ET: Engine (Twin) Air bubbles in Oil Return

[nigsey]

Started my C twin today and removed the oil filler cap to check that engine oil was returning ok but there were a lot of air bubbles coming through, about 50% oil and 50% bubbles. I ran it for 3 or 4 minutes but no change. I changed the oil recently (to a 30 grade) and made sure I squirted oil in the various orifices as recommended. On first start up there were some bubbles coming through but not for long then I took her out for a few miles. I hadn’t started the bike since then until today. Now I’m a bit worried about running the bike like it in case I cause damage. Any advice please? Nigel.

 

[timetraveller]

Difficult to say too much but the Vincent oil pump always pushes air out with the oil, unless the sump is full, as the return side has a larger capacity than the feed side. Does it look different now from what it was like before?

 

[nigsey]

I’ve not experienced this many bubbles before. I guess I could take for a run and then see what it’s like.

 

[Simon Dinsdale]

The oil pump return side has twice the pumping capacity of the feed side so once the sump level has achieved the optimum operational level you will always get bubbles in the oil return as it can only return at the speed of the oil supply side.

If your engine sumps over time then you can initially see constant oil return until the sump level drops to its operating level and then you are back to bubbles.

Simon

 

[nigsey]

The oil pump return side has twice the pumping capacity of the feed side so once the sump level has achieved the optimum operational level you will always get bubbles in the oil return as it can only return at the speed of the oil supply side.

If your engine sumps over time then you can initially see constant oil return until the sump level drops to its operating level and then you are back to bubbles.

Simon

Ok Simon, thank you. I’ll keep an eye on it of course but by the sound of it, it’s nothing to worry about. I’ve had this bike coming on a year and I’m becoming a nervous wreck, slightly exaggerated but I’m constantly worried about things, e.g. I’m hearing noises that I haven’t heard before, bubbles in the oil I haven’t seen before etc. I’m sure most of this is my imagination and being unfamiliar with Vincent twins, so I should stop worrying and enjoy it while I can.

 

[Robert Watson]

The further you get from home, the louder the engine rattles! And of course several weeks and thousands of miles later when you turn into your driveway, it never sounded as good nor ran so well!

 

[vibrac]

The oil pressure is only a few pounds and it looks poor compared to those engines running plain bearings but the Vincent has rollers relax and laugh at the people who fit woven steel oil lines on Vincents

 

[nigsey]

The further you get from home, the louder the engine rattles! And of course several weeks and thousands of miles later when you turn into your driveway, it never sounded as good nor ran so well!

I started wearing ear plugs under my helmet for comfort and to stop me listening for new noises but then the Vincent is such a great sound and I was denying myself half the pleasure, so I’ve abandoned the ear plugs now.

 

[Nigel Spaxman]

On an Egli there is a clear oil line in the return circuit that runs just behind the steering head. You can see the oil circulation well because there are so many bubbles. On Triumphs you have to be careful about the oil supply to the rocker arms. There is a line that tees into the return side of the oil pump that provides the very low pressure oil feed to the rockers. You have to make sure that this line tees in where the oil is going up if you situate this line incorrectly it can syphon off all the air in the return and then almost no oil goes to the rockers. The oil supply lines to the Vincent rockers are similar but none of the air goes down to the rockers, because it is down (the air always floats up to the top)

 

[davidd]

I found that the earplugs allow you to hear more mechanical noises!

I think Simon said it well. The sump oil is whatever oil gets picked up by the flywheels and slung into the sump. If you did an oil change that would have slowed the oil at least until the sump filled up enough to get slung into the sump chamber. The scavenge side of the pump will push oil or air into the return pipe. It does not care. On the Egli, the bubbles would just advance through the clear plastic tubing if there was not much oil in the scavenge chamber.

It is the feed side of the pump that is more important at start-up. This is supplying the crank and cams. If that line is full you are likely to be fine.

David