On the KISS principle

Location: Melbourne. Victoria, Australia.

Gentlemen,it is only a suggestion,I am a belt and braces man myself,as far as KISS is concerned I totally agree,but the mod is a simple one which increases the potential supply for virtually no cost, I used copper brake piping and a brake pipe three way adapter from the old biscuit tin supply.Time for mod I can't recall but was only a few hours. I'm happy knowing oil is splashing around merrily in the crankcase, No oil leaks and low consumption, you pays yer money and takes yer choice.

Location: Piddle Valley

There are some who go to the complications of pressure feeding the crank and that is far more expensive than doubling up on the oil jets. If A7's can be raced reliably with 2 splash feed jets where is the logic for pressure feeding? I have done four engines with 4 jet lube for road cars, 2 with bored out pumps. The main thing for me is it costs nowt, only my time and it might be better than 2 jets. I know this is all old stuff but is there any evidence of the superiority for pressure feeding?
Cheers,
Dave.

Location: Sheffield

I believe the bad reputation for 1 1/2'' splash fed cranks in racing largely came about during the 1950's because of failures with jet fed Nippy big ends. However if you examine a Nippy crank you will see that the oil pickups and drillings are so poor it is little wonder they ran ends, I personally don't believe it has anything to do with just having two jets. I can only speak from experience, and mine is that with a Phoenix crank 2 jets are entirely adequate for 6000 rpm racing in a well prepared seven engine, and certainly more that adequate for a road car. I am sure someone will come along shortly and provide us with all sorts of theoretical calculations as to why pressurisation is desirable, but the proof is in the pudding as they say not the cook book. Obviously if you wish to go down the 4 jet route it is your personal choice and unlikely to do any harm, I am just saying that I do not believe it entirely necessary, particularly on a road car, and that I spend my time focusing on other details.

Location: NZ

Totally agree Ian. I have to say I have never run a big end on a splash fed engine and I've given them more stick than most.
What is not generally understood is the actual mechanics? of big end lubrication. The oil from the jet, or pressure supplied oil is not what creates oil pressure in the bearing - that is done by the relative movement between the crank pin and con rod. This is of the order of several hundred if not thousands of lbs per sq inch. As long as there's an adequate oil supply the bearing will create its own pressure. In the case of an oil jet it's easy to see that is what happens. With pressure feed, you need about 10psi to overcome the centrifugal forces acting on the oil in the crank oil ways. If the pressure is t high enough you can stall the oil flow and still show pressure on the gauge. That's why you need pressure, otherwise just volume would suffice.

Correction That 10psi should read 10psi per 1000 revs.

As a matter of interest, what oilway configuration is adopted within the b.e. for racing with jet feed? Are the drillings in the conrod retained? Is a trench across the top of the bearing as original mid 1930s retained? Is a pocket provided at the dividing line?
Long ago, after reading of the bad effect of interruptions in bearings where heavily loaded, I dispensed with both drillings and trench. Seemed OK to medium rpm. However the oil spray must be very dispersed and probably considerable enters via the drillings.
Has anyone fitted a window to a scrap crankcase and attempted to observe the spray?

The flycut machining of the original crank pockets seems curious. I wondered if it was to avoid a trapped cushion of air. But the success of Phoenix style pockets and the Villiers mod to a Bugatti seems to dispel that notion.

Location: Auckland, NZ

Don't bother fitting a window in the crankcase in an attempt to observe oil spray, you won't see anything Bob. Some of the early Doxford marine engines with a top speed of about 120 RPM had windows in the crankcase with internal lights and you could see what was going on at 30 RPM. However there was so much oil flying around at 50 RPM you couldn't see anything.