Joined: Aug 2017 Posts: 628 Threads: 19
Reputation:
11
Location: Sheffield South Yorks
Car type: 1932 RN saloon
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.
Joined: Mar 2015 Posts: 5,443 Threads: 231
Reputation:
67
Location: Scotchland
Pheonix cranks, and other new cranks that I have fitted, do not have symmetrically positioned oil scoops on each side of the crank and jets require a middle ground set up.
I have surmised, based on many successful middle ground set-ups, that a lot of the lubrication therefore comes from the mist inside the crankcase.
Joined: Aug 2017 Posts: 188 Threads: 21
Reputation:
0
Location: Haverfordwest
Car type: RP Deluxe Saloon 1933
If a two stroke engines can run successfully on 50:1 mix in the petrol then surely as Ruairidh says an Austin Seven system is supplying more than enough under normal circumstances.
Roger
Location:- Haverfordwest, Pembrokeshire.
Joined: Aug 2017 Posts: 2,748 Threads: 31
Reputation:
95
Location: Auckland, NZ
10-12-2021, 07:35 PM
(This post was last modified: 10-12-2021, 07:47 PM by Bob Culver.)
Crankcase compression two strokes of reasonable size and output invariably have roller bearings whcih require only an oil mist.
With the original Seven scoops I wonder what happens to drips which arrive at a larger radius than the hole. Does the impact propel them in, or does centrifugal force fling them to the wind? With a pronounced edge there would seem the possibility of a pocket of moderately compressed air being carried around. Maybe that is the function of the two curious holes on top of the big end. Or are these also inlets as thre mast be droplets everywhere?
If the oil arrives at scoops in a solid stream fine but if it arrives as scatterd drops could make some difference. Anyway the Mays mod appears to involve a lerge unvented scoop so seems the oil wins. (I have eased the drilling somewhat on the inner side)
Joined: Oct 2017 Posts: 1,507 Threads: 54
Reputation:
8
It is no accident that the jets are mounted where they are so as to recharge the crankshaft oil way immediately prior to the point of maximum loading. Also that the oil way is of generous proportions to act as a reservoir to provide oil for a complete revolution of the crankshaft before recharging.
Compare the jet lubrication of the Seven with a steam locomotive or the Rolls Royce Merlin engine and you appreciate it's simplicity. If we take one of the most famous locomotives, the world steam speed record holder Mallard, each big end has an oil well which was filled up prior to leaving the shed and the oil was fed to the bearing via a felt pad. This had to last for 408 miles ( May 1948) whilst running at 200-300 RPM and producing in the order of 1500 horsepower on the non stop Flying Scotsman. Few people know that Mallard suffered a big end failure during its record breaking run 3 July 1938 when running at 126 MPH or 523 RPM, which was basically a design flaw corrected by a ex Great Western Railway Engineer in the 1950s.
On the other hand I am interested in aircraft, particularly those with reciprocating engines and their lubrication when flying inverted. 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. This was a real head scratcher and was finally solved by Wing Commander Boyd of Boscombe Down and I quote from the book. “He took an aircraft up to 30,000 feet, rolled it on it's back, thus loosing oil pressure, over-revved to 3600 RPM and, with a slight negative G force all the way down, held this condition. This meant that the engine was exceeding maximum RPM for at least 30 seconds whilst starved of oil.” unquote. If it took that to run a big end on a Merlin then I feel sure the Austin lubrication system is more than adequate, so less of the hope please. Wing Commander Boyd was a brave man.
Joined: Aug 2017 Posts: 220 Threads: 19
Reputation:
1
As a non racer but one who likes a bit of performance , when I rebuilt my engine (2 bearing) I was a little concerned that the lube system was a bit hit and miss , or should that be mist? I had read about the duplication of the oil jets and decided that the belt and braces approach could only improve the lubrication. I routed a new oil line within the crankcase using copper/nickle brake pipe,made up some jets by peening the ends of the pipe, running a 1.5mm drill through to give a straight stream of oil. spent some time aiming the four jets at the "bath tub" collectors on the crank. A bit messy but worthwhile. With a standard oil pump I have ,when hot and cruising at normal traffic speeds, 2 to 5 psi showing on the gauge. I did not fit the bore oil plates and don't have what I would consider excessive oil consumption .
Joined: Aug 2017 Posts: 2,748 Threads: 31
Reputation:
95
Location: Auckland, NZ
11-12-2021, 07:14 AM
(This post was last modified: 11-12-2021, 07:21 AM by Bob Culver.)
Very heavy rain is forecast. I think i will take my Hillman at 55 mph down the motorway and hold a Seven crank out the window and see what the droplest do.....
OK at the oil inlets but the not so skilled need to recognise that the longevity of Phoenic cranks stems from the protective effect of the in compression nitride layer so this must not be further reduced in any highly stressed areas.
Joined: Jan 2019 Posts: 48 Threads: 9
Reputation:
0
"the longevity of Phoenic cranks stems from the protective effect of the in compression nitride layer so this must not be further reduced in any highly stressed areas"
My wife was highly stressed when she found out how much I'd spent on a new crankshaft!
.
