Old Britts

Oil Lines on a Commando
by Fred Eaton


This article will show how the oil system works and the oil lines are routed on a Commando.

Oil Line routing

The above picture was copied from the Andover Norton workshop manual for the 850 MK3, (part no. 00-4224).

Oil Tank

Most Commandos have the oil tank mounted on the right side of the bike, but some of the early Commandos, with the square oil tank, look different than the above picture, but do have the same fittings.

Engine Breather

On all models the breather goes into the oil tank on top by the filler cap.
For 1971 and earlier models the engine breather comes off the front left side of the crank case.
For 1972 models the breather comes off the lower rear of the crank case.
For all 850s the breather comes off the rear inside of the timing side of the crank case as shown in the above picture.

Oil Tank Breather

This breather is on the top of the oil tank towards the front of the tank. If you mix up the engine breather and the oil tank breather, you will get an excess amount of oil coming out of the oil tank breather, so be careful to hook up the breathers correctly. The oil tank breather is very important since it lets the engine, through the oil tank, breath to the atmosphere. This breather could be just a hose run somewhere on the bike (hopefully somewhere that can stand oil vapors), into a catch bottle or into the air box depending on the model and what modifications the previous owners may have made.

If you run this breather into a catch bottle, which is the most sanitary way, make sure the bottle is open to the atmosphere and that the end of the breather hose does not stick into any oil that may accumulate in the bottom of the bottle. If you use a clear catch bottle, you can see if oil has accumulated in the bottle and dump it when required. If you use a opaque catch bottle, make sure you check it regularly for oil build up.

Feed Line from the Oil Tank

This line comes off the large banjo on the square oil tanks and the only banjo on the other tanks. This line runs to the outer pipe of the oil junction block. If you are adding a check valve to eliminate wet sumping, this is the line you want add the valve to.

Return Line to the Oil Tank

This line comes from the inner pipe of the oil junction block and runs to the oil filter (for models with an oil filter), then to the back of the oil tank or the small banjo on the square oil tanks. Most Commandos that do not have an oil filter can have one added, see Filter Mounting Instructions for more information.

Chain Oiler

The above picture does not show the chain oiler, but does show the location of where it would have come off the return oil line. The chain oiler was done away with in 1975 and most riders block off the chain oiler since modern chain lubes are so much more efficient and less messy than dripping engine oil on the chain.

Rocker feed Lines

The rocker feed lines come off the rear right side of the timing cover and goes up to the right side of the cylinder head to a double banjo and then across the head to the left side.

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