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My 1962 Mark 2 Jaguar

Very unusual 3.4 motor factory modification

Picture taken at "Kaiaua" New Zealand.

More pictures general info

I acquired this car in 1984, a 3.4 litre straight 6 Jaguar MK2. A short  time after while servicing the timing chain, I discovered my car was different. Over the years I have heard several theories and even heard of other cars like it but never fully resolved the issue. I just got used to it and eventually fully restored the beast at home, Auckland New Zealand.

The car still has the modification which gives me no trouble with casual use but could be a nuisance if I drove the car a lot: when the chain wears excessively it loosens and can't be tightened using the usual eccentric adjustment available on virtually every XK engine out there. Instead I must replace it.

For an in-depth explanation of the modifications on my car please read on.

There is no central adjustment to the timing chain, the top chain being adjusted with a hydraulic tensioner instead. See pics below and if you know jag engines you will see straight away the differences. Even the chain housing casting is completely different.

Very rare, and conflicting stories as to why/how it happened:
D-type jags in the 50's used this method (hydraulic) to tension the top chain so a mechanical fuel injector could be fitted to the front of the engine, where the chain adjuster would normally be. There are some theories why a few production cars in 1962 had this mod. Were Jaguar were simply using up spare parts (from the D-Type engines) or actually conducting a "research" experiment. I have written to the factory who subsequently denied ever doing any such mods on production cars, they of course acknowledge the D-Type mods. So there is a little confusion here as to the real reason a few production cars ended up with this change. I should add, there is no mention of it in any workshop manual I have ever seen.

 It has been said that a "trial" run may have been done on 3.4 cars in late 1962, another car with engine numbers close to mine has been found in the UK with the same modification.  It has also been said that the change was subsequently rescinded due to difficulty in servicing the head cylinder quickly, ie changing the shims. The rear four pairs could be changed by loosening the chain and lifting the camshafts up from the back, the above mod put paid to that. Makes sense, but some factory personnel I have met knew nothing of it while some others do.

More Jaguars with the same unusual mod

In April 2001 a communication from Sydney Australia: Two more cars there with the same mod. Both 1962 cars, but one is a Mk10, there goes my 3.4 MK2 theory unless the engine is a replacement.

October 2001. A lightweight E-Type (replica) in New Zealand for a spell,  I saw  the "mod" on that engine, a D-Type engine with mechanical fuel injection. So that bares out the theory above re D-Types.

This February 2003 communication from "Dallas Murray" California USA, "I saw your page on the Jag Web and just want to let you know that I had also run into the same thing back around 1972/3 when I rebuilt the motor in an early 60s MkII" ...."As the dealer would not even admit that it could have come off of any Jaguar we just replaced the whole upper timing chain setup with one from another motor."

September 2012 Barrie Wood from Devon emails that he has a 3.8 E-Type engine with this modification.

Sister car

August 2007, a sister car in Belgium! an email from Jean-Pierre who tells me his MK2 3.4 car has this modification too, we compare chassis/engine numbers and discover our cars were both made September 1962. That's Jean-Pierre's car left (green) and mine right.

Note the wing mirrors, not unusual but does indicates jaguar were doing a "run" of those perhaps at that time as they were not always included. Also, hard to see here, but I smiled when I saw Jean_Pierre's number plate starts with "JA" while mine is "JB".


Details of the modification:
Note in the picture bottom left the casting is different than the norm, if you know Jaguar engines you will spot the difference straight away. Also where the chain adjuster tool would normally fit to the eccentric adjuster there is just a simple bearing.

Note the casting below left. Always two holes left & right to accommodate chain dampeners, mine has only one at left proving this is a different casting than the one used in almost all XK engines.











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