1975 BMW R90/6 - Rocinante

The aforementioned shiny stuff stashed for the winter:


Relax and take the winter off, guys. I'll get back w/ you later. I'm still looking for a solo seat for you and other goodies. Maybe I'll scare up some parts over the winter.
Yup, it's been a while. Life, health, the "winter home" 5th wheel trailer, and anything else you can imagine seem to get into the way. Anyway I'm about to start back in on the thing. If we aren't able to make the trip south for the winter because of health reasons There'll be a path on the snow between the house and shop.

In the mean time I've acquired some goodies. These showed up last fall:




I found these stainless mufflers today: The pix doesn't do justice, they're really nice, maybe not perfect, but nice.

Last edited:
Lester wheels. I passed the factory everyday on my way to work and back home. I almost bought a BMW a few years ago because it had a nice set of Lesters and some other nice pieces.
I decided that if I was going to be around here for the winter ( :( ) I'd get my pig sty of a shop cleaned up, straightened up, and back into working shape so I can spend the winter getting Rocinante together and where she needs, deserves(!), to be. I've had a couple of summer projects that really left the place in total havoc. I do try to put tools away and keep the sawdust vacuumed but it still just all falls into a state of decay after a bit. I used the opportunity to put down a new floor cover of pieces of 36" wide rubber conveyor belt I acquired and I even managed to pitch out a bunch of things, ignoring the ever-present "I might need that some day" syndrome that plagues us old guys.


I even got to a project that's been in the back of my mind for a long time. In the rafters of the garage I found a board, I think Maple, that had to have been old growth wood that had probably been up there since the place was built in the '40s. The thing measured 70.5" long X 23" wide X 1" thick. I cut it into half and glued n screwed the halves together and then squared it all up on my table saw. Then I sanded it progressing from 60 to 220 grit and then oiled and waxed it.


Levi (@Hurco550) came over and helped me get the old girl up onto the table so it's already to work on.


The last build took ten years, I won't let that happen to this one.
Last edited:
With a fresh, full tank of propane for the heater and finding myself stuck in Ohio for the duration I've finally started to get back into this thing. It has amazed me as I slowly work my way, piece by piece, through the various bits of this machine. Most everything is so incredibly filthy with some light rust but when I scrub and scrub and then scrub some more it's slowly coming around and most parts are beginning to look like ones that have come off a bike with 42k miles.

I removed the mufflers and managed to get some shine into them. At the moment they're pretty nice looking and will require only a little more attention to be very nice. There is one OEM and one aftermarket so I'm hoping they are mates for the one OEM and one aftermarket mufflers that @Hurco550 has on his airhead. With any luck he'll end up with a couple of matched sets. I'll put on the SS set I picked up down in Lithopolis.


It might have been humorous to have fired this old girl up without taking the mufflers off; all this mess came out of them. Anyone standing behind would have been blasted!


Levi turned me on to a YouTube vid from a guy pushing Marvel Mystery Oil as an aluminum cleaner for motorcycle aluminum. I figured I wouldn't be out much to give it a try so I picked up a bottle. I tried it on some of the engine aluminum bits and it did OK, not great, probably about the same as glass cooktop cleaner and aluminum foil. I'm thinking about vapor hone, but I'd end up leaving part of the engine/transmission as-is and do just the basic removable parts. It doesn't seem like a great idea to completely disassemble such a low mile engine/trans. Here's a cleaned air cleaner cover half next to the uncleaned engine/trans. Better but not fantastic in my opinion. However the thing IS 50 years old so...


Today I pulled off the rest of the exhaust system and spread the MMO and let it sit for a while then started scrubbing. Though the next pix is poor quality it's an example of what some of the better parts of the head pipes looked like.


And at the moment they look like this, though they are now liberally coated w/ MMO for the night and we'll see if what's left comes off more easily tomorrow.



And the rest of the exhaust parts are soaking in acetone for the night. Those clamps and brackets were directly below where the carbs were dripping the collected 30+ year old gasoline goo.


The next task will be replacing the top end gaskets and seals.
With the TV set to The Expanse (see earlier posts) the crud cleaning goes on and on.


That front cover has a bunch of time in it with just about any every method of cleaning process (except blasting) you can imagine and is being exceedingly stubborn:


After spending so much time and effort, I've come to agree with @Hurco550 who said to me the other day, "Airheads look good with a bit of use apparent on them" Well said my friend, well said. If I were going to take it down completely everything would be going into a box to send to @irk miller for a vapor hone job but I think it would look strange, not to mention frustrating, to have just some of the engine all clean and spanky and parts of it looking weathered, so weathered it will remain, at least for now.

It is coming along, though. Parts are coming off with little trouble, getting cleaned and then stored until reassembly.


