I’m building a slightly custom with Jaguar parts mostly a 1961 Mk2 with a 4 speed transmission out of a '66 420 compact sedan. I now have the short block from the same car. I know the challenges of using a 4.2 in place of the 3.8.
Either way I’m using triple carbs and a 3.8 Straight Port Head and intake. Just trying to get a feel of the better engine to use? 3.8 or 4.2 ?
I went with the 4.2.
I have both 3.8 and 4.2 E types. The 3.8 revs more but the 4.2 has masses of torque.
My car was a 3.4 auto, but a PO had fitted a Toyota 5 speed manual box. What I was looking for in my MK2 was effortless power, and I felt the 4.2 better offered what I wanted.
Fitting the 4.2 was pretty straightforward, although I elected to use twin HS8 SUs to make fitting it under the bonnet easier.
I ended up with 200hp and 300lbft and the car flies.
I’m on the same mission for effortless power and was leaning in that direction of goingwiththe 4.2. I appreciate your reply.
I also went with a 4.2 in my '57 Mk1 (4 speed/OD), but really a toss up which to use. Either way, I think you will have plenty of power.
Tim, my preference is a 3.8 for a manual and a 4.2 on an automatic. I think both motors make ample torque. That slightly better reviness of the 3.8 suits a manual and the 4.2 times the torque converter torque increase really produces a nice push.
I’m going for the 4.2. I really like how my 420 sedan performed. I will keep a 3.8 just in case down the road.
Good choice IMHO. Don’t take too much of the flywheel. Torque is your friend.
A 61 MK2 never came with a 4.2.
Always go for the 3.8, runs much better, and way more balanced.
And a 3.8 is quite valuable today.
A 4.2 is a strange animal with staggered cylinders, and the heads chambers that never align with the cilinders. And will generate much more heat.
Also I think the 4.2 is very common, as most XJ6 has them.
I see it always as a cheap solution to use a 4.2.
That would mean much more fuel consumption, I doubt it.
The 3.8 is a nice engine and a bit stronger, and has a bit less torque. Neither are bad but I would think the 3.8 is a better match unless you want something special.
I have two 4.2 flywheels one standard 20 lbs, one thats been lightened to 18 lbs
My car was a 3.8vauto box from the factory. Engine was long gone when I got the project. It had a 3.8 from a different model and early at that because it had the scroll at the rear.
I have since picked up 2 mid sixties 3.8s from S-types. I also just got a 1966 4.2 from a 420 and the all synchro transmission I’ve since rebuilt. I really like how my 420 compact sedan I ued to own could pull like a freight train. I do want something special. I’m using series 3 seats, custom console, coombs spats and many other touches to make this car mine and hopefully a excellent performer.
Mine performs really well. The engine is from a Mk10.
I couldn’t get my hands on a big valve head, but I did port it and used a D Type cam grind as well.
Well a turn in my story. As I’m removing galley plugs and bits I noticed the rear thrust washer must have dropped. There’s damage that I’m not sure it can be repaired. I was going to take the 4.2 block to the machine shop for new sleeves.
I may go back to my 3.8 for economic reasons. I may take the 3.8 block in to the shop instead…
Picture of the damage…
It’s going to be the 3.8. Thanks for your input.
I was getting set on the 4.2, but discovered the thrust bearing dropped out the rear so damage to the block. It’s probably repairable, but at a cost more than I’m willing to spend at this time.
Maybe I misunderstand but the thrust bearings are two half shells, they sit in the bearing cap. Yours stuck to the crank, spun around and ate into the block? Now the new thrust bearing will not stay in position because the block has been machined away? Couldn’t you have the shop create a little step in the block so the thrust bearing has something to seat against?
Of course if the crank is also damaged…
Not quite. The rear thrust bearing must have worn out and fell out. I bought this 4.2 in peices. The crank was riding on the block. The area where it is located is worn down and won’t retain the new thrust bearing correct. This is such a poor design using only 1/2 washer. Triumph did the same but a smaller bearing and is a weak spot in those engines. I’ve had a few Tr6s and it was an annual thing to check end play of the crank.
This design is why I try to never put my foot on the clutch when starting, especially after standing for the winter.
The repair could be weld the block and machine with a replacement cap. The mains would need to be line bored. An extra expense I’m not willing to deal with right now. I have a perfect crank that was destined for this build as the original is trashed on the rear thrust surface.
