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 left case vent, 850 rear timing side mount, Combat or Maney case lower sump mount and front tac mount (see breather demo).
750 LEFT CASE VENT MOUNT:
Replaces the early 750 Commando and Atlas vent on the left case.
A drop in kit but you should remove the original cam rotary valve with spring and plug timing chest vents for best efficiency if the motor is already apart. See diagram for plugging vents as shown at bottom of page.
850 Mk2 TIMING CASE MOUNT:
Replace the original 850 MK2 timing case vent tube with the one way reed breather valve as below.
850 Mk3 ELECTRIC START TIMING CASE MOUNT WITH AFTER MARKET STARTER:
Replace the original 850 MK3 timing case vent tube with the one way reed breather valve as below. Fits Mk3s with shorter aftermarket starter as below (original airbox should be removed, see next item down for original prestolite starter).
850 Mk3 ELECTRIC START TIMING CASE MOUNT WITH ORIGINAL STARTER:
Replace the original 850 MK3 timing case vent tube with the one way reed breather valve as below. Special angular fitting allows it to fit Mk3s with original prestolite starter (original airbox should be removed).
COMBAT AND MANEY CASE LOWER 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. The 3/8″ and 1/2″ hose barbs both have the same size venting connection. Note that all versions of the JS breathers shown above can be moved to the lower sump later on when you rebuild the motor by enlarging two holes to 1/4″ and making the sump modification as shown below. See diagram for plugging vents to the timing chest as shown at bottom of page.
NOTE THAT YOU CAN DRILL THE TWO ALLEN HEAD THROUGH BOLTS AND USE TIE WIRE FOR RACING AND INCREASED SECURITY.
The Maney and Combat cases are already drilled and threaded to accept the JS breather as below.
OPTIONAL – For those with other types of cases who want the lower sump mounted reed breather – you must drill and tap two small holes and one larger breather hole in the lower left case as shown below. A smaller offset 1/2″ hole is used rather than the larger 3/4″ Combat/Maney hole shown in the image above.
COMBAT CASES – Cut away the web to expose the rear oil pickup hole in the right side case (left photo below). Then plug the forward pickup hole (right photo below). You must vent the reed valve into the oil tank (you may have to add an oil tank fitting).
INLINE BREATHER FITS ALL MODELS – Splice this into any 3/8″ breather hose between the motor and the oil tank. Also works for the new 961 Norton (replaces oil separator) or any vertical twin or single cylinder motor. The interchangeable brass input fitting threads into 1/4″ pipe threads.
For 750 left case vent, Combat type lower sump mount, and front Tac mount reed breathers you can increase efficiency by threading and plugging the breather holes to the timing chest with pipe plugs as shown below (not for 850 timing timing side 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 – instead of using pipe plugs you can avoid threading the breather holes and getting chips in motor by making aluminum plugs and driving them in (see image below).