Engine Noise

[jay79cj7]

I have been trying to hunt down this terrible noise for a few days now. Its coming from the engine compartment and thats all I can figure out so far. It sounds like something vibrating and hitting something else, but it seems too loud to be just a vibration. When it happens, I can easily hear it over road noise, radio, etc. Its loud enough that I thought maybe I had an exhaust leak, but I can't find one. The first time I heard it I thought the fan was hitting something.

It only happens when the engine is in gear, not in park or neutral, which makes it tougher to find on my own. It also usually only happens under a load, almost always accelerating from a stop, but sometimes just speeding up in traffic. Most of the time I won't hear it in gear at idle or cruising, but occassionally I will and its not as bad. Whenever it happens, it speeds up or slows down with RPM.

I have sat there with it in drive and the e-brake on and the wheels blocked revving the engine by hand trying to find the noise. It sounds like it is coming from the engine itself. I have secured everything I can find that might be rattling with zip ties or other things to try to pin it down through the process of elimination. I'm striking out.

So my question is: Does this sound like a symptom of some internal engine problem, or do I just have some strange vibration that is very loud and only resonates at certain engine conditions? I cannot find anything. The engine runs as good as ever.

Thanks!

ps. Its a 79 CJ-7 258 auto

[berettajeep]

double check all bolts, motor mount bolts, fan bolts,trans to block bolts.... How close is the exhaust to the frame or engine?

[jay79cj7]

It got much worse today. It honestly sounds like a jackhammer now. The speed matches the engine speed. It is constant, as if the fan was hitting something. It wasn't drowning out the radio before, but now it is. I was getting alot of looks driving home...

Everything looks tight and secure, nothing is visibly moving. The exhaust isn't touching anything except the mount points, and that's not where the problem is. It won't make the same extremely loud noise when I am at home though. I crawled underneath and there is some noise coming from the rear of the engine, the back oil pan area between the drain plug and the tranny, but its not the same noise.

The big noise still comes and goes. It was fine most of the way to work, and didn't happen at all grabbing lunch. It was awful on the way back from lunch and even worse on the way home. It hardly stopped on the way home. Now it is no longer under acceleration. Now it is most of the time, and if its not, sometimes it will even start doing it when I let off the gas.

I am very worried that I have something bad going on inside my engine here. I just got this CJ put together! Please let me know if you guys think this sounds like internal engine problems.

[mud4feet]

From your description, it doesn't sound like major engine problems, 'tho I could be totally wrong - I'm totally unschooled in mechanics, just experience and common sense. If it comes and goes, as you described, that is actually a good sign. SERIOUS engine problems will just come and STAY! Is there any smoke or oil leaks associated with this noise?? Both bad signs, of course. Internal engine problems (rods, crank, pistons, rings, valves, etc) will definitely let you know - by smoke, distinct noises (heard rods knockin' many times), oil leaks, gauges, engine locking up etc, etc. Wish you luck......hopefully someone here will offer more help.

mechanically challenged mud

[berettajeep]

was the motor every seperated from the trans recently?

Also Have you ever heard of a mechanic's stethoscope?

its is a wonderful thing. press it up to any non-moving parts to try to locate where the sound is from

you could also use a super long screwdriver

+be extremly careful of a moving engine and yourself! Cloth's, hair, limbs, etc;+

[jeepless20]

is it like a loud tick. i had a scooby that did that and it was old oil causing the valves and lifters to stick. have you changed the oil recently. whats your oil level. keep us posted on what goes on. PLEASE

[Inspector-Gadget]

I would start with checking the motor mounts, transmission mount and the transmission torque arm.

I can only guess from your description, but it appears to me that something big is moving around, but only under load.

When I had a broken motor mount, I could -- with the hood opened -- see the engine rotate way over when I started off from a dead stop.

Made big-time banging sounds and would shake the entire Jeep as the engine would rotate over and sort of oscillate until the Jeep was moving.

Just a guess, but hoping it helps.

Regards,

Gadget

[jay79cj7]

Thanks for all the replies guys. I am also thinking that its good news that it comes and goes. I took it out to run an errand tonight and I couldn't get it to make the noise. A far cry from my trip home from work when it wouldn't hardly stop.

I lifted the motor/tranny/tcase as a unit a couple months ago during a rebuild. I have never disconnected the engine from the tranny. The engine is a reman (previous owner) with 40-50k miles and the tranny works fine, so I have not messed with them. Its got a brand new set of motor mounts and a tranny mount/arm thats about a year and a half old. (That broke before, so I know what that's like and unfortunately its not it this time.) All the mounts are secure and the engine doesn't visibly sway when I rev it.

