Restoring a 1973 BMW R75/5 Motorcycle

January 14, 2007

Losing battles

Filed under: 1973, airhead, BMW, motorcycle, R75/5, restoration — Penforhire @ 2:36 pm

I am fond of saying some days you get the bear and some days the bear gets you. Today the bear is one happy animal. Oh, it started off just fine. Went to the swap meet like I said I was going to. Here’s a lame photo of one aisle.


The show was quite worth seeing, free parking and $9 entry fee. If you own a Harley it is a must-see. Hog stuff accounted for about 85% of the booths. There were a couple of Honda specialists and an English bike dude here and there. I saw a couple of vintage sidecars for sale. And maybe 10% of the offerings were for bicycles. Sadly, no BMW specialists. But the mix of pro vendors and private sellers was excellent. I got a chuckle out their re-entry hand stamp.


Seems appropriate for a Harley-dominated show, doesn’t it?

Anyway, I did not leave the show without buying something. I found these for $45 (including tax).


A metric universal-jointed impact socket set that fits my impact driver. More hammer-operated stuff. These could join the favorite tool bin. And yes, they are six-point sockets.

On to the bear baiting. I decided to work some more on the bike today. I should have checked my biorhythm, fortune cookie, or something first. I’m sure it would have said, “today is a most excellent day to float in a pool of water.”

The first thing I tried was to remove the long cylinder studs that I previously noted were likely to harm me. I stacked two nuts on one, even the repair manuals say that is one way, and… nothing turns. No wait, the pair of nuts turn. No matter how tightly I stack them. Even if I change to another stud. Sigh. Maybe I’ll try later with a triple stack of nuts?

My philosophy in attacking this bike has been a little like boxing. Stick and move. If something stops me I change my focus and get back to the problem later. Float like a butterfly, sting like a bee. Lately I’m thinking the bike is on to my strategy and is trying some low blows and kidney shots to slow me down.

I ignore the studs, not really but I pretend to, and move on to the pistons themselves. Good news, they don’t seem to wobble at all on the wrist pins so I’m thinking they could be re-used. Bad news is they’ll probably be reused by someone else, unless the burnt casserole in the cylinders cleans up without requiring an overbore. Right now I’m doubting that but we’ll see after the heads and cylinders get sent to someone who knows what they’re doing. So I read about how to remove the pistons and it seems the wrist pins are held in place with a coil on each side. These are sort of like circlips but without the holes to allow a wrench to grip them. The manual talks about prying them out with a small screwdriver. How fortunate, I have a small screwdriver.

But the coil just spins around when I try to grab the end to lift it out of its channel. Okay, I get a second screwdriver to press on the other end and keep it from spinning. Hmm, the fit is so exact that I’m not getting under the coil. So no prying action is happening. Back to the manual. Yep, just a one liner about prying ’em out. I try some more and even try other sized implements (dental picks and other jeweller’s screwdrivers). Nothing doing. I just can’t get under it. Okay, that’s one more thing to ask Joe about.

I try to save up my ask-a-mechanic questions because otherwise I’d have to buy Joe one of those annoying Nextel walkie-talkie phones. If I don’t restrain myself I’d probably call him hourly. Of course there is a delicate balance between me not annoying Joe with too many questions and me breaking things because I didn’t ask.

Stick and move, right? So the alternator coil and rotor catch my attention as a target of opportunity. Here’s a photo of the front of the engine with the cover off.


At the bottom of the photo are the points and their fly-out weight system. No doubt, a future Joe question. Above the alternator, just out of the picture, is the condenser and above that is a diode board. The alternator looks ripe for the picking. The two brushes that ride on the metal sliprings at the very front are held in with simple coil springs. The electrical connectors pop off. Three allen-head bolts unscrew. After a little yanking and grunting, bingo!, the stator (coil that does not move) pulls off.

The rotor which spins inside the stator is held on with just the center bolt visible in the picture. That bolt is about 3″ long, with only a short threaded length at its end and then a long “shoulder” all the way to its hex-head. It unscrews from some back threads and then re-engages some rotor forward threads (why two sets of threads?) before winding all the way out. At this point my two repair manuals differ.

The Clymers manual says to grab your special BMW rotor pulling tool P/N 12 3 600 and wind it in to push the rotor off the crankshaft wedge it is now stuck to. Well I don’t have a 12 3 600 in my garage. I look through Joe’s special tools that he dropped off (like the clutch centering tool I know I’ll need later) but we have no joy. Maybe it is disguised as something else but I don’t see it. The Haynes manual, on the other hand, assumes the sort of tool set that I happen to own. They describe shoving a 1.5 to 2 inch length of whatever back into the rotor center (where the bolt was) and using the original bolt, now screwed only in to the first set of threads, to push the rotor off the wedge. Sounds clever.

Takes me at least 15 minutes to find something appropriate that seems to fit and that I don’t care about reusing, a household hanger-thingie, and I hack-saw it to length. Toss it in the hole, follow up with the bolt, crank on it, and I feel the resistance. I keep cranking and all seems okay, but the rotor is not moving. I must be collapsing the metal piece I threw in the hole. Uh-oh. The bolt gets past the front threads and spins freely. Okay, don’t panic, just unwind it and find something else to throw in the hole. Uh-oh. The bolt will not engage the forward threads. I don’t give up for a few minutes but you know the word “fruitless?” Well, I taste something sour but it ‘aint fruit. That’s the taste of defeat.

I’m what? 0 for 3 today? My frustration level is high enough. and parts are so expensive, that I know I must stop for a while. Like an episode of Cops, “back away from the bike slowly and put the tool down!” So I decided to run back to my computer with my tail between my legs and post today’s non-progress. I could call Joe but I need to wait until the “need a bigger hammer” impulse passes. Maybe I can tempt him into a personal visit next weekend…


1 Comment »

  1. you need to use a hardened thingus to shove down the hole. The reason there are two sets of threads is so you can the outer set to “pull” the rotor out. Check here for a very good explaination:

    Sounds like you might be screwed though if you put soft metal in there already….

    Comment by defwheezer — February 17, 2007 @ 6:02 pm

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