Airhead stud tool dimensions

Discussion in 'Airheads' started by Bill Harris, Nov 20, 2011.

  1. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Does anyone have, or or know of an online source for, the distances between the cylinder studs on a BMW R-bike? I'm working up a stud repair drilling jig.
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  2. robtg

    robtg Been here awhile

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    Oddly enough, the stud spacing is really close to the same spacing as the holes in the cylinder, head gasket,and the cylinder head. Although you may
    want to use an actual crankcase for an exact fit. :D
    #2
  3. batoutoflahonda

    batoutoflahonda Long timer

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    I'm pulling the jugs off mine this weekend. I could measure, photo, etc if you like. But you are probably looking for engineering drawings. I recall see it some where. I'll look around.
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  4. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    I'll use a head gasket or a /5/6 base gasket for a "template", though there is the possibility of dimensional errors that can creep into transferring measurements from the gaskets. The better way would be to use a bare case and measure the stud distances. I'm doing my top end as we speak, but it's going through it's second stud-thread repair and I'm sure that some creep has crept since I've not always used a mil-spec drilling jig. Just double-checking-- I'm sure that the "correct" dims will be to the nearest millimeter.

    I recalled seeing that stud dimension layout, along with the transmission shim plate dims at one time.

    For 30 years I've used a drilling jig that you have to index to the stud you're repairing, and currently am using a rental jig from Northwoods, but I thought I'd make myself a nice self-indexing jig. Not hard, a couple of dims and a Bridgeport & a lathe and you're done.

    And I might go commercial develop with a nice mahogany or teak drilling jig for the connoisseur... :eek1


    Oh, this top-end work is coming along so nicely...
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  5. wirewrkr

    wirewrkr the thread-killer

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    no need bill, I've got plenty of open engines on the bench at the moment.
    I'll go measure and be right back.......................
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  6. wirewrkr

    wirewrkr the thread-killer

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    I'm reading 72mm x 93mm center to center.
    I agree with ROBTG about using an actual block though.
    I have an R65 block that threw a rod, I'll see if one side is good enough for a jig.
    Maybe I could even cut out the section and send it to you for the shipping.
    I'll check and see, it's in the bottom of my scrap metal drum.

    Attached Files:

    #6
  7. wirewrkr

    wirewrkr the thread-killer

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    So here ya go Mr Harris,
    went through 3 sawzall blades to get'er done, but was worth it.

    Attached Files:

    #7
  8. datchew

    datchew Don't buy from Brad

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    Robert.

    You just brought a new level of awesomeness to this forum.
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  9. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Omygosh, how neat. If you're wanting to part with that prize, I'll take it (check your PM for address).

    93x72mm sounds right (I measured mine, in inches, and those numbers are in the shop at the other end of the house now). I'll check later. The spigot is 97mm for pre-nikasil and 99mm for Nikasil cylinders.
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  10. baldwithglasses

    baldwithglasses Godspeed, Robert

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    wirewrkr, what datchew said.

    Awesome. Sublime.
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  11. disston

    disston ShadeTreeExpert

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    Actually the Nikasils are 99mm but there are some pre Nikasils also 99mm. The division is the last year of /6. 1975 and older are 97mm. 1976 and up are 99mm. So some iron cylinders are 99 but can be updated to Nikasil.

    Nice looking slice from your block. If you welded them back in at an angle you could make it a Moto Guzzi.
    #11
  12. wirewrkr

    wirewrkr the thread-killer

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    luckily, the stud holes are all the same distance from 1970-96.
    This chunk is from a 79 R65.
    #12
  13. wirewrkr

    wirewrkr the thread-killer

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    Bill, PM ed you the info.
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  14. Mugwest

    Mugwest .

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    Cool ++

    That R65 block gave itself to the Larger Good :nod
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  15. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    More than cool. This is art!


    Charlie, thanks for the extra info. I remembered that the early cast iron cylinders were 97mm and the later Nikasil were 99mm and assumed that the division was by cylinder type and not model year.
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  16. disston

    disston ShadeTreeExpert

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    Bill, I've though much worse than that.

    I'm wondering about the design of your tool. The spigot size plays in the design of the ones I've seen pictures for. The main tool takes either of two adapters and is centered by the spigot. Is there another way to do this?

    I've never had to fix one of those threads, yet. Didn't they get fixed, drilled and all, free hand years ago?

    Charlie
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  17. datchew

    datchew Don't buy from Brad

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    if you don't want to hassle making a fixture, cycleworks rents them.
    I have a cylinder from Stagehand (the circlip incident) that I had planned on making into a drill fixture, but once they became available for rent, I peter'd out.
    Just no point anymore.
    #17
  18. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    An interchangable spigot is probably the easiest way. You might be able to have a 97mm spigot on one side and a 99mm on the other side and flip the jig over.
    It is very do-able to drill by hand. If you are skilled and lucky, the hole (and repaired stud) are nice and square. If you have an off-day, or marginal skills, the stud is wonky. I've seen poorly repaired studs fail and then you have one and only one chance to re-repair it. For the average or below-average home mechanic, it's better to have help, and the drilling jig probably boosts the chance of success.


    True that, but some like the idea of making their own tools.
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  19. disston

    disston ShadeTreeExpert

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    Thanks Bill, the description of drilling by hand is exactly what I thought it was. Also like your idea of one spigot on each side.

    But here's a thing. Do you really need to use the spigot to center the tool? There should only be one thread hole to repair? Most of the time I think. So use the good threads to center the tool, no spigot. Might/might not work?
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  20. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Probably not, but the spigot provides an absolute reference point and a higher degree of accuracy. In the worst-case situation you have two or more holes poorly hand drilled and the centering on them is off, the accurate spigot will be necessary. But you're right, in most cases you can center on what studs are there. In fact, on my first homemade drilling jig the stud holes were oversized so taht there was enough play in the jig to accurately index it to the stud being repaired before it was securely bolted down. No spigot adapter and yiu could only do one stud at a time, btu the price was right, even 30 years ago.
    #20