Wednesday 28 February 2024

Velocette Mk 1 KTT Cambox Oil Pumps – Part 3

Well, the pumps are finished.

but they have taken quite some time from the inception and making casting patterns to finished pumps.

Machining the first two major components - the pump body, K-102/2, and the plunger, K-152, had worked out pretty well (see here). There is one last part required, namely the Plunger Locating Pin K-156. Both this and the plunger will be heat treated and so modifying an existing ¼” BSCY screw is not an option and the plunger pin is therefore also made from O1 tool steel which I can heat treat.

Luckily, the offcuts from the plungers provided short lengths of 13mm diameter O1 steel and these were perfect for making the plunger pins. The pins need to be made in their entirety, including the hexagon.

The diameter and radiused end of the pin are important to fit properly in the plunger groove.

Although no parts have yet been heat treated, this does not preclude testing the first pump to see if it actually works. For this, a 5/8” diameter length of steel was machined to give a flat end that would locate in the slot of the plunger.

The pump body was screwed in position on the end of a spare (and damaged) cambox

and one of the brass endplates used to set up the V-Twin camshaft screwed on the other end of the cambox together with an outlet pipe connected to the downstream side of the pump

to make a simple test rig.

Oil was added to one of the gutters immediately adjacent to the cambox and a drill, running at slow speed, was used to drive the shaft.

Fantastic! The pump works just fine and so it was time to start machining the other castings and plungers.

I made one modification to the machining process to improve the ease-of-setup and accuracy for the vertical holes and that was to use a rotary indexer in conjunction with the angle plate, shown below with a ½” aluminium bar

to ensure that the holes would be on-centre. The ½” round bar was inserted into each casting, in turn, and attached to the casting with small dabs of epoxy resin

The angular position of the casting could then be checked easily with a pointer

before rotating through 1800

 clamping and machining.

One slightly tedious aspect of machining these small diameter holes in heat-treated LM25 is that the drill flutes tend to clog - see above picture - which necessitates continually clearing the drill. After machining, the pump body was easily removed from the aluminium bar which was then cleaned up and used for machining the next casting.

Machining of both the castings and plunger spindles went well although quite time consuming. Anyway, after a bit over 2 weeks I had this collection of bits:

At the bottom right of the picture are the offcuts that were used to make the plunger locating pins.

Heat treatment was carried out in the usual way (see eg. here for details) – the picture below shows the plungers coated in anti-scale compound before going into the high temperature furnace

whilst hardening of the contact end of the plunger locating pins was done using oxy-acetylene before going into the lower temperature tempering oven.

After cleanup, the pumps are now completed.

At the bottom right is the original pump (with the broken corner), which also now has a new plunger locating pin.

And finally….

I started this project because I needed one cambox scavenge pump for KTT 55, but making one pump economically really isn’t viable. The amount of work involved in making the casting patterns, setting up the CNC machining for the plunger groove etc for just one item would not be worthwhile. The reason that I then started out making 9 was simple: the CNC machining for the groove required an approximately 11cm length of O1 steel bar and so I bought a 1m length. With 9 short lengths of grooved bar it made sense to get 9 castings. I considered that one of the castings was not good enough to machine and I screwed up the machining of another one.

That’s what happens with a momentary lapse of concentration when the depth of cut is set to 1.75” rather than 1.375” – yes, I admit I make mistakes.

And so, I’ve ended up with 7 new pumps plus the original, which is repairable (in fact I’ll probably chop off the valve-lifter arm from the above pump to weld to the original).

Do I need 7 (or 8)? No, not really. I will use 2 on both KTTs, one on the Special that I’m building concurrently and I’ll save 2 for the V-Twin – just in case (although I think the cambox oil scavenging problems are probably solved so I probably won’t need them). That makes 5. So, there are 2 up for grabs - if anyone needs one please contact me.


  1. Hi , I'm trying to rebuild a Mk1 Kss and would be interested in a pump if one is still available.
    Cheers Mike

  2. Hi Mike, yes, please contact me via email on home page if interested.