steveu812

So I'm installing a '94 Cherokee 4.0 engine in a '74 DJ-5 (Postal Jeep) that had the 258 inline 6. I need to use the DJ-5 motor mount brackets on the 4.0 and the lugs are still cat in the '94 block. Issue is that on the intake and exhaust side of the motor, one of the holes seems to be an odd size. The 2 other holes are tapped for 5/16 course. The 3rd hole is definitely larger and the threads are fine.
A 1/2" fine thread bolt doesn't thread in. I don't have any metric bolts to try. Looking at an old pic, it doesn't look as if anything was threaded in there when I removed the engine from the donor. The Chreokee motor mount bracket used a different 3 holes.

Would the '94 4.0 block have mixed standard and metric holes?
I could probably get away with using only 2 bolts, but I'd like to use 3.

Any help would be appreciated.
​​​​​​​Thanks

cruiser54

That's the threaded boss for the original knock sensor used in the 87 to 90 Jeeps.

dave1123

Try a 7/16 x 20 bolt in it. Same size as a GM lug nut. Fine thread doesn't hold much in cast iron. If it fits the motor mount, helicoil it to 3/8 x 16. You can buy a Helicoil Thread Repair Kit that has inserts, a tap, and an installation tool in it. It should tell you what size drill to use, but If I remember correctly, the hole is already close enough to just run in the tap.

steveu812

Thanks for the replies.
I went to the hardware store with my digital calipers and using that - measured the inside of the SAE and Metric nuts around 1/2" in size.
Turns out that a 12x1.25 was a couple hundreths off. I bought one and it fit perfectly. I'll have to hog out the hole in the bracket a bit, but not an issue for my project.
So yes - the motor does have mixed SAE and Metric holes. Not sure where else, but there is at least one.

Thanks again.

dave1123

As long as you have a nice clean block under your fingertips, settle a question for me. Are there 2 block coolant drains in it? One between #2 and #3, and one between #4 and #5, just under the freeze plugs, or core plugs if you prefer? If so, they must be a PITA to get to after the exhaust manifold is installed, especially with the CA emissions cast iron manifolds. It's no wonder nobody seems to know they are there! It doesn't surprise me that hole is metric if it was used for a sensor. Since that boss is already molded into the block and not used for anything in the later years, why not use it for something?

As I've already said, fine thread in cast iron doesn't have much strength and if torqued or pressured too much, will strip out. I am reminded of MGB sports cars with Whitworth fine threaded exhaust manifold studs. Almost every one I've worked on had at least one stud rethreaded to SAE thread. (Or National Standard if you prefer)

steveu812

There are two plug on that side. On the clean block, I can feel that they are located at the bottom of the coolant area so I suppose they could be use as coolan drains. Let me know if you need any other pics or anything.

Thanks

cruiser54

Those square drive plugs are indeed coolant drains. Even more fun is the fact that they are 5/16 drive.......

dave1123

Perfect! Wouldn't want to make it easy, would they?

cruiser54

Such a pain. First time I encountered it, I welded some plumbing tool into the plug I needed to remove and spun it out.