Two basic styles of pump were used in original production, and are interchangeable in service. The early pump was driven by a flat gearwheel, and this wheel was located onto the pump drive spindle with a “D” arrangement. The round spindle had a “flat” on one side and the wheel had a corresponding built up area to match. The whole affair was held together by a special flat headed screw, driven in two slots by a special tubular peg spanner. This was superseded by a taper drive arrangement. The wheel was thickened in the centre, and the outer cover of the pump thinned to allow a taper to be used between these two components. This arrangement was held together with a thin nut (in fact the same nut as the valve clearance adjusters and pull-rod use as a lock nut) secured by a tab washer. I can hear owners of early machines saying “So that's what that funny little tab is I get in my kit and don't use” The later T160 models were fitted with the large bore oil feed from oil tank to pump, and the matching hole in the back plate of the pump was larger to suit. It is perhaps worth mentioning that all pattern pumps are of the taper drive type.
Frank is right in assuming that it is mainly internal clearances that affect the efficiency of the pump. I have overhauled quite a number of pumps over many years and I have developed the following technique. It is based on accurate measurement of the various pieces with good quality equipment carefully used. I would suggest that an owner takes great care before attempting an overhaul, as once metal has been removed it is gone forever!!
Firstly the pump must be stripped and thoroughly cleaned. Inspect the radial clearance of the gears in their respective housings. No remedial action can be taken if excessive clearance is found, but I've yet to reject a body or gears for faults found in this area. Secondly measure the depth of the feed and scavenge bores from the faces of the pump body. Measure in many places, to build up a “picture” of the depth of the bores. I have found many faults here, especially with the pattern bodies. You may find when the measurements are tabulated that the bores are not “square” to the faces of the body, not “square” to each other, and at considerable variance to the measured lengths of the gears. I always lay out all my measurements in a table so that I don't get confused (easy after dealing with these bikes for many years) and decide what action to take. The end result will have feed gears with an end clearance of .0008" to .0012", and scavenge gears with an end clearance of .0012" to .0018", in a body with “square” bores. Of course the gears have to be flat, and I have seen some considerably tapered.
I will not suggest any methods of attending to the body or gear modifications on purpose. If you don't know how to do it don't, but send the pumps to a firm or individual you trust to undertake the work.
I have found (pattern) bodies with steps between the bores of up to .008" and differential lengths on a pair of gears fitted in a particular pump of .010"! From experience it seems that the best pumps were from the earliest machines, and then the quality slowly deteriorated, until some T160 pumps are quite disgusting. Most, but not all, genuine pumps can be rescued however, by careful manipulation of the body and gears to obtain the suggested clearances. I have yet to find a pattern pump that I can do anything with, and in fact there is no component in these pumps that I will use, except the drive spindle/scavenge drive gear in an extreme emergency.
The scallops in the covers of the pump are there to lubricate the end faces of the gears, and more importantly to vent the chamber formed as the gears mesh. Without this vent there would be a moment of hydraulic lock at every tooth engagement. It should be remembered that the oil flow route through the pump is circular. By that I mean that the pumped oil is carried round by the gear for approximately 270 degrees, and does not pass through the gears.
Please note the following was originally written in December 1993
Now for the advertising: For more than a few months now I have been looking at the possibility of making a quality new pump, and perhaps enlarging the capacity. I was recently introduced to a draughtsman who is very experienced in this area and the project is now close to completion. The new enlarged (50%) pump will be a direct replacement fit, and will be driven by a standard “D” drive wheel. These have been in short supply for some time, but I've already had these made and they are now available. In fact I have had made both forms of the pump wheels, the taper drive in a lightened condition, and a lightened idler wheel. These, together with a special crank drive gear are available in a “Tuftride” heat treated condition. These drive wheels are made in a tougher grade of steel than original, and some years of race experience with heat treated wheels show that life is very considerably extended. Please see this link for greater detail.
Copyright © 2000 Philip Pick
Version 0.1 Date December 2000