Converting a /6 headlight assembly to /5 Nacelle + timing issues...

Discussion in 'Airheads' started by sprouty115, Sep 13, 2017.

  1. sprouty115

    sprouty115 Long timer

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    This is the bike I wanted:
    bmw-r75-lwb.jpg

    This is the bike I bought:
    R90-6 in pickup.jpg

    Close inspection will tell you they are not the same bike. But 13.5K original miles, 150cc increase, an extra gear in the transmission and a disc brake won me over. I'm happy with the bike and I'm even enjoying sorting out 42yrs of issues that come from 42yrs of occasional use, however the aesthetics of the /5 are where my heart is.

    So having said that, and with reassurances of not performing anything that would not be reversible (no chopping or bobbing of anything), I'm thinking of basically changing the components that will make the bike appear closer to a /5 in style*. As far as I can tell most items are available (provided you're will to pay) and are a simple bolt-on process.

    But the one thing that seems like it might be a bit more involved is instrumentation/headlight. Which leads to my question: does anyone have any experience on converting the /6 headlamp and gauges to the /5 nacelle?




    * I realize this may be sacrilege to some, but I'm hoping that might be overlooked considering I won't be ruining anything, nor claiming it is an original /5.
    #1
  2. UnclePete

    UnclePete Been here awhile

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    I recommend that any new owner ride a bike for a season before doing any modifications .
    Just go through it , service it , ride and maintain it ; get to know it .
    Might like it just the way it is .
    #2
  3. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

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    AND, if you do decide to do the swap, remove the headlight and the main wiring harness together and replace them with a /5 wiring harness (around $70). The /6 wiring has all the later style push on connectors, while a lot of the /5 headlight connections are soldered ends with screws holding them in place. You will still have to butcher the /6 handlebar switches wiring to make them work, unless you go to /5 perches and switches... The neutral light wiring, fork ears and starter relay is different too.
    #3
  4. OLD GREEN

    OLD GREEN Long timer

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    It's not a cheap proposition obtaining all the necessary parts to convert it but it is doable. The /5 wiring harness that BB mentioned is about the cheapest piece to the puzzle. The bucket, lens, reflector and a usable speedo/tach are getting very expensive unless you luck into them. The fork ears, perches and switch gear will each set you back about a $100 a set. You'd almost be better off finding a ratty non titled /5 to cannibalize and sell off what you don't use than to try and source all the parts individually.
    #4
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  5. sprouty115

    sprouty115 Long timer

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    TL;DR - that's sound advice.

    So far I've spent some time on the bike but it has some issues that I can't ignore, so I've done the following:
    - inspected all fluids (they looked brand-new, though that was expected as Max BMW had replaced them all a few months before I bought the bike)
    - inspected brakes, wheels, and tires (tires are ok, but not great, everything else seems fine)
    - replaced plugs (both were very black from signaling weak spark or carb issues)
    - replaced plug wires and caps (slightly cracked and definitely old)
    - rebuilt carbs (o-rings, gaskets, floats and float needles)
    - set gap on points
    - balanced the carbs

    Right now the bike runs, but not quite as smoothly as I was expecting, so I started back-tracking. When I set the gap on the points I couldn't even get close with the static and dynamic timing. I assumed I must have been doing something wrong because, as I said, it does run. So after some research, I discovered the issue with the Chinese pints. Now I'm in the process of replacing the points (and condenser) to see if I can get the timing correct. If that all falls into place I'll start riding it



    Good info. I will have a look into the connections.
    #5
  6. sprouty115

    sprouty115 Long timer

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    Yup, I had a line on a full nacelle for around $270 but as you can expect on E-bay it doubled in price in the last few minutes of the auction. Hadn't considered a parts bike...
    #6
  7. blaine.hale

    blaine.hale Long timer

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    I see your problem. You wanted a /5 and got a /6! Silly.

    In all seriousness (I did this) ride and enjoy the r90. It's a powerful beemer and great bike. Maintain it, don't modify anything and keep it clean. A stock, original bike will sell for more. When you're bored, sell it and find the right /5 toaster. Where I live, they're valued similarly.
    #7
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  8. sprouty115

    sprouty115 Long timer

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    I did...not saying I regret it, as doesn't seem like low mileage bikes are common. But it does seem like it might have been easier to start with a /5 and then bump the displacement and swap the transmission, no?
    #8
  9. pkboxer

    pkboxer Been here awhile

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    It's really not all that hard and you can undo it if you must. But why? Resale value? Owning the bike isn't about resale value....

