Motor Swaps

[AshtonFig]

I bought a 86 comanche with the 2.5 which has a rod knock. I am willing to rebuild it but ive been reading that if your going to spend the money to rebuild it you might as well do a motor swap. What would be the easiest and or cheapsest way to go for a motor swap?

 

I do have a 4.3 gm motor out of a s-10 that might work but I'm not sure what trans to run with it or if its even worth it to put it in. 

 

any advice or ideas is welcome 

[89 MJ]

I really like the GM 4.3 V6 and I would say it is probably a worthwhile swap, but I don't know if I would do it myself, unless I had one laying around like you do. These were nice because they shared a lot of parts with the small block V8s, so many conversion parts should work on the 4.3 as well.

 

In terms of transmission to run behind it, that would depend on what you want for the truck. If you want an automatic, I would personally look at the 700R4 unless you have a 4L60E already with the engine. The 700R4 is nice because it is not electronically controlled. If you wanted a manual transmission, there are companies out there that have parts to convert Jeep AX-15s and NV3550s to GM engines or I would do a GM NV3500 that would come out of an 88-98 GM 1/2 ton truck. For a transfer case, I would run a driver side drop GM NP241C if you're running a GM transmission, or the stock Jeep transfer case if you use a Jeep transmission.

[cruiser54]

There is no cheap, easy solution to this problem. 

[derf]

Engine swaps are not cheap or easy.  The engine is a very small part of the overall cost.

 

The easiest swap from a factory 2.5 is to go to a 4.0 that you harvest from a different XJ/MJ.  Even then, you need a whole lot from the donor, especially the wiring harness.

 

Swapping in an engine you have on hand may sound appealing but you'll get bogged down in expensive details fast.

 

If I was going to swap a 6 cyl, I'd go with an XJ donor 4.0.  If I was going with a GM, I'd sell the 4.3 and buy a V8.  Same amount of work and money but you then have a V8.

[pizzaman09]

On 4/9/2024 at 3:19 PM, derf said:

Engine swaps are not cheap or easy.  The engine is a very small part of the overall cost.

 

The easiest swap from a factory 2.5 is to go to a 4.0 that you harvest from a different XJ/MJ.  Even then, you need a whole lot from the donor, especially the wiring harness.

 

Swapping in an engine you have on hand may sound appealing but you'll get bogged down in expensive details fast.

 

If I was going to swap a 6 cyl, I'd go with an XJ donor 4.0.  If I was going with a GM, I'd sell the 4.3 and buy a V8.  Same amount of work and money but you then have a V8.

This exactly.  The most economical thing is to fix the 2.5L you have or swap another identical 2.5L in if you an find one very cheap.

[Eagle]

On 4/9/2024 at 3:19 PM, derf said:

Engine swaps are not cheap or easy.  The engine is a very small part of the overall cost.

 

The easiest swap from a factory 2.5 is to go to a 4.0 that you harvest from a different XJ/MJ.  Even then, you need a whole lot from the donor, especially the wiring harness.

 

Swapping in an engine you have on hand may sound appealing but you'll get bogged down in expensive details fast.

 

If I was going to swap a 6 cyl, I'd go with an XJ donor 4.0.  If I was going with a GM, I'd sell the 4.3 and buy a V8.  Same amount of work and money but you then have a V8.

 

It's an '86 -- the firewall might not be configured to accept a 4.0L.

 

The easiest swap for an '86 2.5 liter (other than another 2.5L) is the GM 3.4L V6. Not the 4.3 -- the 4.3 is a shortened small block V8 -- it's a 90-degree block, so it's a lot wider than the 3.4, which is a 60-degree V6. If you're going to think about a 4.3, you might as well go all the way and just drop in a SBC V8.

 

Personally, I think I'd rebuild the 2.5L and throw in a performance cam and either a real carburetor, or aftermarket fuel injection.

[derf]

13 hours ago, Eagle said:

 

It's an '86 -- the firewall might not be configured to accept a 4.0L.

 

The easiest swap for an '86 2.5 liter (other than another 2.5L) is the GM 3.4L V6. Not the 4.3 -- the 4.3 is a shortened small block V8 -- it's a 90-degree block, so it's a lot wider than the 3.4, which is a 60-degree V6. If you're going to think about a 4.3, you might as well go all the way and just drop in a SBC V8.

