Restoring a 1973 BMW R75/5 Motorcycle

July 22, 2007

Shoemakers get elves but BMW’s get gremlins?

Filed under: /5, 1973, airhead, BMW motorcycle, motorcycle, motorcycle restoration, R75/5, restoration — Penforhire @ 3:29 pm

I’m obsessing a little over one of Grimm’s fairy tales, “The Shoemaker and the Elves.” You know the one, where the shoemaker leaves half-completed shoes in his workshop and some little guys sneak in and finish ‘em in the middle of the night. Well my heart is heavy with the sure and certain knowledge that if I do not do something myself it doesn’t get done. Oh there are some elves out there working for me but they’re not free and, in fact, want my arm & leg as payment. So what do BMW motorcycle owners get instead of elves? Gremlins of course. More than we need.

Ah gremlins. I don’t recall if I mentioned my Shopsmith lost its speed control after all that polishing work I did some weeks back. I was adjusting speed, probably too roughly, something popped, and there was no more speed-adjusting mojo (it has a continuously variable cone-shaped pulley drive). I took a peek inside the headstock but everything looked okay and its manuals don’t give me enough repair detail. Sigh. In an amazing quirk of fate I happen to live about four miles from one of only five authorized Shopsmith service centers in the USA. So I pulled off the headstock (sucker weighs about 60 lbs), stuffed it in my car, and stopped by.

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Those highly paid elves did their thing. They replaced the speed control since some parts had rusted together. We also replaced a few bearings while they were in there and now all is right again with my favorite power tool. This one used to belong to Dan’s dad so it had decades of service before it was mine. Some repairs are expected. It is not as good as, and costs as much as, decent dedicated stations but it takes up very little floor space and is easily moved from storage to use. I use it as a table saw, drill press, band saw, drum sander, lathe, planer, and more. Joe looks askance at it, and knows someone who lost fingers to one, but his garage is overflowing with Delta tools.

I decided to replace my seat with a Sargent “Classic” saddle. Sargent is well known for seats, tanksbags, and such. In theory the replacement sold by Sargent will also mount the Reynolds back rest and they even sell a replacement pad for that. I received the seat this week and I figured I’d show you some comparison shots with my original seat. I do not know for a fact that the original’s cover is correct (I think it was replaced at least once). This seat costs around $300, half of the OEM replacement. Bob’s BMW had some other source of replica saddles at similar price but they had a quality or fit issue so they’re waiting on a new replica design.

2150-sargent-side-view.jpg

2151-sargent-top-view.jpg

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In terms of the look, Sargent matches it pretty well. The side white piping is perfect. It is missing my seat’s front piping and the pleats are not full-length. It is around half the weight of the original, plastic pan versus metal (and vinyl versus leather)? I haven’t figured out if the rear “R75″ ID plate will mount on the seat yet (heck, I haven’t tried to remove it from the original yet!). The pictures seem to show a small difference in overall length but they are actually equal-length. I’ll come back to the seat later in this post.

Hey look!

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Now the tranny is attached to the engine and loaded into the frame. Nothing is ever easy and I seem to have misplaced one of the original tranny bolts. I found another one that fit (odd-ball 1.5 mm thread pitch) but it needed its threads cleaned up. I happened to have the right die and soon all was good again. It is just, well you look at this engine and tranny in the frame and shrug at the length of time it should take. Double that (triple if Gary is estimating) and that’s how long it takes me. I still need to connect the driveshaft to the tranny output. Gosh I look forward so much to working in the teeny tiny gap BMW designed there, with a short rubber boot in the way!

I got to working on the hand controls. Have you ever wondered what the inside of the front brake light switch looks like?

2155-front-brake-light-switch.jpg

The arrow points to a crimped housing edge that holds the guts inside. I had to tear into this because my ohm-meter was telling me this was an unhappy switch, too many ohms when closed and too variable. I was reading anywhere from ten ohms to unstable-open. If I ruined this switch looking into it I’d have to replace it anyway. That crimped edge is the only difficulty in taking it apart and putting it together again. The post at bottom left pokes out to the brake lever’s face. With the lever untouched, it depresses this switch and opens the circuit (the actual “switch” is the part on the lower right). Pull on the brake lever and the post is released, closing the circuit and (hopefully) turning on the brake light.

Here’s the actual switch part.

2156-heart-of-the-switch.jpg

I’m holding it by the two copper (might be brass) terminal blocks that the harness attaches to with set screws. You are looking at the hidden “business end” of it. The metal post presses the plastic button in the center and moves the spring-loaded shorting-disk away from the two conducting arms, left and right in photo. Here’s a shot of me opening the switch.

