mad_22_07

iTrader: (8)

Let me start off first by explaining my car it's a 2002 z28 with a ls1 car was unmodified up until 148k miles when purchased I have all documentation over full service history from 20k miles up until 148k when I purchased. Car was very well taken care of always mobil 1 syn. My problem is I hear what sounds like piston slap on start up that gets a little quieter after warm up but when you slightly raise rpms seems to get quite yet back on idle noise returns. I have used a scope and can't track down the noise it can be heard best at the top center of motor and you can't seem to hear it when you move away from top center. It's a slow noise not indicative of valve train noise. Can holds 40+ psi oil pressure at idle and around 60+ cruising at normal operating temps I run royal purple 5-30w and noise was there when I bought it just assumed piston slap. Reason I made post is because it seems to be in center and I haven't found anyone with a post on that location. I can't make a video at the moment because it's running open headers till my exhaust arrives. And no I haven't driven it like this. And I realize aluminum will amplify noise. Am I being fooled thinking its top center noise and it's really in bottom ? Thanks for the help.

01SilveradoJakie

If it's a bottom end noise, it's just time for a rebuild. Usually ls1 that are modified are usually between 180,000 to 250,000 miles max before its time. LS motors have piston slap upon start up, very normal, I've had it in all my LS motors new and used. I'd try a good oil flush, like BG 109 , hard to get but if you find a shop who does it, great if do that first, then see. If it's too end noise, 2 options, pull the valve cover off, check and see the condition of the valve train. If it's funky or gunked up then clean it with some good cleaner, or you can do a head job and get it rebuilt. Make a video so we can hear it

mad_22_07

iTrader: (8)

Thanks for the advice I'll try and add sound when I can

RockinWs6

At that mileage the oring on oil pickup at the oil pump is starting to deteriorate. It will let small amounts of air into the oil stream causing noises. I would try a few ozs of Transx seal sweller additive in the engine oil to see if the noise stops. I had similar noise that was always diagnosed as piston slap by the dealers...........was the oring, put the Transx in and its quiet as a mouse now. It also helps rejuvenate the valve seals.