This is the 10th in a series of articles.
Spit and Hope lubrication in Austin 7's proved to be a stroke of genius, being the logical step between splash and fully pressure fed big end bearings. A simple eccentric vane pump running at 1/4 engine speed, producing a large volume of oil at little pressure, proved to be so successful that only the end of the production, when slipper big ends were introduced, was any change made to the delivery, and that was the angle of the two oil jets. This was changed from vertical to 45 degrees, in order that the crank web was given an extra 10 degrees in which to collect the oil for the big end. Incidently, depending on R.P.M., effective oil pressure per big end would be about 40-60 P.S.I.
To maintain all this, reconditioning the pump supply and fit a new relief ball, reseating same, and replacing the delivery jets is all that as needed to restore the correct oil delivery.
Well not exactly.
The oil jets need to be the correct ones for the particular engine, whilst they all look alike they are not, all have the same body diameter and the same head diameter, the same overall length is different, as is the hole through the jet itself. Engines 1923-1929 are the longest, 1930-1936 are the medium length 1937-38 the shortest. The 1937-38 also have the smallest hole, in order to increase the oil pressure for the centre main.
You can use the oil jets for the heavy shaft engines in all the early engines as the O/A length difference is only 1/8th but you can not use those oil jets in the late model angle jet engines. Also the smallest oil hole size is more desirable.
So we only have to deal with 2 different oil jets.
I have measured a number of oil jets, collected over the years, and all measure metric sizes. The removal of these oil jets needs care and attention for it is all too easy to mess up.
Select 11/64" diameter drill and remove the head off the jet, taking great care not to drill into the body itself, next take a 5/32" pin punch, locate it in the hole you have just drilled, with one medium blow with a hammer the jet will move downwards, continue with light blows until the jet body is free of the crankcase.
Fitting a new jet requires a 3/16" pin punch, the stepped end of the jet is located in the crankcase and using an appropriate punch, the jet is driven into position. If however, Billy the Barbarous has been there before you, and the jet falls into place too easily, all is not lost, get your soldering kit out and sweat some solder around the 4 mm portion of the jet and try again. You will now understand why the first part of the body is smaller than the main body. This is to align the jet before the cosh onslaught by cretinous mechanic.