I just purchased a new piston kit from Al for a 72 jackpiner,the transfer port on the new piston looks to be about 1/4 inch lower on the new piston then the old piston. Does anyone feel this is something I should be concerened about or if anything needs to be done to compensate for this? Thanks, Glenn
Glenn Berry
This would totally change the port timing of the boost charge but how much effect this would have or why it is that way I do not know. Good question that should be looked into by wiser minds before there are hundreds of these in bikes.
Larry
It could be a problem, when the small hole in the piston isn't hidden anymore by the sleeve when the piston is on it's lowest position. As long as this hole isn't visible through the intake manifold, it would not affect porting. If it's visible, then ofcourse it would cut off the flow through the small transfer ports during the last few degrees.
KTM 495/81; KTM 495/82; KTM 495/84; KTM 500/85
Just installed one of the new pistons for the JPs in Glenn Berry's bike. The difference in the port height does not seem to be causing any problems. So far it seems to run fine. I'll update as he puts some miles on it.
Lew Mayer