"Big valves" vs. "Small valves"

[jsmn4vu]

Size of bore determines the minimum stroke length. A bigger bore requires a longer stroke. If you take out a piston, find two holes that are vertically aligned, and measure from the bottom of one to the bottom of the other, that's the length of stroke for that valve.

[jsmn4vu]

I have an PT-3 that's about 12 years old with "small valves". It has the same bore (.748 graduated to .825) as the current PT-3 that has "big valves". That would indicate to me that bore size may not be a determining factor (at least in some instances).

Kindly note the distinction: it's bore size, not valve size (per se) that puts limits on stroke length.