Mods and Consequences
Colin Chapman founded a whole sports car company using an Austin Seven as his start point, so there’s no shortage of potential with this brilliant pre-war people’s car. Really, your options are only limited by your imagination and budget.
All Sevens featured a 747cc sidevalve engine, apart from the first 100, which had a 696cc unit. Until 1936 there were just two main bearings fitted (one at each end of the crankshaft), while later cars had an extra one – but any Seven crank can break because of flexing. The big end journals were also increased from 1⅛in to 15/ during 1930, but even the larger items can fail after years of hard use.
There are all sorts of things you can do with the engine, including fitting a stronger crankshaft, sportier camshaft and slipper pistons so you can increase the rev limit. The best crankshafts are made by Phoenix, available through A7 Components; these use modern materials and are much more durable than the originals.
Changing from a low-compression to a high compression cylinder head is an easy swap and improves things noticeably, while aluminium heads are available, which pep things up a bit more. When it comes to fuelling, a single 1⅛in SU is fine for normal use while a 1 in unit produces a bit of extra power. If you’re racing you can go up to a 1 in SU but don’t bother with twin carbs as they don’t produce any benefit over a correctly set up single carb; it’s not unusual for a carb to be taken off a Mini or Minor without the needle being replaced. The result is an engine that will run fine, but will over-fuel constantly, washing the bores.
There are numerous options when it comes to uprating the cable-operated, single-leading shoe brakes, depending on the car’s age, including converting to a hydraulic system. But the limiting factor is usually the grip afforded by the tyres, so before you spend a fortune on better anchors make sure it’s going to be of some benefit. Upgraded brakes are advisable because the original system is so poor. You can convert to hydraulic using parts from the early Morris Minor 1000. It’s an effective swap but not a five-minute job because you’ll have to fit a master cylinder, new brake pedal, hydraulic piping and flexible hoses – along with the back plates, which are getting hard to find. Oxfordshire Sevens has developed a twin-leading shoe system that retains the original components, is highly effective, yet retains the cable system so it’s much cheaper and easier to fit.