Another 4.0 piston skirt thread - Repair or replace - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Wrangler Forums > TJ Wrangler Technical Forum > Another 4.0 piston skirt thread - Repair or replace

Dan's Old as Dirt Birthday Sale!Premium LED Lighting by VISION X, Proudly sold at ROCKRIDGGEARSHADE Pocket Tops in stock and available at ROCKRIDGE

Reply
Unread 06-29-2010, 09:28 PM   #1
halo26
Registered User
2000 TJ Wrangler 
 
Join Date: Jun 2010
Location: NH
Posts: 52
Another 4.0 piston skirt thread - Repair or replace

Hey Guys,
Long time reader/fan, first time poster...

A little background on my jeep... its a 2000 TJ Sport with the 4.0 and 'supposedly' is about to join the 200k club. I say supposedly because it runs like a champ, has 0 rust, and (from looking at the CarFax) the first owner put 120k on it in 1 year (we have a few theories, some more plausible than others).

Anywho...
My 4.0 just started making a noise I'm pretty sure is a broken piston skirt. I have no loss of power, etc... just the typical knocking (loud when cold, then much softer when warmed up).
My question is, (after I make certain it is a piston skirt) should I tare down the engine and replace the piston (hoping there's no damage done to the wall) or should I just keep wheeling it until I have an issue (more than just a noise) then replace the whole engine?


I'm very much a newbie, so if this has been hashed 100x or is common sense, please forgive my ignorance!

Any help would be GREATLY appreciated!

Thanks for reading!

halo26 is offline   Reply With Quote
Unread 06-29-2010, 09:54 PM   #2
Nonya
Web Wheeler
1998 TJ Wrangler 
 
Join Date: Feb 2007
Location: Nice
Posts: 1,653
1st thing you wanna do is short each spark plug while it is running and see if the noise changes. Should at least narrow it down to which cylinder is bad.

Keep in mind a chunk of carbon can make alot of noise too. If it was driven slow it maybe carboned up badly at high miles, it can break off and make lots of noise.
Nonya is offline   Reply With Quote
Unread 06-29-2010, 11:43 PM   #3
LRod
Registered User
2006 TJ Wrangler 
 
Join Date: May 2009
Location: S. Cal, CA
Posts: 211
I had a 91 that knocked when cold and my 06 has a slight occassional knock. As I recall there was a class action lawsuit regarding a problem with the 4.0 #6 cylinder being out of round or some such thing, do a search on 4.0 knock or something. As it turned out I think they found Chrysler in the wrong but didn't do anything to help the consumer and your stuck with it.
LRod is offline   Reply With Quote
Unread 06-30-2010, 04:04 AM   #4
halo26
Registered User
2000 TJ Wrangler 
 
Join Date: Jun 2010
Location: NH
Posts: 52
Thanks for the responses, guys!

Quote:
Originally Posted by Nonya View Post
1st thing you wanna do is short each spark plug while it is running and see if the noise changes. Should at least narrow it down to which cylinder is bad.
Nonya - Is there a way to do this with a coil rail? I've read you can put the injector wire (probably saying that wrong ) and accomplish the same thing... not sure though.



Quote:
Originally Posted by LRod View Post
As I recall there was a class action lawsuit regarding a problem with the 4.0 #6 cylinder being out of round or some such thing, do a search on 4.0 knock or something.
LRod - Exactly... a mechanic friend of the family was telling us he replaced 2 #6 cylinders last month. I've been doing some reading on the knock for the past few weeks and playing 'match the sound' . Was your knock just piston slap or did you have to do something to correct it?


Thanks again for he help... I need all of it I can get!
halo26 is offline   Reply With Quote
Unread 06-30-2010, 07:37 AM   #5
Nonya
Web Wheeler
1998 TJ Wrangler 
 
Join Date: Feb 2007
Location: Nice
Posts: 1,653
Pulling each injector connection should unload the cylinders enough to find the noise but i'm afraid you really don't know what you are listening for. A broken piston skirt should be so loud its obvious. If you want to post up a sound sample it would help to ident what you are hearing. A good JEEP dealer service dept might just give you a quick listen for free, ask the service manager for a opinion.

Last edited by Nonya; 06-30-2010 at 07:56 AM..
Nonya is offline   Reply With Quote
Unread 06-30-2010, 10:48 AM   #6
Dryseals
Registered User
2000 TJ Wrangler 
 
Join Date: Apr 2010
Location: Texas
Posts: 628
Knock when cold and then quieting as it warms is usually a rod knock. Piston skirts make more of a slap sound and if they are slapping around will wear into the cylinder wall quickly. If your in the 200K club or nearing, I would suspect a rod bearing. You can continue to drive for a long time on a bad rod bearing if needed. But I would start looking at a rebuild.

No sense in just attacking one piece, freshen it up for another 200K.
Dryseals is offline   Reply With Quote
Unread 06-30-2010, 10:58 AM   #7
TJ311
Registered User
2001 TJ Wrangler 
 
Join Date: Mar 2009
Location: Fort Collins
Posts: 378
Could honestly just be normal wear too. The 4.0 is loud in stock form, but throw a couple hundred thousand miles at it and could be louder. If it's not too loud, I'd say it's just piston slap from wear. As the piston heats up, it expands enough to quiet down. Not sure it's the case in this engine but on some of the engines I've built in the past (with forged pistons) they're a little noisy when cold then quiet down after warm-up.

