what year 4.0 block will fit in a 91

i am thinking of getting a used block from newer jeep from a junkyard. what year 4.0 block will still bolt up. there is a 2002 4.0 from a grand in my area-would that block bolt up to my head and transmission.

jack SF said:

i am thinking of getting a used block from newer jeep from a junkyard. what year 4.0 block will still bolt up. there is a 2002 4.0 from a grand in my area-would that block bolt up to my head and transmission.

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All of them, 1987-2007. The 1987-1990 blocks tend to have thicker cylinder walls, and have the boss on the lower driver's side of the block drilled and tapped for a knock sensor. 1996-up will have the brace for the main bearing cap screws in place. Heads will interchange freely, and the bellhousing pattern did not change.

are the mounting points for the accessory drive all the same, just different brackets for different years?

Seems like I've read that '96-up have Noise Vibration Harshness (NVH) webbing, I don't know if that makes them any better than others though. And, I may be incorrect, someone will need to confirm me.

5-90 said:

All of them, 1987-2007. The 1987-1990 blocks tend to have thicker cylinder walls, and have the boss on the lower driver's side of the block drilled and tapped for a knock sensor. 1996-up will have the brace for the main bearing cap screws in place. Heads will interchange freely, and the bellhousing pattern did not change.

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so a non h.o. motor is a better candidate for an overbore?

Blue_Blooded said:

so a non h.o. motor is a better candidate for an overbore?

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Yes. Mike Parrish (formerly of Accurate Power) took a RENIX block out to 4.000", and I've had occasion to check a couple of blocks at school - and the RENIX blocks were thicker in the cylinder walls.

5-90 said:

Yes. Mike Parrish (formerly of Accurate Power) took a RENIX block out to 4.000", and I've had occasion to check a couple of blocks at school - and the RENIX blocks were thicker in the cylinder walls.

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4.0?!?1 holy crap thanx for the info bro

Blue_Blooded said:

4.0?!?1 holy crap thanx for the info bro

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Hey - it's what I do. (Why do you think I'm writing books? :lecture: I don't want to lose any of this stuff...)

thanks for all that info, but here are some more questions.
what is this NOISE VIBRATION WEBBING ? is that the same as the bearing girdle?.
some one asked about the accessory mounting being the same-i will assume that they are the same?

do the newer engines with direct ignition have a gear in them to drive the distributor?

jack SF said:

thanks for all that info, but here are some more questions.
what is this NOISE VIBRATION WEBBING ? is that the same as the bearing girdle?.
some one asked about the accessory mounting being the same-i will assume that they are the same?

do the newer engines with direct ignition have a gear in them to drive the distributor?

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The 99 and up WJ Grand Cherokees use a slightly different set-up for the accessories, you will need to drill and tap some new holes into the block to get your stuff to mount up. So if you are looking for a straight swap without much problem, then look for any XJ or ZJ 4.0l from 91 to 99 and it should work fine.

Looks like me and 5-90 are talking about the same thing...I'm not positive though.

These might be of interest:

http://www.naxja.org/forum/showthread.php?t=928331

http://www.jeepsunlimited.com/forums/showthread.php?t=722718

JoshRountree said:

Seems like I've read that '96-up have Noise Vibration Harshness (NVH) webbing, I don't know if that makes them any better than others though. And, I may be incorrect, someone will need to confirm me.

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The AMC242 was revised twice for reasons of NVH (Noise, Vibration, Harshness) - the block was lightened by ChryCo for 1991, and lightened a little more - and main stud brace added - in 1996. I have heard reports that the 1996-up main stud brace can be fitted to earlier blocks by using the 1996-up main cap screws, and it may help "maximum-effort" buildups (I used to fit main braces on SBChevvy and SBFord buildups for that reason - to stiffen the bottom end.)

The main stud may have helped to reduce vibrations by stiffening the bottom end, but I've not had the two running side-by-side to compare.

I just don't understand NVH revisions on Jeeps - they're trucks! If you want a quiet, smooth ride - get a Lincoln or a Caddy, dammit!