Jug/cylinder markings

Discussion in 'Airheads' started by TDL028, Aug 6, 2014.

  1. TDL028

    TDL028 man of leisure

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    Howdey ADV,

    just a quick question here. If my jugs are marked "B" and "10" then I would have R100 cylinders on my r80..correct?

    thanks!
    tom
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  2. Rob Farmer

    Rob Farmer Long timer

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    Yep!
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  3. TDL028

    TDL028 man of leisure

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    sweeeet.. thanks dude!
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  4. One Less Harley

    One Less Harley OH.THAT'S GONNA HURT

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    cylinders come in three different grades, A,B and C (smallest to largest), each are matched to one of three different size pistons.
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  5. drhach

    drhach gorillamanufacturing.com

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    So, I should see a "9" on my R90 cylinders? Are the "A,B,C" markings overbore markings or cylinders that were matched at the factory?
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  6. One Less Harley

    One Less Harley OH.THAT'S GONNA HURT

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    they aren't over bore numbers, but just correspond to a specific factory sizing, bores were matched to the appropriate pistons. Check your workshop manual for specific sizes. Chilton gives the specs, which I'm not going to post up here. Cylinders are marked A,B or C, pistons are just stamped with the size on top and the workshop manual assigns the A,B, C designation to the three different sizes. You will want to match cylinders to the corresponding pistons for the best piston to bore clearance. For nickasil it is .03-.04 mm NEW and a max of .08mm.
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  7. Airhead Wrangler

    Airhead Wrangler Adios Mexico

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    It almost sounds like you've had recent experience with this. :D
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  8. drhach

    drhach gorillamanufacturing.com

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    so I have a B stamped on mine and the on a pad there is a 30 with 03 under it. I assume that is an upside down 30. Does the 30 denote R90?
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  9. Airhead Wrangler

    Airhead Wrangler Adios Mexico

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    R90 just has a '9', R80 an '8', R100 a '10', etc.
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  10. bpeckm

    bpeckm Grin!

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    We're talking two different subjects, methinks...

    The "80" "90" and "10" are cast onto the top of the jugs, visible from above when looking at the base of the jugs. I THINK, but not certain, that the early versions had a "6", "8", "9" versus later "80" etc. My 1983 R80 ST has a very clearly stamped "80".

    [​IMG]

    The "a". "b". "c" are markings on the cylinder and piston itself, so that it matches as close as possible wi


    th the range of bores within that engine size.
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  11. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Not sure it was explained clearly enough about the A,B and C. Those aren't over-bores - they're the standard bore - it's just that when the parts were machined some come out a little larger or smaller than the target size. In any manufacturing and machining process tolerances are given. Parts can be within that target size and be acceptable. Not sure what they were in this case - but let's say it was plus or minus a tenth of a millimeter. That means that there could be a difference of .2mm from the smallest to the largest.

    Other manufacturers didn't necessarily pay attention to this and assembled the parts without matching for best fit. What could happen is a cylinder on the large side mated with a piston on the small side - could make for a rattly engine right off the line.
    #11