'76 R75/7 restoration

Discussion in 'Airheads' started by Steril, Mar 26, 2021.

  1. Steril

    Steril Another Millenial

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    I was finally able to pick up the airhead I bought. The front brake is dead so there was a lot of butt-clenching during the 70km ride home.

    IMG_20210325_154026.jpg

    It's in unmolested condition, only the tank was rusted so it was swapped from another airhead. The patina and a bit of rust add to the charisma of the bike.
    I'm going to repair the brake, change all filters and fluids, check the sealing rings, etc to prep it for the summer trips.

    I Will post the process here in hope of getting guidance from local experts, most of my wrenching experience comes from riding a $100 bike in Laos and Vietnam for a few months and this will be a much more serious project.
    #1
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  2. Jim K in PA

    Jim K in PA Long timer Supporter

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    Welcome to the special needs department of the asylum.

    Nice /7. One year only for the 750 version, at least here in the US.
    #2
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  3. Steril

    Steril Another Millenial

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    Thanks Jim!
    My research on realoem says that the European version of 75/7 was manufactured between 05/76 and 01/79. Mine is 08/76 so a relatively early one.
    I took off the tank to see the state of brake M/C. It doesn't look all that great.

    IMG_20210326_101136.jpg IMG_20210326_113305.jpg
    Took it apart and there is some pitting on one side, how does one tell if it's still serviceable? I'm planning on ordering the rebuild kit but it might not seal?
    #3
  4. Pokie

    Pokie Just plain Pokie.

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    08/76 means it's a 1977 model.
    #4
  5. Steril

    Steril Another Millenial

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    I am confused! The Documents say it was first registered 12/78 but the VIN check on realoem says 08/76, which would mean it was in stock unsold for over two years.

    Vin search result.png
    #5
  6. Pokie

    Pokie Just plain Pokie.

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    With European bikes, the new year bikes start being built after summer vacation. That means anything built after summer vacation (08 of any year) will be the next years bikes. Yes, it sure could have sat unsold in a warehouse somewhere for two years. In 1976 and 1977 BMW dealers were still selling off left over 1973 models. Those were European models.
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  7. Jim K in PA

    Jim K in PA Long timer Supporter

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    Yep - my 1966 built /2 was not sold/titled until 1968.
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  8. Jim K in PA

    Jim K in PA Long timer Supporter

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    Bit of a can 'o worms on this topic, but first answer is that the cylinder will need to be at least honed, and likely sleeved. Next question is, do you plan to leave it stock? Add a second ATE caliper? Go full monty and add R90X designs adapters for radial Brembos? Lots of options, including converting to a handlebar MC.

    If leaving the stock single ATE, I would sleeve that down to something smaller than the 14mm piston it came with.
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  9. Steril

    Steril Another Millenial

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    Thanks for the assessment, Jim!
    I've looked into the options and would like to keep it stock and have the handlebar MC option as a last resort. I Will call some hydraulic cylinder repair shops to get quotes and use the $95 Apple Hydraulics is asking as a benchmark.
    #9
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  10. Steril

    Steril Another Millenial

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    I called some hydraulics shops, the quotes for the MC sleeve job were around €100 which sounds reasonable. The problem is timing - the earliest it could be done is in four months!
    I've decided to try to hone my MC as a stopgap measure for this season, following Mr. Ausherman's instructions. Ordered a few sheets of fine sandpaper online today, all non-essential stores are closed due to king-flu lockdowns, so I'll have to wait.

    One unpleasant thing happened - when I went to the garage this morning to work on my other motorbike (new vacuum lines on Aprilia Caponord) while waiting for BMW parts, the BMW tank was on the ground. It somehow fell from the box I've put it on the day before, resulting in scratches and a dent on its side. Having the tank repainted with the original BMW 038 Monza Blue Metallic was planned for the winter but this mishap is probably going to move it up - if the stars align and there will be a shop willing to do it within next month, several inquiries have been sent. I'll have the fenders painted too.

    IMG_20210329_112542.jpg
    #10
  11. Steril

    Steril Another Millenial

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    The quotes for repair and repaint of the tank and fenders are around $1000 which seems fair, considering the white lines are done by hand and they would use the original paint scheme. I'll have it done after this year's season.

    The master cylinder rebuild kit has arrived and the cylinder is ready. It's been honed and it took me a few hours with a wire brush and sandpaper to clean off the rust. Sprayed it with a rattle can matt black, it's going to a repair shop in the autumn so this will do in the meantime. It's surprising that the rebuild kit didn't come with a new circlip, the old one is still luckily okay to use.
    IMG_20210401_174345.jpg IMG_20210401_174834.jpg
    The seat pan seemed to be a bit rusted so I decided to take it off for closer inspection. The paint started to peel off in sheets immediately, so I took the seat cover and foam off. It was not a nice look, heaps of rust!
    IMG_20210401_143636.jpg

    I'm derusting the pan but it might be too far gone, I'll still try to save it since a new one is €300 ($350).

