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125 Crankcase Stuffing?

Discussion in '2-Stroke Machines' started by matt2491, Jun 15, 2022.

  1. parillaguy

    parillaguy vintage+GP racer

    In the 1960s two stroke tuners would 'stuff' crankcases with material to increase the compression ratio. Flywheel holes were filled, etc. However, modern crankcase reed motors don't need an increase in compression. They need flow and if anything extra volume of fuel/oil. In the 1990/2000s Honda RS125/250 tuning included matching the barrel to the cases, smoothing out the bottom end for flow and trying to fit later (bigger volume) reed cages. Looks like your engine was 'tuned' like that.
  2. Toadmeister00

    Toadmeister00 Well-Known Member

    Stuffing still seems to be pretty common in the mx world with case reed motors. This is a friend's KTM 65 bottom end (with an 80cc top end) that was done by PR2. This motor ran the OVRP 4-hour endurance series over a couple of seasons and was a very strong runner on the kart track.

    PR2 65SX bottom end 004 RSZ.jpg PR2 65SX bottom end 005 RSZ.jpg PR2 65SX bottom end 002 RSZ.jpg

    The epoxy work mimics the newer YZ85 cases with the "shelves" covering the crank wheels. s-l1600 RSZ.jpg
    matt2491 likes this.
  3. matt2491

    matt2491 Well-Known Member

    I'd totally do that but I'm leaning towards not re-stuffing the cases, just as I did with the first motor build...
    Toadmeister00 likes this.
  4. matt2491

    matt2491 Well-Known Member

    At the last minute, and perhaps against my better judgement, I decided to re-apply the stuffing in these cases. I figured these cases are somewhat 'experimental' at this point, what with the various mods and repair work that have already been done.

    I used JB Weld. Maybe it's not as good as PRK; we'll see how it holds up over some time.

    I also masked off and sandblasted the intake port and primary crankcase chamber. I believe this will help keep the fuel mix atomized.






    Last edited: Jul 26, 2022
  5. Toadmeister00

    Toadmeister00 Well-Known Member

    Looks good. I think the JB Weld will hold up, it has been used race car intake manifolds and heads forever. I ended up going the same route with my project 4-stroke head, a little JB in the intake port.
    matt2491 likes this.

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