258 4.0 Head Swap Results

[Rescue Diver]

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 AMC 258 i6 / 4.2l valve cover.

Good point. I have to say the hardest part of the swap for me was having to cut a big chunk of the power steering bracket out so it would clear the "header style" stock 4.0 exhaust manifold. I haven't had any issues with the power steering belt after all of these miles, so it's all good. Of course, those that also swap the serpentine belt and brackets from a 4.0 while doing the head swap won't have this issue. I thought about going to the serpentine single belt, but since I haven't had any problems, I'm just sticking with the two V belts.

 

[ThisGuyUKnow]

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 AMC 258 i6 / 4.2l and 4.0 not working together has been totally proven wrong.

If you're thinking of swapping a 4.0 head to your AMC 258 i6 / 4.2l (AMC 258 i6 / 4.2l ) 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 AMC 258 i6 / 4.2l 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!

Ive got over 2k on mine with a junkyard mpfi. I havent had any trouble related to the head and i used 4.0 pushrods but like you said i think that it doesnt matter which rods you use. the only issue I had was when I tried to swap the serp system from a 4.0 but I ironed that issue out.

I like it enough that now that my bottom end is need of replacing I have decided to pick up a rebuilt AMC 258 i6 / 4.2l instead of completely going 4.0.

 

[Rescue Diver]

Ive got over 2k on mine with a junkyard mpfi. I havent had any trouble related to the head and i used 4.0 pushrods but like you said i think that it doesnt matter which rods you use. the only issue I had was when I tried to swap the serp system from a 4.0 but I ironed that issue out.

I like it enough that now that my bottom end is need of replacing I have decided to pick up a rebuilt AMC 258 i6 / 4.2l instead of completely going 4.0.

The really trick settup is to put your AMC 258 i6 / 4.2l crank in a 4.0 block to make a killer stroker motor. I think the only custom part you need is an adapter for the harmonic balancer. That'll be my next engine, but since I rebuilt the AMC 258 i6 / 4.2l when I was building the whole jeep, I don't expect to be building my stroker any time soon.

 

[CJim7]

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 AMC 258 i6 / 4.2l and 4.0 not working together has been totally proven wrong.

If you're thinking of swapping a 4.0 head to your AMC 258 i6 / 4.2l (AMC 258 i6 / 4.2l ) 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 AMC 258 i6 / 4.2l 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!

I put about 20,000 miles on mine before the motor regrettably blew a piston skirt (I had a spare 401 lying around, no rebuild on the 6)

I never ran into ANY issues running this engine. I was pushing 11-11:5 compression with the flattys and never once encountered the dreaded pinging associated with high compression and regular gas.

Likewise, the previous misinformation can just be thrown out the window. The valvetrain between the 4.0 and AMC 258 i6 / 4.2l is identical except for the valves themselves and there may be a slight variance with the pushrods, but I've ran into that between different years of AMC 258 i6 / 4.2l ...so that's not an issue. The rockers and pivots are all the same. Springs...no issue.

I used a TFI ignition, so I didnt get the test the "theory" of worn dizzy gears.

Pound for pound, and dollar for doller I think this is the best modification that can ever be done to the AMC 258 i6 / 4.2l . It makes it a whole different engine

 

[Petescj]

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.

Thanx for making my search so much easier. Im gonna be grabbing a complete 4.0 for $100. From a 94 Yj wich gives me the 7120 head and f.i.

 

[Petescj]

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 AMC 258 i6 / 4.2l valve cover.

The really trick settup is to put your AMC 258 i6 / 4.2l crank in a 4.0 block to make a killer stroker motor. I think the only custom part you need is an adapter for the harmonic balancer. That'll be my next engine, but since I rebuilt the AMC 258 i6 / 4.2l when I was building the whole jeep, I don't expect to be building my stroker any time soon.

I put about 20,000 miles on mine before the motor regrettably blew a piston skirt (I had a spare 401 lying around, no rebuild on the 6)

I never ran into ANY issues running this engine. I was pushing 11-11:5 compression with the flattys and never once encountered the dreaded pinging associated with high compression and regular gas.

Likewise, the previous misinformation can just be thrown out the window. The valvetrain between the 4.0 and AMC 258 i6 / 4.2l is identical except for the valves themselves and there may be a slight variance with the pushrods, but I've ran into that between different years of AMC 258 i6 / 4.2l ...so that's not an issue. The rockers and pivots are all the same. Springs...no issue.

I used a TFI ignition, so I didnt get the test the "theory" of worn dizzy gears.

