TM top end rebuild

[Steve Phaneuf]

I want to put a new ring and piston in, but I've never done one before. What should I be looking for, Where do I find the piston size? Do I need to replace gaskets also?

[Dale Fagg]

Steve,

It is an easy process, drain the water and remove the power valve cover and linkage. You may have to remove the coil and anything else connected to the cylinder. I took a 12mm box end wrench and ground the edges down on a bench grinder to fit the cylinder nuts. Remove the cylinder nuts and raise the cylinder off of the piston. You can leave the head on the cylinder or remove it if you want,I normally remove it. Once you have the cylinder off, place a clean cloth around the piston rod to prevent anything from falling into the lower portion of the motor. The cylinder gasket will not have to be replaced if it doesn't show signs of tearing. If you replace it, make sure to measure the thickness. You will have to remove the circlips from the piston to allow the wrist pin to be pushed through it. I take a 3/8" socket extension and push the wrist-pin out of the piston with both hands. One hand pushing on the extension and wrist-pin, and the other hand pushing on the piston opposite the extension. Keep in mind the piston rod should not have any force applied to it. The new piston will come with a new wrist-pin, ring, and circlips. I would replace the upper bearing also, just for good measure. When installing the new parts, always lube everything with a non-synthetic motor oil. This will allow the new parts to set, during the break-in period. Prior to installing the cylinder, I use scothbrite and WD40 to rough up my nichosil cylinder, and clean all of the ports. Afterwards, I spray brake cleaner through it and compressed air. Before assembly, coat the cylinder walls with non-synthetic motor oil. The TM piston is a 53.94mm, and can be purchased through any TM dealer. I did purchase a 53.96 recently, as my cylinder has two seasons of racing and is slightly worn.

Dale 4E