Wet sumping - quantifying

Previously steve_constable wrote:

My commando loses 700ml per week into the sump, with 20/50W Halfords classic oil.

Does this sound normal or is it a lot for a week?

Steve

I think 700ml is way too much, having said that I don't know what would be normal for an engine with new big end journals and shells and a brand new oil pump, but certainly a lot less than 700ml. Worthwhile servicing or replacing the oil pump and then checking oil pressure with a hot engine (gauge connected to rocker feed inlet, for example) and aim for the factory recommended 45-55lb/in max. pressure. Add or remove shims from PRV. Tickover should be approx. 15lb/in min. When cold the pressure should still be within the 45-55lb/in if the PRV is working properly. I'd also use one of the latest 20/50's.

Steve,

Go to the Roadholder pages of this site, navigate through the archive to Rh 327, February 2015 then read, mark and digest Phil Hannam's most excellent article on refurbishing the Commando oil pump.

From the data you have posted, I think you might be needing to take some action on the issue .........

My commando loses 700ml per week into the sump, with 20/50W Halfords classic oil.

Is that 100 ml overnight? I think that would pump back into the tank pretty quickly. Also it is not really "lost" if it goes right back into the tank. I haven't done this test but I don't think 100 ml would even touch the flywheel (I want to run out and test this with my spare crankcase). I think others should tell us their actual leakdown so we could compare.

The crankcases filling with oil is a symptom of a problem - in this case probably an oil pump significantly worn so as not to provide sufficient oil pressure in a hot engine. Well worth taking the time to service the pump and check/adjust the oil pressure.

The Commando Oil Pumps, made in the 70s, suffered from mass production and poor quality control. I have pulled a good many apart and most have exhibited poor finishing on all of the mating faces. Some have had faces where grinding marks/ridges are so prominent that they will catch a finger nail. This is bad news once the engine oil is hot as it will seep through even the smallest of gaps.

So when you have dismantled the pump remember to check the end plates and their respective mating edges as well as the main mounting face.

The original Pump was designed to last about 100,000 miles before a need for a major service. That was before the driving gears were changed to 6-start and doubled the internal speed of the pump. A great idea, at the time, for increasing the oil pressure but the downside was double the wear, especially on the scavenge side which spends a lot of time running on air. This leads to wear on both the end plate and inside the body behind the gear. Plus wear in the drive shaft tunnel. A point often missed by the DIT refurbisher. If your Commnado has covered 50,000 miles or more on its original oil pump and is wet-sumping badly, it is probably due a service..........possibly a funeral service.

Hi

I have only recently joined NOC having just bought a 1972 750 Commando - so this is my obligatory newbie silly question.

I used to have a fastback back in 1974 and in those days used the bike every day and had never heard of wet sumping!

I have read other threads discussing the problem and various cures but have not seen anything quantifying the problem.

My commando loses 700ml per week into the sump, with 20/50W Halfords classic oil.

Does this sound normal or is it a lot for a week?

Steve

Previously anna jeannette Dixon wrote:

if there is not oil for the oil pump to scavenge then the rockers arms are without oil too and the pressure then drops and the pressure relief valve then closes and the large ends have little oil too until the oil pump regains oil and its pressure back to normal

yours Anna J

I don't think this bit applies to Commando. Rocker feed is from high pressure (engine feed) side.

Hi Steve,

I will check my 850 commando its been stood just over five weeks , i have been working on the primary drive side so i will measure what i caught in the tray the other day also i will drop the sump plug tomorrow and have a measure up and let you know.

Andrew

Need to point out i run a belt drive ,so i run dry, the oil i caught came from behind the primary inner casing..

Andrew

Steve, over seven days I'd hardly expect to be able to see any noticeable drop on the stick. More than a pint over a week is pretty horrendous.

The more recently produced Andover Norton pumps...the last ten or fifteen years or so really are a great improvement in terms of production quality and are a simple answer to the problem. Prior to these, even a new pump wasn't guaranteed to completely solve the problem. I wouldn't bother attempting to recondition a forty-year old original pump anymore.

Strictly speaking, 'wet sumping' is the failure of a dry sump engine to scavenge properly at high r.p.m. but everyone in the world of Nortons uses it to refer to this known habit of draining down past the gear pump when standing. Some smart-arse always comes along to point it out though !

Strictly speaking, 'wet sumping' is the failure of a dry sump engine to scavenge properly at high r.p.m. but everyone in the world of Nortons uses it to refer to this known habit of draining down past the gear pump when standing. Some smart-arse always comes along to point it out though !

