Test fit prep — Engine and gearbox (1)

Hello! It’s been a (long) while since I’ve provided an update, but I haven’t been entirely idle! As mentioned in the last update on the Bodywork, I plan to fit an engine and gearbox from the XJ6 range of Jaguars into my Mk2. I’ve spent a good deal of time researching the changes required and getting the engine ready for a test fit. I’ve also had some work done on my garage to improve the weather sealing; a new roof and lining, better windows, and a proper side door replacing the horrible original tin thing. Things are much cosier now! Oh, and a 15 AMP circuit for a new air compressor … but that’s another story!

Back to the Jag

My Jag is a 2.4-litre with the standard Moss (non-overdrive) gearbox. As the car was built in 1962, this gearbox has no synchromesh in first gear. The all synchromesh gearbox was fitted to the Mk2 range from September 1965. (Original Mk I and Mk II by Nigel Thorley)

Although I drove my MK2 for many years with this engine and gearbox combination, and on a number of long trips, it’s a fact that the 2.4 doesn’t have the same oomph as its larger engined siblings — the 3.4 and 3.8-litre Mk2s. Acceleration, not helped by the old slow Moss gearbox, was 17.3 seconds from 0 – 60 mph. Not swift. (The Classic Jaguar Saloons by Chris Harvey)

Performance isn’t everything, the 2.4 is a very smooth and pleasant car to drive at highway speeds and the engine does have some redeeming features. It was a shortened version of the 3.4-litre with the bore staying the same at 83mm and the stroke reduced from 106mm to 76.5mm. These changes reduced the height of the block by 3in. Thanks to this over square design it’s very smooth and revs more freely than the larger engined models. (Original Mk I and Mk II by Nigel Thorley)

Another upgrade option, which I investigated when I was driving the Jag on a more or less daily basis, is to convert to the later 240 specification. When Jaguar introduced the 240, the successor to the 2.4-litre, in September 1967, the power output went from 120BHP for the 2.4 to 133BHP for the 240. This was achieved by raiding their existing parts bin and fitting the straight port head from the 420 and 420G saloons. The addition of twin 1.75in HS6 SU carburettors, a twin exhaust system, and the all synchromesh gearbox completed the job, improving the 0 – 60 mph time to 12.5 seconds! (Original Mk I and Mk II by Nigel Thorley, Jaguar Saloons, and Classic Jaguar Saloons by Chris Harvey)

This upgrade path is something I have considered but never came across a suitable set of donor parts. A little detail on the books mentioned can be found here.

Some years ago I had the opportunity to purchase a 3.4-litre motor from a Series 3 XJ6, along with an all synchromesh gearbox from a Series 1 XJ6, at a reasonable cost. This seemed to solve two of the issues I had with my Mk2, the lack of power and the Moss gearbox which doesn’t like being rushed. The engine number is 8A13109 which confirms the motor is from a Series 3 XJ6 (Jaguar Series 3 XJ6 parts catalogue). This engine is apparently known as the ‘new’ 3.4, it was introduced in 1975 to replace the 2.8-litre XJ6 engine and was a small bore version of the of the 4.2-litre block, therefore not the same engine as the earlier 3.4. (Jaguar Saloons by Chris Harvey)

I’ve had less luck definitively identifying the gearbox I purchased from its serial number. I will need to have another go at deciphering that. However, I have no reason to doubt that it’s from a Series 1 XJ6. This gearbox has the compact Type ‘A’ overdrive fitted.

Will it fit?

Fitting a later model XK engine is a common enough modification, but as I soon learned memories are fickle and there are so many engine and gearbox combinations that it’s pretty much impossible to find a definitive guide. I found a lot of discussion around which head and carburettor combinations worked. Luckily, I have a complete 3.4-litre engine, including inlet manifold and carburettors. I asked the team at the Daimler and Jaguar Spare Parts Club but it seems that again there was no “blueprint” as it’s the nature of these things that people customise things to meet their requirements.

I started my research online, and thanks to Jag-lovers Forums soon found a useful guide to fitting a 4.2-litre engine into a MK1. And more latterly a thread on XJ6 engines fitted into Mk2s, which was extremely helpful and timely. Thanks to Ian and Theo from the Jag-lovers Saloon forum!

Here is a bullet point summary of what I learned from the above sources:

• XJ front engine mounts are further back than those on the Mk2, Jaguar kept the original mount points on the front of the block and re-purposed them as the mounts for the alternator, air-conditioning compressor, power steering pump, etc. Therefore, you can bolt the original Mk2 engine mounts to these points. However, alternative mounting arrangements are required for the alternator and any other required accessories.

