Lambretta Engine Work




Specialized Tools




Kickstart Disassembly

One of the most important parts of a well operating engine is a good piston and bore to keep compression high and transfer that power to the back wheel. Basic tolerances between a piston and a bore are typically 0.2mm. If you remove your barrel and find deep scoring on the piston and bore it is definitely time for a new piston. Pistons cost between $45 and $70 depending on what bike you are buying for. Whenever a new piston is installed it is important to rebore the barrel to the next oversize if there is major scoring of the surface, or at least hone it to be sure that the wear ridge at the top is removed. The one pictured is from a GP125 motor. The following images show the piston replacement after removal of the old barrel and piston, and in these images the engine is out of the frame but it is not a requirement.

  • A piston kit
  • A rebored or honed barrel
  • Some two stroke oil
  • A new barrel base and head gasket
  • Circlip pliers
  • Possibly a new small end bearing (optional)
  • A set of feeler gauges
  • A 14mm socket and driver

The shot above shows an SX200 chaincase with the kickstart in place. The way the system works is that there is a metal guide held in place by three bolts which retracts a small "shoe" plunger in the end of the kickstart shaft when the kickstart is at rest. When pushed the guide allows the springloaded shoe to extend which messhes with teeth in the face of the first gear cog. Only one of these bolts is fully accessible when the kickstart is at rest.

Start by removing the bolt on the guide that you can see without moving the kickstart.

Once the single bolt you can see is removed use a block of wood to wedge under the kickstart on the outside of the casing. This will allow the heads of the other bolts to be exposed.

Remove the remaining two bolts and the metal guide will come away from the chaincase. Be sure the block stays in place because if it slips the shoe plunger will return very quickly.

Once the guide is removed carefully remove the block and let the plunger & show return to the previous location.

Now flip the casing over and remove the kickstart from the spline. Before removing it is a good idea to mark the shaft at the point where the split in the kickstart pinch is so that you can put it back in the same place. While removing it make sure you have a helper holding the shoe so that it doesn't suddenly spring back.

Use circlip pliers to remove the single clip over the kickstart spline. Also remove the single small washer beneath it.

The spline should now be able to be lightly tapped through the casing.

Remove the oil seal and replace it when rebuilding. The easiest method is to pry it out with a screwdriver.

Remove the spring by pulling the bottom end pin out of the hole in the casing (arrowed).

There is also a brass bushing under the oil seal which can be replaced if really worn, but I skipped that process on this chaincase.