Dick Linn's site




First, why go to the trouble to change the present oiling system that engineers at Harley Davidson designed 70 years ago?

Well, my reason to go to all this trouble is that I’m convinced that Harley flathead engines, at least the Big Twins, are under lubricated.   There’s enough oil there to keep roller bearings lubricated, but not enough to supply the extra cooling that these motors need under modern conditions.  I came to this conclusion through lots of seat of the pants research and development.  Meaning, I’ve been riding Big Twin Flatties since 1974, and been blowing them up almost that long. Now, I’ve done lots of stupid things that I can’t blame Harley for, but the recurring theme is that the top end destroys pistons within 10,000 miles, usually sooner.

I’ve tried several methods to improve this situation. After the first blowup, I added skirt oilers patterned after the ones in K models.  The oil came from the pressure sending unit.

No real help. 


Next, I Built Frankenstein, my 45/KH stroker hybrid. There I first used a sporty pump and used the built in skirt oilers in the KH cylinders.  These were fed from the return oil line. That engine has over 10K miles on it, and the pistons are still in like new shape.

However, as the 45 engine is smaller than the 80, and combustion chamber shapes are different, I’m not sure that this setup would have been adequate on the 80.  Also, Frankenstein used a BSA oil tank, which had a “Y” in the return line at the tank. It was originally there to feed the BSA top end.  I used the “Y” fitting to feed the “K” type skirt oilers.  The Big Twin oil tank doesn’t have such a fitting.  And I wanted a lot of oil for jets on the Big Twins.


My next experiment was to add the sporty pump on my 44U. This I did two years ago, and for the first time used piston jets instead of skirt oilers.


The reason for the jet was to get the cooling oil up on the bottom of the piston crown.  Every rebuild of my big twin came about because the pistons were destroyed in the area nearest the intake valve.  The pistons show signs of seizure at the crown in this area. The cylinder walls show wear here also.

Looking at the carbon deposits left from combustion, there appears to be a hot spot from combustion right over the area where the pistons fail. I presume this is from the shape of the combustion chamber.


In the K series the combustion chamber is differently shaped and doesn’t display this same trait.  Also, the bore is smaller, and that also may play a part. I’m not an engineer and I can’t say with certainty if these factors do play a part.

However, the bottom line is the big twin pistons do get too hot, and so I decided to add piston jets as a cure to piston overheating.


By the way, Harley has added piston jet oil cooling to Twin Cams to help keep their pistons cooler, so there is precedent for what I’ve done.


So that’s the background as to why I’ve done this modification.


Here’s a picture of the conversion on my 46UL Chopper



What to Check First


There are 3 basic steps to performing this conversion.  

But before you start, your motor must be excellent condition.

The cylinders and pistons must be in good condition, preferably just redone.

Be sure to use pistons with a 3 piece oil ring. The valves must also be fitted to proper clearance to the guides, and you must use the earlier screw together valve spring covers.

The later clip type will not hold back all the extra oil that will get up into the covers with the sporty conversion. At least I never was able to get them to seal. 

When I did this conversion I added shovelhead valve guide seals to my guides to keep oil from entering the intakes via the valve guides.  It may have been overkill, but they haven’t given any trouble either, so you may want to consider them.


I had a problem the first time I installed the sporty pump with oil consumption.  The engine was worn and oil went past the rings and valve guides. 

That engine went through one quart every 300 miles, and the combustion chamber carboned up badly from the oil burned.  So I recommend a fresh top end before starting.


What’s Involved in Installing the Sportster Pump


First;  Modifying the Sportster pump to fit the Flathead cases.

Second; Modifying the original supply pump to act as a distribution block for oil to the engine.

Third;  Adding additional lubrication/cooling to the pistons.


The process isn’t too complicated and it can be accomplished with the tools most of us have in the shop. Also, the process is a reversible.  Everything described can be undone   at some future date, if you want to return to the stock oiling system.


This modification will provide about TWELVE TIMES the oil to the motor compared to what the original pump supplied.  With that extra oil, there will be plenty to add cooling jets of oil to the bottom of the pistons, to help them keep cooler and last longer without burning up.  The pump I used is a ’72 and later Sportster pump.  The earlier ones could be used, but the later ones pump more oil.


I have modified 3 different engines to accept the sporty pump.

I’ll describe the latest conversion to my 46UL chopper. This last time around I used the stock mounting studs in the right engine case and modified the pump to match them. On Frankenstein and my 44U, I modified the engine cases to match the sporty pump.


