Hoenestly

Why is this prevalent and said so much? I have a 4.0 and maintenance it religiously can it still happen? Do these engines have these issues if they are not properly maintained? ( if your wondering where I hear this, youtube, forums, around some friends etc)

tkeehn

I'm not a mechanic but have worked on a few vehicles. My thought is that any mechanical device that has moving parts can break. Even if maintained. I had a honda that just randomly threw a rod. I changed the oil with Mobile one every 5k miles. And this still happened at approx 150k. Now my cherokee was abused before I got it. Its a 4.0 and I don't treat it like I should. No issues. with 160k on it.

Does maintenance help prolong wear, yes it does. A lot comes into play operating temps, manufacturing quality, etc etc. When you push machines to the max often eventually they break. Nascar engines blow, lawn mower engines blow, its just a matter of time and how you treat them in my mind.

Bottom line I think is it can happen to any engine at anytime. Again I'm not a mechanic by any means. But by god I can tear one apart!

Fred/N0AZZ

The 4.0's are about as solid an engine as there is for its type and known for ability to go to very high mileage even with some abuse. But like any they do have a bad one every now and then with how well they are taken care of and the way they are driven, both a factor.


That said there are so many on here with 200,000 + miles on them and some with 300,000 or more shows they can be very dependable. Mine has 220,000 on it and runs very well, I do not know the number of owners it has had before me.


I have had engines blow up with less than 20 mi. on them all being 1/4 of a mile at a time

kgm

Riding an 11 year old 4 stroke MX bike these days. Tick tock! Kaboom!

s346k

"blown up" is a blanket term describing any fatal part failure. i've used that phrase when something happened rendering the engine useless. could be a spun bearing, timing chain failure or a window in the block. i've blown up several engines just about every way possible. it is quite impressive what kind of abuse most all engines will take before grenading.

edit: to answer your question(s): yes it can happen due to poor maintenance. it can also happen just because...of a lot of reasons. there are a lot of parts working together in an engine. all it takes is one part not cooperating to cause a detrimental problem. new motors will break or they will break in. once they're broken in properly, assuming proper assembly and quality parts, they will last a long time. of course some will stay together longer than others given equal treatment. im hard on engines but equally as **** about maintenance.

I AM GOD

https://www.cherokeeforum.com/f2/200...-motor-186947/

Waynerd

A blown engine is a blown engine in my opinion. Blown would be a term I would use for major mechanical damage rendering the engine inoperable. Worn cam or bearings or rings technically not blown just worn. If it blows up it's likely not easily repairable.

And I've ran multiple vehicles out of oil. My 94 Chevy G van with a 4.3 I only change the oil once a year or less. And have beat the snot out of countless bikes, atv's and everything in between. Never did any engine damage. And never blew one up.

cruiser54

There is never a shortage of folks who can bend a digging bar in a sand pile.

Fred/N0AZZ

I have a son like that.

diskman

The 4.0 is an "old technology" engine. It loves to run at low to middle speeds. Most engines today will happily spin up to 5-6000K RPMS regularly. The 4.0 is reaching self-destruct territory at those sustained RPMS.

I imagine most of the 4.0s "blowing up" you see are just people abusing them. Off roading in 4-low at at 30 MPH+. Or generally beating the engine to death.

The 4.0 is a bullet-proof motor IF you don't beat it. These were designed to be torquey engines for tractors and forklifts. Not rodding around town at 5K RPMS daily.

I have 300K miles on my 92 4.0 now. Runs about 10PSI oil at hot 75MPH. No knocks and will probably outlast me with regular oil changes and maintenance. If My son drove it? I would give it about a month.

cruiser54

Absolutely unfounded info. That's what the British did with their cars after the war. AMC did not.

It was developed as a CAR engine and nothing else.

You can twist the **** out of them. Mine frequently see 4800 RPM and are smooth as silk. One has 277K on it.

Read this:

https://en.wikipedia.org/wiki/AMC_straight-6_engine

s346k

an engine is an engine. the only thing "old technology" about it is the flat tappet cam, which clearly has no issue living for 2+ decades racking up 2-300k miles. the low rpm operation range is a contributor to its longevity, no doubt, but it certainly is not an inherently weak motor.

cruiser54

Yep. Never was a tractor/forklift motor.

diskman

My bad. Yes, spin your 4.0 regularly up to 5K. Nothing bad will ever happen. The 4.0 was designed to be a performance car motor and can be treated as such.

Carry on then.

cruiser54

I just googled "AMC forklift motor" and "AMC tractor motor"

I'm assuming that's where you got your info.

Some suggested reading:
https://www.hagerty.com/articles-vid...-six-cylinders

https://books.google.com/books?id=20...20race&f=false