Dismantle the crank case?

Discussion in '2-Stroke Engines' started by Rayde, Apr 19, 2011.

  1. Rayde

    Rayde New Member

    I need to pull apart my crank case to replace the clutch shaft. So far, i've managed to separate the case only slightly, and damaged the gasket in the process. I've removed everything from the clutch shaft down to the shaft itself. The crank gear is off, magneto loop is off, but not the magnet. All screws and connecting hardware are out.

    But, i cannot seem to pull the case apart. Any ideas why not?

  2. MikeJ

    MikeJ Member

    Hi Rayde -

    I will offer the first response... I did the very same thing you are doing and had the very same problem. The key phrase you used is "only slightly". In my predicament, the crankcase bearing was getting hung up on the internal crankshaft bearing fitting.

    To overcome, I heated the crankcase area around the crankshaft using a heat gun (or a really hot hair dryer). I don't recommend an open flame propane torch if the engine has had fuel run through it unless you rinse it out with gasoline and take pains to dry it out of all vapors.

    The crankcase, made of aluminum, expands at a rate twice that of steel. If you get the crankcase hot enough (but not so hot to damage the rubber seals around the crankshaft), it will open the crankcase bearing fitting enough that you could tap it apart using a soft mallet or block of wood. Don't use a steel hammer.

    Once apart, you will see that the crankshaft bearing is a press fit into a crankcase housing fitting. This fitting is what has to be expanded with heat.

    Order spare gaskets from a dealer. Gaskets are really, really thin. It is easy to mistake a double layer when you think you have only one gasket.

    Keep in mind that if you use heat to disassemble, you will need heat to assemble. (That housing fitting locks the crankshaft into a fixed position, else the crankshaft will wobble when running). I tried cooling the crankshaft in my engine, but I don't think that did much good. Heating the crankcase to "too hot to handle but below boiling point of water" worked for me.

    I did this and thought I destroyed the engine. But I assembled it and have since run it over 1,200 miles.

    I hope this helps.

  3. Rayde

    Rayde New Member

    This is very Helpful. Only thing i have access to here is a hairdryer, perhaps that would work...

    How difficult will it be to reassemble this? Assuming this will work, i have to reheat the crankcase bearing mount while apart, slide on the gasket, and try to get the crank bearing to seat properly back in the crankcase bearing mount? Also trying not to damage the gasket, make sure all holes are aligned, that the new clutch shaft seats correctly, etc...

    Are the clutch bears press fit as well? I think i may have to replace those, they are very stiff to turn.
  4. goodtime65

    goodtime65 Member

    You do not have to split the case to remove the clutch shaft. If you remove the small drive gear you can tap on the end of the shaft and the whole clutch and shaft will come out as a unit
  5. Rayde

    Rayde New Member

    I thought it should as well, but mine wont. Or, it seems it doesnt want to... i have to split it now though anyway, to replace the gasket.
  6. MikeJ

    MikeJ Member

    Rayde -

    Reassembling is a little tricky, but not impossible. If I can do it, so can you. Heat is your friend during disassembly and reassembly. Use reasonable care. If you tear up a gasket during assembly, try again, using another new gasket. I purchased four of them; they are cheap and I usually sacrifice at least one during the learning process. I now have a couple of spares for future use.

    Setting the part with the crankshaft in some books or 2x4s to keep it oriented the way you can work with it is usually very helpful.
  7. Al.Fisherman

    Al.Fisherman Active Member

  8. Rayde

    Rayde New Member

  9. motorpsycho

    motorpsycho Active Member

    here's a really dumb question....
    you did take the cylinder off before you tried to split the case right?
  10. Rayde

    Rayde New Member

    Yes indeed. I'm down to the bottom end.
  11. Rayde

    Rayde New Member


    I managed to split the case, using MikeJ's heat tip, thank you. However now it appears that my clutch shaft is fine, but the bearings are really bad.

  12. Lazieboy

    Lazieboy Member


    Here's a question for you guys who have taken crank case it apart. my 66cc grubee When manually turning crank it binds up on part of the cycle hard to turn,then it goes easy, etc. Took head off and piston out but still the same. Excited to hear ideas before opening it. Thanks in advance.:cool:
  13. goodtime65

    goodtime65 Member

    seal instalation

    The hardest part I found at first when putting the engine back together was the seals. The little spring seamed to always pop off of the seal lip. Now I put the seals in after the casings are back together. What ways do you guys use for instaling the seals
  14. Rayde

    Rayde New Member

    sounds similar to my original problem, that i traced back to a bad bearing. Mine was clutch problems, but it's quite possible that you have a bad crank bearing.
  15. Lazieboy

    Lazieboy Member


    Whell did'nt crack case. but flushed it out w/WD40:whistling: got some debris and metal flakes out. seems smooth now:sweatdrop:. while putting piston back togather noticed top ring cracked and fell apart, guess this explains why there's a huge gash in cyl. wall and piston head looks like the moon. I just need to get it back on the rode.:veryangry:
  16. GearNut

    GearNut Active Member

    Any of the following that is the same size as the outside of the seal and will not hit the lip of the seal:
    Deep well socket, Sprinkler pipe, Gas pipe, Medicine bottle, Anything similar.
    Always oil the seal well inside and out before installing it.
  17. Lazieboy

    Lazieboy Member

    Crack the case

    Did you have to remove the chain sprocket. If so how. could'nt get mine out. or the Sm. gear by clutch assembly. is this necessary to crack case. need more input please. :bowdown:
  18. GearNut

    GearNut Active Member

    You need to use the tool that is typically supplied with the engine kits.
    Shown in upper left hand corner:
  19. Lazieboy

    Lazieboy Member