258/4.0 replacement engine rebuild

258/4.0 replacement engine rebuild
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rlitavecz

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Location
Merrillville, IN
Vehicle(s)
1973 CJ-5 258 w/7120 head, Comp Cam, Howell TBI, HEI, stock T15 trans, Dana 20 tc, Dana 30 & 44 axles 3.73 gears, Lock Right both ends
I found a used AMC 258 i6 / 4.2l engine cheap ($75) and decided to rebuild it to replace my original 1973 AMC 232 i6 . I replaced the main and rod bearings and honed the cylinders. New rings went on the stock pistons. I figured that a new cam would help, so I purchased a Comp Cams 235 along with lifters a timing set and valve springs and retainers. I also decided to upgrade to a 4.0 head. Found a great deal on a head with fresh valve job and water ports welded and milled. That's when things got difficult. The Comp Cams valve springs and retainers will not work. The only Hi-Perf springs and retainers that I can find are Mopar parts and they are priced outrageous! ($12 per spring, $10.50 per retainer) I am going to try using the stockers unless somebody has a better idea??

I also learned that my headbolts won't work....at least half of them! 7 of the bolts on the 4.0 head are about an inch shorter. I ordered a set from a website that I found. www.headbolts.com Catchy name, eh?:)

I bought a 2 bbl intake from a 90s 4.0 and got a used exhaust from a friend's 95 Cherokee. I need to weld up the exhaust, but that's no big deal. I found a complete used Weber 38 carb kit on Ebay. All of the misc. parts (water & fuel pumps, gaskets, etc.) I got from Autozone.

Sure hope that this works! My junkyard/cheap engine project is pushing $1200:( I figure I can recoup some money by selling what I don't use.
 
The 4.0 head and 4.2head use differant valves so makes sense the springs don't work, I would think the stock 4.0 springs should be fine but?
$1200 may seem like alot but sounds like your getting a freshened up motor and a nice upgrade as well.
 
I'm just getting ready to do the same, and the cam question came up. Was your stock cam still good? Just wondering if it's worth doing the cam, since mine is still good.
I'll also have to look into getting a couple of headbolts, haven't checked mine yet. Did you have 7/16" or 1/2" bolts?

Sasquach, I know you have done this already, so this question might be directed more to you. I've been looking on ebay for a new exhaust, one is $80 or so, but for $8 more, you can get stainless steel. Is one better than the other?
 
tinman said:
I'm just getting ready to do the same, and the cam question came up. Was your stock cam still good? Just wondering if it's worth doing the cam, since mine is still good.
I'll also have to look into getting a couple of headbolts, haven't checked mine yet. Did you have 7/16" or 1/2" bolts?

Sasquach, I know you have done this already, so this question might be directed more to you. I've been looking on ebay for a new exhaust, one is $80 or so, but for $8 more, you can get stainless steel. Is one better than the other?
Click to expand...

The exhaust is kind of confusing at first with all the choices but I went with a 95ish cherokee header used off Ebay fo $20 and it fits and works well, I would recomend it. It is not the one you see with the expansion tubes by the way. Mine had 1/2" head bolts but the length was wrong on a few so got a new set from headbolts.com too.
 
tinman said:
I'm just getting ready to do the same, and the cam question came up. Was your stock cam still good? Just wondering if it's worth doing the cam, since mine is still good.
I'll also have to look into getting a couple of headbolts, haven't checked mine yet. Did you have 7/16" or 1/2" bolts?
Click to expand...

My stock cam appears to be fine, but I thought that as long as the engine is apart, I would replace it with the Comp Cam xtreme 4x4 cam. It isn't a huge cam, but will add more torque at lower rpm. I'll let you know about how the springs work. The stockers coil bind at about .560" and the cam says .477" intake and .493" exhaust lift. Probably OK if I don't push the rpms over 5000 or so.

My headbolts were 1/2", but 7 of them are an inch too long for the 4.0 head. The 14 new bolts were $51.90 delivered to my door via USPS in 3 days! I hope to finish engine assembly this weekend and run the cam in on the engine stand. The engine will not be installed until spring. I keep the CJ in Michigan, about 200 miles from home. It is getting fresh paint right now and I won't be driving it in the slop and snow! This is a garage kept baby, no rust, that is used for the summer in the dunes.
 
Sasquach said:
The 4.0 head and 4.2head use differant valves so makes sense the springs don't work, I would think the stock 4.0 springs should be fine but?
$1200 may seem like alot but sounds like your getting a freshened up motor and a nice upgrade as well.
Click to expand...

True, and at this point I have already spent more on this Jeep than I ever expected. Seats, top, rebuilt the Transmission and Transfer Case , new clutch, lockers at both ends, refinished the dash with all new switches, lights, and speedo <-BAD WORD->'y, spring bushings and shackles. Where does it end??:confused: I still plan on adding some new tires. We'll see :chug:
 
This is the first time I have heard of a stock 4.0 intake being set up for a carb.

Got a casting number?
 
yellow85cj said:
This is the first time I have heard of a stock 4.0 intake being set up for a carb.

Got a casting number?
Click to expand...

Not sure what this manifold came off of. Casting #EF3237858. It has a water jacket and an electric plenum heater that I will not be using. I will need to use some large washers to mount the manifold, but it will work. The Weber carb with it's 2 adapter plates bolts right on.
 
yellow85cj said:
This is the first time I have heard of a stock 4.0 intake being set up for a carb.

Got a casting number?
Click to expand...
I think that I misunderstood your question. I am sure that this manifold if for an injected 4.0 engine, however, I am using it with a carburetor. I have a Weber 38 DGES 2 barrel with the 2 adapter plates. It all seems to fit OK. I plan to start the engine on Monday to break in the new cam. I'll let you know how it works!
 
If I remember right it sounds like you have the AMC 258 i6 / 4.2l intake manifold. double check me but the intake mounting is the same for AMC 258 i6 / 4.2l and 4.0, its the exhaust that it different. I say this is a AMC 258 i6 / 4.2l intake because it has a water jacket and 4.0's do not that is why the water ports must be plugged on the 4.0 head.
I did a Mopar MPI injection kit for a guy last spring and it came with a 4.0 intake for the AMC 258 i6 / 4.2l along with plugs for the AMC 258 i6 / 4.2l water ports.
 
There are a bunch of local yards with 4.0's, so I'll have to go check prices on that exhaust. I wonder why the difference with the expansion tubes anyway?:confused:

I'll have to look into a new cam. The machine shop said they would have a price on everything this week, and it didn't seem like the price was crazy on a new cam. I'll also have to ask them about the size difference on those head bolts.

Thanks for all the info!
 
I knew it was one way or the other.:D
 
Almost finished! I'll install an old distributor (HEI is still in Jeep) and flywheel, bellhousing and starter later and fire her up. :drool:NYJeepEngine043.png
NYJeepEngine043.jpg
 
Looks good! :chug:
 
Does look really good. Is that ford blue?
 
OK It looks good i might use that color on mine thanks.
 
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