Oil jets

["Slack Alice" Simon]

When we were into hovercraft my Dad used to say you can blow at 5 psi - which is all you need to hover.

5 psi through a straw will blow upwards enough to hit a crank web some distance away, so three should be fine.

Simon

[Tony Press]

The origin of oil jet system was raked over previously but cannot recall just when. The Brescia Bugatti model as raced by Raymond Mays in early 20s had system. The model dated from 1910 but may have been variants. One from later model was published in Forum. I have read somewhere that the FN motorcycle engine influenced the Seven. The 748cc 1923 engine at least has Austin sytem. The Belgian firm may not have had UK patent coverage. Or Austin may have fluked gaining it.

just what happens to the flow with the crank whizzing by at 4,000 rpm is anyones guess? I guess the exact aim is academic.

Oil likely both enters and exits the conrod drillings.

At just 3 psi or so how far does the flow from any upward jets project?

As I noted above-


The Bugatti Trust notes-

"During testing in 1921 Bugatti struggled to achieve success with this bottom end lubrication system. A large volume of oil at low pressure would be needed to fill the deep annular grooves in the crank webs against centrifugal force. Double oil pumps had been tried but the total theoretical clearance of 22mm2 for the oil to leak out of the system before any would get to the big ends was too much. Bugatti’s solution to this problem was his invention to inject the oil deep into the crank grooves with cross drilled jets which became the well known standard Bugatti arrangement applied to all Types from 1923".


The Bugatti system, while using a jet to feed oil to the big ends it seems to be quite different arrangement to the Austin 7 jet and would allow a patent to be applied for  - whether Stanley or Herbert came up with this doesn't seem to be mentioned. 

Cheers, Tony.

[Alan]

I’ve always thought that it’s not about oil pressure, but flow rate. You need flow to feed the big end with oil and the hydrodynamic forces in the bearing does the rest. In a conventional system all you need the oil pressure for is to ensure the oil flow doesn’t stall in the oilways in a rotating crank.
It wasn’t just the type13 that used jet lubrication. Bugatti used it quite a lot, but his design was a lot cleverer than Austin’s as it contrived to feed the journals through 360degrees not just as the crank web passsed the jet.

[Mark McKibbin]

Halfway through the production of the Type 35 and 37 Bugatti went to pressure fed so I suppose with the greater horsepower achieved with the supercharged models, Bugatti's squirt was not up to scratch.

[Chris KC]

I’ve always thought that it’s not about oil pressure, but flow rate. You need flow to feed the big end with oil and the hydrodynamic forces in the bearing does the rest. In a conventional system all you need the oil pressure for is to ensure the oil flow doesn’t stall in the oilways in a rotating crank.
It wasn’t just the type13 that used jet lubrication. Bugatti used it quite a lot, but his design was a lot cleverer than Austin’s as it contrived to feed the journals through 360degrees not just as the crank web passsed the jet.

I think you are right Alan. The supply pressure merely assures that there is a good flow of oil to the bearing (although pressure of course is not flow, and may indeed indicate precisely the opposite!)

It has been observed before that the amount of oil needed for lubrication is tiny - the film between journal and bearing is molecules thick - in engines like ours I'd say pressure feed contributes more to cooling than to lubrication.

Centrifugal force is a two-edged sword; it can of course oppose flow but it can also assist it, and on some modern high performance engines the challenge is to make the oilways small enough that they don't starve the supply.