Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties CHP oil pump

CHP oil pump

Post Thu May 19, 2016 3:19 am

Posts: 12
Location: wisconsin
Wondering if the stock scavenger pump will handle the higher flow of the CHP pump, or must the high return kit be fitted ? I know some of you have run this pump for a couple of years; any negatives ?

Post Fri May 20, 2016 5:18 am

Posts: 2
Location: Vinopottula, Finland
You are better off with the improved scavenger pump. At least my mild stroker was flooded with the stock one. Stock pump body can be milled for iron head sportster scavenger gears. Bit tricky, but might be good enough.


Post Mon May 23, 2016 6:37 pm

Posts: 568
Location: Wa, USA
I have the CHP feed pump and scavenge pump upgrade on my U. The only issue is that I must shut off the top cylinder oilers for cold startup until the oil warms up a bit. If I don't, it pukes out the breather. Once it's warm, there is no problem.

Post Thu May 26, 2016 12:48 pm

Posts: 19
Extra S..JPG
Crank vent valve
Extra S..JPG (137.15 KiB) Viewed 11980 times
Extra scavensystem.JPG
modified oil tank cap
Extra scavensystem.JPG (144.7 KiB) Viewed 11980 times
If you run piston cooling jets and prolonged opening time at the pinion oil hole, you end up with too much oil
in the crankcase. The crank vent channel on UL's are very small in fact it's about the same as the 45's. OHV'S have
at least 4 times the area.
So what happens is you get plenty of oil in the crankcase and it acts like a brake. I have measured 1.5 pint
when opening the drain plug after running the bike. To solve that issue I drilled a hole into the vent channel
( rear a bit under the motor mount ) tapped 1/8" NPT and connected a 3/8" hose and a breather valve and then
into the oil tank cap. Now you have two independent scavenge systems and when opening the oil drain plug there is
about 1/2 pint which is good. When the pistons goes down it forces the oil out and when they go up the crank vent closes.
About puking out the breather some pumps are not 100% leak free at the check valve. When it sits oil leaks into the motor
not uncommon on OEM pumps. The latest batch of pumps have improved precision on that seat & ball.

Post Thu May 26, 2016 5:44 pm

Posts: 1726
Location: Interlaken, NY USA

So, help me to understand what you've done. You tapped into the passage at the rear of the motor, that carries oil and exhausts breather air. This is the passage that normally is vented through the return pump timed rotary breather valve, right?
So, I see a white object with a brass top to it in the first picture that has a 3/8" hose coming off the top of it at right angles. I assume this is the line that goes to the oil tank fitting we see in the second picture right?
My question, what is the white object?
May I assume it is some type of one way valve, to let air/oil mist out of the passage, but prevents back flow?
Is the position of this vent passage you've added critical for proper operation?
Can you feel the difference in performance from having less oil in the base?
If this works, it sure solves the breather problems with the big twin. I just recently tried enlarging the exit breather tube and cut down the perforated genny gear until it resembled the single flat washer as used on sportsters. The jury is still out on that mod.
I had put an automotive vacuum/boost gauge via adapter to the timing plug hole, but the results were inconclusive. The response time of the gauge was too slow to give meaningful data. LIkewise I tapped it into cam chest via the fitting normally going to the oil tank breather line, but again, inconclusive results. At low speed, the vacuum pulses are easily seen, and no positive pulses observed. At higher speeds, the gauge just nulled out, not being able to track the rapidly changing conditions.
Glad to see your continuing research on the BTSV.

Post Thu May 26, 2016 6:45 pm

Posts: 568
Location: Wa, USA
I have a ball valve in my feed line to the piston squirters to avoid the seepage past the check ball. If I turn it on before a cold start, I get puking from the breather. If I cold start with it closed and wait until the oil has warmed up a bit, I get no puking when I open the valve.

Post Fri May 27, 2016 12:34 pm

Posts: 19
The white object is actually an aluminum one way valve . Have pictured a similar one attached.
I don't think it's very critical where the hole is positioned as long as it's located in the lower end
of the vent passage. I marked on the pic about where I have it on the test motor ,
I think a bit further rear. It was done with the motor in the frame, only took the primary covers off.
Performance is like day and nite.
P5270201.JPG (153.25 KiB) Viewed 11925 times

Post Fri May 27, 2016 2:49 pm

Posts: 1726
Location: Interlaken, NY USA

Neat, especially if you don't have to pull the engine to try it. Are you thinking that by positioning it low on the passage, it will pick up more oil that mist?
Also, does anyone know where in the States a valve like the one pictured is available? I'm thinking I will have to try this.

Post Fri May 27, 2016 3:17 pm

Posts: 19
The one I have on the test motor is from
The one on the pic is German made sold by www. not tested yet. ( much better price)

Post Fri May 27, 2016 8:13 pm

Posts: 1726
Location: Interlaken, NY USA

After asking the question, I got off my lazy but and did a little web surfing, and found this: ... -9582.html
Sounds as if it will work, I found the Krankvent as well, but figured shipping might make it more expensive.
Can't wait to try this. I've got some clutch hub work to do anyway, so I might as well pull the inner primary and try this mod out. It's easy enough to plug the hole if it doesn't work out.
I don't see me switching to your pump any time soon, only because I'm already gone down the sporty path for more oil. But, I"m betting I'm carrying too much oil in my cases as well.
Have you seen this site? ... opic=105.0
Some interesting views on Big Twin Sidevalves, I'm trying to adsorb the info, but Google's literal translations make it tough going.
I don'

Post Sat May 28, 2016 2:28 am

Posts: 19
There are several cheap valves on the market, some are very restricted in flow.
The Krank Vent flows well and shuts fast. There are others also good. You can easy check by blowing and sucking.

