Source for detailed 4.0L and 4.2L specs?

[blasto9000]

Hi all, new member here. I recently acquired an ’89 Cherokee that has all sorts of mechanical issues that I’m still picking through. It’s the project 4x4 I’ve been wanting to build all my life.

My original project plan included a freshened 4.0L engine, but after browsing the forum for the past week I’m strongly convinced I’d rather build a 4.5L stroker… it’s only a slight cost premium over keeping the 4.0L.

I’m having a devil of a time finding detailed engine specs for this thing. The OE service manual appears to be completely nonexistant on the used book market. And I can’t find simple things like rod big end diameter, big end width, main diameter, crank rod/main journal diameter, OE specified oil clearances, oil pressure, etc etc etc.

I’ve scratched up the following info on the 6.125” rod from a few places online, but can’t verify the accuracy. It’s also not nearly enough info for what I’m tentatively planning on doing.

Big end Bore Diameter 2.208"
Pin Bore Diameter .913"

I recently held a job as an engine builder – mostly Honda. It has crossed my mind to use Honda rod bearing journal sizes (2.0080”) to tightly control the oil clearances. But without knowing some additional critical dimensions I won’t be able to tell if it will work or not.

Of course, I could always get some wrecking yard components and measure them myself, but I’d much rather have the OE blueprint specifications.

I have a Chilton book that came with my Jeep but it totally sucks and has a lot of incorrect info in it. I’m actually starting to think it’s worse than nothing due to the wrong info.

[Exos]

There is a '88 manual here : http://www.greatlakesxj.com/tech.html. Specs should be the same.

[SilverXJ]

Using the honda rod bearing are you planning on using a honda rod and a custom piston as well? Offset grind the crank?

I don't think you will actually find a blueprint file with bore spacing, head bolt spacing,etc. Best bet is the factory FSM for journal, housing, bore diameter measurements, etc.

[blasto9000]

Exos - Thanks for the link! I'll peruse it at length early next year!

SilverXJ - The way I'd probably go to the Honda bearing is to turn down the crank journals and then resize the big ends of the stock 258 rods. The crank could be turned offset or on-center depending on the desired stroke. Resizing the 258 rods by 0.200" is quite a bit of material; I'm not sure it can be safely done without first examining a rod in person. (I can actually do that task in my in-house machine shop.)

Honda rods are a lot shorter than 258 rods. It may be possible to use them but it's not something I'm betting on at this point.

[SilverXJ]

ohhh.. yeahhh.. i don't know if that would work. Sounds like you would be taking too much off the 4.2L rod. unless you go up, where there is a little bit meat. But then you will be shortening it a lot. Maybe try an off set stroke and use a 4.0L rod and try to bring it to the 4.2L length so you can use a 4.0l piston. But you would have to take a lot off both sides of the big end....

I don't see the point unless you offset ground the crank for a long stroke though.