4.0 block compatability

[BG SX4]

Have an ‘83 SX4 we are building and have already done the 4.0 head swap. Using FiTech FI and an hei distributor. The driver side axle mount has already been modified to clear the 4.0 factory header and exhaust. Steering bracket has also been modified to work worth 4.0 head. For driveline, we have an nv3550 mated to the original t4 4 speed bell housing and clutch.

Turns out the original 4.2 bottom end has more miles on it than we thought with a lot of ring blow by once we got it running. So contemplating actually going with a 4.0 block with our 258 crank to create the popular jeep crowd stroker if we are redoing the bottom end anyway, since I believe all the headaches associated with the 4.0 side of it have already been worked out in our combo.

From what I’ve found, the only additional mod might be to the drivers side of the 4.0 block which has some added webbing where our modded front axle bracket would mount. To be sure, I have a few questions:

1. Since we would use the 258 crank and I assume balancer, is it safe to also assume we could use the 258 V belt crank pulley and then all the 258 accessories? Are the 4.0 mounting holes on the front of the motor all the same to allow for this (power steering, alternator and ac brackets)?

2. Again, since the 258 crank will be used, I assume we could also reuse the 258 manual flywheel as well as the 258 starter (will the 258 starter bolt up ok)?

3. I assume the existing 258 Eagle motor mounts will bolt to the 4.0 block with no mods needed?

Thanks.

[mudkicker715]

I ran into issues with the v belt stuff on the power steering bracket. I forget why, but I just modified it and it worked. starter matches flywheel. motor mounts should be fine.

[vangremlin]

I've not done this personally so am just going off what I've read.  But when using a 4.0 block, just make sure it still has the spots to mount the front drive train (left rear of the engine and on the right side near the motor mounts).  If I remember correctly they stopped including those on the block somewhere along the line.  I think I also read that at some point those mounting spots were still there but you may need to tap the holes.

Good luck, sounds like a fun project!

[maddog]

I'm in the process of doing this swap myself and have already ground down the rib on my 4.0. Attached are some pictures of what it looks like and its location after being ground down ignore the pink sparkly paint that's on the ground down section it's just some cheap fingernail polish I used for clearance confirmation.

[BG SX4]

Thanks for all the great info gang. Much appreciated. I also stumbled into a detailed 4.2 to 4.0 swap write up that may be useful to others as well:

https://docs.google.com/document/d/1OFrPDmtJTA8cbtu0DzGItxBQdy9Wo6K3sxZqfpk-pxM/edit

One more thing I didn’t think about, we already had a new 4.0 head on the 258 which we are going to reuse. It’s the one from Clearwater that had the extra triangular water passages already blocked off, which was great for the 258 so we didn’t have to mess with plugging them. They were welded shut before they milled the head. If we are now going to the 4.0 block for the stroker, do I need to open those water passages back up in the 4.0 head? And if so, can I just drill a smaller hole for each? Thanks.

[Canoe]

One of the frustrating things you'll find, is that there are varying opinions on what a Stroker is, or how to do it "right". So make sure you look at multiple writeups, and there are significantly more of those in the Jeep world.

If you'll be using that 4.0 head on a 4.0 block (with 4.2 crank and I think a cam that is not stock in either but made for strokers), then I'd expect/guess/assume that with a 4.0 head on a 4.0 block that it's a given that you'll need that coolant flow that was welded shut. And I'd expect you want to match the same shape & size too, and you may need to grind out all of the weld material that is up those passages, else the resulting turbulence could reduce flow. Do your research on polishing those passages, as sometimes a non-polished or specifically textured passage will have a higher fluid flow due to that textured/rougher surface holding a boundary layer of fluid, which resists fluid flow less than a polished surface that has a low or no boundary layer.
With the extra power/heat a stroker will be outputting, I wouldn't want to have reduced coolant flow. Look at a 4.0 block for the match to those triangular openings.

When I was looking at differences in the various 4.0 heads, I remember being surprised at needing different intake manifolds? I may not be remembering that correctly.

And there are differing opinions on which 4.2 crank is best or even works in a stroker. Early? Mid? Later? You'll have to confirm what that is about. And this is obviously the correct time to get your crank checked by a machine shop for true, etc.. Don't drop it!

I've not built a stroker, and it's been a number of years since I looked at doing so, so I can't give you my opinion of what is best... lol

[BG SX4]

I found the answer here:
https://www.google.com/amp/s/www.jeepforum.com/forum/f8/4-0l-head-4-2l-block-water-jackets-explained-2647586/%3famp=1

The water jackets which have been plugged on the 4.0 head do not pass water through to the block on the 4.0 either. So a 4.0 head which has been plugged for a 4.2 block can be used on a 4.0 block as well.

[Canoe]

With post after post and article after article talking about the necessity of closing off the water passages of a 4.0 head on a 4.2, I sure wasn't expecting that!

there is no coolant passing through these water jackets from the head to the block. They may exist on the 4.0L head as well as the 4.0L block, but they serve one purpose and it was explained to me by Bennie Fulps of Hesco: they are holes that allow sand to escape when the block (and head) is cast. If you still are in doubt, look again at the head gasket for a 4.0L engine: there are no holes matching the water jackets that would allow passage of coolant from the head to the block.

wtf!
First image google gives me for 4.0 head gasket shows the gasket sitting on a 4.0 after the head is pulled. The gasket has triangular cutouts for those triangular openings in the head over the circular holes in the block.
Have I got this right? What am I missing?
dannix.net/lib/truck/jeep-engine-rebuild

[Canoe]

... wtf!
First image google gives me for 4.0 head gasket shows the gasket sitting on a 4.0 after the head is pulled. The gasket has triangular cutouts for those triangular openings in the head over the circular holes in the block.
Have I got this right? What am I missing?

I was missing that I was looking at the wrong side of the head...
Photo has the triangular openings already filled.
(Machinest is working on ending a tiny crack so it can't spread.)