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Solving Wet-Sumping Issues on Norton Commandos

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

timing covers
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

motorcycle sump

Image Keith Fellenstein

1. In a minute we will remove the timing cover, but before that, you’ll need to drain the sump and oil tank. Our bike had sat long enough that most of the oil was in the sump, as you can see here.

removing points cover

Image Keith Fellenstein

2. After all the oil is drained, it’s time to remove the points cover and, depending on your setup, either the points plate and auto advance unit or the electronic points unit and rotor. We had a Boyer, so out comes the sensor plate and magnetic rotor underneath.

bolt

Image Keith Fellenstein

3. The Boyer plate has an M8x1 internal thread, so with a little shop work you can make a tool to remove the plate easily.

tool

Image Keith Fellenstein

4. I had the special tool so I used it instead of the bolt and spacer. In either case, you are pushing against the recessed end of the cam to release the taper holding the rotor in place.

disconnecting oil line

Image Keith Fellenstein

5. Disconnect the oil line to the rocker boxes and let it drain into a small container. There are two copper washers on this junction, be sure to anneal them to red hot with a propane torch before reusing them.

removing gear indicator

Image Keith Fellenstein

6. Remove the gear indicator and shift lever so you can remove the timing cover

removing timing cover

Image Keith Fellenstein

7. After the points plate and shift lever are out of the way, remove the timing cover screws. To remove the cover you’ll probably have to shock it a bit with a rubber hammer to loosen the bond between the cover and gasket. Carefully clean any gasket residue from the crankcase and timing cover.

cover before modification

Image Keith Fellenstein

8. Once the cover is off this job can branch in two directions. In the first, you send the cover (and optionally the oil pump) off to AMR in Tucson so they can modify your cover to MkIII specs. We’ll do that one first. This picture is of the cover before modification.

redirecting pressure relief valve

Image Keith Fellenstein

9. We’ve got our cover back from AMR. The first modification is to redirect the pressure relief valve back to the sump rather than back to the input side of the oil pump. This does away with a back channel for oil to seep into the sump.

plugging the oil passage

Image Keith Fellenstein

10. As a part of this modification, you must plug the oil passage in the crankcase with the supplied set screw and some loctite. The crankcase is already threaded for this set screw. Screw it in until it is just below the sealing face of the crankcase.

modifying the check valve

Image Keith Fellenstein

11. The second modification is the check valve on the pressure side of the oil pump. A light spring holds this ball against the pump output to stop oil from leaking down from the oil tank through the pump. Once the engine starts, oil pressure pushes the ball out of the way and allows normal oiling. The pin on the right holds the ball in place until you have the cover on. The wire tie holds the pin in place until you’re ready to install the cover.

optional modification

Image Keith Fellenstein

12. The optional modification is machining the oil pump so that sealing rings can be fitted to stop oil from leaking past the pump gears. This is sort of a belt and suspenders fix, as the ball valve should stop wet sumping on its own. Also shown is the O-ring that seals the pump output to the newly machined cover surface.

modified cover

Image Keith Fellenstein

13. Here is the modified cover with all new seals installed and ready to be fitted back to the timing side of the crankcase. Remove the safety tie holding the pin in place before fitting the cover, but don’t dislodge the pin or you’ll be chasing a ball and possibly a spring around your shop.

fitting a new gasket

Image Keith Fellenstein

14. Fit a new gasket between the crankcase and timing cover. Once you have the cover fully seated on the case, you can pull the pin, releasing the ball to seal against the O-ring and pump output. Reinstall all the cover screws and attach the rocker oil feed to the timing cover with the freshly annealed copper washers.

oil

Image Keith Fellenstein

15. Seal everything back up, double check your hoses, and start the engine. Look in the oil tank to be sure oil is being pumped back and you’re done. This is a more reasonable amount of oil to drain from the sump in normal use now.

timing cover

Image Keith Fellenstein

16. The second method is faster, but much more expensive. You just buy the MkIII timing cover and parts needed to populate it. Then it’s just a matter of removing the old cover, replacing a few parts and installing the new cover.

Mkill cover

Image Keith Fellenstein

17. The MkIII cover has a cylindrical plunger backed with a spring as the anti-drain valve.

Mkill cover

Image Keith Fellenstein

18. In addition, they have not drilled the passage that would return oil to the feed side of the pump. In the event of the pressure relief valve opening up, the excess oil is dumped into the sump, to be pumped back to the tank. With this hole missing, you don’t need to plug the return gallery in the crankcase.

pump output flange

Image Keith Fellenstein

19. There is a new pump output flange, shown here on the left, to back the seal to the timing cover. The flange and the rubber seal are larger to work with the larger plunger in the cover.

motorcycle interior

Image Keith Fellenstein

20. You’ll carefully pry the old flange out and press the new one in its place. It’s a light press fit, should come out and the new one go in without much trouble.

seal

Image Keith Fellenstein

21. The new seal fits over the flange with the ‘bump’ facing outward

added seal

Image Keith Fellenstein

22. Here it is in place and ready for the cover to be fitted.

crankcase

Image Keith Fellenstein

23. You don’t have to plug the oil gallery in the crankcase when using this cover, but be sure that there is a screw installed in this location in the cover. Loctite it to keep it in place and screw it in flush with the cover. For added security, you can use a pin punch to stake the cover into the screw slot.

check valve

Image Keith Fellenstein

24. Assemble the check valve with the hollow side holding the spring into the cover.

final assembly

Image Keith Fellenstein

25. The final assembly is the same as for the modified cover, just be careful that the check valve doesn’t come out of the cover while installing it. Put everything back the way you found it and enjoy your new non-wet sumping Commando.

Updated on Jun 28, 2021  |  Originally Published on Jan 1, 1970

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