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Old 08-17-2014, 12:14 AM   #1
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Piston slap common in 2003 TJ

I just recently purchased a 2003 tj with 4.0 engine and 156k miles. Manual transmission. When I bought it I didn't notice any engine noise. I have only put about 2k miles on it but recently I am hearing a tapping noise from the bottom of the engine around the rear of engine and bell housing. It is loud at startup till engine gets warm, then quiets down but does not go away. I believe it is piston slap. I was just wondering how common piston slap is in 2003 engines. Based on what I have read it is really common up to model year 2000, but can't find much info on newer models.

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Old 08-17-2014, 12:44 AM   #2
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Piston slap does not get quieter, only louder over time. Then comes loss of compression, blue smoke out the tailpipe, and finally cracked piston skirt scratched cylinder walls ending in engine failuer. You are probably hearing valve lifter noise at best or bad rod bearings at worst.

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Old 08-17-2014, 02:17 PM   #3
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Currently I do not have any blue smoke etc. the engine appears to be running fine. However since I have only owned it for a couple of month I have nothing to compare it against. If it is rod bearings will the sound get worse over time?
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Old 08-17-2014, 10:55 PM   #4
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Quote:
Originally Posted by sccacorrado View Post
Piston slap does not get quieter, only louder over time.
It quiets as the engine warms and the pistons expand and fill the bore better, no? Once you let it cool and fire it up again the process starts all over again.
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Old 08-17-2014, 11:28 PM   #5
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Ot gets louder as the skirts get hammered aginst the cylinder walls and deform into ovals instead of circles.
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Old 08-18-2014, 05:33 AM   #6
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I have the exact issue. In my searches Ive found to reoccurring suggestions. Lifter and exhaust leak. Mine goes away as it warms aswell. The colder outside usually the longer it takes to go away. On a hot day it disappears almost immediately. Interested to see what other suggestions/fixes are made here.
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Old 08-18-2014, 06:27 AM   #7
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what kind of oil are you running?

I'm thinking gummed up lifters that are taking a minute to pump up. Try flushing the system with some BG109 and then going back with a mopar or wix filter. A cheap filter can cause lifter noise too as the anti-drainback valves tend to suck on those. Use a good oil with a high zinc content(1200ppm+) because we have flat tappet cams.

What are you using to pinpoint sound?
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Old 08-18-2014, 09:20 AM   #8
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What you're describing is exactly how I would describe my piston slap before my 4.0 went in my 2000 TJ. I personally would suggest 10w-30 with a thick additive like Lucas.

I tried to extend my engine's life by flushing my engine with some ATF, then seafoam, and then using 5w-30 in it. However, cleaning out all that engine sludge and putting a lighter oil it seemed to only worsen the condition as I broke a piston skirt only a few days later.
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Old 08-24-2014, 02:25 PM   #9
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I am running 10w 30 oil and using mopar filter. Just changed a couple 100 miles ago since I was not sure what oil the dealer put in it and they had put an autolite filter on it. Hope that would be the easy fix but no such luck . I have tried no additives yet.
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Old 08-24-2014, 07:11 PM   #10
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So I finally had a chance to pull the spark plugs. All of them looked normal except they were way past due to be changed except for cyl 6. Cylinder #6 had excessive carbon build up. See Attached photo. What are your thoughts on what caused this and what should I do next.
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Old 08-24-2014, 08:21 PM   #11
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Not an expert and haven't seen your other plugs but to me that's not a carbon buildup. I would say that's more of a soot or ash buildup. I would change plugs, maybe change oil as well and see what that does.
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Old 08-24-2014, 08:29 PM   #12
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Lifter noise I have same noise.i use Lucas oil additive helps a lot . I have 150k. Don't worry. It's a jeep thing.👍
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Old 08-24-2014, 11:44 PM   #13
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Looks like oil build up to me. Compression check and/or leak down test that cylinder and see if it is lower than the rest. You may want to do this cold since that is when you're hearing the noise and then again warm
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Old 09-07-2014, 07:37 PM   #14
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Ok so finally had a chance to compression test the cylinders. Here is what I found
Cold Dry test - cyl 1 170 psi, cyl 2 170 psi, cyl 3 165 psi, cyl 4 166 psi, cyl 5 170 psi, cyl 6 140 psi.
Cold wet test - cyl 1 175 psi, cyl 2 190 psi, cyl 3 185 psi, cyl 4 175 psi, cyl 5 185 psi, cyl 6 155 psi.
Warm dry test - cyl 1 162 psi, cyl 2 165 psi, cyl 3 160 psi, cyl 4 163 psi, cyl 5 166 psi, cyl 6 145 psi.

