Top End Noise Mystery

[focodave]

All,

I decided to open up the top end of my engine to perform a valve adjustment.
It's a 1980 Fuel-Injected 2000.
Here are the clearances I measured:
Intake 1,2,3,4: .016, .017, .016, .016
Exhaust 1,2,3,4: .020, .022, .021, .020

The engine would run fairly quiet until it got up to operating temperature -- then it would exhibit what I thought was valve noise at about 2500 RPM and higher. If I babied it, and tried to keep it at around 2500 RPM without loading it too much, it would run fairly quietly.
So, I am now wondering if my "problem" could be something more serious like piston pin slop or rod bearings.
Given the valve clearances I measured, I don't think the noise is in the valves, or could it still be?
Would 1 or 2 thousandths on the exhaust clearance (the .021 and .022 cylinders) make a noticeable difference in noise??

Also, here are some other facts about my engine:
There are no exhaust leaks
I checked the cam towers for visible cracks and they look very solid and OK
I checked the camshaft bearings to see if there was side play -- none detected
I could not detect any foriegn objects in the cylinder bores, but I have not taken the head off (and prefer not to)
I ran the engine with ignition timing set to both 0 degrees and at 10 degrees, initial advance, and there was no real noticeable difference in the symptoms
I run 91 octane fuel religiously
Cam timing is right-on and so is the auxiliary shaft timing

Any and all educated opinions and/or suggestions are welcome.

Dave

[azruss]

I have noticed that the valves can chatter a little when out to the long end of the tolerances.

[focodave]

Russ,
My manual says that exhaust gap should be set to .020.
Are you implying that you've set yours tighter than that with good results?
.019?
Dave

[majicwrench]

Valve clearances are fine. You are never gonna hear the diff.
Lots of things make noise in a engine like this, hard to guess.
Keith

[azruss]

I just helped one of our local brethren with his valves this week. his book gave a range from .019 to.022. Mine are on the tight side with a new headgasket. Once the car is on the road and everything is broken in, i will re-check. The tighter the tolerance, the sooner the wafer makes contact with the cam lobe. This leaves the valve open slightly longer but also can burn the valves if it doesnt close at the right time. I've always set my in the past to .020-.021 without issues. Maybe the race guys can give you a better answer.

[RoyBatty]

See this post. Might have s similar issue.
Good luck.

http://fiatspider.com/f08/viewtopic.php?f=5&t=19483

[focodave]

Many thanks, all, for responding.
Roy -- I read your post and your engine symptoms sound identical to mine.
So all you did was replace the cam boxes and the symptoms went away?
You did not change anything else? Valve guides? Cams?
Dave