scavenge pump flow rate

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Bench testd my 71 Commandos scavenge pump and with my drill running it at 400 rpm, it puts out 8 oz per minute at room temp with 20W50 oil. Its set up to mimick its function in the bike lifting the sump oil about 6”” to the pump and pumping it up about a foot to the top of the oil tank.
As best i can measure the axial clearance of gear to endplate is about 0.002 to 0.0025”. This is too much but i wanted to get a baseline to see how much i can improve it by lapping the body of the pump as the shop manual describes.
Anybody else have any flow rate info on the scavenge pump??
 

Richard Tool

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Interesting and anxious to see the difference quantified. Did you match the diameters of the oilways/ returns as well ? I suppose for quantifying the difference between extant condition and freshly lapped it doesn’t matter as long as all diameters are the same for both tests .
I was advised when lapping my pump for my ES2 that when lapped it should be barely able to turn by hand with the drive cog on the shaft . This didn’t seem right to me but did it anyway and years later all is fine , although it still wet sumps no matter what .
I can also attest to how durable these pump gears are . On rebuilding my Commando I found a piece of piston ring that had found it’s way to the pump where it was chewed upon by the scavenge gears . A small piece was actually forge welded between the teeth of one cog by the pressure of being squeezed between the gears . I could not turn the pump past this blob by hand yet the engine apparently did so with ease . I have no idea how long this condition existed but likely throughout my ownership of years .
FD920F66-83B3-4E1D-AF3D-FA1E606DDF06.jpeg

41E229A8-9B2D-4155-B551-01E6FD67317B.jpeg
 
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Interesting and anxious to see the difference quantified. Did you match the diameters of the oilways/ returns as well ? I suppose for quantifying the difference between extant condition and freshly lapped it doesn’t matter as long as all diameters are the same for both tests .
I was advised when lapping my pump for my ES2 that when lapped it should be barely able to turn by hand with the drive cog on the shaft . This didn’t seem right to me but did it anyway and years later all is fine , although it still wet sumps no matter what .
I can also attest to how durable these pump gears are . On rebuilding my Commando I found a piece of piston ring that had found it’s way to the pump where it was chewed upon by the scavenge gears . A small piece was actually forge welded between the teeth of one cog by the pressure of being squeezed between the gears . I could not turn the pump past this blob by hand yet the engine apparently did so with ease . I have no idea how long this condition existed but likely throughout my ownership of years .
View attachment 83279
View attachment 83280
Wow, thats a massive crack in the main bearing seat in the first image.
 

Richard Tool

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Wow, thats a massive crack in the main bearing seat in the first image.
Not as bad as it looks - some rocket scientist obviously tried prying against it rather than use a puller . Maybe the same character that left bits of ring in the sump .Fortunately it didn’t go all the way through and I was able to mill the interior surface flat again .
 
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Not as bad as it looks - some rocket scientist obviously tried prying against it rather than use a puller . Maybe the same character that left bits of ring in the sump .Fortunately it didn’t go all the way through and I was able to mill the interior surface flat again .
Yeah sounds about right, i had a very similar crack in my 71 cases in the same spot, fear got the better of me and i sent the cases off to be repaired and tested.
 
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Bench testd my 71 Commandos scavenge pump and with my drill running it at 400 rpm, it puts out 8 oz per minute at room temp with 20W50 oil. Its set up to mimick its function in the bike lifting the sump oil about 6”” to the pump and pumping it up about a foot to the top of the oil tank.
As best i can measure the axial clearance of gear to endplate is about 0.002 to 0.0025”. This is too much but i wanted to get a baseline to see how much i can improve it by lapping the body of the pump as the shop manual describes.
Anybody else have any flow rate info on the scavenge pump??
pump test picspump test
 

texasSlick

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Somewhere I read that the 6 start pump delivers 1 liter per minute at 3K rpm. The Norton Manual states the scavenge side has twice the capacity as the service side.
A liter is 33.8 fluid oz.

Doing the math, extrapolating your data, 3000/400 x 8 = 60 oz, per min. or 60/33.8 = 1.77 liters per minute. And that is, more or less, twice the rated capacity. Thus the data I read somewhere substantiated yours.

I wonder how far up the rpm range the pump output remains linear vs. rpm? Do you have any intentions to graph it out?

Thanks for sharing your data.

Slick
 
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Somewhere I read that the 6 start pump delivers 1 liter per minute at 3K rpm. The Norton Manual states the scavenge side has twice the capacity as the service side.
A liter is 33.8 fluid oz.

Doing the math, extrapolating your data, 3000/400 x 8 = 60 oz, per min. or 60/33.8 = 1.77 liters per minute. And that is, more or less, twice the rated capacity. Thus the data I read somewhere substantiated yours.

I wonder how far up the rpm range the pump output remains linear vs. rpm? Do you have any intentions to graph it out?

Thanks for sharing your data.

Slick
 
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Thanks for YOUR data. Yea, looks like theyre in the same ballpark anyway.
But dont know what pressure or temp, etc. And i think its not linear since % leakage probably varies with rpm. Meanwhile i just spent a good hour sanding the body face down on sandpaper on glass. Trying (assembling and disassembling) it over and over trying to get it good without overshooting it. Finally got it and im quitting for tonite. Plan to clean thoroughly tomorrow, oil and try again on my test stand. Hoping for significantly better than 8 oz per min at 400 rpm. I’ll let u know as soon as i have some more data.
Thanks for your input and interest.
 
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BTW, just to be sure, is your 3000 rpm engine rpm or pump rpm? In the bike the pump runs about 45% of engine rpm. I estimated it watching the crank turn 2 1/4 turns for one rev of pump. I’ll try to get a few points to graph it, we’ll see.
 
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On the return side no pressure is generated as there is no resistance on the route back to the tank. When testing the feedside then pressure does come into play.
 
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Sort of related:
A work mate had a very nice 73 750 and it had a very bad wet sumping problem. It was his first Commando and he asked me for advise. As he had a good engineering back ground I gave him all the usual where to find fixes info etc. But it still wet sumped and he found it had lower that normal oil pressure. I told him to replace the pump. He'd been running the bike for at least two years by then and decided not to replace the pump but to first to fit an inline nonreturn valve . I told him of my fears but he fitted it and it appeared to work. However on the first ride out the bike badly seized. He rebuild the engine and fitted another pump. The bike ran great the oil pressure was normal and with valve removed it hardly wet sumped, great a result.
Later he gave me the old pump when I dissembled it I found the short plain shaft was missing? How long it had been running like that goodness knows but it did. Clearly the nonreturn valve was the last straw.
 
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Fascinating subject, Dunstall's tuning notes seem to imply that the cases are underscavenged...presumably this would lead to flywheel drag
 

Richard Tool

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On the return side no pressure is generated as there is no resistance on the route back to the tank. When testing the feedside then pressure does come into play.
Not trying to be picky here but there must be some pressure however minimal because the pump has to push the column of oil up hill - also , on some arrangements ( ES2 ,etc .) the feed to the rockers is bled off the return side.
 
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Not trying to be picky here but there must be some pressure however minimal because the pump has to push the column of oil up hill - also , on some arrangements ( ES2 ,etc .) the feed to the rockers is bled off the return side.

Exactly and if the height ofthe head ofoilcolumn going (in my case to an oil cooler) is higherthan theoutlet for the tank then the oil goes tothe tank . As the height difference is only 6 or 9 inches at most, then clearly the return is operating under some pressure...
 
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