The KTM300 Thread

Discussion in 'Thumpers' started by GasGas300, Jan 11, 2010.

  1. DougZ73

    DougZ73 Fading off.........

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    Do they have piston ring compressors for two stroke motorcycle motors?? I have used rings compressors when rebuilding four strokes, but never heard of one for a two stroke. The KTM manual I have never mentioned one either.

    This is the third two stroke top end I have done, and never used one. Not sure how you would get it out?? Usual method is to hold rings with hand, and then lower cylinder down onto piston, while squeezing the rings.

    Its not like a four stroke, where the piston and connecting rod goes in from top of head, and gets bolted around crank journal. In two stroke, connecting rod does not come out unless you take whole motor apart.

    Maybe I am missing something. :huh
  2. wayno

    wayno Long timer

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    Ive taken 2 stroke apart for craxcked head bdfor to put new one on and I had no ring compressor then but was back in 80's
  3. HellSickle

    HellSickle Scone Rider

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    2 or 4 stroke, when doing top ends I generally just pull the cylinder. Ring compressors don't care if it's a 2 or 4 stroke.

    With that said, I've never used a ring compressor. I've always well oiled things and jiggered the rings thru the taper at the bottom of the cylinder. Because of the requirement to align the rings with the pins on the piston, a 2 stroke is usually more difficult. I'll probably be visiting Harbor Freight to get a ring compressor for my upcoming 300 top end job.

    The most difficult top end I ever did was a V4 honda. The cylinder banks were cast into the upper case. You had to align all the pistons as you brought the upper case & cylinder down. After that project, I vowed never to own a bike with more than 2 cylinders.

    Currently shopping for a KTM 950/990..... :D
  4. DougZ73

    DougZ73 Fading off.........

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    Take a video of how you do the 300 top end, with a ring compressor. I'd am really interested in how you'd go about it.

    The only way I could see you using a ring compressor, on of these motors, is to use it, to insert the piston, down into the cylinder, from the topside, push it down enough to expose just the wrist pin hole, and then try to put the combo down over the connecting rod, and insert the wrist pin and clip(s), that way, through the connecting rod. Even if that is even possible with motor in bike, I am not sure. Somehow, I doubt it. I know I barely had room to get cylinder on from top, while trying to compress the rings with my hand, and slide down from above, the normal way I know it and have done twice already.
  5. HellSickle

    HellSickle Scone Rider

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    Actually, I have done a variation of this on 2S before. I've installed the piston into the bottom of the cylinder, then mounted the piston onto the connecting rod. This allows you to carefully put the piston into the cylinder while it's sitting on the bench. It does make it awkward trying to get the pin clip into place. Having a helper to hold the cylinder in place is useful.

    I think I see the issue with the ring compressor. There's not enough space below the cylinder to get it in and out of there. What's really needed is a half-height ring compressor. I'm wondering if just a hose clamp couldn't be used on the 2S?
  6. DougZ73

    DougZ73 Fading off.........

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    Ah ha..you now see the issue...which is why typical SOP is just to use your hand. And that method has worked or me a couple times before.

    At the end of the day, it probably was my fault...as I had to take the cylinder off three times to change the gaskets and get the proper Z setting. What a PIA. Once I got the proper gasket on there, the rings/piston gave me a hell of a time going back into the cylinder. Although it did seem OK, once I finally got it.

    This time, I'll be pulling the motor for sure. The nice thing about these two strokes..they make it pretty simple to pull motor. :D
  7. Just John

    Just John Been here awhile

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    What do you suspect went wrong ?
    I don't see anything gained by pulling the motor out.
  8. DougZ73

    DougZ73 Fading off.........

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    I suspect the rings were not seated correctly, when I finally got the cylinder on. Potentially not being lined up on the locating pin like they should have been..at least one anyway. Probably rotated, caught one of the port edges, and broke off. Potentially gauging the cylinder wall. The compression went somewhere, so best case, its just the broken ring, worst case, messed up cylinder wall.

