Jet feed, pressure feed difference

[dickie65]

For Timo,
You need to order the same type of crankshaft that was originally fitted to your car to keep things simple.

[Reckless Rat]

This is a phoenix splash fed crank. The oil is squirted from two jets in the oil gallery into the two hollows which direct it through to the big end bearings



This is a pressure fed crank (a three bearing one from a Nippy) - the hollows are covered over and the oil is fed through the crankshaft from the front of the engine.



Hope that helps.

[dickie65]

Your three bearing crank is different from the last one I saw which had cast brass covers and oil was fed from the centre main bearing, it had the standard starting handle on the front.
It was an 1 1/2" big end crank.
Is yours 1 5/16" ??

[Reckless Rat]

Just a photo I found on the web. Not mine.

[Spex]

A thought or two.
Although The "squirt" is more like a trickle or dribble, a lot of people forget
that there is pressure from the crank hitting the said dribble. Not as much when idling
as at 2000 rpm. At these revs the dribble could be hitting the crank at, at least 70psi.
No wear in the journals (Phoenix 1 1/2splash, two bearing, 15000 miles, 10000 around town) in 15 years.
My friends tell me I flog it. I have no experience with competition.
Peter

[Bob Culver]

To hark back to my near first post on this Forum, Raymond Mays (later of ERA and BRM fame) very successfully competed a 1.5 litre 100 mm stroke Bugatti Brescia post WW1. Amherst Villiers, later of supercharger note, assisted with the mods. Car had FN/Seven type b.e lube with pockets as Phoenix crank. They managed to get the car from 4,000 to 6,000 rpm but the bes then failed. They devised and fitted an extended scoops and then got to 6900 rpm, notably high at the time. In a book "The Man Who Supercharged Bond" (!) by Villiers. Personally I would have thought there was a risk of a trapped air cushion.The circular milled original Seven troughs seem less than ideal. But many cars have run distance with a blocked jet....
It would be interesting to see inside a running crankcase. I doubt if the exact alignment of the jets much matters!
My RP was fitted with an exchange engine at 40,000 miles but with apparentlyorigianl bes. At 100,000 miles signs of cracks but crankpins only about .001" wear (on very basic oils). The bes were refitted at evey frequent main bearing renewal and the regular new surface would have reduced wear.

[Ian Williams]

" I doubt if the exact alignment of the jets much matters! "

It matters quit a lot actually, I can attribute more than one big end failure directly to an unblocked but miss aligned jet

[Terrytuned]

Photo of jet troughs ground out to improve alignment and jets tweaked to suit.  Terry.

[Tony Griffiths]

Might someone with experience in the building, installing and running of a "4-jet" system like to comment?

[Ivor Hawkins]

I am sorry Ivor this is simply not true, myself and numerous others have raced very successfully with jet fed cranks! I have cars with both set ups and in all honesty do not see the need to add the complication of pressure feed unless it is an original set up or you intend to use you car under exceptionally demanding circumstances. It is true that long distance races at sustained high RPM, such as existed at Brooklands, showed weaknesses in the jet feed system however modern oils and small modifications to the Jet set up negate these issues under most modern sprint and race situations.

I bow to your experience Ian, I’ve always used splash fed, even with my Super Sportsman, which was quite highly tuned, I felt My suggestion was erring on the side of safety!