Restoring a 1973 BMW R75/5 Motorcycle

February 10, 2007

Victory!

Filed under: 1973, airhead, BMW motorcycle, motorcycle restoration, R75/5 — Penforhire @ 5:47 pm

Remember ABC’s Wide World of Sports TV show? Where the opening credits included some poor schmoo wiping out on a downhill ski run with the overvoice, “…the thrill of victory and the agony of defeat.” Well late in the week I was dancing a victory celebration. I finally got that rotor off the front of my crank. For weeks, every time I walked into the garage it was sitting on the front of the engine just laughing at me. Well look who’s laughing now.

1817-rotor-on-table.jpg

Some of you posted on 5 United and here explaining the correct technique. Yes, I understand and will be smarter next time, but you missed where I buggered up the threads and the central bolt was (is still) stuck in the rotor. No way to implement the correct technique after muffing that up. Brad loaned me a slide hammer. Despite getting enough impulse to move the whole engine across the table, the rotor shrugged. I read suggestions about tapping it with a hammer, given that the crank fit is a taper. I tapped as hard as I dared, not wanting to damage any crank bearings. I think I heard a whispering “nyaa, nyaa, nyaa, can’t touch this” from the rotor. I must give credit to my new favorite tool, a propane torch. I had to heat the rotor three times, to increasing temperatures, before a hammer tap simultaneous with a pulling force popped it off.

Oh yes, the special smoke came out of the rotor and this is surely a dead fish on my bench. But I had already planned on a charging improvement. The base system on this bike outputs something like 180 Watts and is known to barely maintain charge for city commute duties. I’m a certified wuss, having a Gerbings electric liner and gloves. I also want to run a more powerful H4 bulb and possibly auxilliary lights. It is my opinion that I can’t have too much light at night, as long as I do not blind others. Anyway, there are several options for bumping up the charging capacity and durability of the system.

Motorrad Elektrik sells several stages of improvement. Rewinding the stator and replacing the diode board nets about 280 Watts. The diode board lives under the front engine cover and that is a bad place for semiconductors. The excess heat reduces life. Later years of cover are vented but not the stock 1973 cover. They also sell an “Omega” kit that adds a revised regulator and larger stator & rotor. You have to change the front engine cover to the later year to fit these. That bad boy claims 400 Watts of power! Now we’re talking. Well, I probably don’t need that much power unless I’m packing a beer cooler with me or I need to defribrillate a heart attack.

Although those were some proven solutions I decided to go with the new kid on the block. I like some design aspects of the Euro Motoelectrics EnDuraLast system. They use a magnetic rotor, rather than wound wire, with no slip rings and the diode board function is integrated into the new regulator, placed in cool air. It doesn’t require the instrument bulb to be okay to function (yeah, the OEM system goes down if the instrument bulb goes dead). Output is claimed to be similar to the Omega system, some harness modifications are required (within my skills I believe) and it is a bit cheaper. It is not completely unproven but doesn’t have the track record of the other option. I guess I’ll be part of the expanding database. I’ll detail my install when I get there (not any time soon!).

So I was dancing around like Dorothy singing “ding dong the witch is dead” when I finally saw the front of my crank.

1818-crank-end.jpg

Maybe you’ve never had a mechanical nemesis so you can’t understand my glee? Oh propane torch, my new best buddy…

I got the front wheel off so here are my front brake shoes.

1819-front-brake-shoes.jpg

Nothing special to report. They look, um, used.

Here’s my steering damper knob.

1822-steering-damper-knob.jpg

Do you think they could have made it any longer? Seems odd that they couldn’t relocate the mechanism to above the steering head.

Here’s the cover to one fork along with the pin wrench in the BMW tool kit that turns it. Yay! I found a useful BMW tool in the toolkit.

1823-fork-cover-pin-wrench.jpg

Here is the right side fork spring cap, just under that cover, starting to come out. By luck of the draw I happened to have a proper 36 mm axle socket to fit this.

1824-fork-spring-cap.jpg

Here I tasted a little “agony of defeat” today. This one took liberal application of my new best buddy, the propane torch, to free up. I was beating on it when Joe called and he suggested heat, honest, he did! Well, the other spring cap saw what happened to its brother and hunkered down. Because nothing under the sun got the left side started. I iced the cap, beat it with a hammer, and even tried heating the cap itself later. No go. More tiny laughter from motorcycle parts. I don’t like it. I gave it my best Arnold Schwarzenegger accent and said “I’ll be back.”

And hey, I wasn’t just being paranoid about how my center stand felt. Here’s the bottom.

1826-bottom-of-center-stand.jpg

Niiiice! I feel lucky the whole bike didn’t drop on my foot.

Bryan loaned me his air impact gun to try on the 24 mm drive shaft nut. Bzzzzt! Thanks for playing. Not enough foot-pounds I guess. Sure felt like it was hammering and twisting with vigor. One more part that laughs at me. Stupid nut. Don’t laugh too hard or there will be a nut-splitter in your future!

Oh, and the nice folks over at 5 United have a consensus that my alloy rims should clean up and work fine unless I spot actual cracks. Me, I was worried about age fatigue but they report no such issue.

That’s all for now. I’m scheduled for more Homo Two-Wheelis action with Joe tomorrow, unless it is raining significantly in the morning. If you don’t see another post tomorrow I might be, uh, recovering from whatever happens…

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4 Comments »

  1. Hi,
    BMW Joe here!
    Just to set the record straight.
    I said, “maybe, apply a little heat”.
    I had no idea that Eric had the alias, El Flamo the Pyromaniac!
    I didn’t know that he even owned
    a torch!
    I was refering to A HEAT GUN!!!
    A little heat!!!
    Heaven forbid he ever gets his hands on an oxy-acetylene torch.
    I am sure I will be back again.

    Bmw Joe

    Comment by BMW Joe — February 12, 2007 @ 2:28 pm

  2. Nice article, good looking weblog, added it to my favorites.

    Comment by Inonryhog — November 24, 2009 @ 3:07 am

  3. We sell the Gerbings Range and are always getting questions about how the electrical systems can cope with wired clothing

    Comment by Mike Stephens — October 25, 2011 @ 9:20 am

    • Hello Mike. The original system on these /5’s do not have enough charging capacity if you do a lot of city riding (like me). Their output is next-to-nothing at low RPM. There are numerous upgrades on the market and any one of them will do the trick. The Enduralast system I went with is sort of the nuclear option, much more than necessary, but I wanted capacity for my Gerbings jacket, G3 gloves, AutoCom, GMRS radio and assorted add-ons.

      Comment by Penforhire — October 26, 2011 @ 7:19 am


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