Rebuilding the Oil Pump

[SteveW]

I've been looking at my XPAG oil pump and the clearances between the gears and the oil pump cover are 4 thou (for the driven gear) and 8 thou (for the driving gear on the shaft that leads to the camshaft). The advised clearance is 2 to 4 thou so I need to change the driving gear, but they are only sold in pairs so I had might as well change both.

How do you get the driving gear off the shaft? I've removed the circlip and I can tap the gear about 1/3 of the way off the shaft using a drift but after that it seems to stick. I could just hit it a lot harder, but I want to make sure that I'm not missing anything first. Makes me wonder if the previous owner has forced it on with the slot in the gear not fully lined up with the woodruff key, but then why does it come off part way without too much effort.

I assumed that it would come off quite easily. Any ideas?

[Tom Lange, MGT Repair]

The problem is that there is a Woodruf key in the driving shaft, digging into the bronze bush when you just try to beat out the gear. You need to drive the gear off the shaft a bit, put spacers under the gear and drive it off a bit more, and more spacers until the gear comes free. Then remove the key, and the shaft comes out of the pump body.

The Moss rebuild sheet (on-line through their catalog) is the best guide to how to do these things.

Tom Lange
MGT Repair

[SteveW]

Thanks Tom, very helpful as usual.

I've now taken the gears out and they are both looking good and are exactly the same height. The difference in clearance is therefore down to the body of the pump itself and new gears will not cure it. I guess that this is either wear in the bottom of the body or the face not being true. Either way, the solution seems to be the same - flatten the top face. Looking at the Moss rebuild sheet it seems that the way to do this is to get a flat surface (glass is recommended)and rub it down with fine emery paper (>600 grit).

I guess that an alternative would be to add a shim under the driving gear, but I'm not keen on adding extra components that are not supposed to be there and the top face of the pump body could do with a re-surface anyway.

[Ray White]

I sent my new gears with the pump to Roger Furneaux to sort out. I think it is far better to have the gears and pump cap machined to the correct clearance than to rely on laborious and less accurate work by hand..

That said; each to his own.

[Butch T]

As you have discovered the gears wear differently. The gear attached to the shaft is pulled into the body and the driven gear rests on the cover. When I rebuild the pumps I grind the face of the cover flat(you don't know how many people have used the sandpaper on a sheet of glass method and have formed a dome on the cover). Then I grind the surface of the body to remove any scratches where the cover sits. Finally I grind each gear to fit the body to give the required clearance .0015 to .003 end float. I advise if at all possible to use the same lock ring that you took off instead of replacing them.

Butch

[Warmuthb]

Butch T is the man. Send him your pump if you want it done right. He has done several for me and original water pumps too. See if he is accepting any new work at this time.

Brian W.