The E-Type gets most of the limelight, but it was the XK120 – with its remarkable straight-six – that helped establish Jaguar’ s reputation
That perspective starts with an appreciation for its original engineers.‘ I think we’ ve hit peak XK; I think that peak XK was probably done at Jaguar. All we’ ve done from now on is refine parts. We can’ t buy original parts. We’ ve had to go off and make them.’ William doesn’ t just mean gaskets and ancillaries.‘ Crosthwaite and Gardiner make the most beautiful castings; there’ s no question they are the best in the business. But the problem with that is that everybody buys from the same place. You’ re limited in what you can get out of what everyone else is using. I’ d like to start casting our own engines, basically.’ You can also buy brand new 3.8-litre XK blocks directly from Jaguar Classic.
It’ s not just the performance of these rebuilt XKs that William has on his mind; it’ s the exactness that he wants to achieve.’ On the road engines, even the best in the business haven’ t quite got the details right on casting thickness. If you repattern an engine block, everyone tends to make it thicker or slightly improve it. I don’ t want to do that. I want to make an engine block absolutely the same spec as 1961. It’ s basically refining detail. They were so beautifully made and so beautifully designed that, in my opinion, there is no need for improvement.
‘ Fast forward to where we are today, we can’ t really push the XK engine any further. We’ re really at a maximum of what we can achieve with reliability, part quality and power. Jaguar was getting generally 240hp in 3.8 form as a standard road car. We’ re now getting close to 350 to 360hp for a very, very fast wide-angle 3.8, which, for racing, is phenomenal.’
‘ The issue we have today is that the aluminium cylinder heads are now getting porous, because they are 60 years old. There’ s only so much you can machine a cylinder head down.’
William is yet to commission new loyal reproduction head castings, so a phenomenal amount of work has to go into original cylinder heads.‘ We’ ve come up with a system where
we can weld them up properly and then keep them going. So the hard thing for us is to get something which has been on the bottom of an ocean into something which is dead fast, reliable and machined beautifully. And there are only two machinists who I think are capable of doing it now. The one we use, David Moore Engineering, he’ s probably the most talented machinist I know of. An engine is make-or-break on the machining. We are doing some really cool modern things. We CNC port and CNC cut the cylinder heads now.
‘ Many people don’ t line-bore engines. We think it’ s compulsory. We line bore the entire main journals and the cam journals. We fully balance and grind the crank. Every edge that touches a gasket or seal or bearing is machined. The sump face, block face, cam cover face, everything’ s machined.
‘ What I’ m finding now, with our own engines and our own cars, is that the balance, the pull, they’ re so beautifully smooth and that’ s all down to the quality of parts fitted, the machining. Obviously it takes a lot of skill and knowledge to assemble them correctly; we do that inhouse. I’ m really proud of our assembly, but we can’ t do it all ourselves. So we rely on really good people around us.’
The XK engine won Le Mans five times; three of those wins were with a D-Type
26 The Engine Rebuilder Issue 06