The cars starting to do this more and more after the heads and cam swap. At first you would hear it once or twice while the motor was cold and that was about it now it's doing it a good bit more at idle while the motor is cold. It makes the noise randomly, no real pattern to follow, so basically if it was idle and you had just started it, your not going to be able to predict when it makes the noise. Now once the motor gets hot the noise goes away entirely and the motor makes absolutely zero abnormal noises. The engine oil pressure looks awesome, 40psi on a cold start, right at or a little more then 20 at a hot idle, driving around it's very responsive to throttle, 35ish-40psi depending how heavy your foot is. When the motor makes this noise, it isn't repetitious to a rhythm or increasing in frequency of occurrence with engine RPM. It's metal on metal judging by the sound, so some things hitting some thing. It's really odd, I want to say it's coming from the passenger side of the motor. Just going to throw this out there, using a vented 95+ opti and the car runs great, so it isn't that.

Motor specs

Short Block: Stock 72K mile LT1
Heads & Cam: Late Model Engines Street/Strip Dart Pro-1 / Comp "CC306" 230/244/112 / Impala SS gaskets
Supporting Valve Train: Comp Cams Pushrods, Lifters & Double Roller chain. GMPP Guide Plates. Crane Cams Gold NSA 1.6 Roller Rockers, LT4 Valve Covers
Intake Manifold: MTI Ported 1993 Intake manifold
Throttle Body: Arizona Speed & Marine 54MM
Air Intake: Lingenfelter Cold Air Intake, Trick Flow Intake Elbow
Crank Pulley: ATI Super Dampner
Fuel Injectors: Ford racing 30# "Red Top"
Fuel Pump: Racetronix Walbro 255LPH
Ignition: 1995 Vented Opti Spark, MSD Blaster Coil, Taylor Wires
Cooling: Mezeire EWP
Computer: Stock with MadZ28 Chip
Exhaust: Hooker Long Tubes, Custom Y Pipe, Borla, Custom DMH electric Cut out

 

PISTON SLAP. Now let the debating begin on what that is, and why it happens.

 

+1, I forget where I read about it, but the material the pistons are made of and the fact they are undersized when cold and slowly expand to fit the bore. It's either that or something else .

 

I had a few of these mysterious pinging gremlins in my old engine. Once it was making this ping ping sound like light metal hitting light metal and short after that I blew one of the passenger sides spark plugs blew out of the cylinder head.

Other have been exhaust gaskets, you would be surprised how loud and how bad those leaks sound, once I though I blew my engine but it was a blown exhaust manifold gasket.

Which is why I think is most likely to be since the noise stops at operating temperature.

Now if it was piston slap there is a easy check for it without taring into the engine. Check if you have coolant in your oil. Plus this would not stop when the engine is at operating temperature it would be the exact opposite. Pretty much if you have piston slap your engine is done and you need a rebuild.

 

Why it happens is hard to determine, actually its nearly impossible to figure out why.

As far as what it is, if you're a "true gear head" you should know. Better question is; Why do you think its PISTON SLAP? When he said it stops it does not happen as a constant repetition and that it stops when the engine is hot...???

If you did have this it would not matter if the engine was hot, cold, neutral, underwater or in space, it would CLONK and SHAKE and RATTLE everything and eventually blow or one of the rings would brake loose or crack the block...etc

 

Wrong and thats according to GM. Piston slap is more audible when COLD as aluminum ( which is what the pistons are made of) expands when hot and shrinks when cold. So in the cold your pistons are in effect smaller somewhat and the piston slaps more until the engine warms up and the pistons expands.

Do a google search on Piston Slap 5.3 chevy engine lawsuit and see what you end up with. My 2003 truck motor is going to be pulled this spring as I have BAD piston slap. What we discovered as it got worse, and my local dealership was in on this, is that prolonged piston slap causes cylinder wear which then causes blow by, which in turn " somehow " according to GM " causes massive GUNK build up. Which in turn on a cold cold start clogs up oil passage's and lifters. Mine wa gunked up so bad that when you started the engine on a cold morning " we pulled the valve covers off at the dealership" the lifters at first acted like there were loose, flapping about and making all kinds of racket. Once she warmed up the lifter would pump up and everything would run OK. Well this has gone on for about 3 years now and its gotten to the point where I,m changing my oil every 1000 miles just so I dont blow it up.

