Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Oil pumps

Oil pumps

Post Sun Sep 21, 2008 8:02 am

Posts: 1676
Location: Interlaken, NY USA

Now another question that's bothered me forever on sporty pumps. Just exactly what does the small hole to the left of the gear chamber do? It connects to the passage that leads from the "nose" of the pump. It is beyond the siphon plunger and spring, and before the pressure switch. All opinions welcome.
My guess is some sort of bleed passage to remove pressure from behind the plunger so the light will go off, but that seems like a pretty weak story to me.

Post Sun Sep 21, 2008 1:01 pm

Posts: 93
Location: Norway
Ok, so timing chest is now lubricated from oil mist coming from the big hole in the center of the breather valve?

You say that you had leakage-problems i case-joint. Is it possible that breather valve is timed different on XL and BTSV? Can this be part of the reason?

It might be useful to try to draw a hydraulic flow-diagram over the pump to solve the purpose of the hole you mention. Its difficult to see where the channels is leading in the pictures. A pressure relief to reduse oil flow on high rpm makes sense on a race engine (double rpm do not demand double amount of oil according to David Wizard for instance).

As for lubrication of the tappets/valves: in my motor the intake valve guide is getting good lubrication, but the exhaust guide is running more or less dry. This is causing the exhaust valve guides to wear faster (no tappet lubrication problem though) Or maybe high exhaustvalve temp is causing the oil present to burn up? Is like this on your motors Frankenstein?

My theory is that heavy weight oil is what destroyes the many pistons... This is because heavy oil causes more of the oil to flow to the timing chest and less to the crankcase/pistons (because of the pressure relief valve). Oil circulation with stock upset is low and oil temp in tank is never high, making this worse. Maybe heavy oil gives more problems with cavitation too? I have always used 10W-40 oil, and have never had a burnt piston. I expect alot to desagree... :-)

This sportypump-conversion is very interesting!

Post Mon Sep 22, 2008 8:22 am

Posts: 1676
Location: Interlaken, NY USA

Sidewinder, Yes, the "oil mist" from the center of the breather is lubing the timing chest, but I think "oil Hurricane" is a better description, with a quart of oil per minute mixed with air coming up through the gear. :lol: As for the case joint, that may not be directly related to the new pump, as it leaks standing still. The joint weeps just sitting.
Interesting theory on piston failure due to heavy oil. I won't say it isn't so, I never ran multiweight until I had switched to the sporty pump. Then I saw no difference in oil pressure when warm. But you do have a point that the oil tank doesn't get hot with the stock setup. I'm glad it works for you.
As for guide wear, mine have been loose for years and I hadn't changed them because at first they weren't available, and I didn't realize the importance of a good fit on a flathead 'till recently.
There's more on the oil pump stuff on my website, ... typump.htm

This is the latest conversion, using the stock oil pump mounting holes in the engine case.
Earlier versions required moving the stud mounting holes in the engine case.

Post Sun Nov 30, 2008 5:50 am

Posts: 976
Location: Markt Einersheim, Germany


I guess that you did not receive my PM I will, (again) in public embarrass myself...

"In case you're using an earlier rotor, the 1972-76 rotor (26331-72) is similar (except for the much larger breather opening"...

Does this mean that using the above mentioned part number rotor, having the larger breather opening..........that one would not need to make the "Z" rotor mods??



Post Sun Nov 30, 2008 8:42 am

IMHO the 1972-76 rotor duration is suitable, but the exposed area is larger than I want and will not keep large droplets in suspension into the cam chest.
To casual observation, the obvious mod is to increase the transfer area as much as possible to reduce pumping loss. However, this is clearly not what the factory discovered in extensive testing - the maximum window area in the 1/4-speed pump is far smaller than even the stock 45 pump.

Post Sun Nov 30, 2008 10:27 am

Posts: 1676
Location: Interlaken, NY USA

Panic, Interesting observations on the rotor timing. Of course, the first thing that popped into my head is that at 1/4 speed, the window is exposed 2 twice as long, so the window would be 1/2 as wide just to maintain the same timing. I presume you compensated for that in your observations though. I've never had the opportunity to see the 1/4 pump rotor. I guess the point being that higher velocity maintains better oil suspension and thus better scavenging of the crank chamber. The trade off being slightly higher crank chamber pressure?
The whole process of moving oil with air flow is apparently quite complicated. Guess that's why they ended up just sucking it out of the bottom of the sump.

