Alright, finally tackling my 4.0 head swap.

[NoCoEagle]

My eagle has been sitting in the yard for over a year. While I was driving her, she overheated, and all signs pointed to bad radiator. Got that replaced, big difference in temperatures, until the new found pressure of the good radiator blew my head gasket, warped my head, gunked up the engine... general badness.

Anyway, I pushed her into the garage and started tearing it apart. My AC never worked in the first place, and honestly I don't want it, so I tore it out. Need to figure out how to mount the alternator without the AC. Any ideas?

Found a 4.0 head on craigslist, not sure what it comes with, just says "refurbished". Trying to get more info. 7120 casting. Owner agreed on $100, but I'm not sure if a bare head with no hardware is worth that. Will update with more info when I get it.

In the case that it is a bare head, what do I need to purchase? Can my 258 valve springs be used? I'm on a very tight budget and I just want the thing running again. Nothing crazy. If I do end up needing to purchase new valves, new springs, etc, I will just rebuild the whole thing and throw a better cam in. Do I match the cam to a 4.2 or a 4.0 with the new head? Not sure how that works.

That's it for now, I suppose. Thanks!

[NoCoEagle]

It has springs, do the 4.0 and 4.2 share rockers?

[vangremlin]

If you're on a real tight budget, your cheapest option may be to just find another 258 engine and swap it in.  You can generally find one that runs for around $300 on Craigslist.  You could then sell your old crank, rods, and pistons to somebody that wants to build a stroker and get $100+ for it.  Good luck.

[NoCoEagle]

Well, the reason I'm doing the head swap is because I'm tired of the 258 being a slouch. Otherwise I'd spend $40 getting my 258 head machined flat and call it good.

[captspillane]

I just wrote alot of good information in another thread today that you should read through.

http://forums.amceaglenest.com/index.php?topic=37553.msg306546#msg306546

Here are pictures of several rocker arms next to each other. The one on the far left is a 1992 4.0, the one in the middle is a 1982 4.2, and the one on the right came with my Spirit on a 4.2 with a 4.0 head. It looks like it used to be the original 4.2 rocker and it got put on the 4.0 head without a problem. My conclusion is that they are slightly different but directly interchangeable along with the springs.

You need to match lifters with pushrods because 4.0 pushrods are shorter to go with the longer 4.0 lifters. Its likely no problem using 4.2 lifters but you should replace your camshaft with new 4.0L lifters and pushrods.

A 4.2L camshaft is dramatically different than a 4.0 camshaft. It is the secret that let AMC take a 115 HP motor and get 190 HP from it while reducing its displacement at the same time. The lobes are considerably bigger. A performance camshaft like the Crane RV cam I buy has small changes to the 4.0 cam to make it better at low RPM, but they are neglibile differences (except that a Crane cam comes with a lobe for the option of using it with a mechanical fuel pump in a 4.2, while the 4.0 eliminated that lobe). Make sure you replace the original camshaft while the engine is apart.

[vangremlin]

I'm on a very tight budget and I just want the thing running again.

Sorry, I thought you were looking for a true low cost option.  Good luck.

[NoCoEagle]

Pulling the engine and installing an entirely different 258 that will cost $300 is a lot more expensive than swapping on a good head from a 4.0 as long as I can reuse the cylinder head hardware from the 4.2 head...

[NoCoEagle]

I'm picking up the 4.0 head (with springs, no rockers, so I'll reuse mine), a 4.0 block, and a 4.0 crank (all newly refurbished, crank is still wrapped up) for $100 today. No use for the block and crank but hopefully I can sell them and come out on top!

[vangremlin]

Sounds like a good deal!  You may also need a 4.0 exhaust manifold and some exhaust mods, according to this thread:

http://forums.amceaglenest.com/index.php?topic=37161.0;all

From the 3rd post in the thread (BenM)

"The only necessary parts are a couple of head bolts, possibly a sleeve set if you have the smaller bolts, the exhaust manifold, and some exhaust pipe bending to clear the front differential. Don't forget gaskets.

You need to notch the intake to fit higher and mess with some brackets, but that's just some time, not money. You're throttle assembly rides along on the intake and just needs the kickdown adjusted for the slight difference.

The only thing to beware of is the exposed casting holes that don't always seal."

[NoCoEagle]

I may have gotten an even better deal than I thought! The head is indeed a 7120 casting, and is clean as a whistle. The crankshaft came wrapped up, but the tag on it (from the crankshaft shop) reads: MAKE: AMC MODEL: 258 MAIN SIZE: 010 ROD SIZE: .010

Is this a 258 or 242 crank? The block looks like it was dipped, too, so I should be able to sell it.

[doc65]

Unless that tag is wrong you have most of the makings of a stroker engine

[NoCoEagle]

Checked out the casting number, 3235477. Looks like I've got a brand new crank to put in! 

I'm a huge novice when it comes to the bottom end of engines, what advantage will I see using this crank over the one that's installed? If any?

[doc65]

... you could reference the casting number on the crank to verify... a quick google of that casting number would tell you what it is for certain

[doc65]

That's an 81-86 258 crank, building a stroker is a WHOLE 'nother can of worms & research at least to do it right.  See www.jeepstrokers.com for lots more information & reading with a few conflicting opinions thrown in from time to time.

Basically a 258 crank and a 4.0 block and appropriate pistons/rods gets you 4.5(std bore), 4.6(+.030) or 4.7(+.060) there are two ways to approach it, long rod(4.0) & short rod(4.2/258), the pistons are generally cheaper in the short rod variety as there are cast and Hyperutectic's available while the long rod version are all forged and cost significantly more, you have to watch your recipe pretty close to avoid too high of compression and pinging.

Doc 

[NoCoEagle]

Is it possible to use 258 pistons in a 4.0 block? I wasn't planning on using the 4.0 block, I think I'd prefer to leave my bottom end alone. The head has new springs and valves, so all I need to do is bolt up my rockers and use my existing pushrods (along with the other head swap details) and I'm set. Not to mention I like running a mechanical fuel pump, which I can't do with the 4.0 block.

My intake already has Gronk's (or something like it) adapter for a Motorcraft carb, believe there's a 2100 on it now. Always seemed to run fine, just a little dirty. I remember the previous owner saying something about converting to HEI as well, although the big ugly orange cap on the dizzy doesn't look like any HEI dizzy I've seen on ebay.

So my next course of action is finding a set of headers (there's a set of stainless steel ones, brand new, on craigslist for $125) or finding a stock exhaust manifold. I'd like to keep cost down so I'm not sure which route to go. The headers for sale are Rugged Rock 17660.01 steel headers for 91-99 wranglers. Will they fit?