Need Some Advice on a Engine Knock

[wad_e]

hey guys, i just bought my 3rd xj, it has a knock in the engine. i figured maybe a broken rocker arm, or lifter, or something in the top end. after having two mechanics look at it, they both seem to think its in the bottom end. one said a piston, the other said sounded more like a rod to him. its a 2001, 4.0, 4wd, auto with 140k miles, what would you guys do? ive checked a few diy junk yards and i can probably get another engine for around 200 bucks. should i pull my engine, tear it down, and rebuild it, or should i go pull one from another jeep and take a chance on a $200 junkyard motor that comes with a 30 day warranty? im not a master mechanic but im pretty good with my hands, and have access to the tools one would need to get my jeep back on the road.

[bigjim350]

First thing I would check is the bolts holding the torque converter to the flywheel. Also check for cracks in the flywheel. Its a pretty common XJ problem, mine did it and sounded like a rod knock. If thats good, I would just use a JY motor and rebuild your old one over time as a backup motor.

[BigJeepBigJeep]

Is the "knocking sound" a low dull thump or more of a higher tap?

To designate the cylinder with the problem, with the motor off, pull a spark plug wire then start the engine. Do that to each wire individually until the problem lessens quite a bit/goes away.

Or you can do a leakdown test. :D

[wad_e]

it is a higher tapping sound, thats why i thought top end. how do i do the spark plug wire check when i have coil packs? and to the torque converter/flywheel bolts, will it do it even when im not moving? i would love for it to only be something like that!

[Mudderoy]

it is a higher tapping sound, thats why i thought top end. how do i do the spark plug wire check when i have coil packs? and to the torque converter/flywheel bolts, will it do it even when im not moving? i would love for it to only be something like that!

Remember if the engine is running the torque converter is, so yes moving or still if the engine is on you'll here that noise.

I got under mine and traced the noise to the back of the engine, I thought it was a rod cap, or the rear main. Then I checked the torque converter bolts, BINGO!

If I can remember correctly the noise gets louder after your rev then engine and it is returning to idle, then you get a constant knock. Those bolts were really LOOSE!

I was so happy I just tightened them back, you remember to put locktite on yours, ok! :D

[wad_e]

duh right sorry for the noob question. thank you guys so much im gonna check those bolts out when i get home from work today. this the most helpful forum ive ever been apart of.

[default83]

i know its probably a longshot, but my jeep sounds like its knocking and its just the exhaust rubbing agaisnt the frame at idle.

but if you are to pull the engine, you probably better off just getting a junkyard motor, then you will have a back up engine for parts.

[steph74]

let's talk about that torque converter bolts... on the flywheel ?

Do I have that on my 89 manual shift ? because I have a slight knock at idle when warm engine and the only way I got rid of it was heavier oil weight and increase idle speed a bit ...

(shamelessly taking over your thread sorry)

[4.3LXJ]

let's talk about that torque converter bolts... on the flywheel ?

Do I have that on my 89 manual shift ? because I have a slight knock at idle when warm engine and the only way I got rid of it was heavier oil weight and increase idle speed a bit ...

(shamelessly taking over your thread sorry)

No Steph, you don't. This is for when you have an auto tranny. They have a flex plate that has the torque converter bolted to it with some really short bolts that can work loose after a couple of hundred thousand miles. You have a heavy fly wheel that is bolted down securely to the end of the crank shaft. There are some bolts that hold the pressure plate on the flywheel, but if they get loose, you will loose the function of your clutch and even then they likely would not rattle.

[Mudderoy]

i know its probably a longshot, but my jeep sounds like its knocking and its just the exhaust rubbing agaisnt the frame at idle.

but if you are to pull the engine, you probably better off just getting a junkyard motor, then you will have a back up engine for parts.

Mine used to do that too. I had the new muffler installed and the guy noticed that my pipe was really close to my cross member so he heated up the hanger and bent it up and away. It was really bad when it was cold out.

[Mudderoy]

duh right sorry for the noob question. thank you guys so much im gonna check those bolts out when i get home from work today. this the most helpful forum ive ever been apart of.

This site was started for noobs. :D None of us knew this stuff when we started.

Noobs should feel safe to ask their questions here, bullies, not so much. :smiley-laughing021:

[uberxj92]

i am a second generation grease monkey & fabber. when my 93 xj took a drink of pond water & broke the #6 rod & destroyed the block & pan, i went this route... rebuilds are always a little more money but way worth it. you get a new motor to your specs. i put punched it .030 over & dropped in a 4.2 crank & 4.2 rods. a 3 angle valve job & presto you have a 4.6(ish) stroker . also, check titan motors they build those too & warranty them.

the stroker motor gave me the extra umph for the 35's & about 1.3 mpg more than stock 4.0.

[Mudderoy]

i am a second generation grease monkey & fabber. when my 93 xj took a drink of pond water & broke the #6 rod & destroyed the block & pan, i went this route... rebuilds are always a little more money but way worth it. you get a new motor to your specs. i put punched it .030 over & dropped in a 4.2 crank & 4.2 rods. a 3 angle valve job & presto you have a 4.6(ish) stroker . also, check titan motors they build those too & warranty them.

the stroker motor gave me the extra umph for the 35's & about 1.3 mpg more than stock 4.0.

I look at a junk yard engine as an unknown. Double the work if it is crap. I'd much rather rebuild and know what I have.

[wad_e]

well, i couldnt get lucky enough for it to be my torque converter bolts, so i have started pulling my motor. i guess i'll pick one up from the junk yard for now, just to get me going. meanwhile im going to build a stroker out of the one thats coming out. thanks for all the help!

[Punisher]

when you pull your motor you may want to look at the flywheel to make sure its not crack... i had that problem on my 1991 and that was the knock so I replaced it andit was good to go.. til it happened again where the motor wouldnt start and I thought it was the motor until i got half way rebulding it and saw that the new flywheel i put it from before cracked too in the same place.... so be you go getting another motor and tearing this one apart take a good look at the flywheel in the center area where it bolts to the crank... you may want to take it off the motor for inspection... heres what it should look like.. "This is where both mine cracked"

http://i860.photobucket.com/albums/ab165/punisher1_972/IMG_0675.jpg

http://i860.photobucket.com/albums/ab165/punisher1_972/IMG_0676.jpg

[wad_e]

Well I got my motor out, and the #6 piston skirt was laying in the oil pan. I don't think the cylinder wall is hurt but I guess I will find out. Im gonna do a rebuild and was wondering who to buy a kit from. I found one for a reasonable price from MABBCO, anybody had any experience with these guys?

[wad_e]

They are out of Tyler, Texas. Anybody heard of em? Or does anyone know where to buy a kit from?

[wad_e]

i wanna let anyone looking for an engine rebuild kit know that mabbco is probably the cheapest, however northern auto parts has better quality parts in there engine kits. therefore i went with northern auto. my kit should be here thursday of next week, i'll keep everyone posted on the rebuild.