1LoudTA

iTrader: (11)

someone help me out. i hear that its a pretty big issue in the LS1 world. what is it exactly, and what does it sound like. i know when my cars not all the way up to operating temp i hear a little valvetrain noise so i always baby it until its up to temp. also, i think the noise i hear got louder when i changed from the 0w-30 to 5w-40... is what i have piston slap???

orangeapeel

iTrader: (18)

No it isnt. Just your car warming up it sounds like. Piston slap is when the pistons are physically "slapping" the valves. Makes like a slap click noise. louder than normal valvetrain clicking. Happens with milled heads and oversized cam in most case scenarios. You might have a knock...you have a check engine light or SES light that comes on?

this help?

BackinBlack02SS

iTrader: (7)

Piston slap is not when the piston hits the valves. On some LS1 engines, when cold, and the metal has not yet expanded to take up the slack between the rings and the cylinder bore, the pistons will "slap" the cylinder walls, making a very annoying noise.

Racehead

Piston slap is simply the "rocking" motion of the piston on the wrist pin. Since there is a pretty large gap between the piston and the bore when the engine is cold, the piston rocks back and forth on the wrist pin. Also the longer the piston is, the less it will have a tendency to do this. Since the LS1 piston are a very short skirted piston they have more of a tendency to rock back and forth hence they "piston slap" a little more than most. Not really a problem, they'll go 200-250k with decent maintenance and driving habits.

marine02ss

iTrader: (3)

Yea,what Racehead said, where in there world did you get its called hitting the valves? He will probably have all bent valves by now!

warpwr

GM dealer where I bought my LS1 said they would replace the pistons under "Preliminary Service Bulletin #00150".
I declined because I didn't want them tearing my brand new engine apart. Also because they told me there is nothing (other than the noise) wrong with the original pistons. The piston design has a short skirt to reduce friction. Another option would have been pistons with longer Teflon skirts. Too much $ for a production engine I suppose.

PREDATOR-Z

The tolerance between the stock piston skirt and the cylinder bore is a little on the wide side. So untill the piston warms up and expands, the side skirts slap the walls a little.
There is no skirt on the pin sides and that is not where the piston slaps.
GM fixes that with a piston that has tighter skirt to wall clearance.
This is why forged piston engines do not complain about that.

Racehead

No one said that the pistons slap on the pin side of the pistons, just that the pins represent the axis around which the pistons rock. Kind of obvious since this is where they're connected to the rods lol !

GM might fix this problem with tighter fitting pistons, but forged pistons slap worse than stock cast or hyper pistons. Forged pistons expand more from heat than do cast or hyper piston therefore they are installed with greater clearances therefore they slap more when cold. Once they're warmed up they are just as quiet as any other. My '71 slaps more when cold than does my stock pistoned '01 because of it's forged pistons. Another reason why LS1's slap is because of their very short piston skirts. The longer the piston skirt is, the less the piston will slap. This is true on any piston type.

PREDATOR-Z

You are correct when stating that a forged piston (Old School) will slap more. But We have stepped into the 21st century, and while old style forgings only contain about 7% silicone (making the alloy expand more, hense more clearance needed {as you stated}), the latest forged alloys contain up to 12.5% silicone and that reduced the expension coeficient, which allow for tighter clearances.
A Hypereutectic piston will contain between 16>18% (pretty much reaching melted silicone saturation point for the alloy) and these will expend the least.
The slap factor in LS1 motors is not "Normal", it shouldn't happen, period.
Why do you think GM in all it's might lost in court.
Simply because physically the tolerances should not be that much for the alloy used, if top notch alloys were used.

BTW, that is why when forging a motor, it is good to understand the physics behind it just to know what the hell you are buying and if your parts are up to the task promised.

Racehead

OK I'll bite one more time. Yes silicone content does affect expansion rates, but that's not the whole reason why a forged piston will experience cold slap more than a cast piston will. Forged pistons are denser than are other types. This is because they are forged. This is why they're tougher, and also in large part why they expand more. Because they expand more, they are installed with more piston to bore clearances. Because they are installed with more clearance, they cold slap more. These characteristics are effected some by silicone content, but the basic truth that forged (denser) pistons expand more, is still there and unavoidable. Look at, and compare the recommended piston to bore clearances on any cast,hyper, and forged piston, regardless of silicone content, this alone should tell you if I'm full of it or not.

