Modifying a Sportster Pump — Linn Motorcycles

This shot shows the supply side of the modified Sportster pump. I've blocked off the standard passage
that would feed oil to the motor on the right side. By Drilling a hole in the nut/plug that holds the pressure
spring and ball in place, supply oil under pressure may now be taken from the hole where the pressure
sending unit would normally screw in.
On the left side of the picture, you can see another plug screwed into the pump body. It blocks the passage
that the return oil from the scavenge pump would pass through.

Pressurized Oil Tap

Here's a shot showing how a fitting is used to take the pressure feed from the Sporty Pump. This feed will be routed to a modified flatside sidevalve pump.

In this shot of the stock supply pump, you can see how the rotor chamber is blocked off. You can also see
the tip of the 1/4" aluminum bar stock that was fitted in the supply side feed hole in the bottom of the rotor
chamber. On the right of the pump, you can just barely see the passage that was drilled from the feed to the
exit cavity of the rotor chamber. This lets oil bypass the pump chamber and pass directly on to the passages
in the pump and timing cover that feed oil to oil sending unit and the mainshaft

Here's a better shot of the hole added to connect the feed passage to the pump output passage. From here
Oil will flow under pressure to the channels in the timing cover to the mainshaft feed. In the lower right you
see the fitting that was mounted in place of the cap that used to hold the antisiphon ball and spring. They
are not needed as the one in the sporty pump is doing that job. This fitting, by the way, is the feed to the
Cylinder skirt squirters.

Modified Return Pump Section

This is a shot of the return side of the sporty pump, showing the passage added to route oil to the new port added to the bottom plate of the oil pump. See next pic

Return Pump Reverse

This picture shows the added spigot added to the bottom of the sporty pump to pass return, (scavenged) Oil back to the oil tank. That's just a piece of bar stock turned and drilled with a flat filed on one side. Then the flat is tapped 1/8" pipe to take the fitting.

New Oil Return (inside view)

Here's another shot of the new drilling made to channel return oil from the scavenge pump. This new hole lines up with the fitting brazed to the outside.

Second Feed Hole

This passage in the top of the sporty pump I used fed directly in to the passage to the feed side of the supply pump. This makes 2 connections to that passage. As I don't have a set of sporty cases, I don't know what function it served. However, when we're fitting the pump to a BTSV, it definitely needs to be blocked!!

Here's a couple of pictures of the preliminary mounting of the sporty pump to the BTSV cases.
In the final fitting I hope to be able to twist the pump just enough so that the one mounting bolt seen just
getting a bite in the case flange will have more meat surrounding it.
The standard mounting studs for the original return pump were removed, their holes filled with aluminum threaded
rod, and then new holes placed to line up with the sporty mounting holes.

Test Jig

This is an early shot of the test jig, the case is upside down, and the supply side pump's output is going into a graduated cylinder, just out of the picture.
Test results were; 250ML in 23 seconds at 1000 Pump RPM.
I added drive pins to both the mainshaft and the #2 camshaft so I could choose the speed I was driving the pump. Driving the cam would translate drill speed directly to pump speed. Driving the mainshaft would halve the speed of the pump. I.E., Drill turns the mainshaft at 1000 RPM, the Pump would run at 500RPM.

This shot shows the case right side up, and the pump fully connected into the oiling system. The
Mainshaft is receiving continious flow, the bushing being slotted and the end plug removed on the mainshaft
to accomplish this. The mainshaft has been enclosed so that most of the oil exiting from the mainshaft flywheel
drilling is caught by the tubing and routed to the catch trough. There are holes drilled in the case from the catch trough to the return oil chamber on the opposite side of the very exposed flywheel chamber case. At anything over 500 pump rpm, the catch trough and mainshaft containment system was overwhelmed with oil.

Even with the skirt oiler system in operation. Also in this picture, you can just see inside the number one camshaft bearing in the
cam cover. What you see is the homemade cork gasket instead of the pump rotor if it were a stock setup.
By the way this poor motor blew when the rear rod broke at 50MPH. She kept running on the front cylinder though.
It was easy to remove from the frame, the only engine mounting bolt still doing its job was the one under the generator
on this case fragment.

In this picture you can see the simulated skirt oiler, in this case a Amal mainjet of about .053" dia.
You can also just see one of the holes drilled to drain the catch basin into the return oil chamber on the
other side of the case. It's almost in the center of the picture just to the right of the tube that surrounds
the mainshaft.