Not enough oil return flow

Hi All,

I re-starded my fully rebuilt Commando engine in my featherbed chassis yesterday (lubrication circuit primed, oil returning to the rocker spindles checked OK etc...).

It took about 1 minute before seing the oil returning to the oil tank, which is normal in those circumstances I think.

But what is a bit worrying me is that the return flow is "sporadic". It rather "spits" oil every 2-3 seconds than showing a constant flow as it did previously with my Dominator engine.

I think that the return flow should be more contant and important since the oil pump returns twice as much oil as it sucks as far as I know.

At first thought, I do not suspect the oil pump (carefully checked, re-adjusted and rebuilt by a very experienced guy) neither the oil circuit (no oil leak, hoses and pipes looking fully OK) and I have no other investigation ideas.
The guy who rebuilt the engine pays also particular attention to clearing the oil circuit of any sealant, gasket etc... which may impact the oil circulation of course.

Is it normal and do I have only to run the engine a bit longer?

I imagine that if the return is not sufficient enough, I'll see the oil level in the oil tank go down and will find the "non-returned" oil somewhere in the engine (eg: in the crankcase).

Many thanks for any ideas. Enjoy your Sunday rides!

Laurent

If the tank level is not dropping and the sump is not filling as the engine is running then its the feed side that is not delivering, the return side will only return what it is being fed and if this is low you will get excessive gaps in the oil as it exits the tank return. You need to check the feedside pressure is good before running the engine more.

Hi , did your return "erratic"oil flow happens at idle or when revving a bit ? I ,too, when starting a newly built Cdo last week , I was frightening myself ('as everytime, when I start a new engine), while waiting for the flow to come back from engine to tank , though every thing was primed up! and at idling it was a poor return flow (though I did not let it idle too long ) then after I rev it to 3000 rpm for a while , and it took some times to become more consistant........

Many thanks to you both for your prompt comments.

I think the feed side is OK since there is oil going to the rockers and the oil level in the oil tank gets lower when the engine is running. I'll check and re-check that point before any new test of course.

Pierre-François,
It's low and erratic not only at idle but also after about 2 minutes at 2000 rpm (to start breaking-in the camshaft). I don't dare to go any further before knowing what happens.

What do you think of priming or re-priming as much as possible the feed and return circuits (with a syringue) after having taken off the oil pump, then priming the oil pump, then priming the oil tank-to engine hoses and pipes before trying again?

Cheers,

L.

Hi Laurent, yes you could have a try , and plus that will allow you to check inside the timing cover if the oil pump gaskets (both, paper and rubber) are OK(as well as the oil seal in the timing cover , not upside down or whatever, lips damaged .....?), Just after reving it , before your dismantle anything , did you check the amount of oil in the crankcase.........? on watch, Pierre.

I can remember someone tell me when I put my 850 Commando engine in my Featherbed frame and running a Featherbed oil tank that the return pipe to the oil tank the hole in the tank return needs to be open a bit more as there will be more oil flow from the Commando oil pump, on my bike the oil flow was alright and didn't need to do this, but some builders had to do this.

Ashley

Laurent, since the capacity of the return section of the oil pump is higher than the supply section, you will see oil mixed with air returning to the oil tank.
When the bike has been standing for some time, you will see a constant return flow after initial start up, as result of some amount of wet sumping,
but after some time the flow will become more irregular as result of the fact that oil as well as air returns to the tank.

Thanks again Gents.

What I intend to do once everything has been re-checked is to run the engine for a few seconds with the oil returning straight to a can where I can see what comes out of the engine.

Cheers.

L.

You can't pump out more than you put in . So if the scavenge is twice the speed (edit - not speed, volume) then it has to spit when returning to the pump.

This is a test I did on a Matchless G80CS to check the pumping and return. It uses the Norton Dominator version of the pump. I used a drill to run the pump:


Returning bubbles seen in the clear line.

The oil return on a dry sump system will always include air, due to the greater volume of the scavenge pump. The observation you made is AS (every dry sump system is) DESIGNED.

There is nothing wrong with your Commando. Now go out and ride the thing.

Wow batrider that is very cleaver oil pump tester I'm going to try to mimic. On my Combats after full priming it takes like 45 sec to see sigficant oil return - by holding rather over 2000 rpm while waiting and waiting for the worst. I see spittle brusts in waves slow enough rpm oil don't leak out the opening.

Clear enough gentlemen!

In addition to your explanations, the pump being driven now by a 6 start worm instead of a 3 start on the Dommie, it makes the difference between FEED and RETURN higher in terms of rpm and volume of oil, which may explain that the return flow on the Dommie looked more important and steady than now.

Thanks and rgds,

L.

OH no - you ain't getting off that easy. There's still entirely possible reason to remain Norton variety pensiveness that can't be rationalized away... if engine was rebuild after a blow up that broke up piston or rod or lifter chips etc, then can lodge in side internal case sump passage while tube heat expanded then trap when cooled so nothing can fully clear but wire poked through with cases highly heated, unless of course its been checked how well this useful path flowed.

I too think what you're seeing is all good. In a perfect world scavange would be exactly calibrated to feed back to the tank just what it recieved in the sump after that oil was done with it's lube duties, in a steady stream. But the scavenge side as others and you yourself noted pumps at a higher capacity than feed so what happens is oil runs to the pick-up, gets picked up and spit back to the tank....fast, then pump waits for more oil and just spits froth and air untill "Oh cool here comes some more oil that I get back to the tank" then just waits around spittin' air and froth again untill more oil worthy of a good push dribbles down to the sump giving the poor over achieving scavange side of the pump something to do. Something like that.

Thanks again to you all.

Hobot, the engine has been built either from brand new and checked parts or from second hand checked and cleaned parts. So there is no risk of some broken chips obstructing something somewhere.

I know that our dear old bikes may be sometimes temperamental and reluctant to obey the basic logical laws of physic, gravity etc ... (they are english aren't they, and that's why I love them) but I'm convinced by all your explanations about the difference between Feed and Return capacities and what I see.

Cheers,

L.