I drove by a harbor freight on the way home and tried to pick up one of those stethoscopes. They were out. The darn thing was so loud I was afraid to venture off the path to go somewhere else to get one. Its on the list of things to do this weekend.

I changed the oil maybe 2 weeks ago. Its right at the right level. I used the autozone discount brand Coastal. I have never used it before. I use name brand stuff in my XJ, but I am not as kind to the CJ. I do change it at 3k miles every time though. From what I have read, the discount oil is OK to use as long as you don't go to long with it.

As for whether it sounds like a tick... I don't think so. It sounds more like two things are crashing together. Like if you stuck something in the fan, or the sound an impact wrench makes. Very regular frequency, varies with engine speed, and VERY loud. I've never heard what bad valves/lifters sound like, but my buddy has and he said it doesn't sound like it.

As best as I can tell, the noise is coming from the back of the engine or front of the transmission. And its got me ticked off! Thanks for the help guys. Let me know if this sounds like anything familiar to you, and I will let you know what I find.

[jeepless20]

does it have a manual or automatic trans. man i wish you lived neer me i would fur sure take a look at it with ya and help ya figure it out. but i live here in oregon and thats a long drive from illinois. hope we can figure this out.

[jay79cj7]

I wish somebody would figure it out too! I just want to know I can trust it to not blow up and leave me stranded somewhere. I like it to be my daily driver in the summer.
Its a GM TH400 auto tranny.
One thing I forgot to mention, today on the way home, when it was making the noise at idle, 2 or 3 times I got it to stop making the noise by popping it into neutral or park and then back to drive. It didn't work every time though, not even half the time I tried it. I have also got it to stop, or start, by playing with the gas pedal. I can't make heads or tails of it.
Thanks again for the help.

[Sparky-Watts]

Possibly something rattling around the flywheel, like a rock kicked up from the trail or perhaps a piece of metal from somewhere within or a bolt or nut? Sounds like my old Datsun PU.....a bolt came out of the flywheel and would occasionally get jostled up into the flywheel and make a heckuva racket.....finally took off the inspection cover and dug it out with a magnetized screwdriver.

We had a saying in EMS that could be changed to fit Jeeps: "All bleeding stops eventually, whether you treat it or not."
For the Jeeps: "All (insert word here; leaks, noises, smoke, etc.) stops eventually, whether you treat it or not."

[jay79cj7]

It does have a somewhat hollow sound to it. It sounds like its coming from the bottom of the engine, but I cannot believe that a noise like that would come from a full oil or tranny pan. Maybe the flywheel area is worth a look. Thanks!

[jeepless20]

why didnt i think of that. lol

[LBR]

I would check the 3 bolts holding the torque converter to the flex plate for tightness - when they loosen up it makes a rattling, knocking sound and gets worst as they loosen more. If the are loose, don't retighten them....replace with NEW ones. LBR

[jay79cj7]

I've never been in there before... Can I get to these torque converter bolts without pulling the tranny away from the engine?

[jeepless20]

thats gunna be something your going to have to pull the tranny for. at least in my experiances. it aint hard though. one of the easier big projects id say.

[berettajeep]

Originally Posted by jay79cj7

I've never been in there before... Can I get to these torque converter bolts without pulling the tranny away from the engine?

There should be an inspection plate you can remove to gain access

4 bolts hold it in.

[LBR]

remove the inspection cover and then you can check them - you can tighten them if loose and probably be OK, but I would put new ones in ASAP LBR

[jay79cj7]

LBR- You are a genius!!!

I finally got a chance to spend some time with the CJ this weekend and sure enough, the torque converter bolts were a little loose allowing it to wiggle back and forth. Each was probably between a half and full turn from being tight. I torqued them back down easily enough. Hopefully that cures the noise. I'll have to drive it a bit first and its supposed to rain all week, so I might not know right away, but given the fact that the noise was coming from that area and that was loose, I'm pretty sure its fixed. Also, I had noticed when I put it in gear or turned the engine off, I heard kind of a clunk lately, but that showed up way before the noise ever did so I kind of got used to it and never connected the two. That clunk is not there anymore...

LBR-
Why do I need to replace the bolts ASAP? I will, they should be cheap and its an easy job, but just wondering what your experience is with this...

THANK YOU! Once again, jeepz to the rescue.

[mud4feet]

Another happy ending!!!!!!! Great to hear it, jay79cj7!!!!!! Good jog, LBR. Man, I love this place!!!!