258 4.0 Head Swap Results

[Rescue Diver]

No need to defend yourself. My hopes are to use this on a fresh rebuilt 258. Im still unsure what manifold and carb combo I will use. Im still in the planning phase.

If I were doing a complete fresh rebuild, I'd start with a 4.0 block and head and use a 258 crank to build the ultimate inline 6 stroker motor. That's what I'm wanting to do in the future. I'd love to see well over 200 hp without giving up the low end torque that the 258 is famous for, and great mileage to boot.

 

[Petescj]

Well I already have the 258 and didnt really want to get into trans adapters and such. As far as "bang for the buck" this definately seems worthy of doing.

What kinda mileage do you get ? I dont ecxpect 30 mpg or anything but more than 13 would be nice. :laugh: I'll have to take a peak around here and see what a 4.0 head will run.

 

[Rescue Diver]

Well I already have the 258 and didnt really want to get into trans adapters and such. As far as "bang for the buck" this definately seems worthy of doing.

What kinda mileage do you get ? I dont ecxpect 30 mpg or anything but more than 13 would be nice. :laugh: I'll have to take a peak around here and see what a 4.0 head will run.

I average about 18mpg highway.

 

[ThisGuyUKnow]

I average about 18mpg highway.

I was able to get 23 mpg with my mpfi swap with an ax15 and 31 inch tires.. this is verified with the gps and I had to use only 4th gear because at the time I was running 2.72 gears

 

[coldair]

Ive been reading about the 4.0 head swap and been wondering if anyone has come up with a parts list of everything needed to do this.

 

[CJim7]

Ive been reading about the 4.0 head swap and been wondering if anyone has come up with a parts list of everything needed to do this.

Kinda depends on what you want to do for aspiration....but the general parts are pretty much the same:
4.0 head
4.0 head gasket
Spacers are recommended if the 4.2 uses the 7/16 headbolts. Some 4.2's have ½" headbolts.
re-use 4.2 pushrods, rockers, etc.
4.0 exhaust header, stock or aftermarket.

There are a few options for intake manifold depending on fi or carb. The stock 4.0 manifold if using the stock 4.0 fi is reliable. Remember, you will need a CPS if going this route, there are kits to adapt one for CJ applications.

If going carbed, I highly recommend the Clifford aluminum intake. I used one with my conversion and it worked superb.

 

[coldair]

Found this when i was searching
Tim Weavers 40 Head Article

 

[CJim7]

Found this when i was searching
Tim Weavers 40 Head Article

That's one of the premier sites for the 4.0 headswap. I used Tim's writeup when I did my conversion.

 

[coldair]

Here is some info i found that might be good food for thought. Everything 4.0L, casting#, parts, differences - Great Lakes 4x4. The largest offroad forum in the Midwest

 

[Rescue Diver]

Here is some info i found that might be good food for thought. Everything 4.0L, casting#, parts, differences - Great Lakes 4x4. The largest offroad forum in the Midwest

Thanks Coldair! That's a great site that puts all the info together! Notice how much better the flow numbers are on the 7120 and 0630 head castings than for all of the other stock heads. It really does make a huge difference over the earlier model heads.

 

[CJim7]

Notice how much better the flow numbers are on the 7120 and 0630 head castings than for all of the other stock heads. It really does make a huge difference over the earlier model heads.

A very good point. Anyone doing the conversion should be aware of this. The 7120 and 0630 are the desired heads for this swap.

 

[Rescue Diver]

A very good point. Anyone doing the conversion should be aware of this. The 7120 and 0630 are the desired heads for this swap.

There is one thing on that link that isn't exactly accurate. Some of the earlier 0630 heads do in fact have the temp sender hole. I've seen a couple with my own eyes. Most however do not have it.

 

[CJim7]

There is one thing on that link that isn't exactly accurate. Some of the earlier 0630 heads do in fact have the temp sender hole. I've seen a couple with my own eyes. Most however do not have it.

I agree. My 0630 had the port for the temp sender.

 

[Rescue Diver]

I agree. My 0630 had the port for the temp sender.

I'm guessing that the first couple years of the 0630 1996 and 1997 probably had them.

 

[CJim7]

I'm guessing that the first couple years of the 0630 1996 and 1997 probably had them.

I believe the head I used was a '96

 

[IOPort51]

I don't know if anybody mentioned this and this may be obvious to everybody but me. Pre assemble the manifolds to the head before putting the head on the block. You will, more than likely, need to do a bit of trimming on the intake to clear the exhaust and still line up with the ports. I suggest that you also line the gasket up with the intake and use a felt tipped pen to mark its position. this makes it easier to stay oriented to the ports when you can't see them. It is possible mount the 4.2 intake badly enough to close off almost 1/2 of the port. It's a good idea to know for sure everything will go where it's supposed to go while you can still see and reach everything. I even torque the manifold on the head before putting the head on the block.

 

[ThisGuyUKnow]

A very good point. Anyone doing the conversion should be aware of this. The 7120 and 0630 are the desired heads for this swap.

x2.... find a 91-95 grand or baby cherk in the boneyard yank the head have it magnufuxed and a three angle valve job done at the shop and you should be good to go. Mine ran me about 280 for everything

 

[hutchman]

Some good info there!

 

[Rescue Diver]

Back to the original topic of this thread.

How many miles has everyone put on their motors since the 4.0 head swap, and has anyone had any problems?

So far I have roughly 12,000 miles on mine and all I've had to do to it is change the oil. The engine still runs perfect, and my valve train is still running quiet as can be.

Not wanting to bring up an old argument, but with all the bad info that was floated a while back by someone who had never actually done this swap, but because of his posts, he may have scared others away from doing it, this bears being mentioned.

All of the doom and gloom about the valve train(pushrods etc...) between the 4.2 and 4.0 not working together has been totally proven wrong.

If you're thinking of swapping a 4.0 head to your 4.2(258) don't be scared off by some ill informed previous posts that say things like the valve train in not compatible. Other than some minor mods to the water jackets that are easy to do yourself, the 4.0 head matches up perfectly with the 4.2 block, lifters, and cam. I'm using the 4.0 push rods and they were the perfect length.

Also, though this is a totally different subject, if you choose to swap in an HEI distributor because of its one wire simplicity and ease of maintenance and tuning, don't be scared off by those that say the hardened HEI distributor gear will eat your soft AMC cam gear. That issue only applies to installing an HEI on an AMC V8. My HEI distributor gear and AMC Inline Six cam gear still look like new after all of the miles I've put on them.

To date, quite a few of us have put a lot of miles on our AMC inline 6 cylinders with both of these swaps, and not one post that I've read said anything about any of us who have actually done these mods having either of the problems that we were all warned about by one former member who had no experience doing either swap.

It really pays to learn from the experience of those who have actually done something, rather than listening to those that dabble in theory or read something somewhere. All of us who have made these upgrades are still available today, and are more than willing to answer any questions about our experience for those that are thinking of doing this cheap, easy and very worth while upgrade.
Happy Swapping!

 

[Sasquach]

Well mine would be better measured in "start cycles" because I tow it to location then play so have not accumulated many miles, but it runs perfectly although will have to give much credit for that to the MPI system.
As for negatives,the only one that comes to mind is the power steering pump bracket no longer bolts directly up as before but with slight modification your good.
Positives, Mostly covered but one that gets left out to often is the loss of the oil leaking 4.2 valve cover.