VandykeT/A

I just rebuilt my ls1 and I've noticed at idle a piston slap noise even when hot. It's got almost 300 miles and I took it high rpm for the first time today. Anybody got any ideas of what it could be. Sounds just like piston slap and goes away with a little throttle. Just a mild hollow knock at idle.

Mercier

iTrader: (15)

Take a vid if you can but sounds more like a lifter/rocker issue. How s oil pressure?

VandykeT/A

Oil pressure is around 60-65 psi cold and usually 40 hot. I've ran the crap out of it and it does nothing. Noise doesn't get louder nothing. Car runs strong as can be just has the piston slap noise. It seems to taper down after it runs for a moment and basically only does it at idle.

Mercier

iTrader: (15)

Stick or auto? Different if in/out of gear or clutch in/out? Checked for exhaust leaks? Have you run it without belts to eliminate the accessories?

Also check your plug wires. I've had a boot burn out on the bottom side and it was arcing to the head and made a surprisingly loud tick. Just got so fast at higher RPMs it faded onto all the other engine noises. Best way to check for that is to run the car in a garage at night with the lights off(door open halfway and only for a few seconds; don't kill yourself) As dark as possible however you do it.

VandykeT/A

I looked for arcs last night. I unplugged the injectors to unload the cylinder and the knock stays the same. Its a stick car. Noise sounds the same no matter what. It may only be slightly louder cold or after it sits for 15 minutes but its basically the same hollow knock at all times.

SlasherVRGR

iTrader: (1)

Did you hone and reuse the stock pistons?

If so maybe one or more of the pistons are too small and rocking in the bore like piston slap on a stock car.

VandykeT/A

I did hone and reuse the stock Pistons but I didn't think a light hone would be enough to open the piston to wall clearance enough to knock hot.

Mercier

iTrader: (15)

Only way to know is measure. Did you check the bore and piston sizes upon reassembly?

A.R. Shale Targa

iTrader: (2)

5W30 on the oil ???

VandykeT/A

I didn't check but I should have. And either 5w30 or 10w30 can't remember for sure. I've put almost 700 miles on it just has the noise at idle. Runs perfect just noise at idle.

Mercier

iTrader: (15)

Dang. I am about to do the same on a LS2 I just pulled..and probably wouldn't have measured after had we not had this convo. Will now!

Seems like you should eliminate all other possibilities and then you have to ask yourself if it bothers you enough to pull it back out and bore and all that. Maybe consider it part of the "sleeper effect."

A.R. Shale Targa

iTrader: (2)

Try the Mobil one 0W40 Euro blend to see if the noise subsides at idle

kingtal0n

iTrader: (1)

How loud is the exhaust system? Did you try a stethoscope yet?

Usually when I hear an engine piston slap, it will intensify right around neutral load. For example, it might not be really loud or apprent at idle speed, or when revving, but if you rev the engine gently, just as you are peaking the rpm (say you rev from 800->1500) just after the peak of 1500 as you lift from the throttle and let the idle drop, I would expect to hear the piston slap at that point for an instant.

That from engines with forged pistons. Its hard to imagine a cast piston doing this in an OEM bore. Im guessing you re-used the original pistons, replacing them exactly in the bore they came form, and honed it at home using some kind of home-hone tool. What sort of honing tool did you use?

1970camaroRS

iTrader: (8)

Hone and reuse of stock pistons without measuring anything? Well, if it is the piston rocking it's going to be a difficult diagnosis. And it's 50/50 if it's just going to be an annoyance with perhaps some excessive oil consumption or if you're going to have a very bad day soon.

tgt788

What ever became of this noise? Sorry to bring up an old threat but I have the exact same thing happening to me. Honed cylinders, new piston rings, and reused stock pistons and rods. My question is, did you ever pull the engine apart to figure out what exact it was? Or did the engine continue to run fine with the noise?

RonSSNova

iTrader: (3)

LS1’s piston slapped from the factory.
My 2000 C5 slapped its way to the bottom 11’s for years.
You should have replaced the pistons.
Anyway it just sounds bad. Doesn’t really hurt anything.

VandykeT/A

It wasn’t piston slap. I had ARP rod bolts put in and had the machine shop check for out of round. All came out good. Well when I pulled the motor back apart 2 rods I could see a slight separation mark between the rod and rod cap on two of them. I don’t really know what happened but it was almost as if the bolts backed off or I didn’t torque them which wasn’t the case. I replaced those 2 rods and the crank and went back to stock bolts. It’s been running since then.