Modifications to The Sporty Pump.


These are the areas of the sporty pump that need to be modified:

Mounting holes

Pump bottom plate

Cutting down pump body

Shortening pump “snout”

And although it isn’t done to the pump, I’ve grouped it in that category;

Engine case return oil passage


Laying out the mounting holes.


This latest version uses the stock mounting holes in the right engine case for mounting the sporty pump. I did this for the obvious reason.  I really didn’t like the thought of drilling new holes in original “U” cases.


When making the conversion in this manner, you need some way to lay out the position of the stock stud locations on the sporty pump.  There are 2 existing holes in the sporty pump that almost line up with the stock “U” studs.  One is the inside front mounting hole in the sporty pump.  It only needs slight enlarging to work. The other hole is the original passage that connected the pump output to the engine case when it was on the Sportster. 

However, this hole it does not go completely through the sporty pump body and will need to be drilled so that it does. 


Before laying out and drilling holes in the sporty pump the rear inside original mounting hole on the sporty pump will need to be filled in.  Thread the hole for 5/16” coarse, and thread and install aluminum rod into the hole.  Use Locktite to secure the rod in hole.


To locate the location of the stock “U” pump studs on the sporty pump you’ll need a template. The easiest way to do that is use the tower part of the old flathead return pump as your template to mark off the locations for the new mounting holes.

 Install the sporty breather tower into the original return body. This way the shaft portion of the breather tower will fit in its hole in the sportster pump to give you one solid reference point.   See the picture.  Align the supply body on the Sporty pump body so that it looks pretty much as you see in the picture.


This picture shows the approximate alignment of the original pump body on the sporty pump. This will give the proper alignment to drill new holes in the sporty body.


I started by filing the front inside hole until I got the alignment I was after.  Then I bolted the two pump bodies together and clamped the two into the drill press.  Make sure everything is plumb. You want the new holes to be square in the sporty body. I then used the holes in the old pump body for a template.  I drilled the other front mounting hole, then drilled the inside rear mounting hole.  I put off drilling the outside rear mounting hole until I had made other modifications to the pump body.  You’ll see why later. The final product when all 4 holes are drilled will look like the body in the pictures below.  These pictures show most of the other modifications that are made to the sporty pump body as well.  You’ll see these modifications include some cutting, drilling, and filling with JB weld.


This photo shows the locations of the new mounting holes in the sporty pump.


Here are the mounting holes from the bottom side of the pump


Cutting and modifying the pump body.

This picture shows the pump body after it’s been cut.  This pump had been damaged as noted in the picture.  The missing chunk doesn’t affect pump efficiency.


One thing to keep in mind when looking at these pictures is that this pump had been modified for an earlier conversion setup. 


Steps involved in cutting and shaping the sporty pump


First, you need to make the big cut to the pump body.  This I did with a hacksaw, and the best guide to make the cut is to look at the pictures of the modified pump body.  This shows plainly where to cut.  The location isn’t too critical, but try to copy what I’ve done fairly closely, if only to copy a successful design.

After the body is cut, mill out the channel that used to be the return pump oil channel so that it will be easier to fit a replacement plate of aluminum into it.  You can use the photos as a guide as to how this will fit up.  I tried to cut the channel so that my filler plate actually rested inside the edge of the channel at the forward part.  You can see this in the photos. This was done to give mechanical strength to the positioning of the plate.  I also drilled and tapped a 6-32 hole to position and hold the plate to the pump body.  I counter sunk the hole for the fillister head screw I used. 

By the way, I used a milling cutter in my drill press as I don’t have a vertical mill.  Slow and steady will get the job done.  However, if you have a mill, or have a buddy with a mill, by all means, do it the easy way.

I used JB Weld to fill the voids and holes in the pump that I wasn’t using, and seated the filler plate in it as well.  I used the slow setting version as it has a higher temperature rating.  The photos on page five and six give the information you need regarding where holes are, and what gets filled with JB weld to block off and seal the modified body.

When you’re done, the pump should look like this:


In this picture, the pump body with filler plate has been installed for a test fit. You can see some of the areas that have been filled with JB weld, and the 6-32 Fillister head screw that helps secure the filler plate.


At this point, you can drill the last mounting hole in the pump body, as it can’t be drilled until the filler plate on the side is in place.


