Restoring a 1973 BMW R75/5 Motorcycle

April 15, 2007

Back in the saddle

Filed under: 1973, airhead, BMW motorcycle, motorcycle restoration, R75/5 — Penforhire @ 3:04 pm

So, uh, two fortnights eh? Not as if any of you complainers sent me decent filler material, that I would gladly have posted. How about sending me some of your most traumatic rebuild moments? I’ll make you famous.

I don’t suppose you want to see my work on curing cancer?


Yep, my Playstation has been hard at work doing the “Folding @ Home” thing (see See that dot in near Disneyland? That’s me. This is donated spare computing power applied to parallel processing tasks in research. I read an estimate somewhere that it costs seventy cents or so in electricity per day. Doesn’t sound energy efficient but it must be cost effective for researchers. This sort of donation has been available on PC’s for some time. My brother-in-law told me he used to do a similar donation for SETI, seeking signals from little green men. He’s still batting 0-for-a-trillion processor cycles.

Maybe you want to see some of the home improvements that were so consuming?


Yep, that’s my new kitchen with travertine floor, oak cabinets, underlighting, graphite appliances, granite countertops and … yeah, I’m as excited about a kitchen as most guys are. You can see some of the new laminate floor past the kitchen. We laid 1200 Sq Ft of that crap. So you still want more blog?

My painter sent me pictures of the completed parts! Turns out someone else’s job had a delay so mine slotted right in. The pictures get my heart all a-flutter. Here’s one of them.


Doesn’t that look sweet? Consider these motorcycle ransom photos or mechanic’s porn. Sure got me to pay up in a hurry (only $800 including a fender crack repair, some block sanding on the tank, clear coat over the pinstripes, and shipping)! Can’t wait to see them in the flesh. If they still look as mouth watering in person I’ll give my painter a few more blog kudos and you should be beating a path to his door.

Oh yes, I also got some work done with my own two hands. I figured the wheel hubs needed disassembly before beadblasting and I wanted to rebuild the axle assemblies anyway. Here’s my front hub.


Here are the parts that are easily pulled off the no-brake side of the hub.


And after removing from the shaft.


The paper gasket showing on the backside of the pentagonal cover is annoying. It fell freely from one hub but has to scraped off the other. There is still a shaft seal shown in the cover, to be pried out.

Now the manual has a special treat for us. We have to heat the hub to press out the bearing races. Why was BMW so enamored of press fits? Here’s the outer race still in the hub.


Hmm, what to do? Can’t use that new oven in the kitchen. She’ll see me and everyone has to sleep sometime, right? One 500 watt halogen work light to the rescue. That delivered just enough heat after about five minutes to allow me to tap out the works (also had to find the right diameter tube to tap with). Here are the remaining guts that get pushed out of the hub. The rear bearing got badly abused during the process, hence the twisted part and loose bearings, but I plan to replace all bearing anyway. I just need ot locate more generic sources for each bearing size. BMW shops want far too mush $$ for these, about double what NAPA charges if I can ID the sizes.


Here’s the rear hub.


As near as I can tell, these two hubs are identical except for the shaft drive engagement in the rear hub, seen here.


I also know the bearing preload in these wheels is a big deal, not too loose, not too tight. Get it right, grease them periodically, and they last forever. Get it wrong and you’ll need to replace them frequently. Sadly, the stack of parts that make up the axle section don’t make a lot of sense to me. So despite the photos you see above I am more than likely going to reassemble something not quite right. We’ll see.

But wait, there’s more!

I got to polishing some more components. No, I am not done with even one of the wheel hubs yet. But here are the two hand control levels.


Yucky! Pitted and dull.

And here is what some sandpaper and polishing compound can do in, oh, a half hour. The shiny curves on this lever reminded me of the bad guy in Terminator 2. I think I’m getting faster.


But wait, there’s more! I got to tearing down the front forks. The cast lower legs need to be beadblasted so they need to be isolated. I also have a fork rebuild kit and new progressive springs. You’ll see those in action during the reassembly. Here’s the complete fork.


Here are the guts.


The bottom rubber cap pops off. The large circlip is extracted (an actual circlip wrench is handy for this). The small nut unscrews and its washer falls out. Next is a 30 mm wrench-size cap at the bottom with its metal gasket. Yeah, I don’t have a 30 mm wrench. My metric crescent did the trick on one fork but started to round the head on the other. So off to the auto parts store for a 30 mm socket, no make that two stores before I found it. And I still needed a cheater bar on top of my 18″ long 1/2″ drive handle to break it free! The next circular pieces, sandwiching a metal piece, require some odd pin drive that seems to be missing from my BMW tool kit. Fortunately they were not torqued very tight and the circlip wrench spun them out of there. Lastly, the damper rod comes out as shown.

One of my manuals suggests the damper rod rarely requires any maintenance. That would be good but I’m not convinced. One of my damper rods has some obvious damage so I might be diving into it. The spring tension in the rod is enormous, or else I don’t know where it collapses, because I couldn’t even make it wiggle.

There is one special little part on the right side, not present on the left. This is a little hook that gets captured under the fork gaiter and I believe its purpose is to help route the brake cable.


This is exactly the sort of thing that, months from now, will never get reassembled correctly. Oh yeah, my fork gaitors are tattered but I got 13 rib replica gaitors just waiting for reassembly.

There. That should satisfy your blog jonesing. I know if satisfied mine.


1 Comment »

  1. I gotta say you’ve got me inspired to work on my ’73 /5. The little clip in the last picture is used to hold the brake line close to the gator. The small loop fits inside of the bottom gator hose clamp and is held in place once you tighten the clamp. The brake line slips into the large loop.

    Comment by Blane — July 3, 2007 @ 3:00 pm

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