Exactly what the problem is .. Here is a description of piston slap from the piston slap website (www.pistonslap.com)

Description...

Piston slap is nothing new to piston driven internal combustion engines and compressors. It is the secondary (sideways or perpendicular) movement of a piston against the side of a cylinder bore where the primary movement of a piston is intended to be parallel (up and down) to the cylinder bore. All piston driven internal combustion engines and compressors have a certain amount of piston slap.


Excessive piston slap occurs when the clearance between the piston and the cylinder bore is too great. The piston to cylinder bore clearance becomes too great either through wear, mismatched pistons and cylinder bores at manufacturing or, a combination of both. The audible noise associated with excessive piston slap is due to the perpendicular impact of the piston against the wall of the cylinder bore. Audible piston slap is typically loudest when the engine is first started up. The pistons then expand with heat reducing the piston to cylinder bore clearance thus, reducing the perpendicular impact of the piston against the cylinder wall and its resulting noise.


In the case of the famous GM piston slap engine defect, the piston design with hypereutectic (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. What might have looked really good in testing of hand built engines in the lab hasn't transferred to the production line of this corporate giant.
Make no mistake about it, while a lot of these engines don't appear to be driving rods through the blocks, the ones with louder and longer duration piston slap will wear out before the ones that are basically quiet. The perpendicular heavy impact of the piston against the cylinder wall over time will not come without a price. This is also why GM has released a recent TSB saying that opening 4 quarts of oil to add to your crankcase between a 7,500 mile recommended oil change interval (1 qt per 2K miles on an engine with 36K miles or less is "NORMAL". After 36K miles, all bets are off (there is no abnormal oil usage rate). This is why the now common offer of an engine component letter extending your warranty to 5 years or 100K miles is basically worthless. If the piston isn't laying in the oil pan in pieces, the engine will be operating "NORMAL" according to GM

 

I have an '02 and have very very minor piston slap that becomes audible about 20 seconds after starting the engine when it's cold. It's a very slight ticking noise and has been diagnosed as piston slap (not an exhaust leak) - which the dealer said "deal with it, it's normal". Once the car warms up the noise is completely gone.

I've read, on this site, of some owner's being granted 75k-mile extended warranties for free. No proof if that's true or not though.

 

It doesn't. I was responding to the original question re "cold knocking sound when the fire up thwe vette." Piston slap is often confused with the knocking noise produced by loose wrist pins or carbon buildup, as well as the "normal" valvetrain noise that many people experience. The higher flowing filters only address the valvetrain noise issue.

 

Mine also happens about 20 secounds after start up and is slight. First I thought it was an exhaust leak or maybe clicking of the altenator. I took it to the dealer after I bought it in 2002, and they said it was within limits. It's a little scare hearing it, but didnt effect the performance. A couple months after the warranty expired in 3/2003, I complaint to GM cooperate HQ. I told them the car has 12000 miles and has piston slap. They sent me a letter giving me a total of 6 years 60000 mile warranty for free for everything inside the motor.

In january 2004, I complaint to the dealer again that said that it was within the limits, and complaint about piston slap and oil burning. At that point, the car had 12500 miles on it. They told me to fax them the letter GM sent me about the extended warrant. They called me that afternoon for a re-ring appointment. When the motor was apart and the pistons were out, they still found no issues with the piston slap, but replaced the rings with upgraded rings. They also did all my bolt ons for $700.00. At that point, I had a good relationship with the dealer, and if they had issues with the pistons, they would have replaced it.
I didnt burn a drop of oil for 2200 miles. I recently had the TR224 installed and noticed it was low about a 1/2 a quart about 500 miles later. I dont know if the cam generated a oil burning issue (doubt it ), or when they replaced the cam, oil pump, and chain, I just lost some oil and it's not burning oil.
This summer, ill have the oil changed again. That's my once a year oil change.

 

I use whatever Jiffy Lube puts in. I change my oil every 3500. I get a little sowing machine noise first thing in the morning. But nothing like that piston slap ( I listened to the sound clip). I also don't consume any oil. And have them place 6.5 quarts.

