Drive side crank lubrication

[Jordan]

Warning: armchair engineer's topic.

Nigel recently mentioned in another thread, something that has puzzled.
How is it that oil can make its way, against centrifugal force, through the left side crank cheek, back to near the crankshaft centre axis?

I put this to an ex-engineer friend, who's worked in the motor industry and knows a bit about engines.
He was not surprised that it should work OK.
His reasoning is that the oil under pressure will move along the least-resistant path.
All it takes is some narrow clearance (big end side) to induce a flow in a parallel branch of the circuit.
Sure, there will be a loss of pressure, but the decreased resistance permits.
It sounds to me bit like Ohm's Law in hydraulic terms.
Sound plausible. What do folks reckon?

[blethermaskite]

Just as a practical observation.......anytime I have had a Ducati single crank on the bench and removed the sludge trap for cleaning, after solvent flushing and compressed air blasting to remove as much rubbish as possible I then pressure feed with an oil can about a half pint of new oil through the system from the timing side end,(which interestingly almost always produces a few little missed bits) so despite the clearance/ leakage potential of the big end bearing there is still a copious flow from the primary gear supply drilling on the other side of the crank, obviously when spinning there will be less flow on the primary side due to centrifugal effect but the overall oil pressure should overcome this.......maybe.....I think.....?
Cheers,
George

[LaceyDucati]

Hi Jordan
Thanks for the promotion of my quizzical thought and placing it in it's own topic. I was trying to stimulate thought on a subject, which you bit on

I don't actually know the answer for certain. One day I will probably run a test to prove what actually happens. The pressure "as such" in our engines as you will know is low and probably not much higher than 10psi at best. The oil system is not supposed to be high pressure, unlike a plain bearing engine like the later belt engines.

George, yes I do that with an oil cam on all engine builds and is my test that the bigend is well lubed and the oil ways are flowing well. I also do the same to prime the timing cover/oil pump and the oil gallery to the cam lobes from the timing face before I install the timing cover. Mind you your oil can may be providing more psi than the oil pump and it's still got to overcome either not exiting the pin and then fight against centrifugal forces. I know this sort of issue can be a problem on some old performance car cranks regarding reaching the final rod bearing.

It is probably easily tested by blocking the primary gear feed hole, then fitting an adaptor in the crank end plug for a oil take off. If a clear pipe was then connected and fed back to the crankcases, flow could then be observed. Observation would be needed cold, hot, at tickover and at speed. There is of course the question that if a race bike can survive without feed over many years.....does it need the feed anyway

Anyway one for all the theorists, I'm open minded either way

Regards Nigel

[Jordan]

How about this?
If it is accepted that ANY pressure within the left crank cheek passage must result in oil coming out at the primary gear area, a means of telling the existence of pressure could be tried.
An arrangement to measure it is complicated by the crank moving.
Perhaps a pressure switch could be adapted to the 8mm threaded hole so it turns with the crankshaft, and make contact with an insulated carbon brush or such mounted to the clutch cover. It would then provide the ground path for an indicator lamp circuit.

[veloduke]

OK, imagine you have a 'u' shaped piece of hose with say about 6ft loop hanging down, analogous to the crank with a loop to the big end.
Fill it with water. The pressure at the bottom of the hose will be higher than at the tops. In this case the pressure is produced by gravity rather than centrifugal force.
If you pour water in on one side, it will come out of the other, no?

In the crank the oil pressure due to centrifugal force will be balanced either side of the big end, so an increase in oil pressure on one side of the crank will give flow out of the other side, because the pressure on one side of the big end will be cancelled out by the pressure on the other side.
Obviously there will be some flow through the big end, so the oil pump will need to pump in more the flows out the big end.

This could of course all be BS but it sounds good to me (it would though since I wrote it).

[blethermaskite]

Considering the design and operation of the Ducati pumped oiling system with specific reference to the roller big end bearing from which the biggest loss of pressure is found I would suggest that there will be a certain amount of "oil pressure" in the system (as Nigel has already pointed out) maybe (hot) 10psi probably less, however what the Ducati system has in its favour is flow and lots of it, I think the thing you would want to measure in the analysis of the efficiency of the Ducati single oiling system is quantity of flow rather than pressure (as the owner of a 1930s racing car with white metal bearings pressure gauges are simply known as "worry gauges"). anyone who has been foolish enough to start a Ducati single engine with a valve cover removed will be in no doubt just how significant the flow rate is in one of these engines. Flow equals cooling and to a lesser degree cleanliness, don't forget air cooled engines also depend on the circulation of the lubricating oil to control the temperature of the high load areas in the engine that cooling air can't get anywhere near,however the air can cool the oil and the more flow the more cooling occurs, also a decent flow of oil will pass more oil per minute past the dreaded centrifuge sludge trap in question, resulting in the more efficient removal of "bits". So I would suggest it is as much flow rate as pressure that overcomes centrifugal force in the crankshaft at speed maybe
Cheers,
George

[LaceyDucati]

George
I agree with your analysis regarding flow and my proposed test was observing flow rather than pressure.

One thing I would add is I've strobed many singles and I don't recall seeing significant amounts of oil when I remove the timing disc fixing bolt that is installed with the grub screw removed. Maybe next time I'll look more closely.

Regards Nigel

[veloduke]

Hi George

Agree with everything you said. Pressure and flow are linked of course, and the roller bearing doesn't offer much resistance to oil flow, so low pressure will give good oil flow in this case.

Cheers

[blethermaskite]

So I think this is how you can set up a test on this, remove your primary drive cover, swap the out rigger bearing in the case with a 2rs sealed bearing, refit case, remove grub blanking screw from crank end, mod a scrap blanking plug (for the primary case) by drilling and hard soldering in a 8mm barb bit of tubing, fit a clear plastic tube to this and plumb to a measuring jug......"gentlemen start your engines".....ensure of course that there is plenty of oil in your engine!......try this slow/fast/hot/cold......see how much oil comes out comes out? If the flow is significant STOP you don't want to drain the sump.
Cheers,
George

[blethermaskite]

Sorry, one more process for the above test.......I can't remember, but I think there is an oil feed drilling (for splash) feed to that out rigger bearing in the primary case, you would need to block that off temporarily to ensure no reverse leakage back to the crankcase.
Cheers,
George