Solving Wet-Sumping Issues on Norton Commandos

Learn two ways to stop your classic Norton Commando from wet sumping.

article image
Keith Fellenstein
The new MkIII Commando timing cover (left) next to an original cover from a 1974 Commando, which has been modified.

A common problem with vintage British bikes, due to their dry crankcases and remote oil tanks, is wet sumping. Wet sumping is when the oil from the remote oil tank finds its way into the sump of the engine. In this How-To we’re going to show you two methods of curing the problem as it exists in Norton Commandos.

Both of these methods involve changing the timing cover to incorporate a check valve on the pressure side of the oil pump.
One method is to replace your stock timing cover with one from the MkIII Commando of 1975 and the other is a modification to the pre-MkIII cover that accomplishes the same thing. We’ll detail the differences as we go along so you can decide which method to use if you should want to modify your Norton.

You will need the service manual which is available online from many sources, along with some gaskets and seals. Those are available from many sources, including our advertisers. Let’s get started.
— Keith Fellenstein

Oil in a motorcycle's sump. A points cover being removed. A bolt Closeup of a hand holding a tool to remove a motorcycle part. A close-up of a man disconnecting the oil line of a motorcycle. A close up of the gear indicator of a motorcycle being removed. A motorcycle's timing cover being removed. The cover before modification. A close up of a grey motorcycle part with a tool pointed at a channel in the part. A closeup of a metal motorcycle part. A white hand is using a thin tool on it. A closeup of a hand working on a metal motorcycle part, this time touching a pin. A closeup on the O-ring on a motorcycle part. A closeup of a metal motorcycle part Closeup of a white hand holding a tool near a metal motorcycle part. Close up of a black plastic tray under a motorcycle A closeup of a timing cover and some small parts in a bag. A close up of the interior of the Mkill cover. A white hand holds a tool that points at a plunger. Closeup of a white hand holding a tool that is pointing to a solid metal motorcycle part. Closeup of a white hand holding two small metal parts. A close up of interconnected motorcycle parts. Closeup of a white hand holding a small seal next to motorcycle parts. A closeup of interconnected motorcycle parts. A closeup of a white hand holding a tool near a motorcycle part. Two small motorcycle parts on a towel, next to a metal cover. An assembled motorcycle.
Motorcycle Classics Magazine
Motorcycle Classics Magazine
Motorcycle Classics Magazine Featuring the most brilliant, unusual and popular motorcycles ever made!