Universal Inline Anti-Drain Valve
Part Number 641-21
(The inlet and outlet stubs are 3/8" o.d. and 5/8" long. Two hose clamps included. The body of the anti-drain valve is 1-1/4" long and 1" diameter.)
Is your Norton or BSA single or twin dumping all its oil from the tank into the crankcase when you leave it parked? Make sure you are running thick enough oil (50 wt Summer, 40 wt Fall and early Spring) and are parking it on compression (pistons at top of stroke to block off any conrod oilholes).
If the problem persists, you can replace your gear type oilpump with a new one (expensive and sometimes not easily available), or install one of our Anti-drain valves into the feed line from the tank to the oilpump. Based on a design used by Velocette for many, many years, these spring loaded valves open as soon as the engine is started. Make sure your valve is installed in the correct direction and well primed with oil, and your problem is solved.
Manufacturer's notes: This Anti-drain Valve works on the same principle as the device fitted into the bottom of the Velocette oiltank, in fact it uses the same ball and spring. As with all ball type valves it is essential to ensure that the oil is kept clean, as any dirt may hold the ball off its seat. The valve is fitted into the oil line between the oiltank and the engine, the feed from the tank. It is the pipe that is attached to the outer of the two crankcase oil union pipes on Norton twins. It is most important to ensure that the valve is fitted the correct way round, as catastrophic engine damage may occur if fitted incorrectly; the end marked "IN" goes toward the oil tank. It should be realized that an oil pump that is bone dry may not (theoretically) generate the vacuum required to draw the ball off its seat. Therefore when fitting the valve, before firing up the machine, the pipe between the valve and the motor should be primed with engine oil. This kit is suitable for most vintage British bikes with gear driven oil pumps.