JS Motorsport Technical
Piston weights, lifters & valve spring comparisons

JS lightweight bare pistons 750cc = 185 g 850cc = 210 g
Stock Hepolite bare pistons 750cc = 250 g 850cc = 317 g
JS bushless Carrillo rods small end 105 g big end 326 g
JS bushless Ultralight Carrillo rods small end 95 g big end 307 g
JS DLC pin 750cc = 51 g 850cc = 58 g
Stock pin 750cc = 68 g 850cc = 72 g
JS Beehive valve spring 42.3 g TI retainer 4.7 g Street seat pressure 90 lbs
Race seat pressure 130 lbs
RD racing spring 59.3 g TI retainer 10.8 g Race seat pressure 130 lbs
Stock spring 59.7 g steel retainer 16.1 g Street seat pressure 90 lbs balanced with shims.
100+ lbs shimmed for racing
JS (BSA) radiused lifter 38 g
Stock flat lifter 74.6 g
JS pushrod 31 g
Stock pushrod 32 g