2157-open-switch.jpg

There is not much to go wrong here other than broken springs or contact-surface corrosion. My springs were fine but the copper surfaces must have been corroded. I didn’t see much discoloration but the closed switch resistance was restored to low values by just sanding the disk and the underside of the capture arms. It was a little tricky to get in those small areas. I rolled a tiny cone of sandpaper, wedge it under the arms, and pull it out. Repeat a bunch of times and we’re golden again. If I was smarter I would have remembered the spray bottle of specialty “contact cleaner” I have on a shelf but I forgot I had it until I reassembled the darn thing.

I also cleaned up that metal post since it was dragging in the housing. I’m sure there is a proper crimping tool for the housing but the jaws of an ordinary pliers seemed to work okay, as long as you don’t mind some cosmetic marks on the edge of the crimp.

Here’s a photo of the right hand control area.

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The arrow is pointing to the throttle housing. I’m not sure yet but I think I’ve got the hand control from a 1974 or later bike. The repair manual says 1970-1973 are supposed to have a single throttle cable that goes to a splitter on the side of engine (cables to each carb). I don’t remember such a splitter in teardown and this control has openings and retainers for two throttle cables, as supposed to be used in 1974 or later. I’m short-term screwed either way. I didn’t buy a second replacement throttle cable and even the one I have may be the wrong length (specified for the USA high bar throttle of a 1973 /5). Anyone know if the older single-cable system had a housing for a twin cable? Seems unlikely so I’m probably just short the correct throttle cables (individual to each carb). I’m curious if this was a fix made by an owner or if this is just a late 1973 production change that the manuals pegged as 1974?

Here’s the front end now, starting to look hairy with unrouted cables.

2159-hand-controls-raining-cables.jpg

Anyone have a complete /5 you wouldn’t mind leaving in my garage for me to copy the cable routings from? I’ll only need it for a month or two! I have no idea how to properly rout the cables and I’m sure to be unbolting various things to re-rout when I figure out why something is supposed to go somewhere else. Time to study all the pictures I can find, eh?

By the way, if you have the handlebar electrical control cables off the bike and are unsure about which is right or left, you can tell two ways. The right side control has those two bare wires for the brake switch (you can see them hanging free in the photo above). Also, the switches themselves are mechanically different. The right side must be the turn signals since it flips into two positions. The left side must be high-beam/low-beam headlight control since it only momentary-toggles in one direction (flash the brights). Both sides press in to activate another switch. I believe they are starter on right, horn on left. Sound obvious but BMW controls are not always obvious. I HATE their new design with turn signal paddles on each side instead of one integrated switch (rode with it for 8K miles on my R1200C and never fully adjusted to it)!

I know, hate is strong word. But Hans the Arschloch designer is either still with them today or the next generation is goofing up the finished designs as much or more. In that R1200C they also fitted the battery so that you had to lift or remove the gas tank to get to it. No big deal you say? Sure, if they chose a maintenance-free battery. But Hans struck again and put one in there that requires regular visual checks!

Speaking of other bikes, Brad is selling his Ducati. Edit (bike details) — It is a 1999 SuperSport 750 with carbon cannisters, Power Commander, and raised clip-ons. It only has 3200 miles. His back surgery prevents him from riding so that’s “why the low mileage?” If this is something you’re interested in, contact me and I’ll hook you up with him. I drool over it, like most Ducs. But I wanted a chiropractor after the one time I sat on it and Julie would kill me in my sleep if a third motorcycle took up residence in the garage. I was “this” close to buying Ducati’s ST4s instead of my FJR . Today I might take the ST3 and additional bar risers. How can you not like rattling dry clutches and desmodromic valves?

I wasn’t finished with switch issues. Seems I misplaced one of the screws that holds those control switches on the housing backs that, themselves, screw to the handcontrols.

2160-missing-bar-switch-screw.jpg

These screws are odd little M4x0.7 size. This forced a drive over to Canning’s Hardware because few of the “big box” or auto parts stores locally carry enough weird metric screws. NAPA might but they’re closed on Sunday. No rest for the wicked here. I found something close enough.

We’re not done yet. When I told Gary I was taking Friday off to spend quality time with Julie he said he still expected real progress. You guys are harsh! I went back to working on the seat. Here’s the emblem from the old seat.

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It is held on with a couple of pan-head screws. As shown here.

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Unfortunately the new Sargent seat does NOT have matching threaded holes.

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So it is time to mark and drill. Very nervous stuff, putting holes in a brand new $300 saddle!

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While I was out at Canning’s Hardware I got a couple of longer pan-head screws with mating lockwashers and nuts to mount the seat emblem without a threaded hole. Turned out okay.

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Mounting the seat on the bike was a whole ‘nother wrestling match. The Sargent hinges fit the seat perfectly but the arms are too close together by about 3/8″. One or the other hinge would not reach the frame studs. Grrr. I tried the new front BMW OEM seat hinge I bought to replace the one I destroyed getting the original seat off the bike. That gave me the correct hinge spacing but I had a different problem (not to mention the powder coating preventing that hinge from fitting on the stud!).

