2.8 rebuild and swap options.

[jwidmer]

As of today, I am the proud owner of a 1986 Comanche.  2.8 automatic 4X4.  The engine needs a rebuild so looking for the best and easiest options.  What 3.4 and 3.1 parts are drop in interchangable?  If the 3.4 Cambird swap is an option, which year would be a simple drop in.  If I find a longblock, any issues with the fitment of my 2.8 manifolds carb distributor, etc.  

[Pete M]

don't reuse the 2.8L block/heads!  they are inferior to the 3.1/3.4 in design and construction quality.  Start with a 3.1/3.4 and the reuse your intake/exhaust/accessories/trans/everything.  any year 3.1/3.4 from a Camaro/Firebird will work (I think the
S-10 had the 3.1 at some point around that time). I think they were early 90s but unsure of the exact spread that used the 3.1/3.4.  car-part.com might help in the junkyard hunt.

 

there should be a thread or 2 in the DIY forum (which isn't organized yet). the big differences are that you'll need to add an inline electric fuel pump (the 3.4 doesn't have any boss for the 2.8's mechanical pump) and the flywheel needs to be neutrally balanced (the crank of a 2.8 is not balanced on its own, but the crank of a 3.4 is).

[Strokermjcomanche]

In addition to what Pete said ,a 3.4 out of a 93 /94 Camaro or firebird is the best to use IMO . I put one in my 86 blazer 11 years ago and it's still going strong .

[86FUBAR]

IIRC a 93-95 camaro will work, I used a 94 when I swaped mine a few years back and it was the best thing iv done to my jeep . here's a good link to read about the swap

http://www.lunghd.com/Tech_Articles/Project_XJ/Project_XJ.htm

Also here's a link to my build if you wanted to see what I did

http://comancheclub.com/topic/5194-project-fubar/

[jwidmer]

Thanks guys for the response.  So with the automatic (which I think is Chrysler), Do I keep the flex plate on the 3.4, and will the torque converter mount to it fine?

[Crash]

I would swap the flexplate from your current engine, unless someone here can for sure say it's a direct swap. Even though it is a GM block, the AMC electronics are probably different.

[Pete M]

there's no CPS involved.  the flexplate will need to match the 3.4 for balancing reasons.

 

  can't remember what trans it does have (904?), but it for sure isn't the AW-4.

[jwidmer]

I'm wondering if I can use the flexplate from a 3.1, and drill to mount the Chrysler torque converter?

[86FUBAR]

You might be able to use the 2.8 flex plate if you drilled the spot welds holding the counter weights , iv done this before on other swap projects years ago but it still should get checked for balance

[docivy]

The price of doing all this is pushing me to just buy a whole 4x4 s10 4.3 and swap to a 90 degree v6. It's super easy to slap a carb on , not to mention I would like a 700r over a Ax5

[86FUBAR]

The price of doing all this is pushing me to just buy a whole 4x4 s10 4.3 and swap to a 90 degree v6. It's super easy to slap a carb on , not to mention I would like a 700r over a Ax5

This is a relatively cheap mod ! The only things that "need" to be done are an electric fuel pump and a neutrally balanced flywheel or flexplate other than that it's swaping bits and pieces from one engine to another . That's it ! My swap cost me about 2k and 1k of that was the engine itself and I went with an edelbrock intake , higher end fuel pump and replaced a bunch of other stuff wile I was there . I could have saved at least $500 if I had just done the bare necessities and in most places used engines can be had for a hell of a lot less than I paid . You can't say the same about a 4.3 swap , trust me I looked ! And if you want a 700r4 you can use one from a 2.8 s10 .