Post Sun Nov 30, 2008 1:22 pm

Yes, the window widths must be twice as long.
The duration is defined by the factory as the interval in degrees (or seconds) from when the rotor cracks open .002", gradually exposes its full width to the housing slot, passes by and gets to .002" of closed on the other side.
Only the circumference (not the width, since the contact is on the outer rim) determines the duration, and this is the total of the rotor width + the housing width.
The maximum size is the smaller of the 2 slots, so you can have the same duration with a really wide housing slot and a .002" rotor slot, a really wide rotor slot and a .002" housing slot, etc.
The stock housing slot for all pumps 1937-71 is 11/32" (.34375") wide, or 81° since the rotor is exactly 1.00" diameter. The stock 45, UL, K, KH and 1957-71 XL slot is 3/8" (.375") wide, or 88°. The duration is 169°, only the opening and closing points vary between these engines.
The maximum opening is the (smaller) housing at .34375".

The 1/4-speed housing width is .270°, or 126°. The 1/4-speed rotor width is .214°, or 99°.
The maximum opening is the (smaller) rotor at .214", only 62% of the width (actually, the height is also greater, so the area comparo shouldn't be based entirely on the widths).

Post Sun Nov 30, 2008 7:23 pm

Posts: 1676
Location: Interlaken, NY USA

Thanks for all the info, so the duration on the 1/4 rotor is a total of 225 deg. The smaller opening giving
the higher velocity to the flow.
However, I'm having a problem duplicating your timing in degrees, I'm missing something by a few degrees somewhere.
for instance, I took the standard slot of .375", and determined it was the chord of the arc formed by the opening in the tower, with a Radius of .5". Plugged it into an online arctan calculator. (all I had handy) I got an angle of 41.1 deg. Times 2 for half speed rotation, 82.2 deg. Somewhere I lost 5.8 deg. I had similar errors for the rest of the calc's.
My reasoning was thus:
Radius of the tower: .5"
opening of .375" is chord of arc of the opening.
Chord and 2 radii form an isosceles triangle. Normal of base, (the .375" chord) to the vertex forming a right triangle with a base of 1/2(chord)
ArcTan of angle with opposite= .1875", adjacent= .5". Angle= 20.55deg. Times 2 for total angle of Isosceles triangle, 41.1 degrees. Times 2 again to account for 1/2 speed rotation, 82.2 degrees.
Obviously, I'm missing something, question is, What?

Post Tue Dec 02, 2008 9:04 am

Sorry, I can't find my notes, although I was fairly careful when this was developed (but it was 20 years ago).

Post Tue Dec 02, 2008 11:02 am

Posts: 93
Location: Norway
I think you have to use sinus, not tangens.

Post Tue Dec 02, 2008 1:31 pm

Posts: 1676
Location: Interlaken, NY USA

Panic, I knew you must be right, but couldn't see the forest for the trees. Sidewinder, you're right, that's the error. I should have used arc sine, not arc tangent. Anyhow, I guess the final question is, is it worth switching from the late style 72- breather to an earlier one modified with the "Z" cut? The final result, I would guess, is carrying less oil in the flywheel chamber cutting windage losses, right?
Again, sorry for all the confusion with my lousy math. It was late at night and I'm easily confused and convinced :oops:

Post Wed Dec 03, 2008 10:17 am

Thanks, but please: never "know I'm right".
Everyone macht ein kleine dumheit, jah?

Post Wed Dec 03, 2008 10:27 am

I'm fairly sure the factory did their homework on this - a bigger motor can use more area to get the same scavenging efficiency with lower pumping loss. If they were making a new part I'd have some doubts, but since the change here was already part of the new gear stack (and therefore only required a change of dimensions, not more parts or more complex parts) I don't think it's critical.
However: I'll suggest that an asymmetrical cut (like the Z) is closer to the effect of the 1/4-speed (small window, but lengthy exposure) than any stock breather. They may simply not have considered it, it may have been in testing when the deadline came due, or (most likely) they found that it couldn't be done with the existing tool set-up.
There are even more possible methods (some are tunable), but the better ones are complex and involve external mods.
BTW: this is an example of how WR development in vintage racing has stalled in 1948: the 1/4-speed pump is absolutely an advantage, the 1/4-speed pinion gear is compatible with the WR pinion shaft, and the 1/4-speed rotor can be adapted to a std. pump - yet I'm not aware of any attempts let alone use of such. The innovators like Al Knapp are few and far between, everyone else worships at the altar of "what they did in 1948 was perfect and cannot be changed".

