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Thread: New rings for a 1980 R100T

  1. #1

    New rings for a 1980 R100T

    MOA forum,
    I need your advice again.
    1980 R100T with 97,000. Been sitting 15 years, PO kept adjusting carbs until it would not run.
    I have pretty much taken everything apart except the Transmission and crank and connecting rods. My
    Question is regarding the pistons and rings and seating the rings. I got the machine to fire and run for a while before taking it apart. Ran with lots of smoke. I had rebuild the cards and understand they will need to be adjusted. Choke and throttle cable are stretched and worn and bent. At that time I attributed the smoke to the large amounts of oil I put in the heads so I could turn it over by hand. It has a two in one exhaust so I could not tell if it was all coming from one or both cylinders.

    Compression left cylinder was 115 psi and right cylinder was 125 psi. Leak down test indicated both heads losing almost 20 % with most of if not all of the leakage back through the crank case and none via the intake or exhaust valves. That told me rings need replacement. The machine has iron sleeves and you can see the cross hatch in the cylinder below where the rings would touch. When I took it apart, on both sides the gap on the top two rings were almost in alignment and the top and bottom on the oil scraper were almost in alignment also. Inside the walls it looks polished. Not too much carbon on piston and valves and head from other pictures I have seen.

    My concern is that after I hone the cylinder, and new rings and reassemble I will not do justice to seating the rings while I adjust the cards to get the bike to run correctly.

    Other than that and a few minor opportunities, the rebuild is going well. I cannot believe how much the various parts and rings and gaskets and washers and seals and stuff cost and needs to be renewed. The frame should be painted next week and then we start putting the bits back together.

  2. #2
    I may not understand, but if that were my bike I would tune and balance the carbs, and do an igniton tune up (points and timing) before doing the rings. Then I would be ready to ride and break in the rings per dogma when the cylinders and heads were back on the bike. (Paul)
    Last edited by PGlaves; 01-25-2017 at 05:52 AM.
    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

  3. #3

    rings seating

    I am incline to agree, Ii am putting it back together and will re-do rings after carbs are adjusted,
    Thanks for your comments.

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