 

I have it pretty bad on my '02 WS6, but GM did what they do best...they ran me around and pissed me off so bad I pretty much said screw it.

 

I bet the LS2 and LS7 wont have it. maybe GM heard us and corrected the problem

 

I've had it in every GM car I've ever owned.

I pretend that by adding fuel treatment (to reduce carbon), it gets better.

 

So after all the work did you still have the piston slap?

 

This guy has nailed it exactly and everyone should pay attention

 

I think you should read all the posts before responding to an old thread:
http://forums.corvetteforum.com/show...post1550046046

 

Errr...i did read all the posts post is still active...last post yesterday at 7:12 pm ...i just read post, you just read post and posted response, whats your problem??? BTW,I was referring to piston slap issue, not oil filter question....

 

No problem... just making a suggestion, since you responded to a posting made almost a month ago, which was clarified (post #31) later that same day.


In that case, see item #10 (different forum, but still applies). We're not mind readers.

 

You can always count on a GEEK knowing his ****..

 

You can always count on a GEEK knowing his ****..

 

Yup!

 

Just wondering if the piston slap wear comes on quicker because of the thin oil that GM specifies. A few decades ago when I was around a lot of racers, the norm in the racing AND everybodies sports car engines was straight 30, 40, or 20-50 weights. The runny thin oils could not be used because it was just too thin and would not provide any protection under high heat or RPM loads. The films are just too weak. Has there been a HUGE increase in the viability of water weight oils? ....OR as has been postulated by several knowledgeable engine guys, the thin oils are specified by the automakers not because its good, but because in a fresh engine with good tolerances, the thin oils are lower in scraping friction and can contribute to rated MPG. One thing we know about for sure is that the automakers are under HUGE pressure for increased milaege, not only for consumer demands, but due to government mandated C.A.F.E., Corporate Average Fuel Economy. I can see the reality of an automaker like GM or Ford or Chrysler, fudging all the stops to increase short term mileage improvement in favor of high mileage [ out of warrantee] aggrevated wear.....Like piston slap due to cylinder wall/piston wear which is problematic with short skirt pistons. I used to run custom made Arias forged "skirtless" pistons in my Lotus engines years ago. They were sloppy when cold, but that was a designed fit, and they grew as the heat came on. Tnat slap was not something that developed from wear in an originally quiet engine. It was there from new rebuilds because the alloys grew and if the piston were sized for quiet cold operation, they would get too tight when hot. As ai understand it, the LS-1 slap is a wear problem that develops from originally quiet engines. Mobil 1 and other synthetics now come in slightly thicker weights. I am not going to use the 0-30 or 5-30 weights because I think its too thin....I have a very small amount of cold slap, .....very small and it DOES vanish as the engine warms up. I am going to try thicker oil and see how it affects the small amount od cold slap we have. Oil change is coming up. If it makes a positive result, I'll start a thread on it.

Cheers guys,

 

Howard,

For a monarch sucker, you are a pretty funny guy.




Good point. I don't know the answer, but I do remember running straight 30 racing oil (Valvoline, I think) in my 426 Charger during the early 70s. Dating myself, but I had an Isky 3/4 race cam, Hooker headers, a pair of Carter AFBs, and a flex fan. That engine produced some serious power (and some serious heat!). It would burn right through any multi-weight oil. It would be interesting to see how the multi-weight synthetics of today would hold up.

 

I own a 97. Had the start up tick. Changed oil filter to a Purolator PureOne 0il filter and the start up ticking disappeared. This is fact, not opinion. I read that a few members' start-up tick went away by using a K&N air filter, which I also have and may contribute to my problem going away.

If you change your oil filter to a higher flow type like the PureOne or the Baldwin, your start-up tick will go away.

 

Just my 2 cents.. I am not trying to argue any point. The startup noise you are talking about might be valvetrain noise instead of piston slap. I have tried the K/N filter along with the PureOne or whatever it was called and it didn't make any difference. I even tried different oil weight. If the oil filter did cure the problem then why wouldn't the dealership suggest this or place it in a service bulletin.

On second thought. No need to reply - this is a dead subject - people will have their opinions no matter what.