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
    #1
  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 We can't stop here, this is bat country!!

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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.
    #6
  7. Airhead Wrangler

    Airhead Wrangler Long timer

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

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

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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 Long timer

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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.
    #10
  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
  12. Rvleugel

    Rvleugel Adventurer

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    My R100GS has a 10 stamped into each jug, left has a B crossed out with a C next to it, right has a B. Is this common to have 2 slightly different sized bores on the one bike?
    #12
  13. mark1305

    mark1305 Old Enough To Know Better

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    Ducati also used the A, B, C on cylinder and piston, at least on the 2 valve "rubber band" motors like the ones I had. As mentioned, they are standard bores and like most machining, finished dimensions vary within a range. To simplify assembly and ensure best piston fit the range of tolerances was assigned letters for pistons and cylinders. So the assembly line workers didn't have to measure and pick through the parts to get the right clearances, they just had to put an A into an A and so forth. This is basically a summation of what was said above with the reasoning behind the system.

    I'm trying to remember if my Ducati 900 engines had different cylinder/piston combos. I think one might have. The differences between the codes is not enough to affect balance between cylinders, but just enough to impact piston clearance if not matched for each individual cylinder.

    I just double checked my 83 R80 ST and both barrels are marked 80 and B (the left cylinder is actually a replacement Rob Farmer supplied me with when the original suffered Nikasil failure. I confirmed my letter codes and he matched it with some he had on a shelf).
    #13
  14. halflive

    halflive Been here awhile

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    The A-B-C are tolerances to match the pistons and the cylinders when new in the factory. Nothing to do with overbore. The stamped number in the base are iron liners, 50, 60, 75, 80, 90, 10. The raised numbers are Nicasil cylinders aka 80 and 10.
    #14
  15. Rvleugel

    Rvleugel Adventurer

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    Cool, thanks! Is there any info out there regarding the different letters and numbers strewn around the bike? The vin, frame and engine number are obvious, but what about the others?
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  16. tlub

    tlub Long timer

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    If they are cast into the surface, they are likely mold or cast numbers, of interest and relevant to the foundry, but not us. If they are stamped, they are post-casting and possibly relevant to us, such as this.
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  17. tsADV

    tsADV Been here awhile

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    And, of course, every cast iron lined cylinder stamped 6, 7, 8, 9 or 1 - be it A, B or C original standard size - may have been bored out to the next (or second over) size piston size. The R75 may even have been bored out to any R80 sized pistons.

    If you don't know the history of your bike, and want to know what capacity the engine currently has, you also need to check the numbers stamped on the crown of the pistons.
    #17
  18. halflive

    halflive Been here awhile

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    The post 1980 cylinders with 80 and 10 cast in, laying on the surface are relevant to us. The A-B-C markings do not matter, unless you somehow know to obtain a batch of NOS unmatched cylinders an pistons.

    I would measure the bore diameter. You are a bit on the conservative side. It is possible to bore the cylinders of the /5 to 900cc. Kaiser used R60/5 cylinders for that because they seemed to have thicker linings.
    All engine casing from summer 1975 and later accept 1000cc cylinders but 1050 is also possible.
    #18
  19. georgesgiralt

    georgesgiralt Been here awhile

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    Hello !
    You've forgot the R45~R65 which have a 45 or 65 marking on their jugs.
    I've just bought from BMW a new pair of jugs for my '82 R65. One came in "A" size, the second, in "B" size. So you'd better buy the jugs first and, then, order the correct pistons for the jugs you got. And order them at the same time in order to ensure you got the same weight class ... (there will still be a difference in weight, though, mine are 2.5 g apart )
    These new parts are made by Mahle...
    Just my 2ยข
    #19