Transferring mounting holes to the upper portion of the Sporty pump


After the holes are made in the main body, you can transfer those holes to the upper pump body plate/breather tower.  It’s important to be very careful when laying out and making these holes for the mounting studs.  Small errors can creep in and multiply so that the pump won’t mount easily on the studs.  New longer studs will have to be made/bought to mount the sporty pump as it is obviously thicker.  I’d recommend getting a ¼” 24tpi die and make your own.  This isn’t what I did, but it is the best way to do the job.  That way, the holes in the engine case can be left entirely alone and not tapped to ¼” 20.


Fabricating a new lower plate

The original lower plate of the sporty pump can’t be used in the conversion. 

The reason for this is that the hole drilled for the front outside stud will not leave enough material in the stock bottom plate to form an oil tight seal with the main pump body. 

I fabricated the replacement plate from flat stock.  I’ve done 2 conversions, one plate made using aluminum, one using steel.  Both were ¼” thick.  I used thicker stock so that it would give more “meat” to tap a 1/8” pipe hole to carry the return oil from the return oil pump chamber.


This picture shows where to layout the hole for the return pump elbow.  Drill a hole in the new bottom plate that corresponds to this position.

This picture shows the new fabricated bottom plate and the  position of the return oil fitting.


 In the picture above I was using bolts to hold the pump in place, for ease in test fitting.  I used studs and dome nuts when I did the final installation.  The dome nuts helped seal against oil trying to leak past the studs, especially the one at the front outside, which passes right through the pump output passage.  There is also a close fit between the pump and the case through bolt at the rear of the pump, as can be seen in the above picture. 


This picture shows the recess for clearance for the bottom of the breather tower.  You can also see the tapped hole for the return oil barb. The surface was later smoothed with plate glass and wet/dry paper to remove the filing marks.


The photo above shows the recess that’s machined in the new bottom plate to provide clearance for the bottom of the breather tower/shaft.  I did mine on a lathe, but I suppose you could do it with a drill press if you were careful. Just copy the depth of the recess in the original bottom plate.


Front of pump showing supply pump output and bottom plate overhang


In the picture above you can see how the new bottom late overhangs a little in the area of the front outside mounting stud/bolt.  You need this extra material so that there is adequate material to seal off the bolthole we drilled in the pump body.

On this pump the “snout” was already broken off.  If you have a stock pump you will need to cut off the pressure sending unit extension or “snout” and tap it to take a 1/8” hose barb.  You may have to make an adapter to thread into the pump as I did to make the barb fit.  When doing this make sure that the small passage below the main one is sealed. I gobbed JB weld into the hole on this pump.  On another one, I tapped the hole 6-32 and threaded a small machine screw into the hole to seal it.  If you don’t seal the hole, you will have a leak.


Routing supply pump output, Exhaust pipe clearance issues


The output of the supply half of the sporty pump comes out of the hose barb seen in the picture above.  This particular pump had a broken sending unit “snout”, and was almost ideal for what we were doing.  The hose barb on the pump in the photos points forward.  This bike has drag pipes and an oil cooler mounted in the front of the motor. It was convenient to have the barb point forward for this installation


You can see the wear mark on the engine from the stock pipes.  There would be a clearance problem with a forward pointing barb and stock pipes.   If you were using stock exhaust pipes, you would have to use an arrangement of elbows to make the supply oil line do a very tight 180, so that it passed directly under the oil pump.  You might still have to modify the inside of the stock pipe to get things to fit.


On my other bike, which does have stock pipes, I mounted the pump so that the nose is rotated inward towards the engine cases, and that helps give more clearance between pump and exhaust pipe.  On that conversion , I modified the engine cases by moving the pump studs.  That way I used some of the stock pump mounting holes.  Overall, I prefer the later version that doesn’t move the holes in the engine case. 

I think the stock stud setup will work with stock pipes, but I haven’t done it yet. 


Modifiying Engine case for increased return oil flow


There is one more modification that needs to be done to fit the sporty pump.  The engine case needs to have two holes drilled near the present sump return hole in the case.  These additional holes will line up with the stock passages drilled in the sporty pump to aid getting all the extra oil out of the engine. 


This picture shows the additional holes drilled in the crankcase to increase oil flow from sump to sporty return pump


Again, extra holes will not prevent you from going back to using the original flathead pump should you want to return your engine to original sometime in the future.


That pretty much covers what needs to be done to fit the sporty pump body to the Big Twin cases. 








