this 6.0 i have runs strong but when it is cold and i get to about 1/2 throttle i hear a prety nasty noise kinda like a bad rod bearing. is this piston slap or could i have some loose rod bearings? the noise goes away when fully warmed and i have ran 20-30lbs of nitrous thru it with no problem. just wondering.

i plan a storker build up before too long so i am not real worried about it.

 

Thats what it sounds like.

Ive heard that sound is pretty normal with forged pistons in built engines too, because of the excessive piston to wall clearance until they expand after warmup.

Maybe someone with a built engine can chime in to say if this is true or not

Supposedly these engines can easily go 200K+ miles with piston slap.

 

no kidding? i was kind of hoping for gm's sake i had a worse problem, if i had a $50k escalade or even a $30k HD i would be freeking out over this noise, sounds just like a hammering rod. i kind of figured if i had a bad rod that it would get much worse quickly spraying a 125 on it.

every ls1based motor i have had has had a taping noise at idle, it sometimes fades a little but is there prety much all the time, sounds more like a slight lifter noise. i always figured that this mild noise is what people were complaining about.

 

Yeah, its a pretty bad sound. Mine does it slightly when its cold. I switched from mobil1 to redline, and that quieted it down quite a bit.

My cousin has a 5.3 with 230K on it, and it has been doing it since it was pretty new.

 

My stock 5.3 and the stock 6 liter were quiet as a mouse. My built 6 liter was built at the extreme loose end of the allowed tolerance range (piston to bore clearance especially) and when first started it roars to life with a slight rattle that goes away before I can move the shift lever into reverse. If you have what sounds like a nod rocking it is probably something serious.

 

My 4.8 had it and my 6.0 has it. Just for peace of mind, I never get on it hard til the engine is warmed up. When cold you can hear it,but goes away after everything warms up. I have only heard mine at idle. If you are hearing it during accell there might be more to it.

 

My wifes eclipse gts does it very slightly too.

 

Mine does it too.. sounds like poop when it first starts and then after a few seconds it it runs smoooth. Oh well.

 

I have a forged piston 355 small block in my "race car". Last year I spun 2 rod bearings and now I know first hand what a rod knock sounds like. To be honest with you, my 5.3 truck motor (when cold out) has a worse knock (from piston slap) than my car did with 2 spun rod bearings. When I first bought the truck (used in 02), I thought I got ripped off. Now, I just ride on. Its seems like everyone else is just doing the same. I do however baby it big time until it warms up and the knocking goes away.