4.0 head overlap on 4.2 block - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 08-02-2003, 06:59 AM Thread Starter
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4.0 head overlap on 4.2 block

I'm currently installing a HO 4.0 head (#7120) on an '86 4.2 block (casting# 3227444). Two issues have come up that hopefully, some of the prior head swappers on the board here, can set my mind at ease.

1. Like the subject line implies, I'm concerned about head overlap on the 4.2 block. Other posters on the board have talked about overlap, but never gave specifics. When doing a test fit with my head on the block, I installed two head bolts on each end to make sure it's centered. I have varying degrees of overlap. And when I say overlap, I mean the triangular ports are literally exposed beyond the edge of the block, worst case 3/16" to best case flush with the side of the block. Many posters had success with epoxy, so I had planned to use dissolveable peanuts and seal the 12 ports with marine grade JB Weld. But now wonder if that's a good idea with the amount of overlap I have. Anyone else with the head swap see overlap like this and still use epoxy? Would it still be wise to go with JB Weld, or should I use freeze plugs, pipe plugs, or have them welded shut?

2. I read an '86 4.2 block, casting# 3227444, is supposed to have 7/16" head bolts. But mine has 1/2"X13TPI, verified with my tap & die set. All evidence points to the fact that the 4.2 head hasn't been off since put on at the factory. So since I have 1/2" head bolts, should I use the higher 4.0 torque settings? Anyone else with an '86 CJ-7 with factory 1/2" head bolts? Is it possible since my Jeep was a late model '86 (it has a Dana 44 rearend) a 4.0L block was used? But that wouldn't make sense because of my overlap issue. [img]images/graemlins/confused.gif[/img] Any thoughts?

LargeAl, '86 CJ-7


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post #2 of (permalink) Old 08-02-2003, 09:44 AM
 
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Re: 4.0 head overlap on 4.2 block

It seems that everyones case is different on certainl mods, and this is one of them. So, I can tell you about my 4.0L head swap.

I used JB weld, I have not problems.

I used new 4.0L head bolts and torqued them down to 258 specs, no problems.

Good luck.
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post #3 of (permalink) Old 08-02-2003, 11:32 AM
 
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Re: 4.0 head overlap on 4.2 block

I had absolutely no overlap, so I can't help you there. I can tell you that I used the higher 4.0 torque setting. Just make sure you've got new bolts... Your project will take a bullet if you broke one off while snugging it down....
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post #4 of (permalink) Old 08-02-2003, 04:24 PM Thread Starter
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Re: 4.0 head overlap on 4.2 block

Did you have any overlap of your ports on the block like I have on mine?
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post #5 of (permalink) Old 08-02-2003, 06:39 PM
 
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Re: 4.0 head overlap on 4.2 block

As I mentioned, I didn't have any. But I have a later model 258 block, an 89... The block shouldn't have changed at all, though... It's incredibly odd that the block has 1/2" bolt holes... Are you positive it's the factory block?
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post #6 of (permalink) Old 08-02-2003, 07:13 PM Thread Starter
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Re: 4.0 head overlap on 4.2 block

The Jeep has only had two PO's, and both were meticulous in their recordkeeping and passed it all on to me. And based on previous maintenance done and the condition of what's in there now, I just don't see it.

But you're right...it is really wierd. Aren't the 4.2 and 4.0 blocks alot alike? Maybe during the production changeover the factory drilled the remaining 258 blocks to 1/2" in preparation for the 4.0 block production? Hell, I don't know...just guessing now.

LargeAl
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post #7 of (permalink) Old 08-02-2003, 07:22 PM
 
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Re: 4.0 head overlap on 4.2 block

The blocks are identical, aside from the water jacket issue.... A 4.0 is basically a 258 block w/a different crank... Maybe later model 86's have 1/2" bolt holes. Who knows...
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post #8 of (permalink) Old 08-02-2003, 07:58 PM
 
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Re: 4.0 head overlap on 4.2 block

The blocks are not identical. There are many similarities, but far from identical.

Yes I did have a little hang over. It wansn't that much, in fact hardly anything. I have a 78 block. From 81-85 the blocks had 7/16 head bolts, I don't know why.
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post #9 of (permalink) Old 08-02-2003, 09:43 PM
 
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Re: 4.0 head overlap on 4.2 block

what exactly are the differences that make it far from identical? (not contradicting you, just asking)
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post #10 of (permalink) Old 08-04-2003, 03:05 AM Thread Starter
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Re: 4.0 head overlap on 4.2 block

Just thought I'd let anyone that's interested know what I found out as a cure to my overlap problem. Have decided to nix the epoxy and go with the brass freeze plug process explained at this website: http://members.aol.com/Stvns/XJhelp4.html (halfway down the page).

After a couple emails back and forth with the author, the plug bores were done with a vertical mill slightly shallower than the plug height. The head was then decked for an even flat surface to mate with the head gasket. 7/8" brass plugs were used. Brass was chosen for its thermal properties, expands more than cast iron. With the overlap that I have with my head, I feel that it's a no-worry, permanent fix.

Hope this helps anyone with the same issue.

LargeAl



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