ET: Engine (Twin) Cam Wear

[BigEd]

Question: Why is the end of the return pipe in the UFM closed except for a small hole (1/8"?) from which we see the oil issuing at right angle to the pipe.
Theory: The small hole there to create a restriction. Without a restriction at the end of the line there would be little or no pressure in the return line. If there is no pressure in the return line would less oil find its way down to the rockers and down into the timing case? Comments?

 

[greg brillus]

There are restrictions throughout the entire oiling system, some normal and some what I would call manufacturing defects. You only need to look at the outlet on the feed side of the pump sleeve to see what the restrictions are, a narrow machined slot up the side, then through a passageway into the oil filter housing. Sometimes this has very small hole that I class as a defect, and I always open this up if i find one like it. Hard to say about the outlet in the tank, I think the hole in the "B" tanks is perhaps larger and they do seem to dribble their return oil a bit less than on the "C" tanks. The oil that ends up at the rockers is probably more due to gravity against the extra height pumped back to the neck of the tank. There are improvements that can be done within the timing chest to help with oiling the cams and followers, they are subtle and only need to be to make a difference. As has been shown, if you open up the return to the rockers too much, then the scavenge side of the pump will not keep up.

 

[druridge]

Very interesting experiment with the oil holes, every day's a school-day...
Pressure only flows through a pipe because the pressure is greater at one end than the other. Velocity (flow) will actually increase when the pipe diameter is reduced. I guess our pumps have to raise the scavenged oil about 18" (from the pump to end of return pipe in tank). This is the 'head' to overcome. I think this is found by adding up pressures to overcome gravity , air pressure, restrictions to flow, etc. If we extended the return pipe from the tank straight up into the air, the point at which the oil flow would stop would be the ' static head'.
I'm assuming the extra holes have reduced the return pressure so that the static head is now below the pipe end? Almost everything I know about fluid dynamics is contained within this para, so I am probably on safer ground deferring to PEI!

 

[Simon Dinsdale]

Very interesting experiment with the oil holes, every day's a school-day...
Pressure only flows through a pipe because the pressure is greater at one end than the other. Velocity (flow) will actually increase when the pipe diameter is reduced. I guess our pumps have to raise the scavenged oil about 18" (from the pump to end of return pipe in tank). This is the 'head' to overcome. I think this is found by adding up pressures to overcome gravity , air pressure, restrictions to flow, etc. If we extended the return pipe from the tank straight up into the air, the point at which the oil flow would stop would be the ' static head'.
I'm assuming the extra holes have reduced the return pressure so that the static head is now below the pipe end? Almost everything I know about fluid dynamics is contained within this para, so I am probably on safer ground deferring to PEI!

Thats exactly how I see the problem which doesn't help with the pump been known to be a low pressure pump. I have read somewhere that somebody fitted an oil pressure gauge to a post war Vincent and it read virtually zero.

 

[timetraveller]

Gentlemen, four words only,' twin start oil pumps'.

 

[oexing]

Twin start oil pumps would not change the problem: You´d get double scavenge volume, but also double feed into the engine. So nothing changes.
The scavenge side of the pump is , say, one third bigger than the feed side. So in theory you could use that extra volume for lubrication from the scavenge line. But not any percentage more else the engine will fill up in time.
I´d have to dig into the oil system first, so question is, can there be a leak in the suction side of the pump somewhere in the engine case where air is drawn into the pump ? That would explain the poor scavenge action in our case - apart from a clapped out pump.
The piston type pump could provide quite some pressure, periodically, if there were no effectively open ends in the various lubricating places. So no luck to get a reading on a pressure gauge. But it should not be difficult at all to return oil from down in the engine up into the oil tank , pressure wise. I would not like to have a restriction from the scavenge hose into the oil tank. It does not make much sense I believe, as it should be sufficient to have the rocker feed lines simply filled with oil at close to zero pressure from the height differential rocker-oil tank. Just a gut feeling . . .

Vic

 

[Bill Thomas]

Gentlemen, four words only,' twin start oil pumps'.

Not for me , Thanks. Cheers Bill.

 

[davidd]

The only other item that you can check easily is the screw that is causing the pump to turn. I have found them ready to fall out as well as extremely worn. Both conditions cause low pressure, but a worn one might also give you an indication of how worn the oil pump might be.

David

 

[druridge]

Would a measure of the height of 'static head' - that point at which the pump pressure will support the oil to, be a possible way to measure individual pump efficiency? Imagine the return pipe removed at the bottom banjo bolt, then a clear pipe fitted over the end of a short banjo pipe (the same diam as the return pipe would be good) and pointed straight up. We need the oil to lift the eg 18" back from the pump to the usual pipe exit into the oil tank; we should see the oil in the clear pipe at least get above this point (vertically). If the oil is pumped up to 6" above this point (before the oil level stops rising and it sits at equilibrium in the pipe), that could be seen as good, 12" above this point better, etc? I wonder has anyone done this before on a Vincent? This could also give an indication of 'spare in the system' ,allowing oil flow modifications to be monitored?
Have I got this right?

 

[timetraveller]

I'm not sure you are right about that Vic. A small gedanken experiment for you. Suppose that the two start pump gives twice as much oil flow, then restrict one of the apertures it flows through. What will happen. I guess that we have all done this with a hosepipe. Get the water flowing and then squeeze the end of the pipe with your fingers. You know what happens. The water goes further. There is no more water flowing but the pressure has gone up. One restriction with the Vincent oil return flow is the four small holes in the banjo bolt underneath the oil tank. More oil flowing through that, and other restrictions, will increase the pressure so that all those little holes further down the return will be subject to more pressure and hopefully pass more oil. I don't think that it has anything to do with the ratio of scavenge to feed side of the pumps. Provided that the scavenge is greater than the feed the sump will stay 'dry', which is part of what we are after. Tell me where I am wrong with this if I am.