A: Oil Pipework Check Valve of Unknown Origin...

[ray vinmad]

The pump runs at 1/15th engine speed, so will stop in different positions after each run. Which probably accounts for why sumping is sometimes worse than others
The Vincent oil pump must have a running clearance, say 1/2 a thou.
If you had a 1/2 thou gap between your crankcase halves you would soon have a pool of oil on the garage floor. Thin multigrade oils won't help.
Ray

 

[Peter Holmes]

Using that logic all Vincent B, C, and D, engines must all wet sump, but apparently they all don't.

 

[Bill Thomas]

I have done what Vibrac told us, On my Comet, Come the winter, Roll it back on compression,
Has worked for 2 years !.

 

[Cyborg]

If one port is open the other is closed, however as one port closes it only takes a rotation of about 1 tooth before the other one opens. I haven’t used a degree wheel etc, so it’s just an estimate (but reasonably close). The difference in opening and closing on the return ports may be slightly less. So... if the pump stops when one port has just closed, there is very little surface area to slow the flow. Any wear in that area would aggravate the situation and given that’s where swarf would get snagged and dragged around, wear is going to occur right where it will make sumping worse. Add to that, all the land mines along the road to installing the pump, it’s amazing they don’t all sump. Another pitfall during assembly is if you need to lap the plunger. Great care and perhaps some luck would be needed to remove just the right amount of material and only in the areas that are required. It would be easy to remove too much material around the ports.

 

[Cyborg]

I have done what Vibrac told us, On my Comet, Come the winter, Roll it back on compression,
Has worked for 2 years !.

I would recommend that anyway, just so both valves are closed to keep out the damp air and rodents. Helps to prevent stuck valves in some engines.
So why does that work. Presumably it makes for a more difficult path for the oil. If the pin is above the timing side mainshaft oil passageway, oil would have to climb upward to the pin in order for it to drool out. At BDC, you would get a small amount of siphoning action. A good, properly centred quill would help.

 

[Bill Thomas]

So what position would be right for a Twin ?.

 

[Marcus Bowden]

I use linked cocks between fuel & oil with bell cranks on the "A" & "B" raps, you can't go anywhere without fuel, only two rides last year and none this so far they would have all sumped, so a kick over a few times to swamp the B/E and drain off sump and tip it back into oil tanks on the "C" & "D" raps would be necessary on these bikes, not that the children are coming anytime soon.
bananaman

 

[Cyborg]

Well for sumping, maybe the same theory applies for the twin. Getting the crankpin up top would slow the flow and decent quill would help. As for all valves staying closed that would be a challenge. Where is that damn oil flow drawing?

 

[Bill Thomas]

I have lost the one in colour, Found this from Davidd,

 

[TouringGodet]

My one superstition is to avoid mentioning anything good involving my Rap's ease of starting, oil pump, clutch, dynamo, or magneto for fear of jinxing it immediately. The wood seat base is too hard to reach for "touching/knocking".

Me too, sometimes I wonder if I am going to wake up one day and be in this alternate Vincent universe where there are dozens of things wrong with my bike. One issue I did have, oil leaks, was solved by removing a mod my father did back in the day, he added an extra breather that did not have a check valve. Went back to standard, and bingo, no leaks.