Reporting on the follow-up valvetrain check:

I took the beltside exhaust cam bearing, which had the tiny flecks of material on its surface, and gave it a careful light polish with number-800 paper, then inspected the surface under bright sunlight with a ten-power binocular magnifying headset. No trouble visible other than two or three pretty much microscopic pits.

Pulled the matching cam seal, which had some scuffs on the outer edge. They weren't bad enough to impair the seal itself, but I put a light coat of RTV over them. Then cleaned and dried the seal bore before the seal went back in.

Cam holders went back on, and everything got retorqued with extra care, including the 86 in-lb small bolts. It's easy to overrun those a little bit with a click-type torque wrench.

Valve cover back on, spark leads off, cranked with the starter to move the oil. No clatter.

Spark leads on, start for good. Quiet idle at first, then as the computer kicked the cold idle up from 1000 to 2000 rpm, the clattering noise appears.

Shut down. Restart. Same thing. Clatter seems intermittent. Can't hear it much if at all at idle. I carefully back out and drive a quarter-block. Definitely there, but not constant.

In the driveway, I tap the throttle a few times until I get the rattle steadily, then get out and go around. As near as I can localize the sound, it's coming from the back of the valve cover, near the injectors. Normal injector clatter? I don't think so. They didn't make this sound before the belt job.

Bent exhaust cam or exhaust cam pulley? Why intermittent noise? I would think it would be constant if something were out of alignment in the valvetrain.

Could I have decked a heat shield against something when jacking the engine up and down during the belt change? Can't think of anything that it would have run into.

Weird...

C