125 Crankcase Stuffing?

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

  1. matt2491

    matt2491 Well-Known Member

    I'm rebuilding an '04 RS125 motor. I have everything stripped down, cleaned, and ready to reassemble with new bearings, seals, etc.

    Long story short, someone had stuffed the cases in the past. The stuffing was starting to come loose though, which is half the reason I'm rebuilding this particular motor, as the last thing I need is a nice chunk of epoxy popping off at 13k RPMs.

    So I knocked out all the epoxy only to reveal that whoever applied it had scored up the aluminum in an attempt for it to stick.

    The question is, do I just leave it like this or do I try to smooth it up with a dremel?

    IMG_0759.JPG
     
  2. Toadmeister00

    Toadmeister00 Well-Known Member

    That's a tough call. I would probably just leave it as is, as not to add any more crankcase volume. I'm guessing you don't want to re-epoxy them? I had very good luck with Goodson PRK-99 epoxy in several cases. They held up for many seasons, even with running lots of U4.4 and MRXo2 through them. epoxied cases1 - Resize.jpg
     
  3. Robin172

    Robin172 Well-Known Member

    As a matter of interest why would you fill the transfers? And is that a hole for a cylinder stud right in the middle of the transfer port?
     
  4. Toadmeister00

    Toadmeister00 Well-Known Member

    That hole is for lubrication to the crank bearings.

    The transfers aren't actually filled, the epoxy just "ramps up" underneath the transfers to take some of the dead space out of the cases.
     
    Last edited: Jun 16, 2022
  5. matt2491

    matt2491 Well-Known Member

    I've just never done it. I'm sure it can be done properly, but it seems I only ever see it failing.
     
  6. Robin172

    Robin172 Well-Known Member

    I'm assuming it has a reed valve, does the intake go into the crankcases on those engines or is via the cylinder?
     
  7. Toadmeister00

    Toadmeister00 Well-Known Member

    The cases in that pic are KTM 85/105, they are case reed.
     
  8. Robin172

    Robin172 Well-Known Member

    What about the RS?
     
  9. Toadmeister00

    Toadmeister00 Well-Known Member

    Case reed, as well.
     
  10. Robin172

    Robin172 Well-Known Member

    It's interesting that an engine with direct feed to the crankcase would need those holes for bearing lubrication. I suppose it lets extra oil leach off to the mains as the charge does though the transfer port.

    As to the OP's question regarding smoothing it out, with that bloody great hole there I don't think doing that is going to do anything to reduce turbulence as the mixture passes though the port.
     
  11. matt2491

    matt2491 Well-Known Member

    Here's a pic of some of the stuffing before I removed it:

    IMG_9647-2.jpg
     
  12. backho

    backho Well-Known Member

    Obviously the purpose of the roughed up surfaces is to give a “tooth” for the epoxy to bite into. If you’re going to add new epoxy then I would suggest heating the cases to purge any latent oil and use a carbide burr to expose some fresh surface for the epoxy. You’re probably splitting the cases on a regular basis so you can always check the integrity of the epoxy.
     
    TZ250lover likes this.
  13. matt2491

    matt2491 Well-Known Member

    If I leave these cases alone, will they flow any worse than stock due to the roughed up aluminum or nah?
     
  14. Robin172

    Robin172 Well-Known Member

     
  15. Toadmeister00

    Toadmeister00 Well-Known Member

    I think I would just leave them alone. Removing material to smooth things out (adding crankcase volume) may be worse for performance than leaving them as-is.
     
  16. matt2491

    matt2491 Well-Known Member

    To conclude this thread, I ended up leaving the cases alone and just built the motor as is. I did place the cylinder on each case half to see how the ports aligned. Looked good to me. Seems the factory flow design is pretty optimized to begin with. I think the only benefit to stuffing would be volume related.

    IMG_0767.JPG
     
  17. matt2491

    matt2491 Well-Known Member

    Back with another set of cases (same ones I repaired in this thread). It seems like every motor I split open is or has been stuffed at some point in the past. This particular set of cases also has some interesting shaping work done in the intake:

    IMG_0905.JPG

    Before epoxy removal:
    IMG_0899.JPG

    After epoxy removal:
    IMG_0906.JPG

    Once again I am debating whether to re-apply the epoxy or leave the cases alone...

    And does anyone have any idea why someone carved those 'channels' into the intake walls?
     
  18. Robin172

    Robin172 Well-Known Member

    What does the reed block look like?
     
  19. matt2491

    matt2491 Well-Known Member

    Factory original reed block, but the bike is new to me, so who knows what aftermarket reed block may have been in it in the past.

    IMG_0907.JPG
     
  20. Toadmeister00

    Toadmeister00 Well-Known Member

    Matt, if you decide to re-epoxy those cases, I'd split an order of PRK with you. It's not so much the money, it's just that I'd never use it up before the 2 year shelf life window. I'm working on a couple of mx heads that will need a little epoxy in the intake ports.
     

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