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Thread: k100, new rings?

  1. #1

    k100, new rings?

    anyone have any knowledge of replacing the rings to increase compression value? Is it worth the trouble? How much could it increase?
    thanks.

  2. #2
    Dances With Sheep GREGFEELER's Avatar
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    Quote Originally Posted by rwik81 View Post
    anyone have any knowledge of replacing the rings to increase compression value? Is it worth the trouble? How much could it increase?
    thanks.
    Well, first, I would need more information, like what year K100, how many miles, do you have a confirmed low compression problem, etc.? The classic K-bikes are famous for rings and pistons going 250,000 to 500,000 miles, so yours is an odd question. Thanks!
    Greg Feeler
    Ambassador & amateur K-Bike collector, it seems
    1972 R75/5, 1990 K75, 1990 K1, 1992 K75S, 2003 K1200RS

  3. #3

    right

    it is all true,
    but riders don't care about compression, they just....................ride
    but after 500,000 will rings help? by how much?

  4. #4
    Registered User barryg's Avatar
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    For brick engines; at 500,000 miles it may be time for the engine to be rebuilt. Well, maybe somewhere between 500,000 and 1,000,000. Just sayin.

  5. #5
    Registered User Rinty's Avatar
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    Quote Originally Posted by GREGFEELER View Post
    ...do you have a confirmed low compression problem, etc.?....
    Yes, you'd want to do a leak down / compression test before you did any major work on it.

    Is it worth the trouble? ....rwik81
    If the compression is, in fact, low, it may be more cost effective to replace it with a later, low mileage, unit.
    Last edited by Rinty; 03-16-2020 at 08:50 PM.
    Rinty

  6. #6
    Registered User GTRider's Avatar
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    Quote Originally Posted by rwik81 View Post
    anyone have any knowledge of replacing the rings to increase compression value? Is it worth the trouble? How much could it increase?
    thanks.
    More information is needed:

    1. What year and model, and how many miles on the motor.

    2. What is the current compression reading for the motor?

    3. What symptoms is the motor exhibiting, that you feel indicate a need for service?

    If you furnish this info you’re more likely to get useful and accurate responses to your questions. As pointed out, brick-K bikes normally go 200k+ miles before needing attention to valves, which are likely to need attention long before rings would. And if the bike needs valve work it is probably less expensive to buy a used motor, or even a used k-bike, for less money than going completely through the cylinder head. The last used brick-k engines I saw marketed sold for around $500 and that was a long time ago.

    A noted west-coast long distance rider had a K100RS in for a valve job at 275k miles, after it began to exhibit difficulty in starting. While the head was being redone, the rods, crank, and pistons were removed for inspection. Everything measured within BMW’s published tolerances and no service required—the cross-hatching on the Nikasil cylinders could still be seen. The engine was reassembled with new bearing shells—just because they had been taken apart—and put back into service with a rebuilt cylinder head, likely good for another 275k.

    It’s common to see brick-k bikes go that sort of distance, needing only valve clearance checks every 36k or so, and customary replacement of the rear main seal and clutch o-ring around 65k-75k miles, an interval that can be greatly extended by replacing the OEM buna-n o-ring with a Viton o-ring.

    Gas in the top? Oil in the bottom? It’s a brick-k: GO RIDE!

    Best,
    DeVern
    DGerber
    1983 R80ST — 1984 R80 G/S-PD — 2004 K1200GT w/Hannigan S/C — 2010 K1300GT — 2018 R1200GS
    BMWMOA#52184, AMA#271542, IBA#138

  7. #7
    The simple answer is: Assuming the valves are sound, new rings could bring compression back up to OEM factory specification. No more, and probably not a lot less.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  8. #8
    Registered User
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    Given the value of the old K100s these days, I'd have a hard time spending any kind of money on rebuilding an engine in one. Of course given their reputation for longevity, I also have a hard time believing yours really needs the work. If you've managed to put in the several hundred thousand miles that it typically takes to show some engine wear, it may well be time to just pick up another one.

    Hopefully you're not being mislead by some blue exhaust smoke at start-up?

  9. #9

    hall effect sensor

    yep, your right, my neighbor sold me some old ones 2 fer a bit.

    by the end of this anyone thinkin of duplicatin the way and really just wanna ryd will just go out and buy something that works

    but here is start to rebuild, hope pic uploads otherwise will have to try again.
    Attached Images Attached Images

  10. #10

    Rings

    If you’re just looking for more power rings won’t accomplish that. Buy a bike with a bigger engine. Low compression is another matter and is more likely worn/out of adjustment valves.

  11. #11

    thats an idea!

    I took it apart,
    per my manual
    measured piston ring gap
    old ring new ring
    top 0.017" 0.014
    middle 0.016 0.014
    oil 0.019 0.013

    spec. 0.005"

    looks like new rings wont do alot of good
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  12. #12
    Dances With Sheep GREGFEELER's Avatar
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    Quote Originally Posted by rwik81 View Post
    I took it apart,
    per my manual
    measured piston ring gap
    old ring new ring
    top 0.017" 0.014
    middle 0.016 0.014
    oil 0.019 0.013

    spec. 0.005"

    looks like new rings wont do alot of good


    As expected. And, just think that the last person to look inside your cylinders was some dude at the factory in Germany a very long time ago.
    Greg Feeler
    Ambassador & amateur K-Bike collector, it seems
    1972 R75/5, 1990 K75, 1990 K1, 1992 K75S, 2003 K1200RS

  13. #13

    k100 oil vent hose

    hey everyone, happy trails
    I made this awhile back and have several extra I can give away.
    ..............
    if noone wants one then more for me, if lots want some(which I don't thik will be case, I'll have to figure out)

    send email to bmw@dslextreme.com with your address...........
    I supppose first (maybe only ) response will get it.
    take care during the covid crisis.
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  14. #14
    Bluenoser
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    Those bores look pretty good with cross hatching still visible. Don't know how the rest of the bike is, but seeing as you've come this far it would certainly be worth putting new rings in, if the rest of the bike justified it. Without knowing the compression numbers and mileage on the engine, hard to tell what is the best for your situation.
    1995 R100Rt with Kenna Sidecar, 1986 K100RT

  15. #15

    bore and piston gap

    I tried the new ring thing. stock new rings from factory are out of tolerance, see above.

    this week, piston bore and piston side gap
    @66.89mm, its a grade A which can be between 66.966 & 67.005mm
    unfortunately,
    piston clearance is 0.013" max allowed 0.0006-0.0015"

    apparently the piston wore,
    it might be surmised that little extra gap could cause a "knocking" as the rpm increases leading to more vibration at higher speeds?
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