If Bob Burrell’s Connaught A6 is fitted with a Lea Francis engine, it is only the second “A” series Connaught to be so equipped, although it began life with a 2-litre Connaught engine. The first “A” series car ran from August 1950 to December 1951 with a 1 3/4-litre Lea Francis engine, acquiring the first Connaught 2-litre engine, C1, in December 1951. The wet sump “Leaf” engine has an iron block and chain drive to the high camshafts. The Connaught 2-litre cylinder block is cast in aluminium with wet liners, the camshafts are gear driven, and the dry sump is cast in magnesium alloy.
Lea Francis investigated a 1 1/2-litre aluminium block engine for the American market, but did not proceed with it, and aluminium block castings based on this design were supplied to Connaught, as were camshaft-drive gears, cylinder heads, pushrods, rockers, the timing gear case and the oil pump. Connaught Engineering fully machined the blocks in their own workshops and made the wet liners to their own design. Connecting rods and sump we machined to our own design, cylinder heads were finish-machined to Connaught requirements in their own works, while the camshafts, valve springs and valves and pistons were supplied by the specialist manufacturers to Connaught specification. The crankshaft, flywheel and the cast-magnesium rocker covers were made to Connaught drawings; the rockers supplied by Lea Francis were modified at Connaught’s request.
I produced such drawings as were needed for these and sundry other engine bits and pieces in my first 18 months at Connaught, in addition to work on chassis and bodies. I think this covers just about everything except carburation, induction and exhaust systems, ignition system; these were developed by Mike Oliver and either made for or by Connaught. Why is the “A” series Connaught so often referred to as Lea Francis-engined? How often does one read about Riley-engined ERAs?