Hi all,

If anyone read my other thread, I have a 2000 XJ and two bad 4.0L engines (BOTH with bad #2 cylinder bores). Someone relatively close to me on craigslist has a good 4.2 shortblock... so I got to thinking.

Would this work:

89' Wrangler 4.2 shortblock (block, crank, rods, pistons)
0630 cylinder head
98' 4.0 cam/lifters/valvetrain
2000 XJ intake/exhaust manifolds
2000 XJ accesories, mounting brackets, crank pulley, water pump
2000 XJ ECU and harness

Basically just using the bottom end of the 4.2 with all 4.0 parts and head. I've read people saying the blocks are basically identical, just no end results of someone who did the swap.

Also would the rings and main/rod bearings from a 4.0 fit a 4.2? From what I can tell the 4.2 is a 4.0 with a longer stroke.

 

I've done some more research...

As far as I know my proposed setup (see original post) will work. To use a 4.0 head on a 4.2 you need to close up the coolant passage holes along the driver's side of the head (not the lifter/pushrod side) because the 4.2 block doesn't have those holes. Most people seem to use JB weld with no problems.

You can use the 4.2 shortblock... block, rods, pistons, crank, oil pumps are the same. I believe you can bolt up the 4.0 oil pan. Also I think the 4.0 cam is a better all around than the 4.2, so use that. Rod bearings are the same 4.0 to 4.2, but the 4.2 uses different main bearings.

Piston rings are also different because the 4.0 uses 3.875" pistons and the 4.2 uses 3.75" pistons. I thought the bores were the same and stroke was different, but both bore and stroke are different between the two.

The hole for the distributor, oil dipstick tube, oil pressure fitting, and oil filter are all in the same place so that's not a problem. The 4.2 does have an opening to the right of the distributor for a mechanical cam-driven fuel pump... so you just need a block off plate.

As for the block I believe the mounting holes for the motor mount brackets, A/C bracket, P/S bracket, at are in the same places. I'll have to check on that. But assuming you use a 4.0 head and accessories, there should be no reason the 4.0 intake, exhaust, harness, and ECU won't work with this setup.

Also the 4.2 shares the same bellhousing bolt pattern as the 4.0 so it will bolt up the the AW4 transmission in the XJ, so you can keep the stock crank position sensor. You will have to swap the flex plate/flywheel from the XJ on to the 4.2 crank for the crank sensor to read.

I should be able to verify all of the above for sure in the next few weeks, I found a guy with a 4.2L and 4.0 for sale and wants $300 for both. The 4.0 has 120k on it and is still assembled, the 4.2L is all apart though. I'll be picking them up over the weekend, so I can see which parts from the 4.0 fit on the 4.2.

 

Sub. Don't have anything to offer from experience but excited to follow along

 

Unless this is something you find fun and exciting, I say..... Why?

That's an awful lot of work to go through to build a Frankenstein I6 with only .2 liters gained. If it were me, I'd just swap in a decent 4.0 and run it. Hell, I'd rather do an LS swap before taking on your plan. By piecing together these motors you may find issues that you didn't anticipate. And if it runs like crap, you may not be able to determine what's causing it because it could be the build, a bad part or incompatible components. Just my 2 cents. But I will say good luck and I'll stay tuned to see how it works out for you.

 

I'm subbing as well but only to find out why you'd go through all this work instead of just building a quality 4.0 without all the bull****. And iirc the 4.2 was known for crank walk or some kind of bottom-end issue. Someone feel free to chime in

 

At this point it I'm not dead set on swapping in the 4.2, I'm just curious if it would work. The XJ is for my brother who just got his license, so he isn't going to be putting 50+ miles a day on it.

The 4.2 and 4.0 that I'm buying are kind of a package deal, so I'll probably just swap in the 4.0 and call it a day. But while I have the 4.2L sitting there I figured I'd see what parts bolt up, i.e. how much of a direct swap it would be. I could always turn the 4.2 into a stroker or at least use the crank and rods from it to make another 4.0 into a stroker.

I'd have to look into the crank walk issue, could just be worn out thrust bearings.

 

I would take the crank and rods out of the 4.2 and put them in the 4.0 for a nice stroker build. And put that in the XJ.

 

Until this has been verified it's only value is by the pound.

That's a whole lot of work for nothing when you can buy a good boneyard engine complete and just turn the key and drive.

 

Sounds like a headache to me. Also note, the 2000 exhaust won't match up right on an 0640 head.