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Installing a 4.2L Motor in a '59 MK1

Dawn of Dyslexia
How I stuffed an extra 1.8L under the hood of my Jaguar

This is meant to be a fairly complete description of what it took to replace the 2.4L motor in my 1959 MK1, with a 4.2L motor from a 1983 XJ6.

Some background:
Ever since purchasing my Jaguar in 1992, I toyed with the idea of replacing the motor in it with something larger. The 2.4L motor that came in my MK1 was a real oddity. Jaguar took the 3.4L motor offered in the XK series and de-stroked it to 2.4L for the introduction of the MK1 sedan in 1956. It was carbureted with 2 down-draught Solex carbs (the only post-war Jag to use Solex's), and was, even back in the 50's, considered under powered; though it revved well, being overly square.

By the end of the 50's, even Jaguar recognized the need for a bigger power-plant (especially for the American market) and began offering the 3.4L motor in the MK1. This introduction coincided with the introduction of the wide-grille MK1's for those trivia buffs out there. To the best of my knowledge, almost all the MK1's sold in the US (after the introduction of the 3.4L motor) were of the 3.4L variety.

I believe my car was originally shipped to Spain. It was brought to this country (USA) by a private importer, and as such was a really unusual car for these parts: a left-hand-drive, wide-grille, 2.4L MK1. It also has the original MOSS 4sp; most 3.4L MK1's (ie most late 50's US MK1's) are automatics.

Anyway, back to my story: I've always thought the car was a little under- powered, and had ideas about putting something bigger under the hood. During a visit to a jag owner/dealer in Berkeley, I saw a project that really gave me some ideas- he was installing the motor from a 420G into a MK2. I subsequently learned that the 4.2L and 3.4L motors have the same stroke (major, but not only difference is bore size), and so getting the motor into the engine bay really isn't that difficult.

Then one day, I happen across an email message from Bruce Bowling, who has decided that he wants to install a Chevy 350 into his '83 XJ-6. I decided to buy his old motor, to store, and "one day" rebuild it and install it into my MK1. It was cheap enough, that I thought it was worth it just for parts.

  • Here's a picture of a S3 XJ6 engine bay: the natural home for this motor.
  • Here's a picture of the bare block, after cleaning, machining, and painting... awaiting assembly and installation into my car.
  • And here's the finished product: my 4.2L MK1 engine bay.
  • Only a few months after purchasing this new motor, I had some rather catastrophic failures of my 2.4L motor, and decided that the new motor would have to go in sooner... rather than later.

    The first decision I needed to make was where to splice the drive-train(s) together. I decided to do it at the crank/flywheel interface, using my old flywheel, old (well really, brand new) clutch, old starter, and old bell-housing. With unlimited funds, I would have installed a new transmission too, either a T-5 or a supra-box, but at the time that just wasn't possible.

    Below are some of the problems I found, and how I solved them. I've also included some of the pleasant surprises that I found:

