dumb question

W0rk over for a few days, and visits to this forum over a mince pie or two.
I have a question;
Just been on ebay looking at Browniecaferacer oil tanks, they state "Do NOT vent engine into tank" Ok with all this talk of Mayo building up from combustion products i can understand the reason ....
So my dumb question is : why did Norton and Others design a oil pump that returns 100% more than the feed? The pump is returning 100% more {combustion gas] to the tank.
Why not just 5-10% more than the feed? is it pointless to return all this gas back into the system ? and the gears in the pump doing it make a good job of blending this gas into the oil?
I can guess that Manufactures where aware that engines sumped down and though "we" will make a pump that will quickly clear the crankcase...alas at the constant "Over kill" once this as happened . In an ideal world the pump should return the same amount as delivered . 5% more for safety.

1. I'd be suspcious of a tank sealing quality that warned not to vent engine breathing into oil tank. Be restless till inquiring on reason for their alert.
2. To move enough hard to pump aerated oil to keep a sump essentially dry requires more return side pump capacity and rest assure it ain't got any excess capacity than Norton thought they'd get away with. Real hot rodders may have triple the return volumes capacity than feed side.
3. Mayonnasie formation has nothing to do with where fumes are vented or sump oil pumped to, any more than oil on the floor has anything to do with the engine leaks.
4. Dumb question alright but got to ask enough of em to get smarter and smarter

Triple return ?, Impossible! You cannot feed 1 pint a minute and return 3 pints! its point less sucking up oil and air.. unless froth is your thing. After all wet sump "just" replace the oil delivered. You don't see a old castrol plastic bottle duck tapped to GP Bikes :lol:

hobot said:

1. I'd be suspcious of a tank sealing quality that warned not to vent engine breathing into oil tank. Be restless till inquiring on reason for their alert.
2. To move enough hard to pump aerated oil to keep a sump essentially dry requires more return side pump capacity and rest assure it ain't got any excess capacity than Norton thought they'd get away with. Real hot rodders may have triple the return volumes capacity than feed side.
3. Mayonnasie formation has nothing to do with where fumes are vented or sump oil pumped to, any more than oil on the floor has anything to do with the engine leaks.
4. Dumb question alright but got to ask enough of em to get smarter and smarter

Click to expand...

Ta.

Many engines with dry sump type lubrication systems use oversize scavenge side oil pumps to not only to clear oil but to also to provide a vacuum in the crankcase.

The scavenge must keep up with the feed at all times and clear the crankcase of accumulated oil on startup, while pumping uphill, with a margin of safety.

Or do I misunderstand the question?

The custom oil tank probably does not have a breather outlet of its own, big enough for the crankcase breather.

As Mr. Thrasher says - Many of the aftermarket alloy oil tanks only have a send and return for oil feed and some sort of atmosphere breather. Often the belief is the "monza" cap will breathe enough. This may be true if you don't plumb the crankcase breather back to the tank, but I wouldn't rely on it. For all of our bikes we add 2 fittings to these types of tanks - one with a large return for the crankcase breather hose (usually 1/2 ID hose and fitting), and another with a fitting to attach a hose to vent gasses back out to atmosphere with enough breathing room to prevent the tank from becoming pressurized; this hose terminating into a catch bottle mounted somewhere on the bike.

Later model Commandos have this same design - the feed and return, as well as a crankcase breather which has an adapter taking the ID down from 1/2 to 3/8, and finally the atmosphere breather which originally plumbed back into the airbox so any mist would be burnt off (but after all the years, most of these now just dangle down and drip onto the back tire! :shock: )


HTH

john robert bould said:

W0rk over for a few days, and visits to this forum over a mince pie or two.
I have a question;
Just been on ebay looking at Browniecaferacer oil tanks, they state "Do NOT vent engine into tank" Ok with all this talk of Mayo building up from combustion products i can understand the reason ....
So my dumb question is : why did Norton and Others design a oil pump that returns 100% more than the feed? The pump is returning 100% more {combustion gas] to the tank.
Why not just 5-10% more than the feed? is it pointless to return all this gas back into the system ? and the gears in the pump doing it make a good job of blending this gas into the oil?
I can guess that Manufactures where aware that engines sumped down and though "we" will make a pump that will quickly clear the crankcase...alas at the constant "Over kill" once this as happened . In an ideal world the pump should return the same amount as delivered . 5% more for safety.

Click to expand...

If the crankcase vents into the tank then air will be flowing out of the tank breather. If the tank is not large enough or not designed to keep oil away from the tank vent then oil will be blown out along with the air.
Not a good design in my opinion. Jim

Comnoz wrote:

"If the crankcase vents into the tank then air will be flowing out of the tank breather. If the tank is not large enough or not designed to keep oil away from the tank vent then oil will be blown out along with the air.
Not a good design in my opinion. Jim"

This is my solution to the venting/oil mist problem. A tube (tower) can be welded into any oil tank, space permitting.

atlas-dommie-oil-mist-scrubber-t19002.html

Slick

I use a catch tank for the breathers off both the engine and oil tank. Some early Ducati racers used a large diameter engine breather with a flap valve on the end - led straight out the back of the bike. You cannot do that in road racing these days.

The Original Question is why is pump pumping back 100% more air than oil,and donnot repeat the vacuum rubbish!

I presume engines like ours have been wet sumping for years and so the need to scavenge all that oil quickly needs a high flow pump. I think that explains the need for that pump. Also, under heavy braking, is it possible the oil would be thrown forward enough so the pickup has no oil near it, so when accelerating again, there would be the need to pump like hell, all that built up oil.