I broke out my little ultrasonic cleaner and it did an ok job on the exhaust system bits n pieces.


Almost ready to go back on:


When I brought the old girl home there was a box of assorted parts that came with it and these unique exhaust pipe heat guards were in there. Maybe they were common "back in the day" but I've gone through lots and lots of airhead pictures and have only seen them on one other bike. To me that's enough reason to try and use them and to my eye they fall into the Old Man's Bike look I'm aiming for. They were very corroded and didn't clean up well; some of the chrome was too far gone and irretrievable. I've got some hi-temp engine paint I like so I decided to see if it works out. If I get things together and don't like them in black I'll move on to Plan B, whatever that is.


Little bits at a time I guess.
Last edited:
Still at it. I found a 'lectric heater amongst our stuff that'll keep the place at something workable so I don't need to burn tons of propane to get the place up to a temperature I can work in. Pretty efficient thing, too, I probably won't have to buy a nuclear power plant to run it.

Anyway... still working away at it. More cleaning and scrubbing. After lots of time in the ultrasomic cleaner and working a small wire brush between each of those fins, even the exhaust header nuts are looking acceptable.


And the exhaust is finally looking ok, too:



'Bout as good as I'm gunna get it at least for now. I heard a story about a guy talking w/ a BMW mechanic; he asked, "Is there anything about BMWs you don't like?" After thinking about it the mechanic said, "Well, they turn their pipes blue." Tomorrow I'll start of the top end gaskets n seals; one side at a time.
I think an old bike like this looks proper just cleaned up well with patina. My R75/6 is all original finish - paint, aluminum etc. I did make the mistake of having the rims soda blasted when I relaced them with Buchanan stainless spokes so they're a bit rough and pick up grease stains readily. And my exhaust is a new full stainless kit from Keihan which is pretty awesome but aside from that the finish is 50 years old and looks good IMHO.

I'd never bother breaking my whole engine down just to clean the cases, but if I did they'd get vapour honed for sure. Certainly I'd never paint them - never understood why the Japanese and other manufacturers painted their engines.
I hear ya on all points, Tim. I think I'm going to try and find a place here in town that'll let me use their parts washer. Just a good, professional parts wash job on the rocker cover, head, and cylinder on each side will have the thing looking very presentable. I'll scrub up the engine case and transmission as best I can and call it good. With the low miles it has now I'd think it should be a very long time before it'll need a full take-down, probably as long as I own it.

Paint the engine? No way! Even the frame I'm just going to clean and then touch up the little paint dings from bumps, battery leaks, brake fluid, and stones. The "tins" are cleaned and shined as much as possible and they're "good enough." Speaking of the tins, I was talking w/ the guy I bought it from a while back and I had forgotten he had told me that it was originally Phoenix Gold and that the original rear fender broke and the replacement he got was black so he had the whole thing painted black. (?) I'll have to ask him about it again one of these days, though, because documentation I've found says that was a later year color on R100 machines. The '75 year included a "Curry" color that is gold/orange that could be what it was? I can believe the black is a respray because the pinstripes are single lines rather than double as would have come from the factory. If I were going to change the color I have no idea what I'd pick and I doubt it would be black but I want to leave it as-is because of the "survivor" look it's got.

I got the left rocker cover, head, and cylinder off today and I'm not unhappy w/ what I found. There was a layer of jelled 30+ year old gasoline puddled at the end of the cylinder so I'm sure that for most of it's over 30 years of storage it was on it's kick stand rather than the center stand. All that is cleaning up just fine, though, and other than the usual and expected carbon buildup things look good. The bore is very clean and not scratched or ridged. (The mess on the cylinder wall in the second pix is just residue from the old gas goo, it cleaned right off.)



Last edited:
Another afternoon in "the office" but spent the morning asking around for a place here in town w/ a parts washer. I know of one in town but even though I know the guys who own it I'm sure I'd have to pay the the price of a new space shuttle for them to do anything for me so I looked around and asked around and found one guy who would have been willing but said, "I'd be happy to but I'm almost out of solvent for it and that stuff costs over $70 for a 5 gallon bucket." I ended up leaving the left cylinder and head at Cycle Tech, good guy. I'll pick them up tomorrow.

Back at the cleaning and was fairly pleased to discover that what I thought was nasty rust on the shift lever and left foot peg ended up being some rust but mostly remains of the old gasoline jell that dripped, probably more like oozed, out of the left carb. I'm very pleased w/ how they've ended up:





I also found a ring compressor that's small enough to fit into the limited room available so, hopefully the left side will be back together soon.
Brake MC was really ugly but I didn't get a good before pix. The paint had all been removed by spilled or leaking brake fluid and rust had come to visit. I wasn't optimistic but when I started working w/ it everything moved smoothly but I knew it had to come apart. Yup, crusty inside but, amazingly, after a good cleaning it is as clean and slick as a whistle inside so will just require a rebuild kit and not a hone. Everything is cleaned up and ready to go and the "at that price it must be solid gold!" MC rebuild kit is on the way so another thing is scratched off the list. S1000RR caliper is also on the way and, would't you know it, R90X has everything on backorder!!!!