2168-seat-hinge-misalignment.jpg

Note the third threaded seat insert, with no screw in it. It is not positioned correctly for the BMW hinge. It fit the Sargent hinge fine. The hole centers are not identical. At this point I’m making due with just those two screws in the front hinge because the whole assembly works now, with a Sargent hinge on the rear. I don’t see why Sargent had to mess with the OEM spacing. Their own hinges are noticeably more flimsy than the OEM but it is hard to complain about that since they come with the seat at no additional charge. I don’t care enough to harass them about the hinge-to-hinge spacing not fitting my studs (maybe mine are messed up?) but you are now forewarned.

The reason I think I’m okay with just two screws in the front hinge is the seat is supposed to actually rest on the frame, not the hinges. There are rubber bumpers on the bottom of the seat and, phew, they seem to rest properly. See the arrow in this picture taken from below.

2169-seat-bumper-sargent-hinge.jpg

I reached up and felt all the bumpers and, as near as I can tell, they’re firmly on the rear subframe. A minor miracle! You can also see the stamped-metal design of the Sargent hinge.

Here’s what the finished deal looks like on the bike. Now where did I leave that seat lock key?

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The latch works fine (Sargent has an adjustable-length post) and so did the lock. I actually sat on the bike today for the first time since January! I released the strap pulling the centerstand to the front wheel so I could center the handlebars and feel a complete riding position. Seems okay. Woo-hoo, I sat there and made putt-putt noises! If I ever want to mount the Reynolds back rest I’ll need to do more drilling since it does NOT have any threaded inserts in position for it.

Hey look, my first oil leak!

2170-first-oil-leak.jpg

I didn’t tighten the tranny oil drain plug and that seems to be it so I’m not worried … yet.

Motor Works called. I should have all parts back next week. They used the first overbore so I’m good for a future rebuild. Pistons were more expensive than they estimated (I think they said $149). Actual was $179 each with rings. So they gave me their cost on those instead of adding a usual handling fee. That’s about all I could expect from a vendor. Obviously we’ll have to reserve judgement until after we see these parts and the engine actually fires up. The whole deal of fully rebuilt cylinders, heads, and pistons (with damaged exhaust thread & stuck header) exceeds $1100. I still don’t have a total yet but I’m thinking this is about 20% of the entire rebuild expense. Yow! Kids, don’t forget to loosen your exhaust nuts regularly and slather anti-seize on there (and don’t let your headers rust into your heads).

I’ll leave you with a very obscure-sounding bit of trivia. Name the Formula One driver who in their first F1 race started in both first and last positions.

Why that would be Marcus Winkelhock, driving a Ferrari-powered Spyker in today’s European Grand Prix at Nurburgring, Germany. With the race about to start, on the “formation” or recon lap, he pulled into the pits to change tires from dry to intermediates. Rain was expected in a few minutes but everyone knew that. This forced him to start from the pits, in dead last position, but everyone else on grid had dry tires on. Well, by the second lap it was raining buckets and maybe half the cars slid off course. Marcus actually managed to get in the lead by lap 3! The race was paused under a red flag for about ten minutes while the rain stopped and teams frantically fixed what broken bits they could while cars were kept on the grid. Then they did a rolling re-start after two laps behind a safety car. Everyone started in the position they were in at the red flag. So Marcus restarted in first position! Never mind that two cars passed him by the first corner, he and Spyker definitely had their moment in the sun, er, rain. It was a brilliant tactical decision made by a team that normally plays the role of moving roadblock until their cars either self-destruct or drive into the gravel. Marcus did not, in fact, finish the race but what an amazing bit of trivia/history he wrote today!

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5 Comments »

  1. Two throttle cables is correct. Never even heard of a splitter for the /5.

    Comment by Tim Park — July 23, 2007 @ 8:03 pm

  2. Issue with electrical.
    wondered if you could help.
    no brake lights neutrol light
    does not come on and no
    turn signals. thanks for your time
    have headlite but not running light .patrick

    Comment by patrick — March 6, 2008 @ 11:50 am

  3. Hello Patrick. Your symptoms are pretty broad for an easy answer.

    Have you checked the brake light switches themselves? They should open and close as measured by an ohm-meter.

    If they are fine then check inside your headlight bucket. I can imagine where the wires to the main terminal block could get loose or corroded. Same deal for the running light (or possible bad bulb or bulb base corrosion).

    The neutral light could be the switch inside tranny (no idea how to get to that one), single wire connection to the rear of tranny (a fussy screw-clamp connection), or even the instrument bulb itself (they do burn out).

    Comment by Penforhire — March 10, 2008 @ 9:10 am

  4. Just found this blog….is the restoration complete?

    Comment by Matt — April 16, 2012 @ 6:00 pm


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