The supply pump is not used to pump oil with the sporty pump conversion.  However, it is used as what I call a “distribution block”.  Basically, the pump body is used to get the oil from the sporty supply pump to the  two places it needs to go in the flathead motor.  .


These places are the end of the pinion shaft to feed the big end bearings, and 

the added piston oiling system.

There are several reversible modifications made to the flathead supply pump body to make it work as a distribution block.




First, remove the pump rotor and vanes from the body.

Then, remove the bypass pressure regulating spring and ball. 

I used a flatside pump body to make the modifications.  It should be possible to use the centrifugal bypass body also, but haven’t tried it myself.

As mentioned earlier, the supply oil from the sportster pump enters an oil cooler on my bike after it leaves the pump. One of the main reasons to do this conversion is to help cool the pistons, so an oil cooler seems appropriate.  After leaving the cooler, it is routed via an external oil filter to the standard input fitting on the flathead supply pump.

In the pump, the oil is then routed via a ¼” hole drilled from the pump’s input chamber to the rotor output chamber.

As can be seen in the photos, the rotor chamber is blocked off with an aluminum ring and an aluminum peg so the chamber doesn’t fill with pressurized oil which would then try to flow past the rear cam bearing into the cam chest.  

This picture shows how the rotor chamber is blocked off and how the feed hole in the bottom of the chamber is blocked with ¼” aluminum stock.

This photo shows the passage that is drilled to pass oil from pump input to pump output.


The next modification to the pump is to remove the pressure regulating ball and spring from the pump body.  They won’t be used in the new setup. 


Next, you need to make a fitting to screw in where the cap for the bypass spring used to screw in. This is going to be the take off point for pressurized oil for the piston oiling jets. 

The threads are ½” fine, so I made a plug that threaded into the hole and had a 90 deg hole threaded into it.  This was tapped 1/8” pipe and a hose barb threaded into it.  From here oil is then piped to a banjo fitting on the top case through bolt in the “V” of the cylinders. I’ll explain how that is done later.


This shows the adapter screwed into the pump to feed oil to the piston jets. We used clear tubing for testing purposes only! You can also see the modified Sporty pump mounted and in position.  It takes a close look to see the difference.




The last modification to the supply pump isn’t actually done to the pump.  It’s done to the cam cover.  The hole in the cam cover that used to let oil that was released by the bypass pressure ball needs to be blocked.  This is done by tapping the hole to ¼” NC and threading in an Allen set screw and sealing it in place.  I used silicon sealant.  A major difference with using the sporty pump is that there is no pressure regulation; the supply oil is never bypassed into the cam chamber.  It wasn’t done on the Sportster, and it isn’t done when used on the flatheads either. 

Tapping the bypass hole is that last modification done to the supply pump. 


You can see the setscrew blocking the bypass oil passage in the cam cover. 

Here’s the same passage from the pump side of the cover.  No, I don’t usually glop silicone seal as I did in this picture.  This poor cover went through a fire, and was part of my test jig.  It never went on a bike.





The pistons are fed oil for cooling from a banjo fitting that gets its feed from the old supply pump.  The feed is taken from the fitting screwed into where the bypass spring went.  It is connected with hose/pipe to a banjo fitting from an old British Amal Carburetor.  The one I used had an angled feed that made it easier to clear the engine cases when the banjo was fitted up to the engine case.  The right engine case must be modified to make oil passages for the jets, and the cases must also be drilled and the jets screwed and loctited in place.


First, to make a passageway for the oil, the top motor through bolt hole must be drilled out to 7/16” inch for about 5/8-3/4”deep.  This creates room around the through bolt for the oil to travel.  Then inside the cases, where the 2 tapped holes for cylinder studs meet, a hole is drilled.  This hole is drilled upward toward the enlarged area of the case bolt hole we just made.  The hole should be about 1/8” in diameter. 


In this photo you can see the enlarged case bolt hole, and the smaller hole drilled down to the junction of the cylinder stud drillings.


After drilling this hole, you should drill the two holes for the oil jets themselves.  The jets are made from ¼” aluminum stock, so drill and tap two holes for the jets as seen in the pictures.  The jets will protrude about 1 inch from the case wall, so make them about 1 ¼” overall.  Drill a blind hole through the center of the jet with a number 30 drill.  Don’t let this hole break through the exposed end.  Then drill a number 63 hole in the side of the jet facing the pistons so it will squirt straight up to the underside of the piston.