    Anyway.

    IMHO the /2 bucket was better, the /5 looks like a snake digesting a giant rat. The instrument is too big for the bucket.

    What I (and some others, Brun comes to mind in Australia) did was use a soviet/china BMW knock off bucket.

    Originally I used just an electronic tach, and now have a speed hut speedo in the bucket.

    Cheaper bucket than a /5 too. I put the /6 wiring board inside the bucket and went from there.

    Here's a few pics, good luck.

    top.jpg front.jpg
    #9
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  10. drhach

    drhach We can't stop here, this is bat country!!

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    That's awfully brilliant. How did you sort out the "Gen" light requirement? Is it one of your idiot lights?
    #10
  11. sprouty115

    sprouty115 Long timer

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    To be clear this has nothing to do with resale, it is simply my preference of aesthetics coupled with the fact that my gauges will require service. So if I'm going to spend money, I'd much prefer to have something that looks good to me. Thanks for the suggestion on the alternate source.
    #11
  12. blaine.hale

    blaine.hale Long timer

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    It has a little bit more power and top end than an r75 but you won't miss that in the bump down to an r75. Keep in mind, 4th gear on a /5 is the same as 5th gear on a /6. I personally like the /5 4 speed.
    You're sort of comparing a cow with a slightly smaller cow. I love cows but they aren't the quickest things.
    #12
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  13. pkboxer

    pkboxer Been here awhile

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    How did you sort out the "Gen" light requirement? Is it one of your idiot lights?

    on the right side of the bucket you can see a little red bump. That's a self contained LED from the auto store.

    Also have a resistor in parallel in case.

    Funny - once accidentally removed the resistor (before I was using the light) and the bike would shut off. It was self energizing through that circuit.


    The top two lights are green - neutral light and turn signals red - oil pressure.
    #13
  14. BicyclebBob

    BicyclebBob Been here awhile

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    If you find a parts bike /5 ride the /6 and restore the /5... the 4 speed gearbox and other things you talked about upgrading are what make the /5 awesome. I wouldn't sacrifice a /5 in any condition to make a fake /5.
    #14
  15. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

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    ...or put a "WANTED, BMW motorcycles; Dead or Alive" ad on your local Craigslist, and see what pops up. I paid a total of $1850 for the last SIX bikes I bought, and one was an R60/5 with no title... for FREE! :deal
    #15
  16. spo123

    spo123 Man About Town

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    Usually, DESIRABLE parts WILL double in price, at the last minute....or SECONDS.
    That is how it works, on epay.
    NICE BIKE.
    Leave it alone and deal with what it REALLY needs.
    Have fun.
    #16
  17. Brun

    Brun Been here awhile

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    G'day Sprouty
    Me too. I'm a /5 tragic blessed with a /6. For me, fate intervened in the form of a black cow on a dark night, resulting in a trashed front end. I've had a couple of chinese headlights and a variety of speedos since but now have a 3D printed bucket and ears with a Speedhut GPS speedo:

    [​IMG]

    Here's the next iteration, not yet fitted:

    [​IMG]

    This project is still current - I'm in the process of setting up a bigger and better printer. Here's a thread detailing the adventure so far:

    http://advrider.com/index.php?threads/3d-printing-the-slash-five-headlight-bucket.112399
    #17
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  18. bpeckm

    bpeckm Grin!

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    I have a Slash2 Conversion: I found an off-brand bucket from some other european bike, it looks a lot like the /2 bucket, and then got a cheapy ($15!) speedo from india. The 90/6 speedo cable works perfectly. It does not have a tach, but I haven't needed one (I rev the **** out of it now and then and don't want to know where the needle is going....!). I did my own custom wiring harness and installed all the /6-and-later goodies (kill switch, turn signals on my left perch etc). Full thread is in my sigline if you care to wade through it, but here are a couple of pics of what I did....

    [​IMG]

    [​IMG]

    The headlight is a car sealed-beam/LED style.
    #18
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  19. Jim K in PA

    Jim K in PA Long timer

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    And what is the lead time on international orders, Charlie??

    :D
    #19
  20. sprouty115

    sprouty115 Long timer

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    Just to clear, I wouldn't consider sacrificing a salvageable bike as spare parts for any project. I'm merely considering my options - wanted a /5 but ran across a nice /6, so I'm just trying to sort out a compromise. All I've done to-date is give the bike a much needed time up.

    Again, thanks to everyone for all the ideas - off-brands and 3D printing never occurred to me...
    #20