cylinder base gasket

Discussion in 'Airheads' started by picinisco, Nov 15, 2013.

  1. picinisco

    picinisco Scottish Transplant

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    I am confused. Although the basket case that I bought to build my "GS" was a 1972, the engine that came with it more and more appears to be a 76 R75/6. I bought cylinder base gaskets for the rebuild but they appear to be too small in the bore. Now when relooking at the microfiches, it would appear the the gaskets are good only up to 1975 and that nothing is available after that date. Is there actually no base gasket used on the 1976.
    #1
  2. Horsehockey

    Horsehockey A GPS? Huh?

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  3. picinisco

    picinisco Scottish Transplant

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    #3
  4. tlub

    tlub Long timer

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    Normally, no gasket was used after Sept 1975 (early 76s). Around Jan of 76 they added an o-ring to the base. But you could get a thick base gasket for any of the models to reduce compression and allow lower octane fuel. This was used a lot on the R60/6/7s, as with the cam timing they had, pinging was a lot more of a problem. It only partially helped.
    #4
  5. disston

    disston ShadeTreeExpert

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    The number on the frame is how the bike is registered and the number that appears on the title. There is another number on the engine. If it is the same number as the one on the frame then you have matching numbers. If it is different then you have a different engine which is still legal. The number on the engine is stamped into the engine block above the oil dipstick hole.

    http://realoem.com/bmw/

    Go to the above site and find the motorcycle pages then enter the engine number. It will tell you when the engine was built. 1976 bikes and the engines with bigger spigots start in Sept. 1975.
    #5
  6. picinisco

    picinisco Scottish Transplant

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    In the case of the bike I am building, the frame is an1978 R100. The donor bike is a 1972 R75/5 but as the engine build progresses, it became apparent that the engine is a 1976 R75 and as such there is no engine number stamped on it which would have helped me tremendously at the beginning. But this makes it all the more interesting as little discoveries add to the allure. For example, the valve seats are hardenened inserts. Woo hoo
    #6
  7. tlub

    tlub Long timer

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    My R75/5 is a bitsa. I foolishly sold the original case when I put a /7 engine in it to get the updated electrics, cam seal, etc. But the State of Wisconsin says that for pre-81 bikes (when 17 digit VINs were used) the engine number is the registration. From 1981 and later, the frame number is used. I have no idea what would happen with an 81 frame and a pre-81 engine. Confusingly, my R75/5 is listed as a 1972 R75/5 but the serial number tracks to a 1977 bike. But WI says it is still a 1972. I did not understand why then (1983, when I did it) and still don't. But the frame number is not always the registration number. BTW, when I moved to DE for a few years (1988-1990), they had the same system.
    #7
  8. disston

    disston ShadeTreeExpert

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    Thanks tlub, the fact that different states do this differently I guess should not surprise me. I'm in Maryland. I guess we should count our lucky stars we are not in California, hey!
    #8