Bullshit. Any expecially short skirt pistoned engine will do this, and any aluminum blocked engine will magnify the noise. I don't know why GM lost in court, I suspect that they DID in fact have some engine's that were particularly bad, and they had enough people complain that they were forced to do something to address public perception. I DO know however that most of the people on this board who had it done complained about cold piston slap even after GM put new pistons in their engines. So much for tighter clearances curing cold slap huh ? IMO this is because of the very short skirted pistons being more prone to the "rocking" motion that I already referred to, and an aluminum block making it louder to the ear.

Exactly, so you need to go study some more before trying to school a guy who's been building engines professionally for more than 25 years

orangeapeel

iTrader: (18)

Eek! That was just what i have heard, but... now I know for sure.
thanks for lesson learned. I think i was actually listening to someone that knew less than i thought.

Knowledge has expanded!

orangeapeel

iTrader: (18)

That would be PTV clearance...im a moron.

Lorenz

iTrader: (8)

here's another newbie question, what sound difference is there between piston slap and bended pushrod?

mattr228

iTrader: (10)

but racehead is absolutely right ,

piston hitting the valves?

orangeapeel

iTrader: (18)

we just talked about that "not" being piston slap.

PREDATOR-Z

Look, I hate **** matches.
And mind you, I didn't say that Racehead was wrong, but his explanation is basic and doesn't apply to all piston brands.

I'm no newbie myself, I've tasted Rice and Sauerkraut.
Also, I'm not schooling with the comment about knowing the physics of parts we buy, I was just stating that the more knowledge and info a person has the better prepared that person is.
If you notice, I didn't quote Racehead or called BS on anything he said, I just added info.
Racehead is being defensive, why, I'm sure he knows.

Here is an article worth reading to elaborate:

http://www.hoon.tk/tech_tips/pistons.html

PREDATOR-Z

And this is various professional opinions:
www.pistonslap.com/whatisit.htm

Racehead

"Saying" it and just "implying" it are differant huh ? I think it's pretty obvious what you were "saying".
When I said this ..
You misunderstood my meaning completely. You obviously thought I was saying that the "cold slap" of the piston was occurring on the pin side of the piston, which I did not. You mis-understood, admit it and move on.
And when you say this
You are just plain wrong, It DOES apply to all piston brands. Do you not understand that metalurgical properties of aluminum hold true no matter who is making the piston ? My explanation was the complete one, and yours was actually the incomplete and basic one. According to your post, silicone is the trait solely responsible for the expansion rates of pistons. I "informed" you that "cast versus forged" was as much of a deciding factor as "high versus low" silicone content is, both play a part. Where in any of your posts did you acknowledge this fact ?
Then why is it so hard for you to even admit when you've been taught something ?
This is because you can't. Go ahead and try to call bullshit on anything I've said and I'll provide you with links to the piston manufacturers themselves which explain my position very well. Just because you didn't quote me directly it doesn't mean it isn't obvious who you're replying to. At least when I refute something someone has said, I speak directly to them.
I'm educating you, a person who professes to know the importance of a complete understanding of the physics of pistons, and yet refuses to learn You can lead a horse to water .........

There is nothing in this article that is actually wrong, but much like your posts the information is very superficial and incomplete. Do they mention why you might NOT want high silicone content ? They barely even mention the fact that forged pistons inherently expand more than cast. In fact the whole article is written as if they were trying to introduce a newby high school autoshop student to pistons and didn't want to overwhelm him. It also looks like your entire opinion is based on this one article so I'll provide you with a few links to more advanced stuff ( something Google could have done for you in 5 minutes of your time if you'd tried ) so that you'll more fully understand what I'm trying to show you.

here is a forged piston, not old school, nor out of date that contains 0% silicone. Why would they do that ? Check out the recommended piston to cylinder wall clearances. Click and learn.
Here is also another more in-depth explanation of piston metalurgy. Good information in here.
This is another pretty good explanation. All of these seem to concentrate on differant area's of piston designs. Taken together they provide pretty good insite on piston design, and the why's of differant silicone contents etc. None of these are 100% complete explanations however, that would make for a far too large of an article. That's why you need to google more and read lots of differant publications. So that your own knowledge is more complete

Also providing a link to a lawyers class action suit website who stands to make millions of dollars on the case is not the way to provide unbiased information. Don't you think a lawyer such as that just "might" slant the information his way a little bit ? How about ALOT ?