Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Amount of circulating oil.

Amount of circulating oil.

Moderators: Curt!, Pa

Post Sun Mar 23, 2014 5:43 pm

Posts: 491
Location: Six miles East of Cheney, Wa.
Just curious, for those of you with stock oil pumps, when you look in your oil tank, with the bike at a somewhat fast idle, do you get/see a constant flow of oil from the return pump, or a pulsating, spurt-spurt flow?

Curious minds need to know.

Thanks.

ken.

PS. 45.6 miles...!!

Post Sun Mar 23, 2014 6:32 pm

Posts: 47
If the bike has been sitting for a long time and has sumped you will get a steady stream until the excess oil has been pumped from the crankcase.

If there is not any excess oil in the crankcase, you will only get a spurt, spurt, which is normal.

Post Thu Mar 27, 2014 5:47 pm

Posts: 3061
Location: Central Illinois, USA
Knucklebolt!

Please remember also, that after the sump has been evacuated,
it will be pumping a lot of air along with oil.

Don't know why it spurts though.
It must be the breather window on the return pump opening and closing.

...Cotten

Post Thu Mar 27, 2014 6:36 pm

Posts: 1660
Location: Interlaken, NY USA

Hi K.B, It spurt spurts because it's only pumping one quart every 11 minutes. The sportster setup pumps 1 quart per minute. At that rate, it does flow pretty much continually.
DD

Post Thu Mar 27, 2014 7:59 pm

Posts: 491
Location: Six miles East of Cheney, Wa.
That would explain why my oil stays so cool on these short rides I've been doing, about six to eight miles at a time.

So, along those lines, if you increase oil pressure, are you also increasing volume? If so, is there a linear relationship. ? I would assume not. I realize, with small block Chrysler high volume pumps, and other automotive pumps, you are not increasing oil pressure when you increase volume, but what about visa versa? Same relationship?

However, I'm having trouble wrapping my mind around the concept that more oil pressure, in it's self, does not also increase volume to at least some extant. ??

I probably need to study the oil pump schematics better. !!!

Thanks.

ken.

Post Fri Mar 28, 2014 5:39 am

Posts: 536
Location: Wa, USA
More volume through the same size passage will cause an increase in pressure. The pressure relief spring and ball in the oil pump unseats at the maximum pressure it is set for and the excess oil flows through a passage into the cast well under the rear cam where it gets picked up and thrown all around the cams and then runs down into the hole with the screen at the bottom of the cam chest. Tightening up the pressure relief spring will increase the maximum pressure and send more oil to the rods.

Post Fri Mar 28, 2014 4:57 pm

Posts: 1660
Location: Interlaken, NY USA

As Woody says, raising the relief pressure will send more oil to the rods, but the limiting factor is that the pump just doesn't move very much oil. So, when warm, when the oil thins to operating temps, the volume isn't there to raise the pressure causing the relief ball to actuate. When you've got some time, you should do a search on the board for all the various threads in reference to oiling on the big twin flatheads. Many have contributed to these discussions, including Woody and myself.
DD

Post Sat Mar 29, 2014 8:39 am

Posts: 536
Location: Wa, USA
The Doctor is correct about the stock pump not having enough volume to get more pressure. If the pressure relief spring is adjusted too high the ball doesn't open and no oil goes to the cam chest other than mist circulating in the engine. With pump modifications to increase volume, the spring can be adjusted to a maximum of about 45 psi. A stiffer spring may increase this, but would probably be unnecessary overkill.

Post Sat Mar 29, 2014 6:00 pm

Posts: 491
Location: Six miles East of Cheney, Wa.
Yes, did some searching, and it is a most interesting subject. What I was having trouble understanding, and what seems so simple now, is that the pump pumps "X" amount of oil, regardless of where the pressure is set at. Makes sense!

ken.


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