• Most XJ motors have a sideways mounted spin-off oil filter which won’t fit in the tight confines of the Mk2 engine bay. The most common way around this is to fit a downward pointing filter from an earlier XK engine. There are some alternatives; one is an upward pointing filter that was fitted to some XJ6 engines. I discovered something else that may work … more on this later.

• The XJ engine does not have the camshaft mounted tachometer generator. The simplest approach seems to get the tach converted to operate from the ignition pulses.
• There seems to be some debate as to whether or not the XJ sump will fit; it may well foul the ARB, and perhaps the front suspension cross member. Time will tell.
• The XJ water pump is too long, and the bottom hose outlet is bigger than that of a MK2 radiator, the common solution seems to be to fit a Mk 2 water pump and possibly marry it up with the impellor from the XJ engine.
• The radiator in the 2.4 is 11.4 litres capacity compared with 12.55 for the 3.4 and 3.8-litre cars. I may well need to fit a high capacity core into my existing radiator, and there are a number of aftermarket alternatives available if necessary.
• The clearance between the side of the engine bay and the carburettors with the XJ inlet manifold is very tight. Solutions are to fit the intake arrangement from a 420G (I doubt I’m going to get one), use pancake air filters (might be OK here in NZ), or fabricate a cold air delivery system that brings cold air in from the wheel arch. Lin Rose has a nice example on his site.
• I’ve found no mention of the engine stabiliser, so I assume that all lines up Ok.

So that’s the list I have managed to compile to date as far as the engine goes. I’m sure I will find plenty of other issues as I progress. I suspect there will be fun and games getting the throttle linkages working.

So, moving onto the gearbox and transmission:

• From my measurements comparing my original gearbox and the replacement, it looks like the gear lever will be about 40mm aft of the original. It’s quite tricky to be accurate about this as the original engine and gearbox are tucked away in the corner of a lockup, making accurate measurement difficult.
• The main difference I have seen is the rear engine mount under the gearbox, that is what concerns me the most. You can see from these images that it’s a very different looking arrangement between the XJ and MK2 mounts. All will be revealed in the test fit.

• The location of the rear engine mount stem is a lot different, as the synchromesh gearbox and compact overdrive are way shorter than the original gearbox. I measure the difference as being about 220 mm further forward. In the following image note the length of the extension behind the gearbox. The stem for the rear engine mount is right at the end of the extension.

• Clearly the existing propeller shaft will be too short, this is another thing I will find a solution for later on.
• Of more pressing concern is the rear axle ratio. The rear axle is a Salisbury 4.HA. Early 2.4 Mk 2s had the earlier 3.HA rear axle fitted, according to the service manual the change occurred at chassis number 103511 for RHD standard transmission models. My car’s chassis number is 111582 (Jaguar Heritage Certificate). I need to state right now that I know next to nothing about differentials, but looking at the service manual the axle ratio for the 2.4-litre non-OD is 4.27:1 and for the 3.4/3.8 litre with OD the ratio is 3.77:1.

• I already know finding a crown wheel and pinion from a 3.4/3.8 is going to be a difficult task because I’ve been looking on and off for a while now. I believe from discussions with diff specialists that it’s possible to fit the crown wheel and pinion from an XJ6 into the Mk 2 differential casing. Finding suitable XJ parts seems an easier task if I have no luck the Mk 2 option. I also know from a reader that another option is to fit a Dana 44 LSD into a Mk 2.
• I assume the overall gearing will be fine as the early XJ gearbox ratios seem broadly similar to the later synchromesh 3.4/3.8 gearbox ratios.

Later 3.4/3.8 Mk 2 ratios as follows: 1st & reverse (3.04 : 1), 2nd (1.973 : 1), 3rd (1.328 : 1), 4th (1 : 1), overdrive (0.788 : 1)

Early XJ6 ratios: 1st (2.933 : 1), 2nd (1.906 : 1), 3rd (1.389 : 1), 4th (1 : 1). overdrive (0.778 : 1), reverse (3.378 : 1)

(Mk2 Jaguar Service Manual and Haynes XJ6 Owners Workshop Manual)

The short version of all this is that there is only one way to be sure and that is to undertake a test fit after making the modifications that I believe are required.

Have I missed something? Please let me know!