 

Personally, I think I'd rebuild the 2.5L and throw in a performance cam and either a real carburetor, or aftermarket fuel injection.

I missed that it was an 86 and you make good points there.

 

I always wanted to do an 84-86 with a 3.4/4L60 from a mid 90s F-Body.  That would be an easier swap since the 3.4 block is the same externally (more or less).

[89 MJ]

1 hour ago, derf said:

I missed that it was an 86 and you make good points there.

 

I always wanted to do an 84-86 with a 3.4/4L60 from a mid 90s F-Body.  That would be an easier swap since the 3.4 block is the same externally (more or less).

Have you checked out @Greenjeans XJ build thread? That’s what he did. Except he might have a 700R4 in his. 

[eaglescout526]

15 hours ago, Eagle said:

either a real carburetor

He shouldn’t have one on an 86 MJ. It should be Renix TBI unless someone did some swapping. 

[derf]

22 minutes ago, 89 MJ said:

Have you checked out @Greenjeans XJ build thread? That’s what he did. Except he might have a 700R4 in his. 

Sort of the same thing.  The 700R4 became the 4L60 in 1990.  Just a name change.  They did the electrical conversion to the 4L60E later in 1993.

 

He may have used an older transmission than would have come with the engine donor.

 

I personally would grab the engine and transmission from a donor and throw a new adapter and tailshaft in it to make it 4wd.  I'd harvest the donor wiring harness along with the engine and trans.  That makes it easier.

[89 MJ]

53 minutes ago, derf said:

Sort of the same thing.  The 700R4 became the 4L60 in 1990.  Just a name change.  They did the electrical conversion to the 4L60E later in 1993.

 

He may have used an older transmission than would have come with the engine donor.

 

I personally would grab the engine and transmission from a donor and throw a new adapter and tailshaft in it to make it 4wd.  I'd harvest the donor wiring harness along with the engine and trans.  That makes it easier.

I would do the same thing, makes it a ton simpler. 

[Greenjeans]

Check out my thread in “cool other projects”…

I used a 700r4 to keep everything simple.  Carb and no computers or sensors of any kind was my reason for a 700r4. (88 s10 donor).. A stand alone controller for a 4l60 is super expensive.  A 4.3 in your case is a good option if you already have a good motor.  Wayyy more transmission options.  241c transfer cases are plentiful and very strong.  The early 4.3’s used a carb and aftermarket manifolds are out there.  Headers for an s10 may work.  I’m betting a motor mount for an s10 4.3 may fit your frame or be easy to mod.  If your 4.3 is a later one with TB, or multi port fuel inj etc, you are going to need the 4l60 and an s10 wiring harness.

 

swaps are fun but be prepared for money you had no idea you’d be spending 😁

[derf]

3 hours ago, Greenjeans said:

Check out my thread in “cool other projects”…

I used a 700r4 to keep everything simple.  Carb and no computers or sensors of any kind was my reason for a 700r4. (88 s10 donor).. A stand alone controller for a 4l60 is super expensive.  A 4.3 in your case is a good option if you already have a good motor.  Wayyy more transmission options.  241c transfer cases are plentiful and very strong.  The early 4.3’s used a carb and aftermarket manifolds are out there.  Headers for an s10 may work.  I’m betting a motor mount for an s10 4.3 may fit your frame or be easy to mod.  If your 4.3 is a later one with TB, or multi port fuel inj etc, you are going to need the 4l60 and an s10 wiring harness.

 

swaps are fun but be prepared for money you had no idea you’d be spending 😁

Definitely easier to do the non electronic transmission with a carburetor.

[Eagle]

On 4/11/2024 at 12:22 PM, eaglescout526 said:

He shouldn’t have one on an 86 MJ. It should be Renix TBI unless someone did some swapping. 

 

I understand that an '86 would have TBI. It wouldn't if I were to do a rebuild. I hate the Jeep TBI,, and I would much prefer to have a carburetor -- so that's what I would use.

[eaglescout526]

40 minutes ago, Eagle said:

 

I understand that an '86 would have TBI. It wouldn't if I were to do a rebuild. I hate the Jeep TBI,, and I would much prefer to have a carburetor -- so that's what I would use.

Ahh