Post Sat May 28, 2016 9:44 pm

Posts: 12
Location: wisconsin
Since venting the crankcase in this manner isn't timed, is enough oil being blown into the cam chest through rotary breather to lube cams and gears ? Or does the CHP pump bypass plenty of oil at all RPM ? Would zeeing the rotary breather accomplish the same thing? OM

Post Sun May 29, 2016 9:34 am

Posts: 1726
Location: Interlaken, NY USA

I'm running the late sportster breather which has roughly the equivalent of a "Z'd" rotor I believe. If memory serves me right, Late sporty timing is 20deg after TDC open, 80deg after BDC closure. I still think I'm running too much pressure in the system, as it's difficult to keep oil on the inside. I'm interested in seeing what this mod will do, I"ve ordered a valve, probably get around to it next weekend. It''s easy enough to undo if I'm not happy with the results.

Post Sat Jul 16, 2016 1:29 pm

Posts: 1438
Location: Ojo Caliente,NM,USA
Dis you ever try it? I just got these valves in from Duff over on the Virtual Indian list.
Image Image He calls them Moto Valve they are cast brass with a tool steel pin and stasinless disc. they will either mount to a flat surface with a hole to the crankcase with the two screws or the steel adapters that fit a late Indian timing plug hole. I plan to run two on the Bonneville bike the other two are for the backup engine. they seem to flow well and the responce is amazing. When I ordered they were $38.50 each, the adapters were Either $1.50 or $2.00 CRS again and shipping was $4.00.
I plan to do a thread over on the Indian section about his products when I can get him signed up here. Being a Indian only person he was a little miffed that the person verification question was the name of the wartime Harley 45 he had no clue and wants some Indian questions. :lol:

Post Fri Aug 19, 2016 3:47 pm
Pa Site Admin

Posts: 6226
Location: Ohio USA

Dusty...Did you get the PM I sent to you the other day ?

Post Sat Aug 20, 2016 8:51 am

Posts: 3539
Location: Central Illinois, USA

I received my first Motovalve from Duff perhaps a decade and a half ago, although I still have it un-used for my Chief corpse.

If you need someone to translate brandX to Indian I would offer if it was ordinary, but race stuff is out of my zodiac.
Did you come up with any breathing flow requirements for your displacement? More than enough may be too much.

Big Base Scouts were supposedly faster than Chiefs because their pistons rebounded upon the compression within the cases.


Post Wed Aug 29, 2018 5:33 pm

Posts: 35
Location: San Diego
Interesting, need to do some serious research here.

Post Thu Dec 20, 2018 7:57 pm

Posts: 568
Location: Wa, USA
Do you need a vent line from the oil tank to prevent pressurizing from the extra crankcase vent?

Post Sat Dec 22, 2018 10:51 am

Posts: 568
Location: Wa, USA
Found this on McMaster-Carr.
Is there any reason that wouldn't work?

Post Tue Jun 23, 2020 11:21 pm

Posts: 10
Big Twin Sidevalves need more oil than WL series, that's a fact. It remains to be seen is how much oil is really needed. I see some negative points in the Swedish pump, and I have this pump. The first is excess oil. Although the original return pump has a flow capacity compatible with the gearotor pump, UL's scavenge capacity is poor, hence the need for an upgrade kit for the return pump. For the oil to reach the flywheel chamber you have to use extended/full flow for the crankpin, or skirt oilers/piston jets. Or both. It is not something to just plug and play. If you use the CHP pump, several precautions must be taken, otherwise oil will leak through the crankcase. Crankcase halves have to be flat and WELL sealed. Old threaded type 37-39 valve covers must be used as circlip covers will leak bad. Too little oil is a problem but too much oil brings challenges that must be considered. With such a large amount of oil it would be interesting to use valve guide seals, at least for the intake guides, but how? In CHP pump the oil supply for those who want to use skirt oilers or piston jets is before the inlet checkball valve, this means that if a shut off ball valve is not used in the line, the oil will flood the crankcase.
CHP piston oilers path.jpg
CHP piston oilers path.jpg (71.38 KiB) Viewed 3831 times
A second oil return line with a one way valve, as suggested, is a great idea. I have been lucky with the late factory oil pump with slightly enlarged oil ports, eliminating the low rpm bypass, four vanes rotors I ordered from American Cycle Fab a few years ago and full flow. No leaks, no wetsumping and no overheating. I left the Swedish pump greased and packed if I ever decide to build a big stroker motor. At the moment it is overkill.
ACF 4 vanes rotor.jpg
ACF 4 vanes rotor.jpg (82.96 KiB) Viewed 3831 times
low rpm bypass circuit blocked.jpg
low rpm bypass circuit blocked.jpg (83.24 KiB) Viewed 3831 times


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