We are watching our language evolve (or become more sloppy). In America you ask for a cotter pin and they sell you a split pin.

Strange eh, Jonathan, when I was a lad, 'cotter pins' were those odd things that I could never file the correct taper on...and once they were in, could never drift out without bending the threaded portion. Were they bimetal with a hardened face and a monkey metal thread ?

Previously richard_payne wrote:

Strange eh, Jonathan, when I was a lad, 'cotter pins' were those odd things that I could never file the correct taper on...and once they were in, could never drift out without bending the threaded portion. Were they bimetal with a hardened face and a monkey metal thread ?

That's what they are on my Triumphs and BSAs. Luckily Nortons don't use them. I don't know about bimetal, they always seem to be too soft and the wedging action disappears.

Just don't ask for a petrol tap when in the US of A...

Hi ,

Finally at last the 850 MK 111 oil drained out the sump. Its been stood now for six weeks and i released 1800ml so thats 300ml a week , it seemed a lot, and i was thinking OMG this is like an oil change .

Kind Regards

Andrew

700Ml in three weks on mine and that's with a reground crank and shells. Oil pump reconditioned 8000 miles ago. I've modified my big sump plug with a small drain plug and magnetic pick up so draining down a flooded sump is a 20 minute job.

I've just been playing with an old windscreen washer pump to suck the oil from a banjo bolt where my mag plug is. work in progress. The idea is that before a ride, press the button, and watch the oil being pumped back to your tank. need a better pump at the moment. I know I'm dealing with the symptoms not the cause. The problem doesn't justify a new pump...... yet.

Thanks all

What a great resource this site is!

I will Change the oil to Morris 20/50 as suggested and will investigate the oil pump.

I would still be interested to hear the results if anyone else would take the trouble to measure how much oil travels to the sump in 7 days?....

In 24 hours mine has dropped 180ml, I'll do it again this afternoon and see if it's the same again.

Previously andrew_windsor wrote:

Hi ,

Finally at last the 850 MK 111 oil drained out the sump. Its been stood now for six weeks and i released 1800ml so thats 300ml a week , it seemed a lot, and i was thinking OMG this is like an oil change .

Kind Regards

Andrew

I would check the oil seal in the timing cover

Previously christopher_winsby wrote:

Hi,

I am not a commando expert but my 750 emptied the oil tank into the sump in no time when sitting ,also at that time the pistons were at the bottom of the stroke when the bike was switched off.This made it hard to turn over on start up to bring the pistons up to the top to fire it up.

Don't know why but the old girl began to leave the piston up top when switched off, this made the machine very easy to start and it can now sit for 3 or 4 months without losing much oil(maybe half to three quarters inch on the sight glass) and starts easy with good return to the oil tank.

I did read an article about putting the pistons up top to prevent oil draining to the sump from the tank when the bike is left to sit a while and it is cheaper than a new oil pump.

just my own personal experience on enjoying my 1969 745

best regards JG

If you are getting wet sumping, dismantle the oil pump, and check the clearance on the pressure side gears. That means the thinner side....

Put the pressure gears into the housing, and a good straight edge across. Measure the clearance between gear and the outer face. If it's more than nothing, you need to lap the pump body. If the face is less than nicely smoothe, get lapping. When the clearance is close, but not actualy tight, clean it up and re-assemble. You won't have any wet-sumping

Paul

Hello remember that Commando oil pumps-run faster than the early Dominators do , so they will wear faster too so Checking your oil pump periodically would only be a good thing, and a Good Oil will be better than cheap oil , Morris oils and Millers oils and Castrol are the most recommended , yours Anna J

I plan to refurbthe pump in my fast back this winter

Remember that after cutting your engine there will be a quantity of oil still in the head and other parts of the motor that will drain down to the sump. This is normal as it helps to prime the oil pump on the next start-up. I would have thought that a total of 350ml after a week was acceptable. It would bereasonable to assume that only 220ml of that amount had come via the pump and that a similar amount would arrive by the end of week 2. So after 3 weeks your oil tank would have lost about a pint. The Commando oil tank holds around 5 pints so no need to panic until week 6.

Remember that after cutting your engine there will be a quantity of oil still in the head and other parts of the motor that will drain down to the sump. This is normal as it helps to prime the oil pump on the next start-up. I would have thought that a total of 350ml after a week was acceptable. It would bereasonable to assume that only 220ml of that amount had come via the pump and that a similar amount would arrive by the end of week 2. So after 3 weeks your oil tank would have lost about a pint. The Commando oil tank holds around 5 pints so no need to panic until week 6.