The Norton twin cylinder engine creates a serious amount of pressure in the crankcase as the motor spins. Over the years the factory attempted several methods to reduce this pressure – from a timed breather off the end of the cam on earlier motors, to an outright crude straight pipe from the timing chest on later 850s. While their intentions were good, none of these designs could effectively keep up with a pumping parallel twin motor at high revs.
This Reed Valve Breather effectively releases pressure from the crankcases on the down stroke while preventing air from returning the motor on the up stroke, creating a negative pressure situation which can eliminate leaks and boost performance. Beautifully designed by Comstock Engineering, this breather fits all Commandos that have a large sump screen on the bottom of the motor and installs in minutes with no permanent modifications necessary. Screw it in, plumb it up, and go!
No engine we build leaves our NYC Norton shop without a good breathing setup.
(Note: Commandos built on or before 1971 utilize a crossover frame tube under the motor which, on occasion, can prevent installation of this breather. Any customer with fitment problems may return the valve within 10 days in as-new condition for full credit.)
$289.00 for Reed Valve Sump Breather, complete
Please email to order: firstname.lastname@example.org