I just rebuilt my 86 lt230s. Wiseco 10:1, bored and honed, valve job, the works. Fired right up. But there is a loud hammering noise. I took the head off and checked the valves, piston, rockers, cam, all of it looked fine. Valve lash is good. Exhaust gasket it tight. What am I missing? When I touch a long extension to my engine and my ear, I can't find the knock. I put 93 octane in it, it it possible that it is pre-igniting and not something mechanical?

 

As it turns out I had set my valve lash at exhaust TDC instead of intake TDC, giving me about .125 instead of .002-.003. Duh right? But she runs hard, now I need a 14/39 or 37 tooth sprocket set cause first and second are worthless lol.

 

Sorry to say this but I did the same thing I bored My 87 LT230s out .100 Wiseco Piston and my knocking noise was the Connecting Rod bearing.It just had a little to much play in the rod.I got a new Rod kit n its super quit now.Machine Shop charged Me $80.00 to press on new Rod n Bearing.LT230 Rod kits r about 100.00 bucks on Ebay n you will need complete gasket kit.
Hope you find out its something else then the rod but it sounds exactly like what I went thru.
Let us know what you find out.

 

It turned out that my valve lash was set on TDC exhaust instead of TDC intake. The noise was the valves clacking. My rod was tight, a few thousands side to side, but none up and down, that is within tolerence.

 

Well that's good news,changing the rod is a big job.