Pound for pound, and dollar for doller I think this is the best modification that can ever be done to the AMC 258 i6 / 4.2l . It makes it a whole different engine

Thanx to all you guys for this thread. I know it got "hairy" there for awhile , thanx for stickin with it and getting the facts out guys.

Well Done.

 

[Sasquach]

Keep us posted on the install Pete

 

[Petescj]

Keep us posted on the install Pete

No wiring harness but Im still grabbing it. It'll be awhile before I get around to it but I'll post it up for sure.

 

[Rescue Diver]

No wiring harness but Im still grabbing it. It'll be awhile before I get around to it but I'll post it up for sure.

Uhhh, how about some pics???

 

[Rescue Diver]

No wiring harness but Im still grabbing it. It'll be awhile before I get around to it but I'll post it up for sure.

Uhhh, how about some pics???

 

[Petescj]

Its a guy from my Jeep club. The frame rotted and he parted the whole Jeep. I was a little late and this is whats left.

 

[Rescue Diver]

Its a guy from my Jeep club. The frame rotted and he parted the whole Jeep. I was a little late and this is whats left.

Great buy! I'd love to find a complete servicable 4.0 with everything including the serpentine belt pulleys, brackets and power steering pump for only $100! I'd get the block machined and leave it sitting on my engine stand while take my time collecting everything I need to build it as a 4.6L stroker since my AMC 258 i6 / 4.2l runs perfect.

Here's a great site to check out if you're entertaining the idea of building a stroker with a 4.0 block and AMC 258 i6 / 4.2l crank!

Jeep Strokers • Stroker Basics

 

[coldair]

Here is another site about stroker 4.0 motor Frequently Asked Questions

 

[Petescj]

Great buy! I'd love to find a complete servicable 4.0 with everything including the serpentine belt pulleys, brackets and power steering pump for only $100! I'd get the block machined and leave it sitting on my engine stand while take my time collecting everything I need to build it as a 4.6L stroker since my AMC 258 i6 / 4.2l runs perfect.

Here's a great site to check out if you're entertaining the idea of building a stroker with a 4.0 block and AMC 258 i6 / 4.2l crank!

Jeep Strokers • Stroker Basics

Here is another site about stroker 4.0 motor Frequently Asked Questions

Cosidering I have a AMC 258 i6 / 4.2l already pulled and will be adding the 4.0 here in a couple days Im leaning more towards the stroker. I just need time to research and more money of course. Thanx for the links.

 

[coldair]

I just picked my 4.0 head up its a 0630 need a few more things

 

[Rescue Diver]

I just picked my 4.0 head up its a 0630 need a few more things

Nice! I see from picture 2 your's is a later 0630 without the hole for the temp sender. Are you planning to drill and tapped it or are you planning to find another location to mount it? Did 4.0 push rods come with it? There's a very slight difference in length and the 4.0 ones worked great for mine. You might be able to find an adapter to go in the hole of the 4.0 water neck and mount the yemp sender there? I'm just using the AMC 258 i6 / 4.2l water neck since my 7120 casting had the correct hole for the sender.

 

[coldair]

Nice! I see from picture 2 your's is a later 0630 without the hole for the temp sender. Are you planning to drill and tapped it or are you planning to find another location to mount it? Did 4.0 push rods come with it? There's a very slight difference in length and the 4.0 ones worked great for mine. You might be able to find an adapter to go in the hole of the 4.0 water neck and mount the yemp sender there? I'm just using the AMC 258 i6 / 4.2l water neck since my 7120 casting had the correct hole for the sender.

The head came with rockers, push rods, head bolts, new valve cover gasket, also it has been rebuilt with a 3 angle valve job. picked it up for $100 Im going to drill and tap it for the temp senser.

 

[Rescue Diver]

The head came with rockers, push rods, head bolts, new valve cover gasket, also it has been rebuilt with a 3 angle valve job. picked it up for $100 Im going to drill and tap it for the temp senser.

That's a hell of a deal! I have $140 just in the valve job. How'd you get it so cheap???

 

[coldair]

That's a hell of a deal! I have $140 just in the valve job. How'd you get it so cheap???

I dont know myself just happen to call a guy that had some parts for sale.

 

[Rescue Diver]

I dont know myself just happen to call a guy that had some parts for sale.

Congrats!

Now get her together and let us know how she runs!

One more thing, you might want top remove the metal baffles in the valve cover vents, use a high flowing pcv valce and let it breath more. The higher compression you'll have over the stock head tends to give you more blow by and because of that, higher crank case pressure. That can make even a new front seal leak oil.