JS Motorsport
 
 
motorcycle
HIGH-PERFORMANCE
PARTS
FOR NORTON TWINS
JS Motorsport
4480 North Academy Avenue
Sanger, CA 93657
Phone/Fax: 559 875 0659
Email: jim@jsmotorsport.com
JS Motorsport Technical
Ultralight rods and pistons for Solid frames

The bushless ultralight rod below was designed for solid framed bikes such as the Atlas 750 and 500 to 650 Dominators. This rod is good for long stroke 750s up to 75 hp. Also works for short stroke 500 classic racers. They weigh 10 grams less on the small end than our regular bushless rod. Small end = 95 grams. Big end = 307 grams. This ultralight rod provides maximum smoothness for solid framed bikes. Crank rebalancing required. Requires DLC pins.

 

68 to 69.5mm Hi C.R flat top pistons for 650 SS Dominator

The 68.5mm flat top piston below is refered to as 9:1 C.R. (closer to 8.5:1 C.R.) for a 89mm stroke 650SS Domniracer. Other compression ratios are available. These pistons weigh approx 170 grams and go with our Ultralight 6.4" length rods.

 

68 - 69.5mm domed pistons for 650ss Dominator

The 68 to 69.5mm centrally domed piston below is 10.5 C.R. for a 89mm stroke 650SS Domniracer. Other compression ratios are available. These pistons weigh approx 170 grams and go with our Ultralight 6.4" length rods.

 

66 - 67.5mm domed pistons for 500 Dominator

The 66 to 67.5mm centrally domed piston below is 10.5 C.R. for a 72.6mm stroke 500cc Domniracer. Other compression ratios are available. These pistons weigh approx 170 grams and go with our Ultralight 6.4" length rods.

The bottom side of the dome is 3D undermilled to achieve mimimmum weight as in the photo below.

High domed 10.8 C.R. 73.5mm piston below was designed for a 500 short stroke using a 750 motor destroked to 59.6mm. The higher dome is necessary to restore C.R. with the smaller displacement.

The piston below was designed with a smaller, centrally located dome for an exotic Norton 750 short stroke racer with a welded and re-machined bathtub shaped combustion chamber.

It is assumed that every race engine builder will check squish band, and valve pocket clearances.

 

Ultra lightened piston option

The skirts can be drilled and pins taper bored on special request as below for solid framed bikes and high RPM racers.