I got a note from Matt at R90X telling me they'd be back in stock, hopefully, at the end of next week so that'll be on order soon. R90X makes a machined wheel adapter for the airhead wheel to fit up the 320mm disc from a Ducati and another adapter for the fork leg mount that'll hold the caliper from a BMW S1000RR. This lash-up will bring the old girl into the 21st century, or at least closer to the 21st century, in the brake department. Now in a "Paul Harvey moment" I'll tell The Rest Of The Story. (Prolly nobody cares any way, but...) When you buy the disc and caliper for this conversion you pretty much end up w/ a pair of discs and a pair of calipers. Of course you use the left side parts unless you're going to go full gonzo dual disc on a bike that really doesn't need it. In an email exchange w/ Matt at R90X he told me it's very common for owners to set up their machine w/ a right hand set by simply switching sides w/ the fork lowers and then making some minor changes when reinstalling the fender mount between the fork legs. Because Levi had a right side set the plan was to buy his extras and carry on; I really don't care which side the brake is on. Last Fall I brought over the boxes w/ the disc and caliper and put them w/ the other stuff. A few days ago I opened the other disc box that was still taped and inside were TWO DISCS, a left and a right. Levi purchased a right and left set and somehow ended up with one right and two lefts. I decided to find a single caliper and, of course, they are usually sold in pairs. I found the only single left caliper on eBay AND at a very good price, shipped from somewhere in Europe. So Plan A is off and Plan B is on. Funny how things work out.

The job to re-seal the cylinders is moving along and with the brakes nearly sorted I've got to keep things moving. There is still more chrome to clean up:


And then there'll be the million other things it'll take to get it going.
Last edited:
Hey Cory, if that seat grab bar doesn't spiff up as nice as you'd like, I have a nice one here that you're welcome to
Hey Cory, if that seat grab bar doesn't spiff up as nice as you'd like, I have a nice one here that you're welcome to
Thank you Levi. I didn't start on it yet, just wasn't in the mood today for some reason. That piece and the original crash bar are about the worst things on it, rust wise, and I've already got your crash bar! I hadn't worried about it because I really wanted a solo seat but I'm not finding them available at a price I like so I'll spiff up the original couch as best I can for now. Something will come along, though. So far I'm enjoying working on the thing, aside from all the cleaning. No bolts have been too tight (except the screws on the carb tops) and nothing has broken off or been very frustrating. I've been watching William on the Boxer2Valve YouTube vids again so I shouldn't screw things up too bad when I reassemble. Do you have any of that copper-based anti seize? And what do I need to get for the splines on the rear wheel?
I received the MC rebuild kit and got it installed. It's not solid gold or even gold plated, but everything fit and it went back together fine. I plan to re-use the upper brake line (rubber) but I couldn't get compressed air through it. I used a long bit of very thin wire chucked up in a drill and worked it through along with lots of solvent. Once it was cleared out and clean I put lots of compressed air through it. I'm assuming that when I put brake fluid into the system I may have to flush it all out to make sure it's clean.


On to other stuff!
I received the MC rebuild kit and got it installed. It's not solid gold or even gold plated, but everything fit and it went back together fine. I plan to re-use the upper brake line (rubber) but I couldn't get compressed air through it. I used a long bit of very thin wire chucked up in a drill and worked it through along with lots of solvent. Once it was cleared out and clean I put lots of compressed air through it. I'm assuming that when I put brake fluid into the system I may have to flush it all out to make sure it's clean.

View attachment 238444

On to other stuff!
If you go with the R90x kit, you'll replace the entire brake line anyways. I believe that @Tim may still have the correct code for the brake line to order from Spiegler here in Ohio. The one I ordered ended up being about 1" too short.
Standard Brakeline Quote
Standard Brakeline Quote

Qty: 1

Fitting - F1: 002

Fitting - F2: 510

Length A in mm: 890

Line Color: Black

Fitting Color: Stainless Steel

Bike (Make, Model, Year) : BMW R75/6 1975

Need Grommet or Tab Locator? : None needed
I had originally wanted a black carrier for the rotor, but the gold sort of works with the caliper, reflector, signals and the stainless headers that have taken on a gold tone. I got the rotor from an eBay seller back in 2020 for what seemed to be a good price. I was lucky enough to get a Brembo caliper from Matt at R90X for $66 when I ordered the brake kits.

Screenshot 2023-12-12 at 11.59.52 AM.png
Top Bottom