Restoring a 1973 BMW R75/5 Motorcycle

March 10, 2007

So bright I gotta wear shades

Filed under: 1973, airhead, BMW motorcycle, motorcycle restoration, R75/5 — Penforhire @ 9:55 pm

Well you guys were no help. More than a couple of you suggested taking my parts to a professional for polishing. Yeah, I’m sure that works but I’m in debt to too many professionals as it is. And this is something I really should be able to do. And it will fill the long and lonely hours between now and when the bike is ready for reassembly, if ever. So back to the drawing board (emery board?).

Gary said if the part I was polishing did not get warm then I wasn’t doing much metal polishing. I had to agree. He suggested a bench grinder with a polishing wheel rather than my sorry electric drill. I had an “aha!” moment. I don’t need a bench grinder. I have a Shop Smith widget. Sears has a $12 polishing kit (several sizes of wheel, one arbor, and four small sticks of compound). We have a plan.


At first I could not figure out why the compounds refused to transfer to the wheel. I might as well have been holding a small piece of steel up to the spinning 4″ diameter cloth. Hmm, what to do? I took a piece to the microwave oven to heat it. Disco! A minute or so of nuking and it was softer. Once I got wheel transfer started the compound would heat itself enough. Later I figured my initial mistake was wheel speed. I was running about 1500 RPM. If you run over 3000 RPM the bare wheel will heat the compound enough on its own.

The wheel instructions say not to exceed 5000 RPM. I assume at that point the wheel explodes and whoever finds me will call 911. Anyway, I got excellent results at around 3500 RPM. I started with the black emery compound, coarsest in the kit, and it definitely cuts better than red rubbing compound. The work piece got hot. Woo-hoo! Of course that grit was still not enough to cut the typical pitting of my aluminum parts.

With some trepidation I went back to sandpaper. I first used the proverbial “inconspicuous spot” and discovered that 600 grit is an almost perfect first stage for the black emery compound.

Here’s a handlebar clamp after a thorough 600 grit scrub.


And here’s after polishing with black emery compound.


There’s still a metal polishing stage after this. I’m undecided between Mother’s and Flitz. I think Flitz gives a better finish by hand (and is more expensive) and Mothers (Power Ball formula) works better with power tools.

Anyway, now when you see these clamps across the parking lot and go “ooh” you’ll need to wear shades when you stare at them up close. Mind you, this still isn’t cake to do. I mean, while I could probably train a monkey to do the work it still remains a metric ton of work. So those of you who have your own old sagging-jugs machines at home, when you see my aluminum bits and say, “Dude. You did such a magnificent job on those parts. Would you consider…” No! Hell no! Not for all the tea in China.

Here’s a couple of turn signals, before and after.


The aluminum alloys must vary because while those handlebar clamps shined up neat-and-quick the turn signals take more work, engaging some brown “tripoly” compound before the metal polish. And the gas tank cap is resistant to polishing. It is cleaning up nicely but no mirror shine yet. I may end up wishing I went to a professional before I’m done but I need to save money for the shrink I’ll need at that point.

I got so enthused that I pulled out that rear rim, the one I already polished, and took some 600 grit to it. Now I know I can do better. Well I’m here to tell you that 600 grit is not the answer to all things. I switched to 220 grit and that seems coarse enough to do the job of cutting down the remaining pitting. I’m, oh, maybe a quarter done with the 220 grit treatment of that one rim and I need to knock off for the night. I’m bushed. It is not a one-pass job with 220 grit job either. Some pits are deep. I already know that 600 grit is too big a gap for the next polishing step. It takes too much work to obliterate the 220 grit scratches. Sigh. I need to go buy some 400-odd grit paper.

Hey! Big news on the paint front. Joe got me hooked up with his painter (thanks Joe!) and he’s doing the deed. I stuffed my tank and fenders into two UPS boxes today. The painter is Jim Hansen in Santee CA. He’s a one-man show, does nothing but bikes, and doing it since 1976. He doesn’t seem to advertise, just word-of-mouth. I saw his work on Joe’s old BMW and it was great. He even has a record of using my paint color on another BMW. He uses PPG and House of Kolor paints. Including prep, pinstripes, and a clear-coat OVER the pinstripes his price is around $800. Downside? His average turn time is ninety days. I don’t know if he’s busy or slow but it doesn’t matter does it? Even if my old plastic fender cracks down the road he can paint a new repro fender cheaply enough.

Some of the other painters out there must be inhaling their own fumes if they think their work is worth three times this man’s price. He doesn’t have a web site but if you want to get in touch with him e-mail me and I’ll give you his e-mail address. I just need to sucker, uh, convince ten of you guys to use his services and I’ll get that free paint job…

And now I feel obligated to warn you that my blog may slow down some. Oh I’ll write some filler but I get the feeling I’ll be doing a lot of work with not much to show for a month or more. “Ooh look. Shiny!” I haven’t sent parts out for powder coating yet ( thinking of a classic Star Trek episode “Help…me…Joe”). Even if I had the frame back today I can’t reassemble much without the wheels and engine case (wheels can’t get laced until hubs get beadblasted and engine needs it too) and I finish polishing the rims. The heads, cylinders, and pistons are trivial by comparison since they can be assembled at the very end if necessary. That’s one advantage to having the cylinders sticking out as they do.


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