To fit original aluminum Norton rods or bushless Carrillo stock length rods

Replace the original Hepolite or JCC pistons with high quality American made forged pistons. Stronger and lighter than stock pistons – for stock rods. Uncoated pistons may be graphite coated for an extra fee.

Medium or High Compression 500 to 1007cc

The JSM pistons for stock rods are lighter than the original stock pistons. When you lighten the pistons (reciprocating weight) you reduce the vertical shaking of the motor but the horizontal shaking stays the same.  So your bike and motor will feel smoother and stress on the crank and cases will be reduced. Your balance factor will increase and if you want you can rebalance the crank back to stock balance factor specs to accomodate the lighter pistons –  either way the lighter pistons will give you a smoother ride whether or not you rebalance the crank.

Examples:

A bare stock medium 750 piston weighs approx 250 grams
A JS 750 medium compression piston for stock rods weighs approx 230 grams.

A 750 Commando with the lighter JS pistons for stock rods and no other changes will increase the stock balance factor of 52% to approx 55% and because of the lighter pistons this means you motor will shake less vertically and the same horizontally – a win win situation.  Rebalancing is not necessary.
A bare stock medium 850 piston weighs approx 317 grams
A JS 850 medium compression piston for stock rods weighs approx 255 grams.

An 850 Commando with the lighter JS pistons for stock rods will increase the stock balance factor of 52% to approx 58% and because of the lighter pistons this means you motor will shake less vertically and the same horizontally – a win win situation.  Rebalancing is not required.
A 66% wet balance factor is recommended for solid frames.