Z0600HP

First time post here, and I'm a relative newbie in the LS engine area. I have a 2001 Z06 with 383 stroker kit, AFR1630 heads milled to 59-60cc, FAST90, 7.4" push rods, comp 240/244XER cam...Developed a loud tapping sound (sounds like pushrod) while decelerating...When you increase RPM it goes away...This tapping is much louder than the normal valve train noise BTW...We felt it was collapsed lifter, so tore down and changed with Comp850-16...Put same spec gaskets back on, reassembled...Restart and noise was gone for about 5 minutes, then returned...Did research from the previous owner build sheet, and found they used 15w50 Mobil1...I had changed to 5w30 synthetic when I purchased it back in April...Changed back to 20w50 this week to see if that helped and the noise was noticeably lower but still there...We plan to check OEM rocker pre-load next...oil pressure is at 40 at idle, and any increase in rpm makes the sound go away...I'm running out of ideas...Any thoughts/direction would be much appreciated...

kinglt-1

iTrader: (26)

lifters bleeding down.

Z0600HP

In your experience, are they bleeding down due to oil pump issues? As I said, we replaced all the lifters. It sounds like the noise is coming from #1 cylinder, and coincidently, that cylinder has the lowest compression (180 vs 225). 40 psi oil pressure seems adequate at idle to keep the lifters pumped up, but as soon as it idles the sound is back.

Maxjon97

Welcome