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Unread 02-14-2011, 09:52 PM   #1
MNWJ
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Question Piston Slap Repair?

99 GC 4.7L. It appears that I have piston slap. The symptom was a ticking noise that did not go away when the engine got warm.
When I press on the bottom side of my pistons with a long screwdriver, the #7 (drivers side rear) piston rocks back an forth more than the others and it makes a loud clicking sound. Most of the other piston rock much less and make much less sound.
The #7 cylinder bore has vertical scratches in it. The #1 piston rocks 2nd most and it also has vertical scrathes, but less of them.
Looks like the pistons that are in cylinders that still show nice cross hatches and appear to have no vertical scratches rock the least, which would also make sense.

The piston skirts are not broken off. There was no metal in the bottom of the pan. It has a little over 100,000 miles on it.
I haven't taken the #7 piston out yet. Looks to me like I would have to take the head off to remove the piston (crank counterweights appear to be in the way regarless of cranck angle).

Questions:

1) Is it safe to drive a 4.7L with piston slap when there is no broken skirt (at least not yet), or will something break due to the slap?

2) What is typically involved in repairing piston slap that does not result from a broken piston skirt? Is it usually a rebuild situation (boring and honing all cylinders and replacing all pistons)?

Thanks!!!

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Unread 02-15-2011, 05:00 AM   #2
CarlJH
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you will need to take the heads off first, as pistons are removed and fitted from the top, then measure the bores
to find out how worn they are. If your in luck the pistons have taken all the damage and the bores just need honing
to clean them up. If you do this make sure you cover the crank with something to keep it clean as you hone the bores.
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Unread 02-15-2011, 07:43 AM   #3
MNWJ
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It sounds like piston slap is common with these engines. Given that none of the piston skirts are broken, any estimates on how big a risk of catastrophic failure would I be taking by driving it another 1000-1500 miles without doing anything? If I do, should I go to a heavier oil or make any other changes?

One risk of course would be that the bores may wear more during that time.
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Unread 02-15-2011, 07:53 AM   #4
NorCOWJ
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i wouldnt recommend it. your just delaying the inevitable and it could cost you alot more in the long run. but if you do decide to throw it back together i dont think a heavier oil would hurt
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Unread 02-15-2011, 09:39 AM   #5
1STJEEP97TJ
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I drove mine for 15,000 miles with piston slap. It sounded horrible when started cold and once it warmed up it sounded really bad. Still very noticeable. I tried different weight oils and every additive you can think of. Nothing helped. I didnt care if it blew up as I was rebuilding another engine for it at the time. I completely rebuilt a pull out 4.7 and did the swap over a long weekend. Now it runs like a new Jeep and I should get another 100K out of the new engine. When I checked the mileage I couldnt believe I had driven it for 15K without it giving up but I did and it made it.
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Unread 02-15-2011, 10:07 AM   #6
MNWJ
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Quote:
Originally Posted by 1STJEEP97TJ View Post
I drove mine for 15,000 miles with piston slap. It sounded horrible when started cold and once it warmed up it sounded really bad. Still very noticeable. I tried different weight oils and every additive you can think of. Nothing helped. I didnt care if it blew up as I was rebuilding another engine for it at the time. I completely rebuilt a pull out 4.7 and did the swap over a long weekend. Now it runs like a new Jeep and I should get another 100K out of the new engine. When I checked the mileage I couldnt believe I had driven it for 15K without it giving up but I did and it made it.
Thanks. How much did you pay for the core? Where did you buy it? How much did the rebuild end up costing? Where did you buy the parts? What did you have done to the heads?
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Unread 02-17-2011, 04:06 PM   #7
Double E
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I think piston skirt breakage is a 4.0 issue. I've not seen yet a 4.7 fall to a piston skirt breakage.
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