Restoring a 1973 BMW R75/5 Motorcycle

January 27, 2007

Weird tool blues

Filed under: 1973, airhead, BMW motorcycle, motorcycle restoration, R75/5 — Penforhire @ 9:00 pm

You know the UPS shipping slogan, “what can Brown do for you?” Well, the big brown truck of happiness delivered this week. Here is my POR-15 tank refinishing kit.


I plan to get some muriatic (a.k.a. hydrochloric) acid to do a better strip inside the tank after POR’s Marine Clean degreaser. POR’s acid must contain phosphoric acid since that passivates the freshly stripped surface but doesn’t attack metal-and-rust as strongly as muriatic. Safety note — always wear goggles or splash-safety glasses when handling strong acids or bases. They are especially hazardous to eyes. Never add water to acid, add acid to water. A little water added to strong acid can heat the mix so fast it may splash or melt the container. If I’m doing the job in an environmentally sound fashion I should also get some baking soda to neutralize all acids before throwing them down the drain. If you don’t have a pH meter just mix until it stops visibly reacting. I might get passive-aggressive though since I have to be environmentally friendly 24/7 at work. Maybe the neighbor’s cats would like some, especially the one that poops in my plants and walks on my freshly washed car…

Okay, when I first started running into special BMW tool requirements I thought it was kind of cute. Like BMW saying, “Look, we’re special and any mechanic who wants to work on our bikes has to have the Right Stuff. These tools are emblems of you having the Right Stuff.” But today I just find needing some of these tools tedious and emblematic of a design flaw.

You know I’ve been giving my stuck rotor the evil eye everytime I look at the bike, right (see a prior woe-is-me post on this)? Joe had a reasonable idea. If he also fails to extract the free-spinning bolt we’ll try to hook up a slide-hammer and that might free the rotor. Brad loaned me a gear puller but the jaws were too short, the rotor is too rounded (nowhere to hook the jaws properly), and, even if I could fit it and snag it, the center bolt would press on the stuck rotor’s center bolt. Enough about my rotor. Just know that I still give it a dirty look whenever I can.

I got the starter off today just to show it who was boss. Here it is on my bench flipped upside down, note the submissive posture.


I worked on the swing arm too. It is held to the transmission by the rotating shaft, with four bolts hidden under the rubber boot. There is not a lot of room to get at these. You can only fit a 10 mm box-end wrench in there, no sockets, and did I mention they are weird 12-point heads? Gee, you really do need both 12 point and 6-point sets. “See honey, I told you.”


They are also a stretched-bolt design so we have to throw these away and use new bolts any time we disassemble this. Now I know the picture above fills you with confidence of a job well done, bolt on bench, but it did not go quite as simply as that. It seems I screwed up the disassembly order. I should have left the rear wheel, rear brake, and/or clutch cable in place until I removed these four bolts. Why? Because whenever I applied force to one of these $@!#@ bolts, the crank shaft turned well before the bolt broke loose! You are supposed to use the rear brake to hold against the turning force or else put the bike into 3rd or 4th gear (according to the book).

Stop. Take a break. Call Joe. Okay, he says try harder to use the in-gear resistance. Whack the wrench with a hammer to loosen ’em.

Well, it didn’t seem to matter much what gear I got it into because the crank kept on cranking. I got a bright idea that Joe will surely cringe at when he reads this. I trapped the skirt of a piston against the outside of the engine casting. You DO recall that I haven’t figured out how to remove the pistons’ wristpin gudgeon clips, right? So while I was cranking I noticed the skirts would sometimes get caught. Voila! It worked. Hey, I might not re-use these pistons, okay?

Sadly, the swing arm is still on the bike right now. Why? Well this a “BMW special tool” rant post, so here goes. There is a 27 mm lock-nut on each side on the bike. These lock an allen-head threaded shaft in place and let the swing arm, um, swing. Here is a picture of said lock-nut and shaft (sorry flash blew out the exposure and I’m too lazy to re-take it).


Hmm, I don’t have 27 mm socket, despite rummaging through used tools at pawn shops to fill out my collection. Yeah, I know, that’s not a special tool you say. Well, even if I had a 27 mm socket it would not fit on the nut. Say what? Yeah, BMW in their infinite wisdom decided to make the surrounding swing arm housing too close to the nut to fit a normal-size socket. Joe mentioned he has a ground-down socket head, which is something the repair manual shows, but I figure I need to have my own tools to work on this beast, right? I remembered Joe noticing I had the original under-seat tool kit from BMW. This has tire irons and a neat assortment of tools, one of the best sold-with-the-bike tool kits in the business. Sure enough, there was an odd tool in this kit intended to perform this task.


This is a skeletal 27 mm wrench, welded in place. It doesn’t look very strong but it does fit just right on these nuts. Well, Murphy struck again because the lips of this tool are a bit mashed from some prior misuse (not me, honest) and it just slipped off the nut when hammered. Sigh. So I trudged back to the store to get a 27 mm socket (1/2″ drive) of my own to grind. Do-de-do-de-do, I drive around the corner to Kragen. “Here they are… 24 mm, 25 mm, 26 mm… that’s odd. No 27 mm.” Frickin’ fine. Off to Pepboys who at least had a 27 mm deep socket at a price that guarantees Made in China.

