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As Glyn mentioned on the other thread, the big and desirable difference is the straight port head on the 340. Most parts and ancillaries that may have been improved or changed can be swapped between the two, including the cylinder head. The flywheel of the later engine will be drilled for the diaphragm clutch and, if the gearbox is included in the swap, the later engine has the all-synchro gearbox with very nice ratios.
I'm not sure what date Jaguar switched from a scroll type seal on the rear of the crank to a rope type. It must have been late 1950s. Opinions differ on which is better. If it's not full of dirt, the scroll (a kind of Archimedean screw pump) works well when the engine is running, but leaves the odd drip when stopped, especially if the car is facing uphill.
The blocks of much later XK engines, from the late 1970s and 1980s are possibly inferior. Production had run on much longer than Jaguar had ever intended and the machine tools were well past their best. Also some of the later design improvements to the block were not always as well implemented as they might have been.
Last edited by Peter3442; Apr 12, 2022 at 12:43 PM.
The 3.4 Mk1 also seemed to be quicker than the Mk2. It's difficult to judge precisely how much quicker the Mk1 or 340 were as the contemporary road tests of new 3.4 Mk2 cars (that I know of) were all automatics. For the 340, the straight port head should have been an advantage (though some people disagree) and there's most likely some weight reduction. Apart from eliminating the armco bumpers, Pressed Steel may well have used a thinner gauge steel for some of the pressings and their build quality could only have improved allowing Jaguar to reduce the amount of lead filler.
Then there are the gearboxes. You have to be unsympathetic to achieve fast 0-60 times with a Moss box. I don't know how the Moss with OD compares with the all-synchro with OD for efficiency in transmitting torque.
Much the same, but it's also necessary to change the tacho drive and probably swap the oil filter arrangement. As I wrote earlier, a later 4.2 block needs closer examination and may be more expensive to restore. Some suffer from cracks between the bores. An old 3.4 is a fairly bullet proof 200,000 mile engine.
The 3.4 & 3.8 with its Brivadium sleeves are probably the toughest engines Jaguar made in that era. Regards rebuilding the 3.4 can be re-bored to 60 thou oversize. The 3.8 can be re-bored to 30 thou oversize before you replace the sleeves. So lots of potential life in a 3.4 before a block is either trashed or sleeved (aftermarket).
It is perfectly possible to make a very nice engine starting from a 4.2. But, it demands some extra effort and cost, stainless studs, tophat liners, extra machining. Still you end up with more cubes, some useful squish. Almost everyone seems to favour the later 4.2 con rods as being stronger. Stronger isn't necessarily better. The older ones survived the 24 hours of Le Mans so I'm not convinced the extra weight of the later rods, which must cost smoothness at high engine speed, justifies any gain in strength.
One certainly can but the cost differential of just re-boring a 3.4 & fitting oversize pistons vs the major surgery required to revive a 4.2 with cracked block back to good health would be considerable on my side of the pond. I think the smooth revving 3.4 engine is a gem. I love my balanced & weight matched rods & pistons 3.8. My crank & flywheel/clutch assembly were way out of balance when we started my restoration.
Finished cranks & cams were part of the CKD kit we received from Jaguar. We only machined blank heads & blocks here to meet Lyons arrangement with government on our local content program which at the time was based on weight (Phase 2 = 55%). All upholstery was local as were items like batteries, springs etc. Silverton made tropical radiators locally as an example. Finished woodwork was part of the kit. Book-matched veneering was not a developed SA skill set at the time. We could do it but not on a volume basis. (Lyons was clever. He managed to get UK castings of heavy components accepted into the weight deal)
CKD S Type.
Last edited by Glyn M Ruck; Apr 16, 2022 at 04:30 PM.
Depending on what you want to do, I preferred the 4.2 block simply for the bosses cast into it. If you wan to mount a modern alternator and power steering, and maybe ditch the unique double groove belt, it would be nice to have extra places to bolt brackets to the block. The 4.2 has that, the 3.4/3.8 doesn't.
I did manufacture an adapter system to use a modern alternator with the original power steering pump on the back, but it would have been nicer to mount them separately on their own brackets with a modern style belt tensioner.
Jaguar did not make a big song & dance about it but the real on road performance of the 340 car was quite a bit better than a Mk2 3.4.
Did the Mark 2 3.4 and 340 have the same axle ratio? That could account for better performance rather than a head change.
Not sure about the 3.4, but certainly for the 2.4 I read the straight port head actually reduced the torque produced and moved the torque range up the rev band.
Did the Mark 2 3.4 and 340 have the same axle ratio? That could account for better performance rather than a head change.
Not sure about the 3.4, but certainly for the 2.4 I read the straight port head actually reduced the torque produced and moved the torque range up the rev band.
Where ever the torque curve is, my 340 certainly has lots.
I was behind this rather new Jeep Cherokee just pulling away from the light approaching a rather steep hill _ I was in fourth gear.
I could smell the Jeep's catalytic converter working and the hear the trans kicking into a lower gear as he tried to pull away from me as I came upon his bumper.
He could not lose me if that's what he was trying to do _ the 340 had mountains of torque _ I was surprised !
There was no hesitation in the Jag at all.
Did the Mark 2 3.4 and 340 have the same axle ratio? That could account for better performance rather than a head change.
Not sure about the 3.4, but certainly for the 2.4 I read the straight port head actually reduced the torque produced and moved the torque range up the rev band.
Yes they had the same axle ratio Manual & OD = 3.54 to 1
Jaguar surprised themselves. The 340 just performed all round better in standard form vs Mk2 3.4 ~ synergy & some weight shedding. From things like Armco bumpers to carpeting. The gas flow is far better on a 340 than a B Head Mk2.
The 2.4 engine reacted differently but still became a genuine 100 mph car in 240 form.
Last edited by Glyn M Ruck; Apr 17, 2022 at 04:07 AM.
I also have a theory that the Armco bumpers bugger up the aerodynamics of the Mk2. The S Type was measured as the most aerodynamic of the Compacts in a wind tunnel. (incl. 420). It's in one of my books somewhere. The 240 & 340 have S type front bumpers. Their rears are unique.
Last edited by Glyn M Ruck; Apr 18, 2022 at 10:48 AM.
Anything on the aerodynamics of the whole family would be interesting. I'm convinced they all suffer from the absence of a front valence (chin spoiler in modern terms). The tail shape can be important, but that's sensitive to nose up or down. Ultimately, given identical engines, drag can be related to maximum speed.
Last edited by Peter3442; Apr 18, 2022 at 03:35 AM.
Exactly Peter. Just wider tyres create more drag. Note how manufacturers always do their CD quote by testing the base model with skinny tyres. I'm an F1 fanatic so drag means a lot in my life.
See what this Australian chap did to his S Type ~ front behind bumper ledge down. I don't know how much science went into it. Not many of us have access to a wind tunnel. Best I can do from the pics I have. Callum did the same thing in his own way with his CMC Mk2.
To my knowledge only the CSIR has a suite of wind tunnels in South Africa unless SASTECH owned by Sasol have one. They have altitude compensating Dyno facilities. Why we see F1 engines running here from time to time. (more taxpayer money spent)
Last edited by Glyn M Ruck; Apr 18, 2022 at 05:21 PM.
