Restoring a 1973 BMW R75/5 Motorcycle

March 3, 2007

In the tank

Filed under: 1973, airhead, BMW motorcycle, motorcycle restoration, R75/5 — Penforhire @ 6:42 pm

Enough dilly-dallying, it is time to finish off the fuel tank. My wife works with a fellow who paints motorcycles on the side. He specializes in customizing V-twins and goes by the moniker of Mad Mike. His partner is Rottweiler. I just have to meet these guys. Anyway, I needed to finish my end of the tank so Mike could get a look at the job. Compared to some of their work this job is plain vanilla but it has to be done right or why do it at all. Joe is still working on hooking me up with his painter. Someone’s going to paint something and soon.

I didn’t take pictures of me pouring chemicals, the POR-15 motorcycle kit, into the tank and sloshing it around because that was just too boring. I used some rubber plugs to seal the petcock drains. I wore nitrile gloves and goggles for safety. I also kept my hose running to dilute the chemicals into my sewer.

Here’s my first shot at drying the tank after the last acid etch.


The instructions give dire warnings about getting the inside of the tank dry before putting in the final sealant. This is a space heater blowing into the tank but I wasn’t getting any air flow out the petcock drains so…


The gorgon gave me quite the evil eye when I asked where she kept this but it sure blows hot air!

The coating itself reminds me of silver paint. It had to be thoroughly stirred and has a paint-like consistency. Seems to take forever to dry while rotating the tank to prevent puddling. Instructions say to cure at least four days before adding gas, not a problem for me. I poured out the excess after a few spins and that was fun. Just when I thought nothing was coming out, while aiming the petcock drain at the original jar, I got a big delayed pour. Of course I was no longer holding it over the jar! The coating must go on fairly thin because I’m sure I got most of the original jar back out again. This was mostly a preventive measure anyway.

Then I thought I’d take a whack at polishing the rear rim some more.


I stumbled across a Mother’s Mini Power Ball when I was at Pep Boys last. I don’t watch many infomercials so I had never heard of these but it looked like just the thing for the lazy polisher. Truth is, it did a fine job of polishing the alloy rim. The rim looks 100% better than it did after that Simple Green scrub. But metal restoration seems to be mirage-like. Even though the appearance is vastly improved the finish line seems to move further away. Here’s a close-up (that’s one spoke opening at the left).


I still have dark pitting, worse than this shows, and hazy areas. If I just stare at the rim I feel bad but if I put it next to the untouched front rim I feel a little ray of sunshine.

Gee, I’m feeling so good and I’ve got my nitrile gloves out. Why not try that uber-nasty etching cleaner on some of the many cast alloy parts with that white corrosion? I checked the 5 United board again and some guys swear by this stuff while others say it just darkened the metal. I figure I had nothing to lose, except my eyeballs, since I’ll likely be beadblasting if this doesn’t work. This is a section of the front engine cover after etching for a few minutes.


Well, I’ve got the alloy that just darkens. It didn’t seem to touch my corrosion and I even tried wire brushing while the part was wet with acid. I read about one guy who had good luck with a wire brush and mineral spirits. Having tried some wire brush action I’d say that guy was nuts. Maybe a steel brush but that’ll scratch the cast finish. I tried a paint stripping wheel, sort of a seriously stiff Scotchbrite material, but that managed to scratch the cast metal as well.

Seems like beadblasting is in my future. For the price of the service I COULD consider trying some cheap blasting equipment at home. I’m sure my wife would appreciate the fine powder that’ll get everywhere since I have no booth or even an exhaust hood. It would be driveway work for me. Hmm, maybe I should leave this to professionals? Marriage sure is rough on restoration work!


1 Comment »

  1. nice one …

    Comment by Mike — April 12, 2007 @ 6:36 pm

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