Lambretta Engine Work
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.
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
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
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
Once the guide is removed
carefully remove the block and let the plunger & show return to the
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
Remove the spring by pulling
the bottom end pin out of the hole in the casing (arrowed).