  • Flywheel bolt patterns did not change:
    The interface between the crank and flywheel apparently did not change between 1959 and 1983. My old flywheel bolted right up to the 4.2L crank. Note- it was important to use the old (flywheel) bolts, they are slightly longer to account for the flywheel being slightly thicker than the drive-plate used on automatics.
  • Bell housing bolt patterns did not change:
    I was warned that 1 or 2 bell housing bolts wouldn't fit; that Jaguar had made some changes to the pattern during the XK production. This proved to be false, all the bolt holes lined up perfectly.
  • Motor mounts:
    On an XJ6, the motor mounts are located down low, approximately between cylinders 4 and 5. The MK1 (and many older Jags) is configured to use motor mounts at the front of the block (Cylinder 6). Fortunately, Jaguar left the old-style motor mount holes in the block castings, even when they added additional mounting points further back on the block. So, the older motor mounts will bolt right up to the new motor. Unfortunately, Jaguar used these holes for ancillary equipment mounts (alternator, power steering pump, etc). So, using these holes for the motor mounts, leaves you short of mounting points for the ancillaries.
  • Alternator:
    The only ancillary I had to worry about was the alternator. Research (poking my head under a bunch of Jags) showed that Jaguar E-types used an alternator mount that would work for my case. It is sort of a corner mount, that bolts in with the water-pump and timing cover on the front, and uses one of the high holes cast into the block. I purchased one of these mounts used, and it solved my problem quite nicely. I had to bend it slightly, to account for the slightly thicker water pump that I used (thicker than an E-type pump).
  • Water pump:
    The XJ-6 water pump is simply to long (fore/aft) to fit into the MK1. But, my (old) 2.4 pump, being quite a bit smaller, and with fewer impeller blades, didn't look up to the task of pushing fluid through the 4.2L motor. My solution was to have a custom pump made, grafting the two together. I used the 4.2L body and impeller, but the 2.4L shaft (the 2 are interchangeable) and pulley. I got lucky, and got a workable pulley position on the first try; I expected to have to go through several iterations.
  • Radiator:
    Just for good measure, I had a new, high capacity radiator core put in. The MK1/2 radiator is actually pretty big... but the old (cellular) core design is terribly inefficient. I have had no overheating problems at all with the car.
  • Oil Filter:
    There isn't room to use the sideways mounted, spin-on filter from the XJ-6 in the MK1/2 engine bay. I really wasn't very excited about trying to use the old paper style filter from my 2.4L motor; wasn't sure if it had the necessary capacity; and wasn't sure it would fit with the new intake manifold and carbs anyway. But, in the mid 70's, on some (all?) Series 2 XJ-6's, Jaguar offered a vertically orientated spin on filter. I managed to find one of these at Jaguar Heaven, and it solved my problem very nicely, even if I did have to pay through the nose for it.
  • Oil Sump:
    I was concerned that the sump from the 4.2L motor wouldn't clear the front-suspension cross-member. On the other hand, I wasn't sure if the 2.4L sump would mate with the rear main-seal on the 4.2L motor. Test-fit's showed that the 4.2L sump would fit, and so I went that route. I have subsequently learned that rear seal retro-fits (from old to new) are quite common, using the old sump, and so I think either would have worked. It turns out that the 4.2L sump does have an interference problem- but it is with the anti-sway bar, not the front suspension cross-member.
  • Anti Sway Bar:
    I used the anti-sway bar from a Jaguar 3.8S. The 3.8S sump is similar in shape to the 4.2L sump, and it has the requisite bends to clear everything. It's a bit thicker (bonus: stiffer) than the MK1 sway bar, and so squeezing it into the mounts was a bit of a chore.
  • Carburetors/Intake Manifold:
    I was tempted to try and use the fuel injected intake from the 4.2L motor... but, I lacked the expensive ECU, and it would take some pretty serious modifications to my fender well. Also, since my car is (now) right hand drive, I had additional stuff in that space to contend with. I did quite a bit of research/shopping, finally deciding on the intake manifold and carburetors from a 420 (or 420 Compact as it is known elsewhere... not 420G). This is a dual SU HD-8 setup. I was very interested in a triple SU setup, but in retrospect, I don't think they would have fit (battery clearance on back, fender clearance up front) anyway. The 420 setup is very tight, but it does fit. I was even able to get some small foam air filters from XK's Unlimited to fit. I also ended up having to use different carburetor needles. The foam air cleaners I used are much less restrictive than the stock intake setup for a 420. As such, the needles didn't deliver enough fuel at higher RPM's, and my motor fuel-starved as it revved up. I didn't see any overheating or anything, just a big lack of power and even stumbling above 3000rpm. I replaced the stock "UM" needles with the "UO" profile needles, and the difference was astounding.
  • Cam Covers:
    With the shiny HD-8's in there, I really desired to use my polished aluminum cam covers. Unfortunately, my head was not setup to accept them. The biggest problem being, the hole in the back where the tach-generator once was. I used 2 aluminum plugs (one from my old motor, one I purchased used), as used on the exhaust side of older motors to plug the back of the head. I had to carefully drill and tap mounting holes for them. I also used the right rear cam-shaft bearing cap from the 2.4L motor, which had the seal interface for the RHS cam cover. Liberal RTV was used, and I have not seen any evidence of any leaks.
  • Air injection ports in the head:
    I simply plugged these with shiny brass dome plugs. These are standard 1/4 inch pipe thread, and the parts can be bought at any decent plumbing shop.
  • Exhaust:
    I used the XJ6 manifolds. The biggest problem I encountered was trying to plug the large hole on the top of the rear manifold (I still don't know why it's there). I ended up having to drill and tap that hole, putting a large bolt into it. From the manifolds back, I have an all custom setup, using dual 2 inch pipes all the way; exiting under the center of the rear bumper.
  • And, I'd be happy to try to answer any additional questions.


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