The idea of that return pump helping with the vacuum [ sorry low pressure to purists ] is interesting as well. Twins need all the help they can get to remove the excess gas from the crank case so a little help from the scavenge pump would be appreciated. Even the best engines bleed a little blowby gases into the crankcase. The design of the oil tank has a tower in it to help get rid of oil from the breather mist, but what surprises me , is that it isn't really big enough, and worse, the breather from the engine on my 850 starts off in a 1/2 inch hose then steps down to a 3/8 hose, and the exit to the air filter is still only 3/8. In my opinion, the breather hoses should get bigger, not smaller.

Hope this helps.
Merry Christmas.
Dereck

venting the case is not a oil pump job, breathers do that. I will grind down the return gears to be 10% thicker and add spacers to make up the differance...

kerinorton said:

I presume engines like ours have been wet sumping for years and so the need to scavenge all that oil quickly needs a high flow pump. I think that explains the need for that pump. Also, under heavy braking, is it possible the oil would be thrown forward enough so the pickup has no oil near it, so when accelerating again, there would be the need to pump like hell, all that built up oil.

The idea of that return pump helping with the vacuum [ sorry low pressure to purists ] is interesting as well. Twins need all the help they can get to remove the excess gas from the crank case so a little help from the scavenge pump would be appreciated. Even the best engines bleed a little blowby gases into the crankcase. The design of the oil tank has a tower in it to help get rid of oil from the breather mist, but what surprises me , is that it isn't really big enough, and worse, the breather from the engine on my 850 starts off in a 1/2 inch hose then steps down to a 3/8 hose, and the exit to the air filter is still only 3/8. In my opinion, the breather hoses should get bigger, not smaller.

Hope this helps.
Merry Christmas.
Dereck

Click to expand...

john robert bould said:

The Original Question is why is pump pumping back 100% more air than oil,and donnot repeat the vacuum rubbish!

Click to expand...

Reference: Norton Owners Manual (no date of pub.)
The following statement is found under Heavyweight Twins, and Models ES2 & 50

"Engine Oil Pump.
This is of the gear type. The pump contains two pairs of gears, one on the feed side and the other on the return side.

The gears on the return side are twice the width of those on the feed, having twice the pumping capacity. This ensures that the crankcase is free from oil when the engine is running.

......After the engine has been running for a few minutes, the oil return flow will be spasmodic, due to the greater capacity of the return gears."

John, it would seem that 50% more return capacity would be adequate, but maybe Norton learned something from their years of racing. Gear-rotor pumps do not pump air very well, if at all....perhaps Norton found a frothy mixture of air and oil simply requires 100% more capacity to scavenge the sump.

Slick

Ta.

Hi Tex
Lets hope the pump will move air, if not the engine will be starved when the sump is empty..ie when the case is drained during oil changes. :?:

texasSlick said:

john robert bould said:

The Original Question is why is pump pumping back 100% more air than oil,and donnot repeat the vacuum rubbish!

Click to expand...

Reference: Norton Owners Manual (no date of pub.)
The following statement is found under Heavyweight Twins, and Models ES2 & 50

"Engine Oil Pump.
This is of the gear type. The pump contains two pairs of gears, one on the feed side and the other on the return side.

The gears on the return side are twice the width of those on the feed, having twice the pumping capacity. This ensures that the crankcase is free from oil when the engine is running.

......After the engine has been running for a few minutes, the oil return flow will be spasmodic, due to the greater capacity of the return gears."

John, it would seem that 50% more return capacity would be adequate, but maybe Norton learned something from their years of racing. Gear-rotor pumps do not pump air very well, if at all....perhaps Norton found a frothy mixture of air and oil simply requires 100% more capacity to scavenge the sump.

Slick

Click to expand...

Enjoying your learning curves on this well studied issue.
1. Needing did a cold oil blender test to show it get very aerated. This is what happened to Norton oil sprayed and slung out of big ends then churned to blasted mist further heated by crank windage so oil entering sump side of pump with be as mush or more air than oil.
2. Aerated oil is not efficient to pump, similar to stirring then mayonnaise just moves around spoon or compresses w/o flowing, so sump side has to be bigger to keep ahead of the feed side. Sump side oil gets a good bit of the non emlusified air bubbles compressed to actually pump decently and then re-expand and coalesce to bigger bubble seen exiting on tank wall.
3. Must be a pretty fancy looking tank to want to drill and weld on it to adapt to your ride.
4. Neither Ms Peel nor Trixie run long hours &/or into 2S cam zone ever showed drip out end of factory tank breather as factory oil tank baffle exit worked well enough to de mist any pressure venting outward so no catch bottle or dipper needed.
5. Dumb questions are based on ignorance of the facts while intelligent questions probe the implications of known facts.
6. Peel must expel blow by pressure out exhaust system and no OIF ambient vent provided [upside down concerns] so could blow frame apart or suck to collapse so ask what you'all are betting on?

Dry sump aircraft engines have a similar arrangement of a much higher capacity scavenge pump than the pressure pump. Engines used for extended inverted flight have an elaborate system of lines or a double scavenge pump so that oil is always returned to the tank no matter what the attitude. The tank is a bit complicated as well to insure the pressure pump is always supplied.

Not the same as the original question, but those not connecting the engine breather to the oil tank....on start up I get quite a bit of oil return via the breather pipe. Those not connected just dump the oil or do you drain the sump before starting? Seems like a long proceedure before starting a ride.

Ta.