I found the proper spot to drill the hole by trial and error.  I screwed the jets into place, then marked a spot that would point straight up.  However, when you take out the jet, drill it, then remount it, it will screw in slightly farther than the first time. So, you need to take this into account and mark your spot to allow for this shift!

When I drilled the .063 hole, I flattened the up side of the end of the jet, to make it easier to drill the 63 hole.  I used an old fashioned hand powered drill so as to be gentler on the small bit.


Before you screw in the jets for the final time, you need to fill the cavity where the two cylinder studs meet with JB Weld.  You want to form a plug with JB that won’t come out, but you don’t want to fill in the drillings you’ve made for oil.  You should locktite the jet in place after you’ve done the final fitting. 


In this picture you can see the rear piston jet in place.  The centerline of the jet is roughly even with the old crankcase baffle that has been removed.

In this picture of the front Jet, you can see how it is positioned in the engine case.  It is IMPORTANT to Clearance the pistons after the jets have been installed to be sure they clear.


It is important to remember to clearance the pistons so that they will clear the piston jets you’ve just installed.  You’ll need to fit up the flywheel ass’y and mark off the point of interference on the pistons.  I filed a notch in the pistons to give plenty of room for the jet. 


To fit up the banjo fitting to the engine case you need to make a longer case stud that will protrude out past the case and banjo fitting enough to get a dome nut on its end.  What worked for me was a sandwich of fiber washer between case and banjo, fiber washer  between banjo and flat washer, and small “O” ring that just fits over the case stud. Then another flat washer, then the dome nut.  On the left side of the cases, just a fiber washer, flat washer and a dome nut are needed. 


This photo shows the banjo fitting that routes oil to the piston jets via crankcase drillings.


That pretty much covers the necessary operations to install a Sportster oil pump on a Big Twin Flattie.  The process would be much the same for a 45 engine.

Although I did put a Sporty pump on Frankenstein, the 45/KH hybrid, As my first conversion, it differs considerably from what I’ve described here.  I believe this is best way to perform the conversion, at least the best I’ve done to date. 







  As I noted several times in this dialog, I’ve made this conversion on 3 different engines, and each time I learned more and incorporated changes in the next installation. The obvious difference externally was to cut down the pump body considerably from its stock appearance. There were two reasons for this.  The first was to gain clearance for the pump within the frame rails of the Big Twin Rigid frame.  The second was to increase oil tightness.  By moving the point where the return oil is tapped from the pump, I decreased the area of the body that had to be sealed.  The rear portion of the pump had proved problematic to keep sealed on the first 2 conversions.

Another change incorporated from earlier conversions was using the stock engine case mounting holes.  Besides conserving old engine cases for posterity, it allowed for all 4 mounting studs to be firmly mounted in the engine case.  Earlier versions had either added metal for the front outside mounting stud to mount in or forced rotation of the pump body to get the outside stud mounting point into existing metal on the engine case. Although the installation was a success, the stud just didn’t have enough “meat” around it to make me happy.

Another discovery made between the second and this conversion was the importance of  clearance around the top case through bolt to act as an oil passage.  Earlier versions had   used a 3/8” drill to add clearance for oil flow.  Bench testing before doing the current conversion disclosed that additional clearance around the bolt made a significant difference in oil flow to the piston jets.  An indirect result of this change was differences in oil pressure the 2 conversions carry. The current motor pumps around 20-25 psi cold, 10-12 hot. The previous conversion carried 60 psi cold , 15-18 hot.  The only difference in the motors is the diameter of the clearance drilling. 

The last item of interest is the huge increase in oil reaching the tappets with this conversion. I tried various tactics to decrease leaking around the late style tappet covers on the earlier conversion, with no success. I tried “O” rings, Thick cork washers,  and blocking the oil groove in the tappet block.  The last in the vain hope that although it might slow oil return, it might also decrease oil supply.  The engine coked up heavily, and the intake port was always slick with oil on disassembly.  Granted the guides were pretty worn, approx. 007 loose.  So, my addition of valve guide seals may have been overkill when I installed new guides, but I was determined to have an oil tight machine.


The screw type tappet covers have worked out fine. I use Sportster tappet block “O” rings to seal all the joints instead of the standard “stuff”.  They need to stretch a bit to fit, but they get the job done.


I hope this has been of interest, and perhaps sparked you to undertake this modification yourself.  These old motors need to be seen and heard, and this modification, I believe, will make it possible for them to spend more time in the breeze.

Happy Motoring. 

Dick Linn, Aka Frankenstein