Jet feed, pressure feed difference

[Reckless Rat]

Cue the catchphrase of the Bullseye comedian and presenter, Jim Bowen: "Tell 'em nowt, make 'em buy a programme."

[Tony Griffiths]

So I was interested to read in “Hives and the Merlin” by sir Ian Lloyd and Peter Pugh about the problems of big end failure on the Merlin.

Thanks for that, Dave. It's a book I've missed; just found one on abebooks.co.uk

---

Hi Tony,
As you probably know I have fitted 4 jet crankshaft lube on your blue chummy and on 3 other cars but I have never exceeded 5000 rpm and then only occasionally. Never  raced any car, only the blue chummy in about 1970 and unfortunately ran a big end but the white metalling was poorly executed and it had 2 jet lube at the time. Some people on A7 Friends think it is unnecessary but it gives me peace of mind zooming up hills in the Peak district. It is not too difficult a job to do it. The method is in " Design for Competition " I think.

Thank you, Dave. Yes, I recall from your copious notes on rebuilding YC that it has 4-jet. A great comfort, if one jet is blocked there's a chance that the "opposite" one won't be. You are correct; it's all very well tootling along the flat lanes of Norfolk, another matter altogether getting around the Peak District (or even Sheffield).

[Ruairidh Dunford]

Out of interest, is it possible to clean the two additional jets, if they bock?

[Greig Smith]

We built the double oil jet conversion following Mike Forrest's guidelines when we built the engine in our supercharged single seater. We managed to buy a job lot of bits which included a new Phoenix crank, it was splash fed so we then chose to drive the blower off the nose of the crank

A blank off plug was removed from the crank case next to the oil pump and replaced with a suitable fitting. The mountings were some brass bar Dad had under the lathe, we drilled it out and the top takes a home made jet which is just copper pipe but with the end tapped narrower and then drilled out. The opposite end was tapped for the mounting screws. The whole caboodle was silver soldered together and has proven to be quite durable. I annealed the copper lines and filled them with dry sand before bending over some old water pipe in the garage.

Interesting that the jet spray from now both top and bottom had to be tweaked and re-tweaked to ensure that both sets of jets have suitable spray angles for both sides of the crank by pumping paraffin via a plastic pipe into the bottom of the oil pick up using a small rotary pump driven by my battery drill. The amount of fluid flow through the jets is astounding. As per Mike Forrest the jets were all angled towards the crank which gives a near 90* arc coverage of the crank trough x 2 for the second set of jets, so I'm getting oiled big ends for approximately 180* out of 360* revolution. Austin originally had the 2 jets straight down so around 30 to 35* out of 360* and it's perfectly adequate.

1/32" overbore on the oil pump & blue printing the assembly gives over 10lbs cold, with between 5 & 6 on hot. OK granted with the 1 gallon sump it's never really very hot. I expect longer events to run the usual 1 to 3lbs which with the double oiler is more than adequate. I probably should run a smaller sump but the big finned job looks the part

No way of cleaning the second jets without pulling the sump, but regular oil changes are in order with a race car, I have to confess I've seen 6500 rpm in top gear at 6.5lbs boost and zero issues with the bearings

There's more here including duplicate pictures--> Supercharged Single Seater (austinsevenfriends.co.uk)

Eagle eyes will spot very slight differences in the brass blocks in the 2 crankcase pictures, that's because we built a second conversion for the green race car when rebuilding that engine

Season's Greetings from the Colonies


Aye
Greig

[Bob Culver]

Another project. Now I will have to live to 110.
Many will be astonished, but at revs the greatest bearing load is upward at the end of the exh stroke when there is no pressure to counter the inertia of the piston assembly. Even on the firing stroke the net force can be upward. Your car is propelled by part or totally camcelling the inertia force!
Relating the load on the oil film to efective oil/air feed pressure in the be would be no mean exercise.
Becasue road cars spend a lot of time at full throttle and modest rpm the top cap usually wears most and fatigues first.