Hello everyone, I recently just pulled out my 4.0 motor and set it to BMS Machine in San Bernardino. The guy who owns the place name is David, worked for banks for a while and then opened his own shop so he's a smart guy. After talking to him he said that he personally believes it's going to be difficult to make the 4.0 any more reliable than it already is. So I want to hear what you folks have to say.

For my sake I'm going to include the clutch in this as well so I don't have to make a whole new thread about which clutch I should get.

So let's see what you guys think?

My first personal idea was changing the flat tap lifters to roller which very few shops sell and since you'll need a different cam the kit is around 1500 bucks but **** if that means the motor is going to go another 50,000 it's worth it to me. Maybe upgraded rods, pistons, and rings. This is the first motor I've pulled so I'm interested to see what you guys have to say!

Ps 1995 jeep Cherokee manual 5speed

 

AMC made them reliable to begin with. Do a good rebuild, mountain it properly and don't overheat it and they will go 300K or more.

 

Don’t fix what isn’t broken. The 4.0 has been through millions/billions of miles of trials and tribulations by an astonishing amount of people. What you’re actually suggesting isn’t MORE reliable because it hasn’t been done millions of times like the factory set up... trust the shop he’s right !

 

I put a luk gold clutch in mind.
think my odometer says 230k

Change the oil and make sure it's not eating dirt.
My pickup also a inline 6 is at 350k and still going strong had it for 15 years.

I plan to keep my 4.0 going for alot longer.

Doing transmission right now and tackling all oil leaks. Went through the coolant system a few months ago.


Amzoil synthetic might help it go a few miles farther than dyno oil but that's debatable

 

You can balance the engine, which isn't normally part of a rebuild. You can shot-peen the rods. If there are forged rods and pistons available, that would help. A few tricks like that which are popular with racers....

Really, though, I'm not sure you'll get much bang for the buck. Run good oil, good filters (not FRAM!), change them often. Keep the cooling system properly maintained, and it's probably good for a half million miles in stock form.

 

the 4.0 is a 400k mile engine when properly taken care of in stock form. dont fix whats not broken, keep up on proper maintenance religiously, and it will out live the life of the vehicle.

 

Not much you can do as far as reliability with a 4L. Probably balance the rotating assembly and go with a hyper-eutectic piston with moly rings. Maybe a good set of Johnson lifters too. Roller lifters in this motor have been long forgotten. Everyone who has tried has ended up with a catastrophic failure. The 4L doesn't have any issues with cam or lifter wear anyway. The only improvements that could've been made by Chrysler are hyper pistons, rings, better gaskets and cooling. You could try opening up oil and cooling passages in the head and block. Maybe try a remote mounted electric water pump with a big radiator and big electric fans. Maybe run 4 hole injectors from a GM Northstar V8 with proper heat shielding.