Cylinders / Pistons

Basics

The 250, 280, and 300 engines all used a common 60mm stroke and the same crankshaft.  Bore sizes and actual displacement are as follows:

250 (72.5mm bore) 247.7cc

280 (76mm bore) 272.2cc

300 (79mm bore) 294.1cc

Each piston will be available in multiple sizes to make the piston-to-cylinder clearance perfect.

Size A: 72.46mm and 75.96mm and 78.96mm

Size B: 72.47mm and 75.97mm and 78.97mm

Size C: 72.48mm and 75.98mm and 78.98mm

GasGas, Vertex, and S3 all are possible sources for replacement pistons and rings. 

Port Timing

These measurements were made with a degree wheel.  They were taken when I first got my TR280i.  I would not bet my life on them, but they should be close.

Exhaust duration: 158 degrees

Transfer duration: 135 degrees

Blowdown duration: 23 degrees

I then back-calculated that the connecting rod needs to be 130mm (center to center) to get dial gauge measurements to agree with the degree wheel.  

Note: the connecting rod center to center length has been measured at approximately 118mm.