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ATTN newer chevy owners PISTON SLAP!

B

burbBoy

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www.pistonslap.com

Sounds like GM is trying to cover it up and not do waranty work. Anyone have one with bad piston slap? Just wondering what you guys have heard on this subject.
 
This has been around for a couple of years. GM wasn't doing a good job of rectifying the situation (last I hard they said it wasn't an issue) so it made them look pretty bad at the time.
 
without even clicking your link, i can assume you are referring to the LS1 series engine.. its normal, swap to straight 50 weight oil like GM did..
 
My LS1 in the Firehawk rattles like crazy.
GM said its not a problem and should switch to Mobil-1 10-30. Still noisy. Especially when cold. They wont do anything about it.
 
Forged pistons are just that way. If you wanted them to be quiet all of the time you should have used cast pistons which can be run tighter in the bores.
 
Ive run forged pistons before. Had some noise. My LS1 has one fairly loud piston. For $36K I would have expected a quieter motor and not to find fine flakes in the oil.
 
My cousin has a newer Chev w/ a 6.0 in it.... louder than hell. The dealer where he bought it told him it was supposed to be that way... Doesn't sound to me like an engine that is supposed to have a very long lifespan.
 
Man the timing is great on this post....Me and Dad went out this morning to start the car/my Jimmy and I thought it was my truck knockin but it was his 2000 Buick w/ the 3.1 I had forgotten all about the piston slap thing. We're goin to the dealer this week to have a little chat...
 
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Forged pistons are just that way. If you wanted them to be quiet all of the time you should have used cast pistons which can be run tighter in the bores.

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Am I missing something here? I'd be relatively surprised to find forged pistons in any new factory motor. (gasoline anyways) Everything I'm aware of anymore is hypereutectic.
 
Nope. GM is basically using forged pistons across the board and that's why they have slap issues. As you probably already know, forged pistons have to run looser in the bores to allow for them to swell up. My buddy built a very mild 383 for his C10 and it sounded like a Diesel on startup. After 5-10 minutes it got quiet and ran great, had tons of torque and he pulled trailers with it all over.

EDIT:

If I were GM, I'd humor the whiners by yanking their short block, boring it .030", installing CAST pistons, and throwing it back together with a new gasket set. I'd make the customer eat half the cost.

If their complaint is that they got a more durable product that makes an unusual noise, take it away from them, charge them to do so, and they can quit their whining then. Hopefully the first punk that had that knocking Camaro or Corvette that assumed that it had forged pistons will spray enough nitrous to melt one and then feel like a complete idiot for complaining in the first place.
 
I have seen different postings on the pistons.
Sallee Chevrolet, in the advertisement for the LS-1 engine kit specs them as Cast Flattops. GM told me they were Forged and will knock. GM Performance Parts lists this p/n as factory pistons for LS-1 " 88984245 Piston Assembly "
I cant find if theyre cast or forged.

Like I said, mine knocks pretty loud with 20K on the motor. I have tried different oils and nothing. I was told by a GM tech to switch oil filters over to a NAPA Gold, Wix or Pureolator cuz they have a better anit-drain back valve that helps the noise. I will try that next.

What does concern me is I have found small chunks of metal in the oil during changes (not silvery oil, actual pieces.) GM said this could be reminates from the motor build cuz the blocks may not have been cleaned well during mfg /forums/images/graemlins/confused.gif I changed the oil at 500, 1000, 1500, 2500, and about every 3000 after that. Last change I found some pieces but didnt clean the drain pan first so cant verify it was from the oil. The pieces are not magnetic as they dont stick to the drain plug, the other fine metal does.

The only GM dealer up here is a joke and the dealer I bought it from is 3 hours away. My friend test drove a car from the local dealer and the engine blew when he was flooring it getting on the freeway. The dealer said it was his fault and wanted to charge him for it /forums/images/graemlins/eek.gif He told them to F.O. and walked away. Not sure where to go from here. Im thinking about taking out an 100K warranty that covers the full replacement of the motor. I dont care for the lawsuit, eventhough I just dont want the engine to croke before a good 100K miles.

Also, its hard to convince people the car your selling came with that piston knock and its fine so buy it and dont worry about it.
 
"Also, its hard to convince people the car your selling came with that piston knock and its fine so buy it and dont worry about it."

