Has anyone ever fit a 4.0 into an 86?

[TheSiLvAPython]

I know the firewall is said to be different in 1986 compared to 87+ because the 4.0 wasn't an option/made yet(although yes amc had other inline 6 engine, but the 4.0 itself wasnt manufactured/put into the jeeps until 87. I have had my 89 side by side with an 86 and the firewalls looked IDENTICAL. I didn't measure it or anything but i was curious if anyone has ever done the swap. I believe somewhere on here I read that it can be done with some persuasive hammer massaging to the firewall but I have searched the internet and  comanche club and can't seem to find any info on whether or not anyone has successfully done the swap. 

[Pete M]

late 86s got the 4.0 firewall.   but even yours was different, a couple whacks with a big hammer will make the small change needed. 

 

the bigger issue is the hood and hood latches that changed to fit the longer engine.

[aris_garage_builds]

Here's an older thread with pictures showing the differences - BIG Swap Help. The main difference is right above the exhaust tunnel, but bashing it in with a hammer has worked for most folks. As mentioned above, the bigger issue is the hood latches will need updating as well as the radiator support is slightly different. Some late model 86's got the new firewall, so you might get lucky!

[TheSiLvAPython]

On 3/8/2025 at 10:20 AM, Pete M said:

late 86s got the 4.0 firewall.   but even yours was different, a couple whacks with a big hammer will make the small change needed. 

 

the bigger issue is the hood and hood latches that changed to fit the longer engine.

Could I use a later model hood and front end? 

[TheSiLvAPython]

On 3/12/2025 at 2:48 PM, aris_garage_builds said:

Here's an older thread with pictures showing the differences - BIG Swap Help. The main difference is right above the exhaust tunnel, but bashing it in with a hammer has worked for most folks. As mentioned above, the bigger issue is the hood latches will need updating as well as the radiator support is slightly different. Some late model 86's got the new firewall, so you might get lucky!

I just read that thread, answered many questions and i see the firewall diffences without the engines in the way. Thanks for sharing.

[Pete M]

6 hours ago, TheSiLvAPython said:

Could I use a later model hood and front end? 

 

 

absolutely.   but the radiator core is welded in, so be prepared.

[TheSiLvAPython]

11 hours ago, Pete M said:

 

 

absolutely.   but the radiator core is welded in, so be prepared.

Thanks for the heads up,. Wait the raidiator core is welded in? The "core", is that the main support holding the radiator in place? It's not the radiator itself welded in right? 

[Pete M]

core supports.  sorry, I missed a word.  the top cross bit bolts on (and is how you pull the radiator out) but the rest is welded to the side structure.