Post Thu Dec 11, 2008 2:43 am

Posts: 93
Location: Norway
What do you mean with asymetrical cut / Z-cut? I do not understand what type of modification this is.

Post Thu Dec 11, 2008 9:04 pm

The duration is increased by only widening part of the rotor on both sides. The center where piston speed is highest still sees the original maximum window area.

Post Fri Dec 26, 2008 1:10 pm

Posts: 2399
Location: atascadero cal usa
correct me if i'm wrong but the rear cam always sits in a puddle of oil creating a slinger that sends oil flying thru the cam chest cavity creating plenty of mist drops and a pretty violent storm of oil air air in there
pointed out is a ledge in the case that once the cover is on causes this puddled area
my point is no matter what there should always be enough oil in there for lube to get to the guides
i suspect the oil thats too thin isnt getting to the exaust guides cause of heat and the oil being so thin doesn't stick to the valve stem long enough to get up in the guide

Post Sun May 10, 2009 5:30 pm

Posts: 543
Location: Wa, USA
Well, I finally got everything to work right on my modified oil system. This is with a spacer body in the scavenger pump with an extra set of gears for a feed pump and driven by a Sportster breather gear. I used an early feed pump body with the late spring and screw for pressure relief and distribution. The stock pump cavity is blocked with a plug. I have posted the unrestricted capacity of this pump in earlier posts, so I won't cover that ground again.

Final test results showed that this system will pump more than enough oil when using a stock pinion shaft. Testing with a shaft modified for full feed showed a lack of capacity to feed both the shaft and skirt oilers. Listed below are the results of the testing at different RPMs. The speeds may look a little odd, but that is because I used a Bridgeport to drive this test, and I only have a step pulley unit so I am stuck with the speeds that it has.

Some other things that I noted during this process: A hard line (I used copper) to the skirt oilers must be used. Plastic is too flexible and used enough pressure for the system to operate. The cam cover bushing for the rear cam (feed pump drive) must be drilled for oiling like the other bushings in the cam cover. Blocking the rotor cavity in the feed pump means that this bushing does not get any oil from the pump. Drilling a bleed hole in the plug would result in a pressure buildup that would push the cam toward the inside and wear on the inner bushing face. All speeds had good return flow. I ended up with skirt oiler jet size at .030". Smaller did not flow and larger flowed too much. At 1750 RPM, they squirted 12 feet across my shop.

All test numbers are with the pressure relief screw set at the stock setting. (3/8"below the surface) Screwing the adjuster down more did not have any real benefit as this system maxes out at about 55PSI and at that setting, it does not bypass until very high RPM and the cam chest gets starved for oil.

660 RPM: 20 PSI, good rod flow, oilers dribble.

1110 RPM: 30 PSI, oilers dribble more.

1720 RPM: 45 PSI, oilers squirt very well, good bypass flow to cam chest.

2720 RPM: 45 PSI, lots of oil to oilers and cam chest.

I have pictures, but I am having trouble posting them here, so if anyone would like to see them, please email me and I will send you the pics.

Post Sun May 10, 2009 8:30 pm

Posts: 976
Location: Markt Einersheim, Germany


Do you still have my email address??


Post Mon May 11, 2009 5:32 pm

Posts: 83
I would love to see these pictures!
If it doesn't bother you, please send them to me thanks

Post Mon May 11, 2009 6:31 pm

Posts: 543
Location: Wa, USA
George and helsingborg, pics are on the way.

Something that I left out of my last post: I tried 1/8" copper line and it was too small to flow enough. I used 1/4" copper for the successful testing. I think that 3/16 might also work, but while I have some copper line in that size, I could not find fittings for it.


Return to Big Twin Flatties