Ok for now thats all, nit pick and I,ll fill in the holes later. Dont flame, I dont call myself an expert by any means I just know what Ive been told by very good ASE certified GM mechanics and Quaility control people at GM that I know personally.

 

Yeah, I took that personal and now I'm on fire! LOL! Nah man I'm always open to debates.

I understand what occurs after piston slap, the list of possible damages goes on for a mile. I feel bad for you and your Truck though but that truck has had this problem from the first day it came from the factory. It didn't just start. Now your just dealing with the aftermath of that issue.

You get piston slap when you install pistons that are not made for the block and there is too much room between the wall and piston. Yes, every metal shrinks and expands but its aluminum and that's why they use it because it does it at a minimal rate.

Piston has these rings, 4 to be exact to create that pressure and vacuum needed to operate the engine. Pistons are made for the block to have space between the block and piston of .001-.010 inch. Now if there is a defect in the manufacturing of the piston, this can cause extreme flexing and cause failure in engine which is what happening with your truck. Or a ring can fail and set the piston loose inside of the cylinder which will cause the piston slap which will shortly thereafter be followed by black smoke coming out of your tailpipe.

Original post is for a 70K+ miles 93 LT1 - Engine is almost 20 years old so I can guaranty its not the piston slap. I've seem people take their cars to shops to do an engine overhaul because of a blown exhaust manifold gasket. Its that bad of a sound, and actually there was a show on tv a few days ago about it...I'll see if I can youtube that...

 

Short block was dead quiet before heads and cam, only 500 or so miles on this entire set up. The short block wasn't removed from the car or touched far as the rotating assembly goes. I can't see why after heads and cam it would start having a piston slap issues, I don't think pistons have jealousy issues caused by new heads. I have heard piston slap in LS1s/V6s and this isn't it. We did obviously remove the headers since they were attached to the old heads heads, new gaskets were installed. I've heard piston slap and spun bearings and they have a predictable constant rhythm to them, this does not. That makes me think it isn't a apart of any thing rotating or in constant motion while the engine is on, or it would make the noise constantly. A blown header gasket does sound plausible though.

 

here are some videos that may help...let me know which sound best describes your sound.

#1) http://www.youtube.com/watch?v=f2ApIE2paOg

#2) http://www.youtube.com/watch?v=ZbxxG45fzI8

#3) http://www.youtube.com/watch?v=CulI5D0RgCQ this could be an issue?

#4) http://www.youtube.com/watch?v=KQkCJ9e4O18

#5) http://www.youtube.com/watch?v=WA4G_LDEflo

#6) http://www.youtube.com/watch?v=o0lEBIcPy_A

#7) http://www.youtube.com/watch?v=nTDaq1tY7tY

#8) http://www.youtube.com/watch?v=AnTvKD1TunI

#9) http://www.youtube.com/watch?v=LSOzH2m62aA

#10) http://www.youtube.com/watch?v=M70r6WC_9Dw

Let me know if any of these came close or if you can record the sound a post it, would help a lot.

 

Try it and see what happens, that why thought about it, usually axhaust you have a knock that it stops after a while. SO I put my money of the exhaust somewhere, either header or maybe collector.

 

Thanks for all the links, I would say most like #2. I'll take a vid in the morning.

Neil

 

If its #2 its you tensioner pulley that gave out. Its nothing internal nor an exhaust leak. If its not the tensioner pulley maybe a power steering pulley.

Easy test, take off the serpentine belt and start the car and run it for a min or so. See if you can hear the tone...

 

That very well could be it, to me it's sounding like it comes from the pass side motor, near the accessory bracket. Fast93Z was saying I may have had some thing come loose when I put that bracket back on. I replaced the belt tensioner for maintenance reasons during the heads and cam swap.

 

The LT1 engine, EVEN BRAND NEW, was prone to piston slap on cold startup. The noise went away as the engine warmed up. Its been known for years.

Its' even in the 4th Gen FAQ:

http://www.f-body.org/faq/4/4_2.htm#ch4_2ay

 

If you know "what it is" wouldn't you also know "why it occurs"?

Something to do with dissimilar metal expansion rates and piston to cylinder wall clearance. But don't quote me on that.