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post #1 of (permalink) Old 08-09-2001, 02:50 AM
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Need Advice re:Cracked Block = 4.2 or 4.0 Rebuild

Hi, I'm not sure what to do here... (sorry this is so long)

I have been reading through many articles and various other postings all over the Web for the last week and have gathered a lot of information around my issue. I know you guys receive a lot of questions and post tons of information on the AMC 4.2's and 4.0's, but I haven't been able to piece together all information I've been looking for. I now believe I have a lot of information, but need some advice on choosing the best course of action with so many variables.

Here is my dilemma:

I have an '81 CJ8 with a 258 that has a cracked block that leaks coolant from under the intake/exhaust side of the block. It's not a head gasket. I guess this is not all that uncommon from what I've learned in the last week. I am trying to see if I can get the crack welded or something (without pulling the motor) to hold for awhile, but I know this is probably a short term fix if it can even be done. Can the block be welded well enough not to worry about? The motor is running pretty well and burns no oil. I don't see any coolant in the oil either.

So now I'm debating some things:

1. Buy rebuilt 258 longblock and keep stock carb.

2. Buy rebuilt 258 longblock with intent of adding FI kit down the road. (This seems to be the most expensive route. Not sure on what year/s block to consider if going to add FI kit later. Are there differences between the years?)

3. Look for a complete new/rebuilt 4.0 I6 (or one with low mileage) and swap out everything. (Not sure what year/s motors work or are the best. What possible salvage vehicles should I be looking for? YJ, Cherokee, etc?) What all should I be bargain for off the salvage vehicle, computer etc?

4. Does a 4.0 motor perform better than a 4.2 FI converted motor, HP, reliability etc?

5. Should I consider a 5 spd. transmission if I come across one. If so, are some better than others?

6. I've thought about trying to have a motor "over built" with cam, special pistons and other performance parts just trying to make it more reliable and have fewer oil leaks (valve cover), but yet keeping the stock straight six configuration. The problem with this, from what I hear, is that a non-stock motor may cause problems if I ever added fuel injection. True?

7. Have any suggestions on where to find a reasonably priced motor? I've been searching and calling all the way up into Canada. Longblock prices range from $800 - $2000.

My goals are:
1. Reliable strong motor.
2. Cost effective solution.
3. Easy swap.
4. Improved performance and gas mileage.

Additional info:
Stock manual 4 spd.
I currently have split headers. (Will these get in the way of FI kit or not work with 4.0 motor?)

Could you please help point me in the right direction here? There are a lot of variables and I'm not quite sure what to do.

Again, sorry this is so long.

Thank you very much for your time and advice.

Best regards,

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post #2 of (permalink) Old 08-09-2001, 04:45 AM
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Re: Need Advice re:Cracked Block = 4.2 or 4.0 Rebuild

it seems you are pretty set on FI... so i would go with that route.. i would look for a low milage 4.0.. in a wrangler/cherokee.. but make sure its the "high output" 4.0... im not up on the exact years.. but its the later version.. 94 and up maybe.. one from a yard with computer and wireharness should be 1000-1500 i would say.. those are the prices i have seen others pay.. as for a 5 speed.. i would try to find a T-5... that would be your easiest swap... and probably cheapest route.. and still have the FI..

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post #3 of (permalink) Old 08-09-2001, 08:13 AM
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Re: Need Advice re:Cracked Block = 4.2 or 4.0 Rebuild

4.2 blocks are prone to crack across the centerline of the three freeze plugs on that side. You'd be driving on borrowed time trying to repair it which would take considerable work just to get to with epoxy or a welder.
Here is one source for engines you might want to look at... then there is always HESCO and Clifford Performance who build custom.
If I were you, I'd be thinking a 4.0 swap or a 4.0 head on a 4.2 combo.
Fuel inject it in either case using a 1991 - 1996 stock unit or the MPI kit.
For the latter you'll need a 4.2 block with 1/2" head bolts but there is a way to get around that by using a pair of Clifford centering washers.
The best least expensive route is finding a good used 1991 - 1996 4.0 mill and use it's wiring harness if available. Or you can get a harness from HESCO who can also provide you with a dyno proven cam ground for your particular setup and use.
There is a page on my Jeep web site that tells you which 4.2 blocks have what head bolt sizes. Plus there you will find other I-6 info you might be interesting reading for you. The link is by my sig. below.

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post #4 of (permalink) Old 08-09-2001, 09:14 AM
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Re: Need Advice re:Cracked Block = 4.2 or 4.0 Rebuild

I have found good luck using when looking for parts.

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