7120, 0331 head differences

[dwg86]

I just removed the cracked 0331 head from the 2000 donor engine that I am using for my stroker build. I was comparing it to the 7120 head that I am using for my stroker build.I have noticed 2 differences.

1) the 0331 head has a bolt hole in the front on the lower right side where the idler pulley mounts. I need this hole in the 7120 head as this is where the idler pulley goes on my 2003 TJ.

2)The 0331 head has 2 dowl pin holes in the front and back on the right side, where the 7120 head does not. The locator pins are in the block. The holes for the locator pins cannot be drilled in the 7120 head, because there is no metal there.

Also the Mopar Performance head gasket has 2 small holes for the locator pins.

What did the earlier blocks use to locate the head, or were there no locaters? I have seen a sleeve used on other engines where the head bolt passes though. The bolt hole in the head and the block has a bigger diameter were the locator sits.

Has anyone run into these problems? If so what is being done to correct them?

[SilverXJ]

1) the 0331 head has a bolt hole in the front on the lower right side where the idler pulley mounts. I need this hole in the 7120 head as this is where the idler pulley goes on my 2003 TJ.

I've heard of this before recently. Just have the machine shop drill and tap it

2)The 0331 head has 2 dowl pin holes in the front and back on the right side, where the 7120 head does not. The locator pins are in the block. The holes for the locator pins cannot be drilled in the 7120 head, because there is no metal there.

The 0630 head doe shave these holes. However, what you might want to do is cut the head off an old head bolt and cut a slot in the top for a flat head screw driver. Use that as the dowel, then remove it when you have some new head bolts in to hold it.

[Muad'Dib]

1) the 0331 head has a bolt hole in the front on the lower right side where the idler pulley mounts. I need this hole in the 7120 head as this is where the idler pulley goes on my 2003 TJ.

I've heard of this before recently. Just have the machine shop drill and tap it

2)The 0331 head has 2 dowl pin holes in the front and back on the right side, where the 7120 head does not. The locator pins are in the block. The holes for the locator pins cannot be drilled in the 7120 head, because there is no metal there.

The 0630 head doe shave these holes. However, what you might want to do is cut the head off an old head bolt and cut a slot in the top for a flat head screw driver. Use that as the dowel, then remove it when you have some new head bolts in to hold it.

x2... When i had to fix the head on my renix, i used threaded rod in the same way SilverXJ used old head bolts. I cut the rod to protrude from the block about 1-2 inches, and cut a slit in them for a standard screw driver. Once the head was carefully on the block, the rods are easily unscrewed with a standard screwdriver. Then i used a magnetic pic up tool to remove the loose rod from the head bolt holes.
I did this while the block was still in the Jeep, thats why the rods were cut so short. I needed as much clearance as i could get. If it was on an engine stand for instance, it would be much easier to get away with longer rod lengths so that you wouldnt have to mess with a magnetic pic up tool.

[fishyjeep]

I'm not understanding why you even need the locating dowls/bolts. What's wrong with just putting the gasket on followed by the head and then a couple head bolts on opposite ends to line everything up? That's how I do it.

[1bolt]

ditto, the head bolts fit so snug by the time you get all of them in place there's no way you are un aligned.

Then again if you want to be absolutely confident then I guess the pro way to do this is to get some ARP head studs. Assuming that have them for our app. I've heard there are other advantages to studs as well... Though with the apparently very tiny incidences of blown head gaskets with the 4.0 I don't guess we really NEED better head bolts.

[Muad'Dib]

Im sure anyone can get away with just putting the head on the gasket / block... but then again what if you dont line it up just quite right? Some may slide the head just a tad which ever way it needs to go, and that would score the head gasket.

This is especially a problem if the block is still in the engine bay. I would say its mandatory then... If on an engine stand.. you could get away with something else im sure.

[Alex22]

ditto, the head bolts fit so snug by the time you get all of them in place there's no way you are un aligned.

Then again if you want to be absolutely confident then I guess the pro way to do this is to get some ARP head studs. Assuming that have them for our app. I've heard there are other advantages to studs as well... Though with the apparently very tiny incidences of blown head gaskets with the 4.0 I don't guess we really NEED better head bolts.

Aside from the higher tensile strength of the ARP fasteners the main reason that studs get used in many high performance engines is that they put less stress on the threads in the block. After repeated torque cycles on an iron block the iron will become weak and eventually strip right out or loosen up while the engine is running.
Ford uses their stock head bolts as a boost limiting device, they are designed to hold in the pressure in the chamber of a stock tuned engine. Over boosting the engines will stretch the head bolts and pop a head gasket. That voids the factory warranty which is why a lot of Powerstroke owners use the stronger ARP head bolts or studs then put the stockers back in when they go in for service.

If I was to run over 10.5:1 compression or forced induction in my engine I would upgrade to ARP head bolts and maybe main bolts as well. Since I'm not, I'm just going to use stock fasteners.

~Alex

[Texacoon]

My gut whether you have a dowel to alignment your head or not doesn't make that much different.

As the manufacture in the auto industry this would save time assembling the engine together.
Now for the million dollar question!
How many times have you found something manufactured (machined) by auto manufactures that were not even or to the same specs? .. I know I have found several especially in castings!

Use bluing on the block to match your new head - THEN - accurately measuring the circumference of the markings on the head to assure it is properly aligned. I don't need all of that "micro-managing" the engine block to head in that kind of detail. If I was building the very best racing engine on the circuit I would purchase an aluminum head and have a specialized engine block with all the hardening components (rods, pistons..etc) I could add..

Just because you do not have dowel pins doesn't mean it is squarely centered. The use of all bolts in place would be just as accurate and verifying the head and gasket on the block to me would be more appropriate.