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
One way reed valve crank case breather

Pumping out positive crank case pressure and leaving a slight negative pressure is a great way to eliminate oil leaks. This simple breather uses the proven stainless steel reed valve from the BMW twin (street and track tested). Body is machined from highest quality 7075 Alum. Stainless steel fasteners. Easy installation with no machining necessary. Available in 4 versions - 750 camshaft vent mount, 850 timing side mount, Combat or Maney case sump mount and front tac mount (see breather demo).

750 CAM END MOUNT:

Replaces the early 750 Commando and Atlas vent on the right side.

OPTIONAL - You will no longer need the original cam rotary valve and spring - best to remove them whenever its convenient.

850 Mk2 TIMING CASE MOUNT:

Replace the original 850 MK2 vent tube with the one way reed breather valve as below.

850 Mk3 ELECTRIC START TIMING CASE MOUNT:

Replace the original 850 MK3 vent tube with the one way reed breather valve as below. Fits Mk3s with shorter aftermarket starter as below. Contact us to special order for the original presolite starter.

COMBAT AND MANEY CASE REAR SUMP MOUNT:

Bolts right up to Combat and Maney heavy duty cases (no machining necessary). Other cases can be modified to use this breather (page down). Only two screws are necessary. Reusable crush proof gasket provided. Note that all versions of the JS breathers shown above can be moved to the sump later on when you rebuild the motor and make the sump modification shown below.

OPTIONAL - For those with other types of cases who want the sump mounted reed breather - you must drill and tap two small holes and one central breather hole in the lower left case as below.

Both 750s and 850 Commandos can use the front tac drive mount for the breather. For those who don't need a Tac or have an electronic Tac. No modifications or machining necessary.

OPTIONAL - For cam vent, sump mount, and front Tac mount reed breathers you can increase efficiency by plugging the breather holes to the timing chest as below (not for 850 timing case mounted breathers). If you plug the original oil return hole (far left) then you must also add a new oil return hole below the oil pump (for tilted motors only). See breather plugs below.

OPTIONAL - For those who don't want to disassemble your crankcases - you can avoid threading the breather holes and getting chips in motor by making aluminum plugs and driving them in (see image below).