[Pete M]

The price of doing all this is pushing me to just buy a whole 4x4 s10 4.3 and swap to a 90 degree v6. It's super easy to slap a carb on , not to mention I would like a 700r over a Ax5

 

 

I can't argue against the 4.3 swap, as it is a fine motor, but you need to replace pretty much everything to make it work.  the carb is the least of your worries.  but if you've got the budget for it, go for it.  :thumbsup:

[Eagle]

The price of doing all this is pushing me to just buy a whole 4x4 s10 4.3 and swap to a 90 degree v6. It's super easy to slap a carb on , not to mention I would like a 700r over a Ax5

The 4.3L is basically a SBC V-8 with two cylinders cut off. It's much wider than the 2.8/3.1/3.4 and barely fits the MJ engine compartment. Back in the early days of NAXJA one of the guys who lived near me had an XJ that he had put a 4.3L into. I asked him how much work it was to do it. His response was: "Let me put it this way -- I love working on cars, but NEVER AGAIN."

 

Once you decide to go with a 4.3L you might as well go all the way and do a SBC.

[1stDeuce]

I'd suggest you're on the right track with looking into the 3.4L out of a camaro.  Putting a 4.3L or any GM V-8 in an XJ/MJ is a LOT of work.  (I had thought about a nice 4.8L, but it's not an easy swap at all from what I've read...) 

 

You can strip and swap over all the 2.8L stuff to the 3.4L, and it'll run better than the 2.8L ever did, but I'd recommend taking the time to bring it out of the horseless carriage era by keeping the 3.4L FI setup.  (Or the 3.1L setup if you find a 3.1L instead...) 

 

I have a 3.4L out of a '95 camaro in my truck.  I put an XJ fuel pump in the tank (bent slightly to reach the bottom better) and re-used the factory fuel supply and return lines.  (They're steel, so pressure is not an issue.)   Put the Camaro computer on the pass side inner fender and hooked up the wiring.  It runs great.  

I used a Taurus 2-speed fan, since I didn't have one around that would fit the Camaro engine easily, but I'm on the lookout for one that will work.  (Perhaps off a later 2.8L S-10?  Probably have to swap the water pump too...)  

 

Downsides to this route:  The throttle body is about 1" from the underside of the hood.  It's going to leave a mark if you really thrash it.   The Camaro oil pan gives up about 1" of clearance to the axle also...  A 4wd S-10 oil pan off a later 2.8L fixes this issue, but they're almost impossible to find.  You'd have to bottom it HARD for it to be an issue...

 

You'll need an A/C eliminator bracket.  The Comanche motor mount uses bosses that the Camaro A/C pump covers.  I will probably try to make a new mount using the Camaro bracket, and put the A/C pump back on, but the eliminator bracket works fine if you don't care for A/C.

Comanche exhaust bolted right onto the Camaro manifulds.  Radiator for the 2.8L works fine.  Bolts up to everything else, no clearnace isues to frame or steering.  I did have to make an intake system with elbows and a filter...

 

 

Your 2.8L flexplate will have some weights on it, and that's no good.  You MUST use a flexplate/flywheel that's not externally balanced.   I used an S-10 flywheel for an '88+ 2.8L, which was internally balanced.    I'm not sure what flexplate would work best, but perhaps Google can help...  

 

 

Good luck!!

Chris

[docivy]

That's why I had said a whole donor truck. I've got a friend with one that was rear ended so I can get literally everything for $500. As far as motor mounts and the transfer case mount I'm able to fab those and I'm a while by trade so I can do all that at home. My biggest reason to consider it is my whole drivetrain in my truck is rough. Not to mention I have an 86 with a non 4.0 firewall. Over heating is the reason I don't go Sbc

[1stDeuce]

Well, if you can do some fab work for mounts, go for it!  Swap the whole driveline if it's 4wd.  You may find that it'll still overheat if you work it, but a thick core aluminum radiator might help.  Or do some work on the radiator mount and run a wide 4.0L radiator.  If you've got the whole truck, and it runs, why would you even consider putting a carb on it??  The TBI harness is almost stand-alone already if I recall correctly.  You just need to clean out a few extra wires and hook up the Comanche connections for power, oil and temp, and charge...  It's NOT that hard, and the TBI 4.3's are torquey little engines that run great, so it's time well spent.  :)