Dec 18th, Updating oil pump — Linn Motorcycles

The flathead oil pump puts out a volume of about 1 quart/8 minutes. Not alot for sure. I guess if you were considering that the VL series was measuring oil in drips is was an improvement, but as times changed and road speeds increased, the UL’s had a tough time coping. By doubling the number of vanes on the pump rotor, you roughly double the pump’s output.

So, here we go: First, cut a second slot in the rotor to take the additional vanes. As the rotor is hardened, I’m using a carbide cutter in the Bridgeport.

Here goes the first cut. As it’s a small carbide cutter, slow and easy is the rule. I use many light passes so as not to stress the cutter and perhaps break it! (H’mm, sounds like the voice of experience)

When finished, the rotor looks like this.

After cutting the rotor, the vanes have to be fitted in the slots. First they are shortened so that the ends don’t strike each other when they are fully retracted in their slots. Then you make the “spider” to hold the springs in place. I use a couple of nails to make the cross.

Two nails soldered together, with their notches overlapping to make a compact cross.

finished “spider” with cut down tensioning springs in place

Here’s the finished assembly, just before it’s placed in pump body.

The above series of pictures shows some of the major steps in building up the improved pump rotor. Unfortunately, I don’t have a pic of the assembled pump, I just painted the body and didn’t want to handle it to show the finished assembly. Maybe next time

I have a blown motor that I can use for a test jig, and have mounted the modified pump and verified that it does double the pump’s output, which has got to be a good thing.

Now I realize that 45’s have been using these pumps for many years apparently with no problems, but again that motor is half the size of stroker Big Twin flathead!. I have several of these pumps on friend’s bikes, and the results have been good to date. (My personal Flatty has a “not ready for prime time” experimental system that we won’t go into just now).

Stay tuned, there’s more to come on this build.

Screw blocking bypass passage to centrifugal bypass valve.

Here’s a couple of pictures that show the modified rotor installed, and the screw that blocks the centrifugal bypass passage.