Restoring a 1973 BMW R75/5 Motorcycle

January 13, 2007

Point of No Return

Filed under: 1973, airhead, BMW, motorcycle, R75/5, restoration — Penforhire @ 7:03 pm

Up until now I was confident that I could reassemble whatever I removed and probably be no worse off than I started. By the end of today I passed through the door marked “abandon hope all ye who enter.” But the day started off innocently enough.

I got all the keys that my dad left behind because I had not yet found the column lock/seat lock key (lucky they were unlocked) nor the ignition key, which at least is universal and easy to replace. Here’s the pile of keys I had to sort through.


Hmm, it seems my dad never met a key he didn’t like. I think I recognize keys to at least a half-dozen vehicles my dad sold before I graduated high school. And what’s up with the ten Master lock keys that don’t have a padlock to go with? Remember the movie “Ghost Busters?” Rick Moranis was not the only keymaster. So setting the tone for today’s work, out of the dozen candidate keys that were small enough and shaped about right, not one fit the bike. Sigh. New locks required on the bike, check. I’ll bet they don’t make ’em especially easy to remove without a key.

Okay, another friend at work, Bob, had a great suggestion about my frozen right-side header pipe. If I disassemble the cross-piece I should be able to separate the left side, apply a twisting force to the remainder, and break it loose from the head. The clamp nuts come off the cross-piece with no problem but once again I discover it is essentially welded to the left header with corrosion. I’m already considering replacing the three-piece header because of prior damage and its awful cosmetic finish. So I open up the left side clamp section of the cross-piece like a can of sardines and eventually I separate the left header. Yay!

Time to twist the right header out of the head. Um, no. Check that. I have lots of leverage but no twisting is happening. I bang on the cross-piece with a hammer until it bends. The header still laughs at me. I take yet another of my favorite tools and apply it liberally to the header, gripping it right where it comes out of the head.


I’m not having any luck today. The header starts to wrinkle and warp but zero motion in the head itself. Grrr. I give up on that for now. Maybe after the head is disassembled I can heat-shock it or something. Joe will know what to do.

I decided to do someting about another issue I tended to stare at for the past couple of weeks. The seat mounts to two pivot-hooks. Here’s a picture of a healthy pivot hook. Well, ignore the damaged Phillips-head bolts for the moment.


Since day one I could not get the three bolts to budge that hold the hook to the seat. That meant I couldn’t remove the seat because the pivots slide on studs that face each other. The rear fender got in the way of getting an impact wrench in there and Joe explained that rain gets through the seat and tends to rust those bolts. I have a 90-degree racheting screwdriver with a bit that was perfectly sized. But no matter how I applied the bit, and after old and new application of Liquid Wrench, it started camming out of the Phillips head. Grrr.

So I worked on other things and gave the seat dirty looks for a few weeks. My backup plan, similar to most of my plans, involved cutting the thing to pieces and replacing it. That’d show it who was boss. Once I had it on a bench I’d be able to apply my impact wrench and all would be right with the world. The first part went according to plan today. Another of favorite tools, a Dremel cut-off wheel, made short work of one pivot. Here’s the result.


Woo-hoo, right? One new pivot piece and I’m golden. Not so fast there, buck-o. I then discovered my impact wrench had no more effect on the bolts than my screwdriver did. It started to round the heads instead of breaking them loose. I’m not entirely sure where the seat goes from here. I mean, a screw extractor will not help if the body of the screw is still frozen. They are flush-mount so I can’t just cut a bigger slot in the heads. Feh! Maybe weld pry-pieces to each head? Joe will know what to do so I set the seat aside and look to see what other trouble I can get into.

I was thinking about taking off the front wheel but I’m starting to notice my center stand is wobbling dangerously as-is. The rusted-out foot-tang side is looking weak, flexing, and every time I’m next to bike on the left side I worry it’ll fall over on me. So I’m leaving both wheels in place at least until the engine is out to keep the bike from see-sawing too much. Also the engine is the heaviest part I can think of pulling off.

One repair manual talks about removing the engine and tranny as a unit. For who, King Kong? I take the other manual’s advice about removing bits and pieces to lighten it up first. Here’s exactly where I passed what I consider the point of no return. I’ve known about engine internals since I was a child. I’ve helped other, masterful, mechanics tear engines down. I can even give some advice (“maybe your framistat is not engaging the winkelator correctly”). But holding engine guts in your own hands and not following someone else’s instruction is an entirely different experience. I can continue now after the panic attack subsides.

Why should I figure all that carb splooge would stay in the carbs? Guess which side these rockers belong to?


C’mon, that’s not a disgusting enough picture of the situation. Try this one (I feel like a fighter pilot trying to make a ride-along puke).


This is what the rocker arm parts look like. One advantage to a two-cylinder two-valve engine is I only have four to mess with.


The wear doesn’t look too bad. I had to clean up just the one nasty assembly pictured above. The brass insert is very clever. I am not certain about the quality of my rocker-arm followers. There is slight pitting on some. How perfect do they need to be?

Here’s one of the four pushrods. The repair manual suggested writing the ID and even which end is which to re-assemble in the same orientation. Why is that important? The ends are just hard hemispheres, right?


Well, only a few minutes later I’m looking at valves and even pistons. Sure came apart fast. I’ll bet it doesn’t go together nearly as quickly. Here are the left side valves.


Why do they look like someone burned a casserole in there? I’d show you the right side valves but that head hasn’t separated from its cylinder yet. They should have. The head and the cylinder came off together. Imagine my surprise, since the left side played nice. The manual recommended a soft mallet or wide pry surface so I’ll be trying those later. Anyway, here’s what the right side piston top looks like.


Yep. More burnt casserole.

Here’s a wider view of the right side. The left looks the same right now.


I give myself 50-50 odds that I hurt myself on those cylinder studs, maybe even bend one, before I figure out how to remove them.

There’s a motorcycle swap meet in Long Beach tomorrow. It is a monthly sister-show to the car swap meet Alex likes (one of the guys restoring old cars). See I’ve never been there so I’m going to see if I can find anything useful in the morning.



  1. Here is a resource you will need if you are going to be a serious airhead wrencher! Ed korn sells good stuff at great prices! another great source is and their marketplace section for bikes, parts and other stuff BMW.

    Good luck!


    Comment by Al — January 20, 2007 @ 6:23 am

  2. I have been enjoying following your progress been a follow /5 wrencher.

    On the seat you may have already seen Duane Ausherman’s fix (

    Just a thought, I’m sure applying it to a /5 would be easier (and cheaper) than replacing the pan.



    Comment by Tim Park — April 12, 2007 @ 4:52 pm

  3. Howdy! I know this is somewhat off topic but I was wondering if you knew
    where I could locate a captcha plugin for my comment
    form? I’m using the same blog platform as yours and I’m having trouble finding one?
    Thanks a lot!

    Comment by Sherita — September 7, 2014 @ 11:25 pm

    • Sorry, no idea how to add a captcha. Try searching for it in the WordPress help files.

      Comment by Penforhire — September 8, 2014 @ 7:47 am

  4. If you still have the original shocks do you want to sell or give them away? Thanks, Rob,

    Comment by Robert Haag — April 3, 2016 @ 8:42 am

  5. Hello Robert. All my spare parts went with the bike, as I did not expect to ever restore another R75.

    Comment by Penforhire — May 8, 2016 @ 7:25 am

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