NEW PRODUCT RELEASE This new reed valve breather fits all models of Commandos & Atlas without any machining necessary. The 750 Commando and Atlas version screws into the original breather vent on the left side case near the cam. Simply remove the breather vent and install the new one way reed breather. If (or whenever) your lower end is apart you can remove the original rotary valve and spring because you will no longer need it. The 850 Mk 2 version screws into the original vent at the rear of the timing chest. Just remove the old vent tube and install the new reed breather (see Mk3 elect start version at bottom). For those who have an electronic tac (or no tac) the front tac mount version fits all 750/850 Commandos. Bolts right on with no machining but you have the option of plugging the vents in the timing chest (plugs provided). 850 owners should plug the original vent at the rear of the timing chest. For Maney cases and Combat versions you replace the original vent at the rear case. You have the option of plugging the timing chest vents (plugs provided). This breather uses a high quality stainless steel reed valve from the BMW twin. The reed allows positive air pressure to escape on the down stroke and then shuts to prevent air from re-entering on the upstroke. This reduces crank pressure and helps prevent oil leaks. Go here for more details: http://www.jsmotorsport.com/technical_r ... eather.asp EDITED Here's an added photo of the new reed breather on a Mk3 electric start (edit - with aftermarket starter). Remove the original vent tube and install the new breather it its place.