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Old 04-08-2007, 03:45 PM   #1 (permalink)
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4.0 and 4.2 . . . differences and similarities??

Scored a good deal on an 88 XJ with a lower rod knock. I was hoping to just drop the pan throw in some new rod bearings and have a driver. But, after I put the new bearing in rod #1, it still had some slop in it.

I've got a 4.2 with a fresh rebuild on it sitting in the corner of the garage (out of an '88 YJ which is now running a small block).

My question is:

How similar are the two motors, i.e. could I swap the long blocks and run a fuel injected 4.2?? (quicker and cheaper) Would I be better off stroking the 4.0 with the 4.2 crank and rods?? (more time/cash, but cooler )

What are my options/what would you do?
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Old 04-08-2007, 04:19 PM   #2 (permalink)
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Do the stroker. Since you have all the stuff you need I would run with it. You will really like the torque you will get out of it.

When it comes to the blocks they have some differences. The 4.2 has a manual fuel pump on the side of the block which the 4.0 doesnt(pump in the tank) There is a couple other differences but i cant think of them right now. We did a stroker on my buddies CJ and were very happy with the results.
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Old 04-08-2007, 07:35 PM   #3 (permalink)
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I'm doin research on just that same question.

I have
1. Soon to be retired 95XJ sport daily driver, engine in great condition, 4.0 HO, auto transmission.
2. My baby, 90 YJ 4.2, auto transmission.


Try this, http://jeep.off-road.com/jeep/articl....jsp?id=277013

Good luck.
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Old 04-10-2007, 04:46 PM   #4 (permalink)
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Thanks for all the help guys!

I think if I were trying to upgrade a carbed 4.2 in a CJ or YJ, I would go with the head swap, but it looks like there are enough differences that it would be worth the extra cash/time to do the stroker. So . . .

I'll keep you posted as to the stroking progress
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Old 04-10-2007, 11:38 PM   #5 (permalink)
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4.2s and 4.0 electronics dont really mix well.. its possible but from what ive heard its to much of a hassle. i would say fix the 4.0 or go to a junkyard and pick up a spare one with low miles for $600 bucks.
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