What weight oil are you running in it?
TJ311 is offline   Reply With Quote
Unread 06-30-2010, 11:01 AM   #8
Nonya
Web Wheeler
1998 TJ Wrangler 
 
Join Date: Feb 2007
Location: Nice
Posts: 1,653
Quote:
Originally Posted by Dryseals View Post
Knock when cold and then quieting as it warms is usually a rod knock. Piston skirts make more of a slap sound and if they are slapping around will wear into the cylinder wall quickly. If your in the 200K club or nearing, I would suspect a rod bearing. You can continue to drive for a long time on a bad rod bearing if needed. But I would start looking at a rebuild.

No sense in just attacking one piece, freshen it up for another 200K.
BS this guy is wrong...rod bearing noise gets ALOT LOUDER hot
Nonya is offline   Reply With Quote
Unread 06-30-2010, 11:06 AM   #9
TJ311
Registered User
2001 TJ Wrangler 
 
Join Date: Mar 2009
Location: Fort Collins
Posts: 378
Quote:
Originally Posted by Nonya View Post
BS this guy is wrong...rod bearing noise gets ALOT LOUDER hot
I was thinking the same thing. I don't think I've personally ever heard a rod knock get quieter as it warmed up.
TJ311 is offline   Reply With Quote
Unread 06-30-2010, 12:30 PM   #10
Nonya
Web Wheeler
1998 TJ Wrangler 
 
Join Date: Feb 2007
Location: Nice
Posts: 1,653
Hes just posting up garbage to aggravate, I have no idea why the owners of this forum put up with it. Him and a few others feel the need to post in every thread i post....weird i know....
Nonya is offline   Reply With Quote
Unread 06-30-2010, 06:03 PM   #11
Knuckelhead
AFSOC Retired
 
Knuckelhead's Avatar
2000 TJ Wrangler 
 
Join Date: Aug 2005
Location: Colorado
Posts: 14,982
Quote:
Originally Posted by halo26 View Post

Anywho...
My 4.0 just started making a noise I'm pretty sure is a broken piston skirt. I have no loss of power, etc... just the typical knocking (loud when cold, then much softer when warmed up).
My question is, (after I make certain it is a piston skirt) should I tare down the engine and replace the piston (hoping there's no damage done to the wall) or should I just keep wheeling it until I have an issue (more than just a noise) then replace the whole engine?


I'm very much a newbie, so if this has been hashed 100x or is common sense, please forgive my ignorance!

Any help would be GREATLY appreciated!

Thanks for reading!
Have you changed the oil and looked for aluminum debris in the drained oil? You could also cut the oil filter open and check there.

I bought a tool for cutting my filters open to inspect them.
Like this:
HAND CRANK OIL FILTER CUTTING TOOL from Aircraft Spruce
The one I bought cost around $60...
__________________
TSB Information: http://www.automd.com/tsb/jeep_m/wrangler_mm/2000_y/
Knuckelhead is offline   Reply With Quote
Unread 06-30-2010, 08:48 PM   #12
Nonya
Web Wheeler
1998 TJ Wrangler 
 
Join Date: Feb 2007
Location: Nice
Posts: 1,653
heres the other guy that feels the need to post up when ever i post.
Nonya is offline   Reply With Quote
Unread 06-30-2010, 08:52 PM   #13
Nonya
Web Wheeler
1998 TJ Wrangler 
 
Join Date: Feb 2007
Location: Nice
Posts: 1,653
Quote:
Originally Posted by Knuckelhead View Post
Have you changed the oil and looked for aluminum debris in the drained oil? You could also cut the oil filter open and check there.

I bought a tool for cutting my filters open to inspect them.
Like this:
HAND CRANK OIL FILTER CUTTING TOOL from Aircraft Spruce
The one I bought cost around $60...
Useless info........take it to a good mechanic and have the noise diagnosed.
Nonya is offline   Reply With Quote
Unread 06-30-2010, 09:06 PM   #14
halo26
Registered User
2000 TJ Wrangler 
 
Join Date: Jun 2010
Location: NH
Posts: 52
Hey Guys,
Thanks again for the responses!

Quote:
Originally Posted by Nonya View Post
i'm afraid you really don't know what you are listening for. A broken piston skirt should be so loud its obvious. If you want to post up a sound sample it would help to ident what you are hearing..
I'm beginning to think you're right . Posting a sounds is a really good idea, Iíll go grab my camera here and try to get one up (1 when cold, 1 when warm).


Piston slap is my other thought as well.. and the more I listen to you guys, the more possible it sounds.


Right now I have diesel oil & 1 qt of MMO in it... I read on a few threads that people with certain knocks found some relief running it. For me, itís done nothing (possibly even made it a tiny bit worse). I plan on draining it soon (has about 100mi on it) and replacing it with a high mileage oil in the recommended weight.

I'm currently not blowing any oil into the intake and my oil pressure (I think) is ok. It usually sits, after warm, a little above 20 (I think its 20, its the first line after 0.. not near the jeep right now).


Sorry for the delay in posts... GF got into a fender bender today, so I've been pulling the bumper-cover / bumper off her car all night


Thanks guys!!
halo26 is offline   Reply With Quote
Unread 06-30-2010, 09:07 PM   #15
Nonya
Web Wheeler
1998 TJ Wrangler 
 
Join Date: Feb 2007
Location: Nice
Posts: 1,653
If you had some idea what the noise was and were sure its from the lower end you could easily pull the oil pan and inspect the pistons. Easy job but i would get a good opinion 1st. A good mechanic should easily be able diagnose the noise in 1 hrs time. Shorting each plug or pulling each injector plug should tell you which cylinder it is and even if its a bearing or piston if the mechanic is good. With the oil pan off you inspect everything BUT you need pro help IMO. Too much basic knowledge is needed to check bearings etc to actually explain how to do it.
Nonya is offline   Reply With Quote
Reply

Tags
piston skirt , tj , wrangler , repair , replace
Thread Tools


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.