    Pulling the motor will make it easier to get cylinder on correctly, for me anyway. When I did the top end on a YZ125, I did it on bike and had no issues. This motor, I have done out of frame, and had no issue. This last time, motor was in frame, and I had room issues. Not sure why...but I did.

    Also, if I have to send cylinder out to get redone, I'd rather have motor in house, and not out in weather*temp) changes in shed.
  9. DougZ73

    DougZ73 Fading off.........

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    On a side note, I did watch a bunch of vids this morning with the KTM 300 EXC in them, and my bike does sound normal.....you know, when running. :D
  10. RideFreak

    RideFreak Torque Junkie

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    I do the z setting with the rings off, figure out the gaskets and install the rings just prior to final reassembly. I've seen a ring compressor that would work on the 300 (about 1/2" top to bottom) but truthfully once you figure the cyl install out, proper installation takes a couple seconds. Now the piston pin clips are a different story, the stock KTM units are a huge PITA. Why did they go away from the old style that worked with a pair of needle nose plyers.

    Yeah I know, the old ones are still available.

    My hardest cyl install was a VW waterboxer, seperate cyl liners that fit down into a non removable waterjacket that pretty much blocks all access for a mortal like me. :cry
  11. DougZ73

    DougZ73 Fading off.........

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    Damn...that is genius. I should have thought about doing the Z gap setting with out the rings in the piston. That has just changed how I will do top ends forever.

    Probably would have saved the issue I have now. ( bangs head on wall)

    Thanks for the tip RF.
  12. DougZ73

    DougZ73 Fading off.........

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    Found where my compression went.
    [​IMG]

    Not 100% sure what scratched it. Rings seemed to be correct spot and not broken at all. Cylinder looks worse than piston too. ????

    Sent from my DROIDX using Tapatalk
  13. Wallace

    Wallace Seat belt tight babe?

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    Looks like a cold seize. :(:
  14. DougZ73

    DougZ73 Fading off.........

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    Cold seize?? Please define. I am somewhat new to 2T's, and have never heard that term.


    This is piston:

    [​IMG]

    [​IMG]

    other side:

    [​IMG]

    head seemed to be in good shape:

    [​IMG]


    So, what is opinion on best method to get this fixed?? Powerseal USA weld, rebore and Nikasil again??? Eric Gorr Iron sleeve and overbore( that is what I had on YZ125)???
  15. RideFreak

    RideFreak Torque Junkie

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    It looks like something got caught in there, the grooves look pretty deep for just a siezeure. To me it looks like whatever did that caused the ring lands to lock the rings up against the piston resulting in blowby. It that point it's a lit fuse.

    The cyl grooving looks pretty deep, I don't think you'll get away with relining the cyl. I've heard they can can do a weld repair of some types of damage prior to recoating it.
  16. DougZ73

    DougZ73 Fading off.........

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    Yeah, looking at powerseal pricing now. looks like it will be a weld repair, rehone, and new nikasil coating.

    I also just pryed rings off piston. Looked like they were lined up right and pins did not fall out or break off.

    Still not sure what caused the really deep scratches.
  17. RideFreak

    RideFreak Torque Junkie

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    Was the motor open awhile? It almost looks like something came up from the bottom end, possibly something that fell into the motor. The problem with that scenero is the item in question, is it still there, are there more pieces? The fact that the head looks fine sort of goes against that theory. Usally you'll see where gouges and pits develop in the head if there's something bouncing around in there.
  18. Gordy

    Gordy Team Listo

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    Did you drop something in the bottom when you were in there? Old circlip or something???
    It almost looks like something came up through the transfer port. :dunno
  19. Just John

    Just John Been here awhile

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    Piston appears to be scored from one side to the other. Like it was too tight to the bore.
    Or it got very hot very rapidly.

    Was there coolant in the bike ?
    Did you heat cycle it ?
  20. RideFreak

    RideFreak Torque Junkie

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    Beat ya to it by 60 sec :lol3