12 January, 2014

Engine Assembly

I got the engine assembled for the project bike.  It is a Yamaha GT80 base, which is a 80cc two-stroke with 7-ports and reed valves.  Very solid runner used in a previous bike for a short time, I had aleady fit a new piston and ring, and honed the cylinder lightly.  

For this bike, i milled a bit off the cylinder head to give a tighter squish area.  I also followed some info I found in an old Yamaha tuning manual by filing a small "notch" into the top of the piston where it covers/uncovers the exhaust port, for a slightly longer exhaust duration.  I also cleaned up the intake ports and transfer ports a bit, getting rid of some flash, and putting a radius on the edges.

Lastly, I built a new intake manifold that mounts the rebuilt 20mm carb.  I still need to get some proper case bolts, and cut a few gaskets, but it is assembled and turns over with lots of compression.

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