4.0 L HO Valvetrain Noises

My lifters/valvetrain makes a lot of racket. I have never abused this engine and don't know that I have ever heard a similar sound coming from any other engine. I remember one fellow here saying that his 4 liter sounded like it had marbles rolling around in the top end, but the critter still ran for over 200k without missing a beat! Is this something that is typical for this design? I had a slight lifter tap but after I changed over to Castrol Syntec that went away. I am just wondering if there is something like a valve adjustment that can be done to quiten the beast down. I don't think so, but it never hurts to ask.

I dream of building up a killer stroker mill with roller rockers.....AHHHH ..... has anyone here ever gotten that kind of project to completion? I would sure like to see a tech article on that one.... Thanks..... Bill-93XJ

Hi Bill,

My 4.0 has nearly 200,000 miles and I have just a touch of valvetrain chatterm, which I consider normal for the mileage. I might be wrong but I don't believe the 4.0 has adjustable valves. However, for a definitive answer to this as well as other questions, the following link will take you to the entire Chilton 84-98 Jeep manual. The FSM can't be beat, but Chilton's is a good place to start.

http://www.cybrrpartspro.com/Chilton Manuals/9107m/9107.HTML

Erik
88 Comanche

Hydraulic lifters. I know they are adjustable on Chevy V-8s, but not on the 4.0L. They are torqued down and that's that.

This doesn't mean that you don't have a bad lifter. It can happen, especially if you bought it used and the previous owner wasn't good about oil changes. If you have any other XJs among your friends and neighbors, get with them and take a listen for comparison. If yours is much worse, consider pulling the valve cover to see if it's a general noise or if you can isolate it to one cylinder or one valve.

I don't even like to mention this, but it's remotely possible it's a bent valve. The 4.0L generally can't rev high enough to make that happen, but some people have an innate ability to screw up engines.

Are you sure it's the valve train and not piston slap? That's pretty common too.

I second the comment about piston slap. I have NEVER heard an engine with more piston slap (normal) than a 4.0 AMC six cylinder engine. It's atrocious. But then again, it will make that racket for 100's of thousands of miles with no harm.

Coming from Chevy and Ford in-line sixes, this 4.0 has taken some getting used to, but it seems sturdy enough.

Are you SURE it's actual valve train clatter?

Mine rattles worse than any I have heard. I have checked the push rods to see if one was loose, thinking of a bad lifter or two, but all were tight, checked while rolling the engine over. Still does not mean I don't have a couple bad ones, but at lease they are not completely collapsed. It sounds like a can full of marbles rattling around. If you find what's wrong, let me know. I suspect lifters though.

I plan on building a stroker, so I am not too concerned, as long as it lasts that long.

My 93 is plenty noisy too. It seems that the 93s were particularly prone to that joyous piston-slap sound. I've had more than a handful of people ask me if mine was a diesel! No kidding.
Fear not, though. It's completely normal - I have 235k on mine so far and it just keeps on going.
If you're getting actual valvetrain noise especially on startup, I have a suggestion that will sound strange. Try using a better oil filter. For a while I was getting some pretty bad chatter on startup about one time in three. This noise would either "resolve" itself in 10 to 15 seconds, or I'd shut down and restart at which point it would not reappear. After reading an article comparing oil filters (it's been linked here before but I no longer have it - anyone?) it occurred to me that I could be experiencing a dry valvetrain at startup due to a cheap oil filter allowing the oil to drain out of the engine and back into the pan. I switched to using Mobil1 oil filters exclusively and have never had that chatter on startup since.
Just my experience, YMMV.

Here's the link to the oil filter comparison. Interesting reading, especially if a person uses Fram filters!

http://minimopar.net/oilfilterstudy.html

Erik
88 Comanche

I've owned my 91XJ since new.... and about 2-3 years later it started making what sounded like loose lifter or diesel noise at idle---the oil has been changed every 3K miles.

I've also had friends ask me if it had a bad lifter........ and that it sounded like a diesel. I tried finding the source for years.... kept thinking it was the valvetrain.... the only problem is they have hydraulic lifters----I just learned to ignore it.

Then, a couple years ago my idler pulley started making random squeeling noises at certain RPM's. I ignored that too until it got real bad..... I had the dealer change the idler pulley and also changed the serpentine while they were at it.... guess what?? .... that damned lifter noise went away.

Before ripping into the head and messing with the valvetrain I would change that idler first.... its cheap and if its never been changed, more than likely it will need to be changed soon anyway.

Good luck!
Bob

I had a similar problem with the engine sounding like a diesel.

I did the stethoscope thing to try and isolate the noise, but couldn't track it down. I noticed that the sound was coming from the driver's side of the engine and further attempted to isolate it.

After about another 3000 miles, the noise got worse. It ended up being the power steering pump. I didn't have any problems with the steering but, wow it was loud.

I replaced the pump, put on a new belt and the engine is very quiet now.

The moral of the story, I guess, would be to eliminate other problems before you go yoinkin' apart the engine.

Cheers.