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  #1  
Old March 10th, 2009, 10:14
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xjh3 xjh3 is offline
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Piston Slap?

Kind of a lame vid. But what does that knocking sound like? Did I crack ANOTHER #5 piston? I sure hope not...


Last edited by xjh3; March 10th, 2009 at 10:46.
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  #2  
Old March 10th, 2009, 14:04
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Re: Piston Slap?

That sounds worse than piston slap. If you cracked another piston on the same cylinder, you probably have a damaged rod. Could be valve train related too. Pull the rocker cover off and see if you can pinpoint it to a single rocker.
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Old March 10th, 2009, 14:46
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Re: Piston Slap?

Quote:
Originally Posted by Talyn View Post
If you cracked another piston on the same cylinder, you probably have a damaged rod.
Not entirely sure what you mean, but it's an entirely different motor from the first one. I've heard the NVH stuff they did causes the number 5 piston to crack.
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Old March 10th, 2009, 15:24
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Re: Piston Slap?

Oh.. new block. I thought you cracked a piston then replaced only the piston in the same block. Whats the story on this block then?
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Old March 10th, 2009, 17:08
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Re: Piston Slap?

Jeep is a 97. Cracked the #5 piston in the original motor at about 135k. New motor went in; 98 from the junkyard with 88k. Got about 168k on the clock now (about 121k on new motor) and this happening.

Also, I can only hear it when it is relatively warm. It seems like the warmer it is, the more noticeable it is. In the video I was over 210 on the temp gauge and that is the loudest its ever been.
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Old March 10th, 2009, 17:12
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Re: Piston Slap?

sounds like lifters........
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Old March 10th, 2009, 17:39
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Re: Piston Slap?

Quote:
Originally Posted by xjh3 View Post
Also, I can only hear it when it is relatively warm. It seems like the warmer it is, the more noticeable it is. In the video I was over 210 on the temp gauge and that is the loudest its ever been.
Hold on for a second! I've had bad "lifter noise" for the last two years that was driving me nuts. It was intermittent but always got worse and worse the hotter it got. It was definately louder than any lifter I had heard and I wondered if it was worn wrist pins or rod knock. I finally came across a post on where someone talked about excessive carbon buildup on valves or piston tops causing some horrible noises that sounded like a bad lifter or rod knock. I finally fixed the problem with two cans of Mopar Combustion Chamber Cleaner hot-soaked through the throttle body on seperate days. No more "clatter/knock" that I've been living with for the last 2 years (yes, 2 years of listening to the damn thing tick away like a bomb).
Heres a quote from an external site that also helped me out. This guy recommends using ATF down the carb throat (old mechanics trick), but I just played it safe and used MCCC:

Quote:
Sometimes, a carbon knock will sound just like a rod knock. It will sound like it's ready to throw a rod. I can't even count how many times I have fixed this with about half a bottle of transmission fluid.

Start the engine; remove the air cleaner; rev the engine up to about 2500 rpm and start slowly pouring the transmission fluid down the carburetor throat. Don't let the engine die. (if it does, you might have to pull & clean the plugs, then resume the procedure). Pour the XMF fast enough to lug the engine down.

Voila -- no more knock. Gone for good. This apparently happens when a little piece of carbon breaks off inside one of the cylinders or something..... but I've fixed 'em numerous times this way when I thought I had lost a rod bearing.
This was the post on that got me started:
Quote:
Originally Posted by 88XJSport View Post
UPDATE:

Turns out that it was not a cracked manifold problem, or anything that an oil additive used in the oil could fix.

As I was growing more pissed off at my 4.0 as the days went on, (been ticking since Oct 07) and after a straight year of MMO, type F ATF, cans of seafoam in the oil, (sometimes as low as 3 qts of normal oil, and a cluster**** of additives and changing my manifold... nothing was close to improving the issue.

Last week I bought another can of seafoam, and instead of throwing the whole can in the oil, I sucked the whole thing into the intake. Took about a minute to use the whole can. I let it sit a half hour. When I fired it up, it didnt tick at first, but when I went to rev the engine to start clearing the smoke, it went "tap-tap-ta" and it was gone. As soon as the smoke cleared, I drove around for a half hour in silence. I can't tell you how many times at red lights I had to look at my tach to see if the engine was still on.

It has been 2 weeks, and I have not had my engine tap since I used one can of foam in the intake.

All I hear at idle now is my injectors and my noisy HB.

Question: What was ticking that mimmicked a lifter tap? Im guessing carbon buildup on valves...anyone?
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Old March 11th, 2009, 07:35
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Re: Piston Slap?

I was chasing a problem a while ago in my 4.0L. Non existent when cold and got louder when warm. Replaced the lifters twice. Installed a new cam with no relief. Finally #5 piston let go and took up residence in the oil pan. I don't contribute min to a problem with the NVH block, but hydro locking my engine while off road.

I think your best bet is to get the engine warmed up, shut it down then pull the valve cover and see if you can find the source of the sound and go from there.
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Old March 11th, 2009, 15:35
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Re: Piston Slap?

This would make a lot of sense. I just started driving my Jeep to and from class everyday in the cold weather instead of walking. It's probably a 2 minute drive at most. Doesn't this kind of driving increase carbon build up?
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Old March 11th, 2009, 18:49
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Re: Piston Slap?

It can. Do a seafoam treatment in the intake and go from there.
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  #11  
Old March 11th, 2009, 22:30
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Re: Piston Slap?

Sounds like a plan. Thanks
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  #12  
Old March 16th, 2009, 20:09
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Re: Piston Slap?

what was the outcome of this? I am chasing a similar problem on my 90.
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Old March 17th, 2009, 08:38
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Re: Piston Slap?

Quote:
Originally Posted by Red90Laredo View Post
what was the outcome of this? I am chasing a similar problem on my 90.
try the MCCC. I thought my engine was toast until I used the 2 cans in there a few weeks ago. I've put on over 2k kilometres in the last week since using the MCCC and havn't heard a peep out of the engine, runs like new.
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  #14  
Old March 17th, 2009, 15:41
stephenspann27 stephenspann27 is offline
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Re: Piston Slap?

Sounds exactly like my bad alternator.. I thought it was piston slap.. the valve clatter.. then was so sure it was timing chain slap.. I used a stethoscope to narrow it down to the alternator.
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Old March 17th, 2009, 19:45
stephenspann27 stephenspann27 is offline
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Re: Piston Slap?

ppl will tell you to check your flex plate bolts as well.
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