Some months back, Randall Washington (Randakk) and I were in discussions about the clutch cavity oil scavenge pump. He was having difficulty changing gear and found that the oil level in the clutch housing was way too high. Obviously the scavenge pump was not doing it's job.

He thought he had a problem with the drive for the pump.  We both did some investigating and what we found has implications for all the four cylinder Wings.

When his pump was removed, he found that the inlet was almost completely blocked.

The two pumps I had to hand at that time also had partial blockages from the same cause.  I have just removed a third pump from a spare engine and found exactly the same thing.

These blockages are not debris from the clutch, as you might think.  The problem is the paper gasket that seals the two halves of the pump body.

As you can see from this picture, that section of the gasket does nothing in the way of sealing the two halves. But it gets caught by the passage of oil  through the small orifice and pulled into the opening. Any small debris from the clutch can then catch and further tear at it or get lodged behing it, forcing it further into the opening.

When this happens the pump can no longer properly do it's job of returning the clutch cavity oil to the crankcase, causing the cavity oil level to rise and the crankcase oil level to drop.

In the severe case that Randall had, the heightened oil level was also causing a difficult gear change, which returned to normal once this problem was solved.

The solution is as seen in tne two pictures. On the left is a standard pump gasket; on the right a modified gasket with the linking section cut away. The gasket is only a form of paper, easily cut with a modeling knife or scalpel.

It would be possible to trim this gasket back without opening up the pump by using a long narrow scalpel blade, but whist you have the pump out it would be a good idea to check it over thoroughly.

First, check the outside diameter of the outer rotor cavity and the back face for heavy scoring. The pump, being a scavenge pump, has over capacity so some slight internal leakage will probably not do any harm, but any real tearing up of these surfaces will render the pump unusable.

Check the face of the other half of the pump. The same comments apply.

Now check the rotors for damage. The tips of the inner rotor are the most likey to suffer, along with the high inside points of the outer rotor. Again, some small nicks wiil most likely be ok, but anything more than that the parts are junk.

Both faces of both rotors also need to be free of scoring.

Unfortunately these parts are discontinued, so you will have to hunt for NOS from one of the dealers that specialises in them or try to find a good used one.

Any part that is help together with screws or bolts around the periphery is likely to have some distortion.

Tape some very fine Emery paper to an old morror or piece of optically flat plate glass and check the flatness of each half of the pump body.

'Paint' the surface of the pump body halfs lightly with a 'magic marker', then using a circular motion, GENTLY rub the suface down, changing the position in which you hold the body frequently, to minimise any tendency to press harder on one side or the other.

ALL YOU ARE TRYING TO DO HERE IS OBTAIN A FLAT SURFACE.

TAKE OFF AS LITTLE MATERIAL AS POSSIBLE.

You can see here how I have stopped at this point while you can still JUST see the marker. Now do the same for the pump cover.

You can still JUST see the marker, but this is flat enought for the gasket to take up any descrepancy.

Now clean everything thoroughly. Carborundum grit will not help your pump's efficiency!

Put the locating pins back in and fit the modified gasket.

Oil the inner surfaces of the pump bodies, the drive collar and all of the rotor surfaces.

Refit the rotors into the body and then fit the drive collar into the rotors before trying to fit the other pump half.

If you fit the drive collar to the outer pump half first, you can have hours of fun trying to find the one position where rotors, drive pegs, collar and locating pins all line up!

Refit the screws.

Note that there are two different lengths of screw. The two long ones go into the two thicker bosses. Obvious; easily missed!

So here is the finished article, all ready for another 30 years of service

(provided the oil changes are done regularly!)