I may be opening a can of worms here, but aren't the camshafts different. That is (and to confine the argument) don't the 2.4 engines (B type head in Mk2 and straight port in 240) have different camshafts from the 3.4/3.8 engines (B type head in Mk2, S type, ... , and straight port in 340)?

I've a vague memory that the part numbers are different and the duration may be shorter for the 2.4. I imagine the very last 240 and 340 cars probably had undrilled cams, but that's a separate issue.

Edit: according to the parts book, my last paragraph is wrong and the 240 and 340 had the earlier drilled inlet camshafts. But ....

 

Yes they do Peter. You are correct! One of the reasons that the 340 outperformed the Mk2 3.4. It, as an example, ran more aggressive cams that Jaguar kept quiet about. The 340 was a bit of a rocketship for the day. An easy 120mph + car. I'm not sure I would want to take one on in my 3.8 S Type. Everything was not down to the straight port head.

 

Refresh page for my edits. I don't know what you are seeing. And don't take the parts book as gospel ~ many mistakes & omissions. You need to restore a car from shell up. Not one nut & bolt & no harnesses to appreciate this. As I did.

 

My parts book is not enlightening about anything special in terms of inlet cams for the 340. As Glyn wrote, it shouldn't be taken as gospel. It lists only two inlet camshafts for Mk2 3.4, 3.8, and 340. These are C 14985 and C17138, respectively drilled and not drilled. They started out with drilled, switched to not drilled, and then back to drilled before the arrival of the 340. Jaguar were obviously undecided as to whether extra oil quietened the cams. Supposedly, the only difference is the drilling; the cam profile is said to be the same. Later, with the XJ6, the parabolic profile arrived to reduce noise and allow wider clearances. I've no idea whether that profile improved the breathing or not or if it might have been tried out on the 340? Sorry, this is all off topic for the 2.4.

In the Mk2/240 period, the 2.4 inlet camshafts went through the same drilled, not drilled, drilled cycle with camshaft part numbers (I think) C 14986 and C 17137. According to Roger Bywater, the 240 inlet cam had 5/16 inch lift instead of the 3/8 inch of larger XK engines and a duration reduced by 30°. If the parts books are to be believed and the cam profile wasn't changed for the 240, then that applies to the 2.4 Mk2 as well.

It would be nice to know more about the 240, 340, and 2.8 XJ engines. For hasty improvisations, they seem to have had some good qualities.

 

Yes ~ One of my books somewhere specifically mentions that 340 cam profiles were changed ~ so one does not know what to believe. I have not found which book made that statement but I clearly remember it. I don't think I'm going mad yet. It was along the lines of while cheapening of the cars to Ambla, no Fograngers etc. That gains were made in both the 240 & 340 engine department and that gains went beyond just the straight port head & SU carbs in the case of the 240. Paul Skilleter or Nigel Thorley sticks in my mind but I may well be wrong. It might be hidden in a Jaguar Technical Bulletin somewhere which can be well over a year late.

My experience is that drilled cams do quieten initial cam rattle on start up. My car does not rattle at all but many do. But I Plastgauged all bearings including cams. As mentioned elsewhere my engine seems too quite to the degree that I went back & rechecked all the cam to tappet/bucket clearances & found them to be correct hot. Every piston & rod is weight matched & the whole assembly balanced with clutch in place.

It's confusing to say the least. BTW my cams have no flats on them from careless maintenance & excessive clearances. A typical Alfa malady if careless with maintenance. Once you have flats on the cams the engine will remain noisy at correct clearances.