A little airhead help, please

Discussion in 'Airheads' started by oldroadie, Dec 22, 2011.

  1. oldroadie

    oldroadie Two wheel addict

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    So I've got a 1972 R75/5 in my little shop and I'm close to getting it road worthy; it was only running on one cylinder when I picked it up due to an over bent float tab. A complete Bing overhaul kit cured the neglect. It does seem that the starter struggles to spin the motor over, quickly draining the 18ah eBay gel battery below it's ability to spin the starter. Common? Would a dedicated ground line to the motor help significantly?

    Odo shows 36K miles but it can't be confirmed it's the original gauge. I have removed more oil/tar build up from this motor unit than I have ever seen on a bike and there's still a lot more to go. I have managed to rotate out all of the fluids, set valves and points gap and set the timing; thanks to Jeff Trapp for the cool tools. And, I have attempted to wade through Snowbum's epic site but the yellow background and mulit-colored font makes that an exercise in patience and I can only take it in small chunks before my bifocals mist up. Good information trapped in a hard to read website. But I digress...

    [​IMG]
    #1
  2. fishkens

    fishkens Long timer

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    Starter problems on an airhead common? Yep.

    Could be a number of things: the bushing on the starter may be worn causing the starter to draw excess current. The cables may be corroded causing the same. The battery may be weak. You can start by confirming a healthy battery. Then measure voltage drop along the cables, pull the starter and check it's readiness.

    Others will pipe in with ideas. Just remember that it's a system so there's no single silver bullet and there may be multiple issues.

    More pics. :D
    #2
  3. Beater

    Beater The Bavarian Butcher

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    Of the MG! That's beautiful!
    #3
  4. oldroadie

    oldroadie Two wheel addict

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    That's next in line for reconditioning. It's a mid 80's British Coach Works replicar on a Chevette platform; one of maybe as many as 50 made for Schweppe's as a contest prize. I got lucky finding this one. They built the body onto the completed platform and I've got some cutting and fab-ing to commission to replace the transmission mount. Should be loads of fun when it's done. The BCW guys were pretty thorough as all of the MG repop parts will fit the body so it can really be made to look authentic.

    the core bike:

    [​IMG]

    new fenders from 7 Metal West, will have to massage the rear to fit so it looks right:

    [​IMG]
    [​IMG]

    going to be a scrambler-esque bike like way back in the day when you changed out tires, fenders and handlebars and crushed your low hanging exhaust running dirt roads and fire trails.
    #4
  5. disston

    disston ShadeTreeExpert

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    The starters can be rebuilt. Kits available, a brush kit and an everything else kit but I don't know if the bushing is part of that. I just looked a a parts picture, looks like the bushing is in the everything else kit.

    You have the 8 tooth starter. Later starters, starting in '81 I think, are 9 tooth. The two don't mix or interchange. Used starters also available. People who rebuild them if you don't want to do it yourself but they are a fairly easy to do with a little patience.

    Extra ground wires are sometimes a benefit but the stock wiring should not be the problem if in good clean shape.
    #5
  6. azcycle

    azcycle Chihuahua Wrangler

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    No advice to offer, but looking forward to seeing your progress. :evil
    #6
  7. oldroadie

    oldroadie Two wheel addict

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    It seems to be a stock harness but the ground is attached to the frame; I was thinking it should be to the motor but there doesn't appear to be a sturdy bolt handy. I saw an unused threaded boss in the timing case and thought I might fish a wire out of there thru the air intake so I could have a clean ground. I'm certain this is not an unmolested original bike since there's no frame # sticker and the subframe was well bent; I'm just going off the motor number and lack of welded extension on the driveshaft when I describe it as a 1972 R75/5 SWB. I've been using the Clymer big book as a guide but that's just no substitute for real experience.

    Here's a look at the bike when I picked it up in back in Feb:
    [​IMG]
    #7
  8. wirewrkr

    wirewrkr the thread-killer

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    the 9 tooth starter started with the 1977 model year bikes.
    The bushings are sold separately, the front nose bushing is the most common to wear and is pretty easy to replace.
    It's amazing how much better that starter works when it has a fresh bushing.
    #8
  9. Renner

    Renner combustophile

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    #9
  10. Hawk Medicine

    Hawk Medicine Coyote's Brother

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    If the ground wire is going to the frame, someone moved it. AFAIK, all of the stock ones go to the trans case. What I'd do is add a ground wire that goes to the stock position, service the starter and see what happens.

    By the way, Those SWB Toasters Tank /5 are getting to be pretty rare, so take good care of that bike and keep whatever parts you strip off of it. Someone might want to return it to stock some day!
    #10
  11. oldroadie

    oldroadie Two wheel addict

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    Yep, I'm keeping all the pull offs in dry storage for some future owner. Won't be cutting anything off, either, just taking some weight off and adjusting it to suit it's new purpose, back road riding. New stuff came in the mail today, turn signals and a tail light:
    just tape and blocks holding the mock up in place, got some angled spacers to make so it all sits square.
    [​IMG]
    #11
  12. Hawk Medicine

    Hawk Medicine Coyote's Brother

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    Oh...! OK! :1drink

    I had to go back and look at a couple of photos to understand how you constructed your muffler. Thats some good thinking!

    Please remember to report back let us know how it works.
    #12
  13. oldroadie

    oldroadie Two wheel addict

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    Thanks, I didn't really construct anything; I cut off 4 or 5 inches including the flared end and then had the stub expanded at my local muffler shop so that off-the-shelf Supertrapp end would fit snugly. Some RTV and a bolt secure the tuning disc end and I added the off-the-shelf heat shield so it doesn't cook the final drive. With the kit's full set of 12 discs it's already much quieter than the old pipe while retaining a nice throaty growl. Ought to make final A/F tuning fun.
    #13
  14. bmwrench

    bmwrench Long timer

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    Even at it's best, a /5 starter is rather wimpy. A really good battery-Odyseys come to mind- will make the most of it. You might also find a /6 starter (another .1 horsepower) and rebuild that. There should be a lot of them around, too.

    It seems to me that Robert VV looked into putting a /5 starter drive on a /7 starter, but I can't remember if that worked out.
    #14
  15. kbasa

    kbasa Roubaix! Super Moderator

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    While the Snowbum site has plenty of good information, it's almost impenetrable, which really reduces its usefulness for many.
    #15
  16. disston

    disston ShadeTreeExpert

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    It is a fact that the starter motors got a little bit more powerful almost every year. It is actually one of the theories for the slash numbers. This theory would have the /5 starters being lowest, /6 a little bit more and /7 the most powerful. I've even seen that equated to starter motor horsepower. Well I don't know about all this but the starters do get a bit more powerful.

    Putting an 8 tooth drive gear in a /7 starter makes sense. Seems to me straight forward. But I've never done it.

    Charlie
    #16
  17. MrBob

    MrBob Knee-jerk liberal

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  18. bereahorn

    bereahorn Long timer

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    :lurk
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  19. oldroadie

    oldroadie Two wheel addict

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    #19