I have a 155 rwhp shot on my ls1. On the way home from the track I noticed a tapping sound comeing from the left side of the engine at 3000 rpm and then at wot. Its not real loud and you have to have the window down to hear it. It also has the piston slap when cold. I just got done pulling all the pushrods and they all looked straight, nothing bent. I put it all the back together and drove it today. I'm not sure what it could be, it is a real fast tapping/knock noise though. Oil pressure in good no oil burning and no other problems.

 

sure you got the rockers on tight? How loud is the sound?
rod knock? Is it RPM dependant?

 

Is is there when on cold start ups? The first startup of the day? Or only when its warm?

 

I think its a rod myself. It'll do it cold or hot and does it under load.

 

well if it does it cold and you have good oil pressure why would you think its a rod? rods wont knock when cold because the the oil is thicker. Kinda hard to explain. Maybe someone can chime in here.

You ever think about lifters? Maybe your stockers decided to finally let go? I had a very similar knocking sound as your describing. When I put in my cam I changed my lifters out to comp-oe and the knock has gone away. Sometimes its there when its pretty cold outside for the first start then goes away after 3-4mins of idling. Plus I may have more lash than needed, need more preload. If I were you, I would double check your pushrods. Also, check your exhaust manifold gaskets, and all exhaust connections.

 

Keep in mind how fast the "knock" is. Remember valvetrain is gover'nd from the cam itself, which in turn spins half as fast as the crank. Just something to keep in mind.

 

 

Something else, if you can guess which cylinder it is, pull spark from it. If the noise goes away it is probably a rod because there is no pressure on the piston from firing so you no longer hear the noise (not always, but I've seen it a lot in the shop). If the noise is still there it is probably valvetrain related. Just like rebelord said, probably a lifter, I've seen the rollers lock up, but it's usually on the 5.3 trucks, and if it is locking and unlocking it can cause a chirp/tapping noise.

 

If its a tapping sound it may be a failed lifter. If its more of a knocking sound, it could be a spun bearing or a rod bolt thats stretched alittle.

 

Drove it again last night and free revving you can't hear it, in first gear its barely heard. 2nd and 3rd it there, hard to tell with windows up but windows down its coming from the driver side. It sounds alittle louder and deeper then spark knock. I checked the rockers, pushrods and what not when I had the valve covers off. Everything looked good. I may go spray it at the track today and see what happens. Might as well go out with a bang.

 

Go ahead. But if I were you I would try to figure out what it is first.