I have an '87 IROC that I recently did an engine swap on. Currently it has a 406 small block in it: with short travel hydraulic roller lifters, thick wall push rods, roller rockers, and AFR 220cc race ready heads and valve springs. The engine has barely 1,000 miles on it, but ever since it's first run, the valve train has made ano obnoxiously loud tapping noise. It only seems to be coming from two distinct spots on the top end of the motor. The strange thing is, after the engine is revved up past about 3,000 rpm, the tapping ceases. I've been looking everywhere for a possible for an answer, but I simply don't know. I've adjusted the pre-load twice, once 1/4 turn, once 1/2 turn, but it didn't make any difference whatsoever. I was thiningredients about calling the manufacturer, but once again I do not know which part of the engine is making this tapping sound. I've checked my valve train components once before (I put the wrong main seal in it)and nothing seems to be broken or not working. Any thoughts? Any help would be appreciated

 

Other things besides clearance can make tapping sounds.

Any number of things can happen with springs for example. I built a motor once that did that; narrowed it down to a particular valve with a piece of heater hose stuck in my ear; turned out when I was adjusting the valves, (solid cam) that particular one made a "skreeeeeeeeeeeeeeek" kinda sound as it operated. Upon closer inspection it was the spring rubbing the damper. Replaced it, sound disappeared.

Another time, the motor in question had stock rockers. Used. I could turn th emotor by hand and at some random point in the valve motion cycle, it would tap. Upon closer inspection that one turned out to be that the rocker was riding on the valve stem with an unworn surface, but as it moved, eventually the stem tip would fall into the wear groove that was already there. Replaced the rocker, sound gone.

Gotta keep your mind open and LOOK at the parts making the noise. Don't be afraid to investigate the unusual. I'm not talking alien abduction or Elvis sighting type unusual; but, be prepared for something other than vertical clearance to be th ecause.

 

well i am going to assume you are using guide plates with your roller rockers.... but on the other hand you could also check to see if you put your timing chain on correctly. make sure you didnt skip a tooth or any thing. also a lot of people mistake an exhaust leak between the headers and heads for noisy valve train. you could even be knocking (or pinging). just trying to give you other ideas and other things to check, so take it for what its worth. good luck

 

Put this one at the bottom of the list under the heading "when all else fails":

Severely worn valve guide. I know, I know, everything is new. Doesn't matter. Sometimes the guides are too tight or don't get enough lubrication or... could be any number of a million things, and a guide or two gets eaten. Like REALLY bad. Bad enough you can wiggle the valve stem back and forth 1/8". You'll never find it in the usual ways because the valve promptly stands straight up when it's closed under valve spring tension. But in operation the thing is flopping around so bad you won't even believe it until the first time you encounter this and see it with your own eyes.

It can give the most annoying, impossible-to-find, valve tap sounds you've ever tried to diagnose.

How to check in the car.... going one cylinder at a time, remove rocker arms, hold valves closed with compressed air, remove valve springs. Make sure the valves can't drop down through their guides (most positive-style valve guide seals will provide sufficient holding power) and remove the compressed air source. Open one valve at a time about 1/4-1/2" off it's seat and try to wiggle the valve stem in the same direction as the rocker arm scrubs across it's tip. If it's shot, it will be VERY OBVIOUS. Big 'ol click-clunk back and forth.

 

That's a good observation and one I have experience with.
In our attempt to dial in the proper Valve Train Geometry, or in my case, failing to re-address the VGT after a short block swap, the guides, because of pushrods the wrong length, took a beating. Having the head on the bench, it was found that there was .030" lateral movement of the valve head when lifted from the seat by about a half inch or so (demonstrating a worn guide). Determining that to be on the edge of serviceability, and having corrected the VGT issue, (with the correct length pushrods and Crower's offset trunion rocker arms) the heads were put back into service. But not without an incessant tapping from one or two valves that has never gone away or become worse.
Something to think about. Especially if you haven't done a thorough examination of the rocker tip to valve tip interface (VGT). Bronze guides will go away in a hurry.