    The frame is a bit rusty too, especially under the tank, probably due to the brake fluid leak. I'll sandpaper and rattle can that, so the bike is okay to ride this season.
    Right after that, the plan is to reinstall the MC, seat, and the tank, ride around a bit to see if it really brakes, and heat the oil so it can be drained. I have bought oil pan gaskets to be able to take the pan off, clean it, and see if there are some metal shavings in it.
    The other things planned for next weeks are valve adjustment, main drive inspection and lubing, oil and air filter replacement, flushing and changing all the oils, new spark plugs, fuel lines replacement, carb cleaning (when the gaskets arrive), new tires, replacement of all bolts since they are a bit rusty.
    Krauser keys have arrived too, S150 for the cases, and S324 for the rack locking mechanism, both fit and work, €17.50 for each is a bit steep but it's a price for owning an oldtimer I guess.
    #11
  12. Steril

    Steril Another Millenial

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    I've reinstalled the MC and filled the system with brake fluid. It works and no leaks so far! The test ride will have to wait, the motorbike is still in pieces.
    IMG_20210404_111424.jpg

    Took the airbox clamshell apart to change the filter and the fuel line that leads through there. Lots of dirt and dead insects inside. Found out that the rubber suction hood grid is missing so that might be a partial reason. The filter is totally knackered, hoping the oil and filter will be in better shape, won't find out until the bike is ready for an oil warm-up ride.
    IMG_20210404_112642.jpg
    Some of the bolts on the engine were a bit rusty so I ordered a new bolt set from Louis.eu - one of the the biggest motorbike e-commerces in Europe. The order page required me to specify the type and year of manufacture of my motorbike so it was supposed to be a safe bet. Something went wrong and the bolts don't fit at all. My engine number is the same as the frame so I'd guess it's not on my side.
    IMG_20210403_192525.jpg
    Right is original, left is louis.
    #12
  13. Steril

    Steril Another Millenial

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    tl;dr it's going good and steady. The front M/C brake light switch is probably faulty, only the rear brake lights up. Any ideas on the reason, other than the switch?
    The switch is not that expensive (€23) but the shipping is almost as much as the part (€15), and that sucks.

    I live in a semi-derelict building where the only occupied apartment is mine, so I park the motorbike in the corridor. It's dark and cold there, working on the parts in my living room is much more practical. That's how I live now.
    IMG_20210407_140005 (2).jpg
    The seat pan was too rusted for my liking, found a much better one on German classifieds and ordered it for €240 including shipping. A sweet deal, a not that great replica is €270 and the nice one is 760! I'll restore the old seat and sell it for some change.
    IMG_20210412_142133.jpg
    I got the aluminum Krauser T-set luggage rack as an extra but I prefer the chrome that's on the bike, let me know if you want to buy it. Some screws might be missing but the hardware seems to be complete.
    IMG_20210424_203805.jpg

    The battery holder was rusty so I took it off and destroyed the rubber buffers under it in the process. The nuts were so rusted I had to cut them off. Cleaned and resprayed it, waited a week for the parts to come, and put it back.

    I changed the fuel lines and added inline filters, rebuilt the petcocks with new seals and that holed rubber disc. Changed the mesh screens in the tank, they were in a bad shape. The thing about the petcock rebuild is that the internal spring (part 16121236390) needs replacing and it's nowhere to be found, had to put a large spring washer there but it's far from ideal. I'm looking into buying a wide spring and cutting it to fit.

    I've noticed the throttle cables are fraying on the carb end, ordered new ones. The screws holding the front fender to the fork brace just fell apart when I took it off, waiting for new ones to arrive. The rubber washers that are supposed to go under them are unobtainium so I'll have to macgyver something out of an old tire tube.

    The bike starts and brakes, the electric works, the only thing stopping me from hitting the road now is the front brake light switch, damn, the weather is getting good.

    I log the expenses if someone is interested in how much it is to restore an airhead in Europe. It's €1000 now, the seat (240) and master cylinder rebuild kit (90) being the biggest single expenses so far, the rest is tires, bolts, oils, gaskets, filters, etc, will share the sheet when everything is complete.
    #13
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  14. Disston

    Disston ShadeTreeExpert Supporter

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    The only parts available for the petcocks are the rubber thingies. No spring, no levers, no click stop things. nada.

    Usually the throttle cables outer shell gets kinked at the carb end. Riders set the carbs level, it looks good. They are supposed to be angled a slight amount inward to relive the stress on the cables. Gives the cables a more straight shot at the carb.

    Being frayed sounds like just age tho.

    If you want nice shinny petcocks with all the proper function buy new ones. But the rubber parts usually will take care of the leaks. I forget the currant source of good prices on petcocks. Somebody will chime in I think.
    #14
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  15. Steril

    Steril Another Millenial

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    Thanks, Disston, I was afraid that's the case, and improvising or buying new petcocks are the only options. Siebenrock is selling Karcomas for €43, which is not all that bad.

    I had no idea about the carb angle, will set them slightly inwards - after I take them off and clean them when the rebuild kit finally arrives.
    #15
  16. Disston

    Disston ShadeTreeExpert Supporter

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    Just noticed you're in Europe. No idea about where to buy there.
    #16
  17. PaulBarton

    PaulBarton Long timer Supporter

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    #17
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  18. korinthias

    korinthias slightly behind the curve…

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    What PaulBarton says – Motobins/Motorworks have all the parts for the petcocks, springs, washers, filters, rubber washer with multiple holes etc. etc. Also an overhaul kit for both the Karcoma and Germa taps (never seen a Germa tap?). All reasonably priced…

    6FB0088F-1A09-4D82-A44D-0D6C4F3EA548.jpeg
    #18
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  19. Steril

    Steril Another Millenial

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    Wow, motobins indeed has the fuel tap springs, and a much cheaper brake light switch I need, thank you guys! I've been on their page sometime in the past but forgot about them for some reason.
    #19
  20. Beemeup

    Beemeup 1978 R100/7

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    The switch could be kaput or it may just need a good cleaning. Electrical spray and even WD40 might do it.
    #20
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