fizzwater2 wrote:I think you'll find that the top of the piston is quite a ways further down the sleeve when it closes the exhaust port than .151, .154, etc.
The numbers that people throw out are measurements of the difference between the top of the piston at top dead center, and the top of the sleeve flange. Yes, larger numbers imply that the sleeve is higher, which raises the edge of the exhaust (and intake) ports with respect to the centerline of the crankshaft, which increases the timing duration in degrees.. so it's a way of getting relative numbers without using a degree wheel. The degree wheel would be the proper way to measure actual port timing.
and the .015 is the distance between the top of the piston at TDC, and the squish band of the head.
Thank you Gordon.
Yes, the distance between the top of the piston when the exhaust port closes and the top of the liner will not be the same as the TDC measurement I understand (and I suppose is more precisely measured with a degree wheel as you say). That's kind of why I used the term "code" meaning, when using the TDC measurement, we are really using it as a relative reference to the timing.