The sun went down and enthusiasm fled from my garage before I got to grind it yet. I figure to use a half inch-to-3/8″ drive adapter to chuck it into my drill press. That should give me an even grind when I thin it. Hmm, only if the side pressure down at the working end doesn’t pull it off the drive adapter while spinning at 1,000 RPM and knock me out. I’ll have to give this a little more thought (press on the other side with a cloth?) before I use power tools. If you have any wonderful alternate ideas please comment… soon.

My special-tool rant is not over yet. Here is the grease fitting on the end of the rear brake lever pedal pivot. It looks harmless enough.


Some sort of hexagonal fitting with a ball-bearing-like seal in the center. The grease pushes through the hollow pivot, out through a hole, and into the gap between this pivot and the frame. There is even a nifty-looking grove cut on the cylindrical face of the pivot that I assume retains grease and helps spread it around. Why am I bitching about this grease fitting? Well, I own a “standard” grease gun. It probably looks a lot like the grease guns you own. Let me assure you, the end of a standard grease gun does not mate up in any way with this weird hexagonal fitting. While I was out looking for that 27 mm socket I also took this fitting with me to find an adapter. At Kragen the counter-monkey just pointed to where his available fittings were and could offer no words of advice. Nothing even remotely hex-like. At Pep Boys the counter-monkey had evolved the power of speech. He gave it a good look-see, pondered a bit, scratched himself, and then pronounced, “I ‘aint never seen a fitting like that. Must be a special one.” Thanks for the assistance, I’m feeling special.

The good news is I managed to make a grease gun needle tip work on this, while also wasting big wad of grease. I figure that’s not a good long term solution because this needle is very hypodermic-like and I am sure to jab myself hard with it in the future. If this is not a dealer special fitting please let me know where else to look.

My day continued. I am still going through my dad’s stuff and I probably will be for some more weeks to come. I came across three keys on a BMW keychain and that set my heart to racing. None were the ignition semi-key but one or more looked a likely suspect for the column/seat locks. Where did I put that subframe with the seat lock? Ahhhh. It fits and it turns. Oh happy days! Put in in the column lock. No joy. Wait, what about this other key. It was bent exactly like you’d expect a column lock key to bend if you leave it in the lock and accidentally straighten the column. You could call that key an interference fit. It went in okay and seems to turn the lock cylinder but I can’t get it to push in and lock. Oh so bittersweet! I tried wiggling the column at different angles but I’m still S.O.L.. Damn that was exciting though! Maybe Joe will point out what I’m missing. The third key is most likely to the Krauser hard bags that were always on the bike but now nowhere to be found.

One of the other things I find in my dad’s things are old photos. Here’s one of the three of us. Me, dad, and the bike. This must be about seventeen years ago.


Look! I had hair back then and I was only chubby. You see me messing with my dad here and you’d probably tell me to leave him alone. Here’s the thing though, he always fought dirty.


1 Comment »

  1. I seem to be commenting on your posts in reverse order, oh well.
    Seems to be a weird karmic commonality going on here. You see, I too used to have hair, LOL. Did you inherit the bike from your Dad? I bought mine at a local cycle wreckers back in the winter of 80/81. My dad used to own a ’39 Indian Big Chief with princess sidecar, away back before I was even a twinkle in his eye. Re crashed it into a bridge apporach on a country road on the way home from a dance one Saturday night. Claimed a log truck cut him off (sure dad!). He always claimed motorcycles were “death machines”. I owned mine for about a year before he came outside one Sunday after I finished washing it and demanded the keys and a brief rundown on the controls. Declining a helmet, he fired it up and after just a wee bit of a wobbly start, he toddled off down the street. About five minutes later when I was torn between missing my bike and having to explain how dad died on my motorcycle, he reappeared, pulled into the driveway and parked it. Handing me the keys he said “It’s OK…for a death machine.”
    you hit the nail on the head with the POR15 kit. I used their stripper as per the directions yet the old “Red Barons revenge” just would not give it up. It took a hopt application of a 20% dilution of muriatic (also known as hydrochloric0 acid and a blast from my pressure washer to finally see it come out in great sheets. The acid really etched the steel nice. The POR coating I also did to an extreme, leaving it in the tank and rolling it around for over an hour. Funny how that stuff works. I got almost all of it back in the drain pan. I guess I really didn’t need the extra pint can. Oh well, it’ll be enough for the next three or four tanks.
    My bike is sort of special. The P.O., bless his (or her?) heart, did a good many performance and ease of maintenance mods to the bike, including replacing that “special” grease fitting with a standard zerk fitting. It does not interfere at all with my foot when riding, though I can feel it against my boot. No big deal. I have a grease gun adaptor tip that fits into the standard end. It has a conical tip which would work Ok for that special fitting. It is commonly used to grease the double cardan style u-joints on the front driveshaft of 4X4’s. The “proper” grease gun for this fitting is one of those small push type things most often found in stores where chainsaws and related accessories are sold. Kept in a heavy duty ziplock baggie, they fit well in your on-the-road tool kit. I suspect the factory offering had some sort of rubberized coating on the nozzle. regardless, I’d just replace it with a standard metric thread zerk. they also sell mini grease guns with the real world normal end.
    Oh yeah, your alternator rotor thing. Wasn’t aware that the bolt was just loosely spinning. Maybe some pressure outwards while turning it? let us know how that adventure turns out. This has been discussed on the 5united list ad infinitum so research the old posts. I’m sure many will be more than willing to hash it out agian.

    Comment by Brent Schapansky — February 8, 2007 @ 8:24 pm

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