Home Forums Tech Talk How to Split kt100 crankcase?

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    • #46045
      Erich Moorman

      Any pointers out there on how to split the crankcase on a Kt100s?

      If anyone saw my earlier post I need to replace the PTO side of the crank since an incident occurred where my clutch mechanism got hung-up on a dropped chain and bent the crankshaft.

    • #46052
      Dan Brown

      You need to really consider taking it to a shop. You can’t press the crank apart and back together unless you have the proper jigs to align the crank perfectly, and the crank width needs to be set for endplay , so they will need your cases for that anyways. Its not a job for beginners.

    • #46057
      tony zambos

      +1 on Dan’s comments. Plus a shop is going to find any other problems with the engine and fix them. You don’t want to do a crank by yourself and have it blow up due to another problem or assembly error the first time you start it back up. As a reference, you can download manuals from this site. http://www.yamahaownershandbook.com.au/?r=0

      LAD Specialties customer / tony kart / rotax / kt100

    • #46058
      Will McDonough

      I have too broke my pto side crank. I split the case with no problem. But yes you need to take the crank at lest to a shop. No way to do it your self.

    • #46203
      Walt Gifford

      You have to pull the flywheel and coil off first and it takes a special tool to get the nut off and a special puller, a regular puller will ruin it. After that take the case bolts out. Then you need a steel bar that bolts onto the case across the end of the crankshaft to split the cases.

      BTW none of that is necessary if you can straighten the PTO shaft. Just put the starter nut on up to the bent part then grab it with vise grips and bend it straight. Are you sure it’s bent? Sometimes the crank isn’t bent it just slips and can be re-aligned. Is the flywheel side wobbly too?

      Also from another post looks like your clutch gear is welded on from running it in a parking lot and not oiling it? You can get that off and clean the bushing area with a file then polish.

      If you take it to a kart shop they’re going to want you to replace the whole shaft and add crank sleeves new bearings and seals cost you hundreds. If you live near south jersey bring it by the shop and we’ll get it going or at least I can shoot you straight on what’s wrong with it.


      FAA certified jet engine and aircraft technician,
      Nicholson Speedway class champion 2001,
      Yamaha KT100 Service Center,
      41 years karting experience

    • #46292
      Erich Moorman

      Thanks guys. Hadnt revisited since I posted. The whole crank assembly is solid, the portion that bent resides from the clutch gear outwards towards the starter nut. I tried explaining how i best think it happened as the chain dropped, it makes sense to me since I cant think of any other way around it.


      I ordered a used crank (both sides,piston, etc) from ebay for cheap so that way if I had managed to open it up and see more broken bits I could reuse these old bits, if those parts are junk, well I just purchased some expensive paper weights. If i take it to the guys up north “Franklin Motorsports” in New Berlin, WI and they will cost me hundreds I may as well buy a used inexpensive replacement. I would like to do all the work myself to cut costs. I have access to lathes, presses, the works, but am willing to send it to those guys but I dont wanna put too much $$$ into the kart. I realize the tolerances are TIGHT which is my only concern.

      I know ill add a 3rd bearing support from here on out.

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