Friday, 8 January 2016

Lea Francis: A competition engine.



I thought I would share with you some photographs taken during the rebuilding of a very special engine.


The engine that is the subject of this blog is a true competition unit of 1496cc, purpose made for Speedway or Midget Racing, popular at the time in both the US and Australia. The engine was designed by Ken Rose and featured a dry-sump, gear driven double hi-camshafts and a significantly increased compression ratio to run on alcohol fuels. It was fitted with four Amal TT competition carburettors and a racing Lucas magneto and had a very respectable power output of 118bhp when run on Methanol.


Dog clutch and twin SU version of the engine


A total of nine engines were produced by Lea Francis in Coventry during the period 1948 – 1950, making it a very rare engine indeed. Quite simply they did not manage a breakthrough in the Speedway market against units such as Offenhauser and hence did not achieve the commercial success required and production was halted.


Albert Ludgate and Ken Rose


Continental Cars of Surrey who produced the Connaught subsequently developed the LF competition engine still further and considerably reduced the weight by casting the engine block in alloy. This LF derived engine was installed in their A type Formula 2 single seater racing car.


Connaught single seater racing car


The actual engine in question is that fitted to H3, the third and final Special built and raced by Ian Hopper of Glasgow. The rolling chassis was made as a one-off by Joe Potts of Bellshill and featured a tubular chassis, suspension and wheels of a type used in his JP racing cars.
John Cushley, also of Bellshill and who worked at Potts as a machinist at the time, clearly remembered a large wooden packing case from Coventry being delivered to the premises one morning. He recollected the wooden case was a work of art and that it took four of them to manhandle it off the lorry and carry it into the workshop without dropping it. He told the story, that at the time no-one knew what was inside this case and that the whole workshop stopped and watched with eager eyes as the lid was lifted. The assembled group gasped as they saw what was inside, the most beautiful engine they had ever seen.  



Lea Francis competition engine


Put simply, the car used the very best component parts available at the time and was finished to an exacting standard throughout. The bodywork was designed by Ian Hopper as a true all-round sports car and incorporated a covered spare wheel and seating compartment for his German Shepherd dog. It was extremely successful during the period 1951 – 1953, with wins and fastest times at many National and International race meetings and hill-climbs.


Ian Hopper working on H3


The engine had been removed from the car and rebuilt approximately 35 years ago, but had lain dormant since then. As the engine was stripped it became apparent that the previous rebuild left a lot to be desired and the only way forward was to start from scratch.



Engine as found



The engine was completely stripped and it was found that amongst many other faults, there was a lack of clearance to both main and big-end bearings, all which needed rectification before re-assembly.


Laystall crankshaft


Ian Hopper had fitted a Laystall crankshaft made for the Connaught and later Connaught camshafts to this engine, but removed both the Lucas magneto and Amal carburettors. Twin SU carburettors were fitted in their place in addition to a distributor and coil ignition.


Installing the crankshaft



The crankshaft is quite heavy in weight and having a centre bearing, is hard to install in the block without the use of an overhead crane. The con-rods were also exceedingly hard to fit, as the big-ends are of a large diameter and the bore small. The rods are also relatively short in length meaning that when fitted to the crankshaft and at TDC, the little end eye barely clears the top face of the block. This makes the fitting of the piston hard, as the skirt is well engaged in the bore and it is awkward to align and fit the gudgeon pin.


Fitting the gudgeon pin
  

New rings were fitted to the pistons after they had been lapped to the bores and their gaps set. The ends of the over-size rings were machined at 45 degrees before the lapping and clearance took place, this was normal practice at the time and allows for a greater radial movement of the ring for any given clearance.


Head with valves and cam-followers fitted


The new valves were fitted to the head using new springs/retainers and collets, as the retainers had thinned considerably due to their fretting against the springs. The valves had been lightened in accordance with Ian’s wishes, the subject of which is in an earlier blog. Please see:-

Valves for the Hopper Special

As the cam-followers are retained and operate at an angle within the cylinder head, they have to be wired during assembly to stop them falling as the head is put in place upon the block.

Cylinder head in place on the block


Previously to this the clearances in the gear drive train to the cam-shafts and the valve timing were set. A new crankshaft oil-seal sleeve was machined and fitted at the same time.

Timing gears in place





The head was finally put in place and the remainder of the engine assembled. The rocker arm pads were re-profiled at their bearing faces on the valves and new rocker shafts fitted to make accurate valve clearance setting possible.






So that is it, a job well done.


Hopefully Ian Hopper would have approved of the work carried out, thankfully he left some notes to help us on our way.



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