That is why folks like myself, (Whiners, as I believe we were called in a post above), don't appreciate dropping 30K on a new truck to have it start knocking like a diesel a year later. If it is normal then I wonder why it did not start happening until after 20,000 miles. If it was normal it seems like it should have done it the day I test drove it. I have a 2001 and I like the truck, but have absolutely no chance of ever selling it to anyone if I wanted to switch to something else as it knocks like crazy, and not just on startup, all the time hot or cold.

Russ
 
Since you have to register, I'll quote some posts from LS1.com. (all in a thread titled "This darn Piston Slap!" no less)

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Basic Q-tips and a little soap and water for those ears. These "ain't got" forged pistons.

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The pistons (I know full well they aren't forged) have short (almost non-existent) skirts to minimize friction to deliver those 30mpg trips that the LS1 is so famous for.

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Not all of the LS1's have it, only the defective ones. I'm not just talking about slight cold start noise. I'm talking about constant noise at any temp. The engines that made so many of us into GM fans didn't do this even cold. Once again, who cares about Fords or forged pistons? These are GM engines with cast pistons.

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So apparently they are/were still cast.
 
I know they were light weight design.
The slap has got louder since I bought it.
If they're cast, there should be no slap. Wonder if its due to the short skirts. Really annoying, and yes, I spent 36K on this car, last year of Trans-AM and the SLP version #139 and it didnt do it when it was new. Guess it needed a little carbon buildup to get it going.
 
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Wonder if its due to the short skirts.

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That's my take on it.
GM has been using short skirt pistons since the late '80s that I know of. 2.2L I4, 2.8/3.1 V6. I had a 3.1 with 200K on it that knocked like mad in the winter. Seen many L05 350 TBI motors in the Roadmasters repaired/replaced due to CSK, that was in the early '90s.
 
Chevy has posted a BB message saying if you take your vehicle in that has piston slap and get the carbon cleaned off the pistons with the kit that the dealers use it will quit making the noise for about 15k miles. They say the noise has to do with carbon build up on the pistons.
 
That was what they told me also when I took it in for the first time it started knocking. I have done that twice now and it did not make any difference with the noise at all. The last time they finally told me it was not carbon build up but rather a piston problem, but they were instructed by Chevrolet to not do anything about it.

Russ
 
If that piston slap website is the same one I looked over a year or two ago, people were attributing the slap to the cylinder tolerances, COUPLED with the short skirts.

Still kind of odd that some engines do it and some don't. It's pretty ridiculous of GM to say it's normal. No self respecting automaker in this day and age would make something that INCREASES the noise level to the vehicle occupants. Thats exactly backwards of the way automakers have headed in the last 100 years.

It may or may not hurt longevity (although if the noise gets worse, it's still an annoyance) but I can sure see where people come from with trying to get any resale from them. If GM actually cared about their customers (I think they stopped that in the late 70's or 80's) they would at LEAST offer to buy them back for fair market value when you wanted to get rid of it. If nothing else, apply that money as credit to a newer, non-piston slapping GM vehicle. /forums/images/graemlins/smile.gif

GM's probably walking a fine line between admitting there is an actual problem, and fixing a select number of vehicles that have noise or problems worse than all the other piston slappers. If they started fixing all of these vehicles across the board, it would be seen as an admission of a real problem, and there would shortly be a class action lawsuit, I'm sure.
 
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If I were GM, I'd humor the whiners by yanking their short block, boring it .030", installing CAST pistons, and throwing it back together with a new gasket set. I'd make the customer eat half the cost.


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See the below taken from the link i posted. Try reading before you call everyone whiners there bud. I will also point out this part of that site.

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In the case of the famous GM piston slap engine defect, the piston design with hypereutic (high silicon content aluminum alloy) pistons, reduced or eliminated piston skirts (to reduce reciprocating mass), and a higher ring pack to reduce unburned fuel mixture on the sides of the piston crown have made piston to cylinder bore fit much more critical. The amount of tolerance (variation or margin) in allowable clearance between the piston and cylinder bore to prevent audible piston slap has been reduced by a factor of at least 50%. Consistently hitting the narrower margin for piston to cylinder bore tolerance has not happened for GM during mass production. Thus, some engines have no audible piston slap and some have piston slap on only one or two cylinders.

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Too lazy to read that site, but is the piston slap affecting the knock sensor? I kind of doubt it, but then again, you can test knock sensors by hitting the manifolds with a hammer.

I'd love to see the knock counts on a non "piston slapping" motor and on that did. If the knock count is higher, performance is reduced, and I'd find it hard for GM to make up an excuse for that.
 
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