Engine oil for Austin SEVENS

The latest oil is rated SP Introduced in May 2020, designed to provide protection against low-speed pre-ignition (LSPI), timing chain wear protection, improved high temperature deposit protection for pistons and turbochargers, and more stringent sludge and varnish control. API SP with Resource Conserving matches ILSAC GF-6A by combining API SP performance with improved fuel economy, emission control system protection and protection of engines operating on ethanol-containing fuels up to E85.

I would not recommend using a high specification oil or synthetic oil, they are designed to be used in modern engines with tight engineering tolerances with highly stressed parts and efficient oil filters.
The description of Morris Golden film below is an example of the specification of an oil to use, although I have not used it.

“Morris Golden Film SAE 20W-50 API/SF Classic Oil is recommended for use in veteran, classic and vintage cars, motorcycles, commercial vehicles and tractors, where engine design and tolerances prohibit the use of modern high additive level oils. Modern dispersant additives keep combustion chamber contamination suspended in the lubricant, allowing full flow cartridge filters to remove it. Early oil filtration, usually in the form of a mesh gauze or strainer, is not efficient enough to remove this suspended material. Golden Film SAE 20W-50 Classic Oil is a low dispersant oil and allows the suspended matter to harmlessly settle into the sump.”

To see a large range of suitable oils for your Austin 7 look at www.classic-oil.net

In conclusion.
If you have been using an API/SA oil, continue to use it and change it frequently, 600 miles is recommended, the engine will have a lot of sludge in it. If you start using a later rated oil without cleaning all the sludge out of the engine the detergent in the later oil may dislodge the sludge and the sludge may block an oil hole causing oil starvation to some part of your engine. I have always used an API/SB or SE in my Austin 7 engines. I recently dropped the sump on my Austin RM after many thousands of miles, there was a small layer of sludge in the bottom of the sump pan but apart from that the engine was relatively clean.

I prefer mutigrade oil to a straight 30 or 40 grade. When starting up 20w/50 multigrade oil, being thinner, will get around the engine more quickly to lubricate the moving parts and will be thicker when it is hot and less likely to leak out.
Roger Ballard DA7C