Volume vs. Depth of Black Ariel Oil Tanks

[IanSlade]

One thing I have found with my '27 B is that because the oil side works on suction, that the further down the level of the oil in the tank, the harder the pump has to work to suck it out. If the tank is nearly full then it will actually syphon out, whereas if it is low but still covering the suction tube then the engine can be starved of oil. Would I be correct in thinking that the pump probably needs a rebuild or do you guys keep your oil level at just the 'correct' height which I assume you would have to determine by experience, and if so it would be interesting to know what others have found to be an ideal level.

[cmfalco]

the further down the level of the oil in the tank, the harder the pump has to work to suck it out.

The required pressure difference (vacuum) is linear in the difference in height between the top of the oil and the outlet of the pipe in the sight glass. My Ariel is in a crate on its way to the east coast so I can't measure any values but, roughly, if when full the oil level is ~2" below the sight glass then when empty it will be ~7" so it will require the pump to supply 3.5x the pressure drop toward the end than when it is full.

It's worth pointing out that it isn't so much an oil pump as it is an air pump. With only one drop every few seconds passing through the sight glass the pump mostly moves air. This is important because air can leak through passages much easier than oil can so it doesn't take much increase in clearance between the plunger and body to cause a decrease in pumping efficiency.

If you want to see what's involved with rebuilding an oil pump, start at the following and continue reading the posts that follow for the next week or so:

http://www.britbike.com/forums/ubbthrea ... Post739912

See also:

http://www.britbike.com/forums/ubbthrea ... Post740969