2000JordanTransAm

ok, ive been trying to find out as much as possible about this piston slap, i've had my car since july 2008, and have heard the "knocking" noise since then. but my noise doesnt go away when my car warms up, yet it does get quieter. the guy who owned the car before didn't really take care or the, at all. i'm just wondering if it could still be piston slap, just worse than what others have because the guy before me was an idiot. my car runs fine, and from what i can tell, runs exactly the same way(if not better) as when i got it. it has 87,000 miles on it.

I've been searching around and found this article
http://www.pistonslap.com/

"Essentially, the piston moves sideways and “slaps” or “knocks” hard against the cylinder bore and causes damage to the engine pistons and cylinders, excessive smoke emissions, excessive oil consumption, carbon buildup on piston heads, decreased mileage, and a loud and obnoxious “slapping” or “knocking” noise, all of which diminishes vehicle resale value in the trade."

briannutter

It's very possible to design a piston with so much taper that it's really loud when cold and still plenty loud when it warms up. That's not a good design. It's the piston designers job to have "just enough" taper to make up for thermal expansion-yet not seize when it's really seeing a lot of heat. Overall top to bottom taper on a forged small block piston is usually .045 to .055". Pin offset reduces the severity of the switchover of the top land at tdc.

fauslpss

iTrader: (6)

Mine knocked and when I took the top end off I cleaned the piston tops and now no more knock.

briannutter

I think you're talking about detonation though right? 2000jordantransam has a mechanical issue.

2000JordanTransAm

thx. i just wish i could fix it. i tried listening to my friends 2000 camero with a stock lS1(like mine) and i thought i heard some knocking, but it was to quiet to telling if it actually was his engine or not. mine you can tell. even if its warmed up

fast01

iTrader: (16)

What year is the car? I believe the early LS1's were notorious for "piston slap". I think GM's fix was coated skirts. I've got an '01 Z28 that shattered a piston and when I needed a quick, cheap fix I won a full set of pistons and rods from a '99 Vette on e-Bay and when I got them I noticed the skirts were coated. Where as the pistons out of my '01 were not. That's my theory anyway.

Feel free to flame me if this is too far off!

2000JordanTransAm

its a 2000. As for the coated skirts, i have no clue about that. I'm relatively new with this, got the car back in uly 08', and that was the first thing i really new about anything. Tho, i know a lot more now, i;m still bot sure on alot of stuff. But, i'm thinking of just getting new pistons and everything, but idk if i can afford doing that at the moment.

Breathing Fire

Piston slap in these cars is not caused by cheap manufacturing. The sleves are iron and the pistons are Al. They have different expansion rates and therefore the pistons have to be small enough to "expand into place" once the engine reaches temp. The slap is supposed to go away when the engine warms up. The coating was added for quieter start up. If it doesn't the piston(s) may have become misshapen like an oval which is not good.

willizm

iTrader: (10)

Since we are on the topic, what is the diagnosing differences between piston slap and lifter knock. I've listened to video's about both issues on youtube, but I'm having a hard time diagnosing if it's just piston slap or lifter knock. I just got the car so I changed the oil with synthetic 10w30 and it seems to have reduced the noise, but it's still there.

sman

iTrader: (4)

Both my camaro, with the 5.3, and our sierra, with the 6.0, have piston slap when cold. You can still hear a little bit of it once warmed up.

Phil'sC5vette

iTrader: (4)

My 200 C5 has it. I added 200 HP to the motor and a louder exhuast, and I no longer here the piston slap. I think that's the fix.

fast01

iTrader: (16)

I agree 100%! Lol!


2000JordanTransAm, I really wouldn't worry too much about the slap, it's more annoying than damaging. Besisdes, if you were to swap pistons and were to go to forged slugs, your piston to wall clearance will increase making the slap worse....when the engine's cold anyway.

willizm, I think the lifters make more of a tapping noise than a knock. Another thing our cars are known for is a loud valvetrain. Again, not too much to worry about. I have heard that the noise seems to get better and worse with different oils. It's been posted on here before.

2000JordanTransAm

thany you guys, and yea i agree. more horsepower and louder exhaust is the fix haha

99RTA

iTrader: (-1)

I can tell you this most knock heard in these engines is from carbon build up. I had TERRIBLE cold knock, after running carbon cleaner through the engine its quiet as a mouse!

2000JordanTransAm

yea i seafoamed the car and it made the noise a bit louder i think. only because i dont think its piston slap anymore, but the o-ring on the oil pump. my frined told me they sometimes get pinched in the factory the break later. the broken o-ring lets in air and the lifters tap. so seafoaming got all the dirt and crap out a gave the lifters more room to tap i think. so we are going to replace the o-ring and hope it works otherwise idk wtf to do.

2000JordanTransAm

well its the tapping is most likely a spun bearing

chrisfrost

iTrader: (8)

Hey guys , actually the piston slap is there because to save weight on the rotating assembly thus freeing up more power GM's designers made the piston skirts shorter . The 99-06 5.3L pistons when new have a piston to bore of .002" Starting in 2007 they decreased the piston to bore to .0007" . So anyone rebuilding an earlier engine could go with the 07 on pistons but You'd have to use the 07 on connecting rods as the compression height and pin diameter is a little different . just chug You a cpl beers or so ,,,,,,,,,,,that piston slap won't be anywhere close to You're ears although I would'nt suggest driving in that condition ,,,,,,,Lol just kidding . Good luck