and the work will be slow? Well slow is not the correct word. They’re not even taking this work again until October! Grrr. They recommended Craig Vechorik at Bench Mark Works (see and I have an e-mail out to him now. Brown BMW in Pomona does not do this work at all and Irv Seaver BMW in Orange doesn’t inspire me. They said it’d be time and materials. Hmm, if Bob’s can quote a flat rate then why can’t someone else who knows what they’re doing? BMW Joe told me they send this work out to someone. Angel City Cycles is another local who didn’t inspire me when I communicated with them (though he was a well-regarded mechanic at Marty’s BMW). Anyway, if you have a suggestion other than Bench Mark Works please post a comment, if not for me (I’ll go with Mr. Vechorik if he’ll do the work)then maybe some other monkey could use the tip.

Here is the state of the union, ignoring my need to remove that wheel (again) and fix the brakes —

Okay, Sunday is time for more Homo Two-Wheelis. “Put the wrench down and back away slowly.” This was the Dog Days of Summer ride and I think it was hosted by the SC-MA governing board. BMW Joe and I started at Huntington Beach Honda.

That is a VW powered trike on the left, a husband and wife team of regulars. We used to wonder about the driver’s seat belt until we noticed the gear shift about two inches in front of the driver’s pants zipper. That could seriously hurt if you’re not wearing your belt!

One of the high points was before the ride even started, seeing Karyn pull up in the lot on her GL1800 blue monster Goldwing. I think it was back in last October, before I started this blog, during the annual Cemetary Ride when BMW Joe and I were first responders at her accident. She got thrown off at near-zero speed and broke her hip in the hills outside Santa Paula. It’s a long story but that section of Balcom Canyon Road, uphilll from S. Mountain Road, is so steep (and severely cambered) that another rider who stopped to see if we needed help fell over. Broken hip, not such a big deal you say? Well, she’s in her mid-60’s and lots of folks that age don’t always heal well. We stayed with her until an ambulance came and we loaded her Wing onto a flatbed to send to Hollywood Honda for minor repairs. I think today was the first time we saw her at a ride since and she was walking fine.

Today’s ride started down the coast, through Newport and Laguna Beach. I call that an ‘envy tour’ because, similar to Palos Verdes or Malibu, that part of the ride just rubs your nose in real estate most people on Earth can’t afford. Joe and I gawk and chatter about the natives. Then we went inland, just touching Ortega Highway and passing by Cooks Corner in Santiago Canyon.

One of my favorite stretches of road is Live Oak Canyon Road, leading up to Cook’s Corner from the coast. The curves are mild and nothing special but the Oak trees form a living dazzling canopy over the road. That’s my idea of road zen. The road is similar to Woodside Road near San Francisco. Bliss.

When we’re on Santiago Canyon Road I remembered the last time we were there I was soaking wet. I get this double-vision thing going for 10 miles. I’m riding on a perfect sunny day overlaid with a vision of pouring rain. Live Oaks cause flashbacks?

Gary didn’t come with us. He would have been disappointed by the number of city streets we travelled but the best was saved for last. We rode up Mt Baldy Road, over Glendora Ridge Road, and down Glendora Mountain Road, ending at Camp Williams Cafe in the mountains north of Azusa. These are some of the finest twisty roads around.

And today’s ride pin —

One more thing, the Pasadena Motorcycle Club is celebrating its 100th anniversary on the 23rd. Stop for a moment and consider. What other clubs, related to internal combustion engines, do you know that are 100 years old? This is pretty special, even if none of the founders are around (we kid with some of their older members that they ARE founding members). They have to be one of the oldest clubs still in existence. A schedule of their dinner celebration can be found on the SC-MA site.

I think I need to draw up a personal club patch. How about a monkey swinging a stick? And my theme song can be that famous monkey-moment in “2001: A Space Odyssey,” Richard Strauss’s “Also sprach Zarathustra.”


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