Jaguar XK and Lea-Francis


In a footnote to a letter in a current issue you wonder whether W. Heynes took some of his ideas for the Jaguar XK tzo engine from the Sunbeam 3-litre. Apart from many other influences I think Lea-Francis was the course of much inspiration.

Heynes was a junior member of the Coventry IAE when Charles van Engel) was chairman and chief designer at Lea-Francis. In his recently published book, The Lea-Francis Story, Barrie Price reveals that the two engineers knew each other well certainly some aspects of Leaf chassis philosophy were incorporated into the SS range. It is interesting to note that the XK loo four cylinder engine had much the same stroke as the two Leaf OHC engines of the late twenties SS 98 mm. to the 100 mm. of the Leal’s, and like the XK the Lea-Francis Ace of Spades engine started life as a four cylinder. Likewise there is obvious similar thinking in the chain sprocket props on both Lea-Francis and XK.

Leafs held patents covering the all chain drive to their twin 011C, and all such engines in my possession carry patent plates. The earlier series, designed by Lord, bear very little resemblance to the second batch, designated LES 2, which in turn have a strong resemblance to the XK engine. In fact, if I broke the sump on the LFS 2, it would take only a few hours work to fit one from any XK, whereas only the finger tappets and flywheel are interchangeable between the two Leaf engines which were being produced at the same time! I enclose some photographs of the LES 2.

Having acquired a certain working knowledge of Leafs over the last twenty years or so it is my opinion that Leafs had a significant hand in modifying the Vulcan twin cam which resulted in the excellent LFS 2. Van Eugen denies this, and Barrie Price tactfully gives it a scant mention. Vulcan had nothing to do with the Lea-Francis racing programme, but this engine has the hallmark of LeaF engineering, and of a Leaf engineer who intended to go racing with it, at that! If one were to place the complete bottom end assembly beside that of a Talbot 90 of about the same era only the knowledgeable could tell them apart. It is arguable that the very narrow main bearings of the Leal’ predated the Talbot design by a year or two, but this is immaterial. The resemblance between the two seven main bearing layouts is very striking, even including dimensions. George Rocsch and Charles Van Eugen were well acquainted. Tom Delaney tells me that a Cozette blower was tried on a Talbot 75 in about 1928, and damn’ well it went, too. Tom’s father, L. T. Delaney, was instrumental in importing the Cozette, and he was also a director of Lea-Francis. Van Eugen’s design, the Ace of Spades, had only four mains for its six cylinders, but it was a very beautiful Cromard casting and I have heard it said that it was the first such use of the American black heart ironcasting system in England. Unfortunately the money ran out, so the cylinder heads were made of traditional UK materials and methods. But the combined crankcase and block were deliciously neat and clean, and light too. And the SOHC was chain driven by a system in which the only difference from the LFS a was the single cam sprocket! Perhaps an old man’s memory is getting a little selective, as it has every right to do!

Be that as it may, I just wonder whether Heynes learned his lessons from Van’s (he was always known thus) beautiful light iron castings, and, dare I say it, earlier narrow seven main bearing lay out with the twin cams. And did he see how strong and reliable were the Roesch Talbots I believe XK connecting rods can be fitted to Talbots.

The ideas, the men, and their engines were all there at the same time. And perhaps that melting pot was the origin of one of the greatest engines of all time.