Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties U-model oiling

U-model oiling

Moderators: Curt!, Pa

Post Tue Nov 07, 2006 9:10 am

Posts: 640
Location: Wisconsin, USA
I know this has been discussed before, but I want to try it one more time. Is there any doubt about whether or not the scavange pump can properly evacuate the oil from the crankcase if the pinion feed is continuous? I am about to finish up a 41ULH motor and would love to pull the plug from the end of the original shaft and notch the bushing so I could end feed a continuous supply like the 73^ big twins. It is not a race machine, so a little extra oil in the crankcase would not be a concern unless it can reach a point where the crankcase pressure is high enough to cause the usual wet sumping problems. I would appreciate any opinions. Thanks, Kyle

Post Wed Nov 08, 2006 5:22 am

Posts: 11
Location: The Netherlands
Don't do it, you will be over-oiling the engine. I did it once with my '43 WLC. Had to change to pistons with modern rings. Even then it was a disaster, oil was coming out everywhere, through the generator, breather, and so on. Reverted to a home-made two-hole pinion shaft bushing, a compromise that works well in combination with modern piston rings (Hastings narrow compression rings and wide three-piece oil control rings). Oil consumption is about 5000 (yes, five thousand!) mpg.
The '73 shovel engine had full flow indeed, but it was not any more the high pressure oil that was fed to the pinion shaft bushing. A common misunderstanding that led to many disastrous full-flow conversions (not enough pressure left to properly lubricate the top-end).
JW

Post Wed Nov 08, 2006 6:11 am

Posts: 11
Location: The Netherlands
P.S.: The scavenger pump will manage it, because the total flow to be returned does not change much. With full-flow almost all of the oil passes through the crankshaft and crankcase and timed breather to the gearcase, with the factory system almost all of the oil goes directly to the gearcase via the by-pass valve.
JW

Post Wed Nov 08, 2006 8:15 am

Posts: 640
Location: Wisconsin, USA
Thanks JW for your thoughts. Your experience says that continuous supply caused wet sumping and created enough crankcase pressure to push oil out in the WL motor. I wonder if the UL would be affected the same way, given the larger crankcase volume. You made a good point about the scavange pump having to return the same amount of oil regardless of whether it was gearcase or crankcase. Maybe some compromise between the timed for vacuum enhancement drip and full flow would be the way to go. How did you locate the additional hole?

Post Wed Nov 08, 2006 9:23 am

Posts: 542
Location: Wa, USA
I did the full flow on my U with a groove around the pinion shaft and had the same problems with too much oil in the crank case. I would not do it again. This year, I have just opened the hole on the pinion shaft a little to make the oil shot to the bearings a little longer. End feeding on a motor without Timken bearings pushes the crank over and wears out the thrust washers.

Post Thu Nov 09, 2006 5:42 am

Posts: 11
Location: The Netherlands
The second hole in the bushing was placed at 180 degrees from the original one. I probably had to make a groove in the outside of the bushing to connect the holes - can't remember, it's decades ago now.
The crankshaft side-load is another con indeed: at 30 psi oil pressure it mounts to approx. 5 pounds.
JW

Post Thu Nov 09, 2006 8:50 am

Posts: 640
Location: Wisconsin, USA
There is a groove all the way around on the od of the bushing. Thats how the oil is passed to the 10 o'clock hole in the bushing. Given that end feed may cause the flywheel assembly to work against the left race, I suppose that it's not a good idea. I like the idea of a second hole, when the pistons are on their way up the rods get a blast of oil. Considering that big flat cylinders seem to wear much faster than overhead models, and heat is likely the major cause, it is reasonable to think that the greatest amount of oil flow short of wet sumping would be optimum. I think rod endplay would have a lot to do with flow as well. At the minumum spec the stuff has a hard time getting out of there. If you could just figure out a good way to evacuate the crankcase, you could push a lot more oil thru the rods for splash to cylinders. Would it be practical to draw oil to the scavage pump from a line to the bottom of the crankcase as Indian did? It would be less noticable than a skirt oiler.

Post Fri Nov 10, 2006 9:15 am
panic

A line from the sludge trap opening looks like a good idea, but it violates a basic law of hydraulics: any additional opening in the suction line is a syphon break.
The pump will always prefer to pull air rather than oil. If either of the 2 feeds (external line or drain in case) loses prime, the other one will also, and re-priming them may need to be done manually by shutting one line off. This can only work if you have a way to keep both feeds submerged at all times. Otherwise, oil will build up in the section that's full until the OTHER line is wet - hard to regulate.
In some chassis (not stock) where space permits, this could be cured by fabricating a driveshaft for the rotor in the return pump, and lowering the pump to level with the bottom of the case so any openings will self-prime from gravity.
The factory cured this in 1977 by making the return pump feed only from the sump, and cam cover oil drained through the right wall into the case.

Post Sat Nov 11, 2006 9:11 am

Posts: 640
Location: Wisconsin, USA
Panic, I thought about this a bit and I can't see a problem in this intance, based on the assumption that there is already a lot more oil in the crankcase. Since the pump is getting return oil by gravity rather than having to pull it from the crankcase scrapers as well as the gearcase it shouldn't suffer from a flow loss. If the gravity flow was lost for any reason, the crankcase would likely have plenty of oil to fill the added return line. I can't imagine a time when the gears would be spinning in air.

Post Sat Nov 11, 2006 9:25 am
panic

The pump never gets oil by gravity except from the gearcase (pressure relief), and at low speed there isn't much.
Only 1 of the 2 points needs to have aerated oil around it for suction to be lost. More oil removed by the pipe from the case = air in the return pump inlet from the rotor. I agree that the oil level will build up eventually, but can the return pump self-prime when there is expandable gas, rather than liquid, in the line?
If it wasn't a problem, why did H-D throw away the cases and pump and start over?

Post Sat Nov 11, 2006 3:46 pm

Posts: 1675
Location: Interlaken, NY USA

So I guess I'm going to jump in on this and ask why I haven't had problems with Frankenstein?? Did I do enough wrongs to make a right? First, I have no problems with the oiling system. oil returns, and mostly stays inside the motor, except for some typical weeping at the valve covers and a little at the oil pump/case gasket, neither of which indicate anything but a backyard engineering job with inadequate sealing at these points.
With the Sporty pump and full flow to the pinion I'm adding more oil to the flywheel chamber over stock 45 I'm sure. With no breather slinger on the generator gear cause the gear just isn't there I've created another potential problem, and I also do not run the vent line from the cam chest to the oil tank. That hole is plugged off because the BSA Oil tank vents to atmosphere with no provision for the 45 vent line.
The end result is as I've said, the oil stays inside. The breather seems to be every bit as dry of oil mist as my "80SV. And as I've said, there's no sign of an unstable oil scavenging system. Maybe the lack of tank-cam chest connection is responsible for my differing results? I don't know, but it does work. I've certainly run the machine at high rpms and ridden it hard.
Don't pretend to have the answers, just relating my personal experience.
Dr. Dick


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