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Unread 06-12-2003, 03:28 PM   #1
bowlsy23
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Join Date: Jun 2003
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Advice on swapping a 2.5 to the 2.8 V6

Hello I'm in the process of buying a 1985 CJ7 with a bad 2.5 V4 motor and I'm wondering on the difficulty of swapping it to a 258 V6. Can anyone tell me the pros and cons. For instance will I need new motor mounts and will I have to modify anything to swap these 2 motors. Any advice would be appreciated!!!

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Unread 06-13-2003, 03:49 PM   #2
CoryB
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First off, the 258 is an I6, not a V6. And it's a 4.2, not a 2.8.

Now that that's out of the way, in addition to the complete engine assembly, you'll need:

New engine mount frame brackets
Different bellhousing and/or transmission (if it's an SR4, just throw it out now and be done with it. It's not even a good door stop)
Different radiator
Probably a different wiring harness
Different clutch linkage if it's a manual tranny - the throw on a 4-banger clutch slave isn't quite enough for a 6 from what I've been told
Probably more, but those things spring to mind...

Basically, everything under the hood will need to be replaced except the transfer case.

The good thing is that the axles will already have 3.73 or 4.1 gears in them so you don't have a regearing expense if you want to run 33" tires.
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Unread 06-16-2003, 10:45 AM   #3
twmattox
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Not quite correct (from my experience)...

The transfer over from the I-4 to the I-6 woild require yanking the motor, replacing it with the new one, and getting a new radiator. The motors share the same bolt pattern. The things to remember would be that the tranny has a different input shaft (and when you get a new clutch) you will need the one for the 4-cylinder engine.

that being said, KEEP THE 4-CYLINDER!!!

These are same motor as the 258 (with the last 2 cylinders lopped off). They are very strong motors and can take a lot of abuse. I can drive mine at highway speeds (65-70) and still get around 20mpg. Spend the money you would spend swapping out the motor on basic upgrades. I have had great luck with the following:
-Rebuild at a machine shop with 3-angle valve job and slight over cam.
-Use a webber 32/36 carb (eliminate the shoddy Carter YFA)
-Upgrade ignition to the Flame Thrower FC-1000 and coil to the C-4 (this, coupled with the Webber will completely get rid of emission controls on the vehicle).
-New exhaust (with a highflow cat and exhaust system) I used the Dynomax

If you have money left, regear to 3.73, and get an NV-3500 tranny. This gives you more of take off power and the overdrive keeps your RPMs in line at highway speeds.
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Unread 06-16-2003, 06:23 PM   #4
CSP
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Quote:
Originally posted by twmattox
Not quite correct (from my experience)...

The transfer over from the I-4 to the I-6 woild require yanking the motor, replacing it with the new one, and getting a new radiator. The motors share the same bolt pattern. The things to remember would be that the tranny has a different input shaft (and when you get a new clutch) you will need the one for the 4-cylinder engine.
Are you sure about that? The last two AMC four cylinders that I have plucked shared the bellhousing bolt pattern with the GM 60 V6's (2.8, 3.4, etc). Not even close to the AMC six cylinders or V8s.
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Unread 06-17-2003, 08:55 AM   #5
twmattox
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4 cyl. bellhousing bolt pattern has to do with the year. Prior to 1984, the AMC 4-cylinder of choice was the Pontiac Iron Duke (151 ci). However, in 1984, the 4-cylinder was changed to an AMC designed 150 ci (basically a 258 with the last 2 cylinders removed). As the original post was regarding an '85, I assumed that this is in fact the AMC 150 (not the Pontiac 151).

Incidentally, many of the auto parts retailers haven't gotten this correct. Whenever I get parts for my engine, I have to request for a Wrangler 4-cylinder (1987 or later). However, the engine change occured in 1984 (the 4-cylinder that is in Wranglers today is the same design as the 1984 with fuel injection added).

Finally, another difference in the 1983 4-cylinder and the 1984 4-cylinder has to do with emissions. The 1984 had a "computer" that was used to regulate carb ratio and timing. The 1983 didn't.

Probably more 4-cyl. info than most wanted...
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Unread 06-17-2003, 09:45 AM   #6
CSP
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Yep, I was aware of those differences. That's why I stated AMC four cylinders. The Iron Duke shares it's bellhousing pattern with the small block Chevy V8 and 90 V6 engines.

Like I said, every AMC four cylinder and current four cylinder (DC I guess you would call them) share bellhousing patterns with the GM 60 V6, not the AMC I6.
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