Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Modified two-section return pump

Modified two-section return pump

Post Sat Sep 09, 2017 4:58 am

Posts: 7
Location: Dresden, GERMANY
Hi guys,

first I want to say thanks to Frankenstein, Woody, Georg Greer, Pa, Tim and Panic and all the others who share their knowledge in this board.

I have built a two-cavity return pump like it is explained in victory's 80 performance book to feed two piston skirt oilers for my 4-5/8 stroker. Now the problem is lots of burned oil and wet combustion chambers. The compression rings (new pistons, correct ring gap) seem not to be able to handle the additional oil in the crank case. I am grateful for every suggestion. May be a Krank Vent can solve my little problem? Or should I install thinner XL gears and everything is fine?

A few details:
- stock feed pump
- breather rotor slot is enlarged to xl size (20° ATDC to 65°ABDC)
- breather tower slot enlarged
- both return pump cavities are fed from the oil in the gear case
- upper gear cavity (std thickness of 0.315) acts as return pump
- lower gear cavity (also std 0.315 gears) has 2 outlets. One to feed the oil jets. The second outlet runs into a return line and is equipped with a manually bypass valve. With this bypass I try to regulate volume and pressure to the skirt oilers. If the valve is shut, the oilers squirt very well just slightly above idle speed but its too much oil for the compression rings. If I open the valve to the point where no oil is burned anymore, the pressure is not enough to let the oil jets squirt.

Best Regards!

Post Sun Sep 17, 2017 12:21 pm

Posts: 1701
Location: Interlaken, NY USA

I'm not familiar with the 2 cavity pump layout Panic proposes, so I'm not sure what proportions the oil between the two cavities. I don't know if that will make a difference or not, just wondering if it could affect evacuation of the crankcases.
I am concerned with enlarging the slot in the breather tower. I've not read anywhere that is of help. The "Z" slot modification calls for the tower slot to be left alone. Likewise, my experience with the "dash"72 sporty pump shows that the tower slot in those pumps is the same dimensions as the original "45" return pump. I'm thinking opening up the tower slot could adversely affect crankcase scavenging.
Also, are you using modern 3 piece style oil control rings? They are a must with any mod that puts more oil back in the crankcase.
Just to encourage you a bit, I built Frankenstein with the "dash" 52 sporty/K pump, which, although pumps less oil than the -72 pump, outputs way more than the stock supply pump.
Just as a reminder, stock pump 1 qt/8minutes, -72 pump, 1 qt/minute.
Frankenstein uses the stock "K" skirt oiler orifices, fed from a split in the return line to the oil tank.
At any rate, that bike has no problems whatsoever with consuming oil.
The stroke is 4 13/16", by the way.

Post Tue Sep 19, 2017 6:33 am

Posts: 7
Location: Dresden, GERMANY
Thanks for the response! So I am going to order the 3piece oil rings this week. These are recommened quite often.
I enlarged the tower slot just in high, so it matches the bottom and the top of the XL rotor slot. May be enlarging it was a mistake but it was done after the oil problem appeared. It can't be the cause for it. Anyway the tower slot of the next pump will remain stock! The jets are made of aluminum tube as shown on your web site with 0,8mm (0.0315") holes.

You were a great help.

Post Tue Sep 19, 2017 5:18 pm

Posts: 1701
Location: Interlaken, NY USA

Glad to be of service,

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