Obviously I have some issues with cyl 6. Anybody have any thoughts based on these findings. What should be next course of action? Also if it is indeed piston slap, how much longer can I expect to run the engine before overhaul with these readings.
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Old 09-08-2014, 12:21 PM   #15
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Bump
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Old 09-08-2014, 06:52 PM   #16
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Do a leak down test to determine where you're losing compression.
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Old 09-08-2014, 06:57 PM   #17
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Because the compression raised from 140 to 155 that would point to an issue with the rings sealing properly, if it was a valve issue the compression wouldn't go up for the wet test. If you would like to verify you could do a leak down test and check for pressure loss into the crankcase., or check for excessive pressure out of the dipstick tube or oil cap while the engine is running.

Your guess is as good as mine as to how long it will last if you drive it like this. Could be a long time before it gets worse and all you have to do is keep changing spark plugs or it could get worse and worse over the next weeks/months until you need to do something about it.

Can't tell if it is repairable or not until you pull the head and inspect if the cylinder wall is damaged, the longer you drive it the worse the damage will be.
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Old 09-08-2014, 09:12 PM   #18
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Maybe but depends how much oil he added because as a non compressible liquid it raises the effective compression ratio

Bore and stroke remain the same but adding oil reduces the total volume without changing displacement and just like a domed piston it increases effective compression ratio

Each piston displaces roughly 667 cc so if 9:1 cr around 750cc to 750- 667 is about 83cc final volume
Note 83 times 9 is 747

Adding 10cc of oil will rise compression test result on an engine with properly sealing rings

Now you taking 10 cc off each volume you go from 740 to 73 with an effective compression ratio of just over 10 by just adding 10cc oil

So with 10cc oil I increased effective compression ratio by 10%
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Old 09-08-2014, 09:44 PM   #19
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Oh I'm certain adding oil will raise compression in good cylinder also, as demonstrated by the above numbers bubba A has posted. They rose from 5-20psi. But take into consideration the suspected piston slap noise that the engine makes, the low compression in cylinder #6 compared to all of the other cylinders, and the large amount of oil build up on the #6 plug.

Some more scratch pad theory: A valve sealing issue would not change with the wet compression test nor would it create oil deposits on the spark plug. Valve seals leaking could cause oil deposits but would not lower compression. A bent rod could lower compression but that alone would not explain the oil build up. I'm out of ideas.

I reserve the right to being wrong, but all signs are pointing towards a piston ring sealing issue from my computer screen. I would certainly be doing a leak down test at this point were it in my shop.
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Old 09-14-2014, 02:27 PM   #20
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Ok so have not had a chance to do the leak down test yet due to time and not being able to find a loaner tester. I have been doing some research on doing the test so I have some questions. What is the easiest way to get the pistons to top dead center, and also what is the best way to confirm it is at top dead center? My 2003 engine does not have a distributer but a cam position sensor. Also a little leery of sticking something down in the cylinder head to see when it gets to top dead center since the spark plug is on the side.
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Old 09-14-2014, 04:43 PM   #21
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Be leary, but do it anyway. Pull the plug and get a chop stick or something similar in size and length that won't fall all the way in the cylinder when it is down and put it in there. Just be sure to hold it in the straight up position when you are turning over the engine by hand with a socket and ratchet on the crank pulley bolt and don't let the chop stick fall to the side and get stuck between the piston coming up and the threads for the spark plugs.

As for making sure it is TDC of the compression stroke once you get the leak tester you screw in the adapter that goes into the spark plug hole (it's just like the hose for a compression tester only with out the one way schrader valve in it) and put your thumb over the hole on the other end that goes to the leak down tester. When you turn the engine over by hand on the compression stroke at TDC you will feel the pressure trying to escape from under your thumb. Alternatively you could shove a rag in the spark plug hole and it will 'poof' out on the compression stroke.

In case you didn't know you will need an air compressor to do the leak down test.
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Old 09-14-2014, 05:15 PM   #22
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I have nearly 300,000 miles, if I run a 10w/30 I will get a lifter noise after first start.

I changed to 20W/50 Castrol racing oil, no noise, and I am no longer using oil.

To me 10W/30 is too light of oil on an engine with high miles. Change your oil to something heavier like I did. Your compression in #6 is acceptable, may come up with heavier oil.

Then drive your jeep, they are more fun when you stop worrying about them.

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