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Old 01-02-2013, 09:19 PM   #1
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Join Date: Sep 2012
Location: princeton kentucky (southwest)
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Question 2.5 to 4.2? advice and opinions

Advice and opinions on this please:

I own a 93 yj 2.5 mpfi that needs top end rebuilt... I prefer swapping motors since the lil 2.5 is low on horses, and I think I could do this for cheaper than a rebuild.

I found a 4.2 out of a 90 wrangler.... But everyone seems to hate on these motors compared to a 4.0. Why? Has anyone had both? I've had neither. Do you think I would be happy with this swap? Has anyone done this? What are pros and cons of the 4.2?

Any information on the 4.2 , the swap into a 2.5 mpfi jeep, and opinions are welcome.

I have the ax-5 trans... Will it bolt up? Or hold up? This is mainly a street jeep with slight offroading.

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Old 01-02-2013, 11:14 PM   #2
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I do not know specifically about the 4.2 but everything I have read says that any other engine than the 2.5 would require a major change including engine mounts that are welded to the frame. The AX-5 transmission in 2.5 is not strong enough for anything with more power.

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Old 01-03-2013, 12:41 AM   #3
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I have always heard that the trans wouldn't hold up but I didn't know, just wanting my jeep back. In reality I would like to swap in a 4.3 vortec.
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Old 01-03-2013, 09:35 AM   #4
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4.2 is old school, not quite the horsepower of the 4.0. Probably the only real difference.

The AX5, well I wouldnt suggest running it, but like anything you can get away with a lot if you are really careful. But then, I thought that of the Peugeot in my jeep when I rebuilt the reverse set. Lasted a month.

Personally, I would either rebuild what you have and run it, or I would sell it and find an I6 and buy that, or shoot for the V6 and upgrade the drivetrain while I was at it.
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