Hardee46360

A well known shop for over 30 years just rebuilt my 95 LT1 engine and tranny. I had the heads ported and new valve job done somewhere else. I also bought a new timing chain. Heres the problem, after all the nnew parts were installed, even new comp cam lifters to go with the Lt4 hotcam, there is a certain "knocking" noise coming from somewhere. This noise is there on intitial startup for ~5 min, then it goes away. It doesnt come back until you put stress on the drivtrain(put in in gear(automatic)) Once in gear it still comes and goes. We just found the noise today, and we checked with the local Chevy shops, some of them came and listened to it, but it had them stumped too. Our best guess without taking the engine apart is a possible bent valve in one of the heads. ITS NOT IN THE BOTTOM END! we pulled the pan off and made sure. Another guess was maybe a faulty timing chain, but i just replaced the timing chain. After I had the heads worked on, I spun 3 rod bearings and one of the pistons was hitting. SO guys, what is your opinion on this matter? Any suggestions will be greatly apprieciated.

BUBBA

Determine if the noise is coming from just one of the banks and pull the valve cover. Did you go with RRs? How's the geometry? Are your spring pressures adequate? How about your adjustments? What oil wt are you using? Are any of your lifters bleeding down to quickly?

You said it wasn't a bottom end problem, so it must be a top end problem.

If it is a bent valve, then you should be able to tell which one. Do you have SA adjusting RRs or NSAs, in which case you need guides and hardended push rods.

So-called mechanics, I've found, can't figure out some noises either unless they actually try by the process of isolation and elimination. JMHO

BUBBA

BTW, as most know, I am not an expert in any sense of the word-just thought I'd give you some food for thought.

Hardee46360

10w40 oil, lifters are fine, valve job rebuilt but before I spun the 3 rod bearings.

BUBBA

Are you sure that your valves are still not smacking your pistons, either because of timing or inadeqate piston to valve clearance. When you have one guy do the bottom end and another do the top, chances are that no one clayed the pistons to see if you have adeqate clearances.

Smack those suckers too had for too long and u may drop a valve when it is smacked off the retainers. Just a dumb guess, but there is something about having heads done that causes me concern, epecially when the installer fails to check clearances.JMHO

Hardee46360

Problem solved....First they told me in no way could it be a lifter, then guess what...the noise just dissapeared after they let it run for about an half hour. Know they say it was a lifter problem. As long as the noise stays away, and the engine runs good, i am Happy. Thanks guys for the advise