awesome, thanks for the tip. i will check on the timing chain stretch tomorrow. the procedure i followed was what i read on the factory service manual. i used the specs printed on the sticker by the radiator, 0.1mm intake, 0.35mm exhaust with the engine cold. i adjust with the cam lobe at about 1 o'clock and check the gap btw the lobe and the lifter.

i actually pulled the valve cover right after i pulled the car off the road, and checked to make sure all the adjusting nuts were tight. everything looked fine and nothing came loose.. they were tightened pretty tight to begin with. would it be stupid or a waste of time to try tightening the valves a little bit? i.e. would the gap being too big cause a knock? honestly it sounds like one of the valves is hitting the piston, its a really loud very noticeable hammering that increases in volume and frequency with the rpm of the engine. i only turned the crankshaft clockwise, which is the correct way to turn it, so i dont think the chain would have skipped a tooth. and if it is just worn out, i would have noticed the same problem on the 500 mile drive i did yesterday.

another thing to point out is that right when i finished the valve job i started the engine and let it run for about 10 seconds just to make sure it started okay, which it did, and it sounded fine. then maybe 15 min later i took it for a drive, where as i was leaving the neighborhood and pulling out onto the main street the knock appeared. i immediately let off the gas which caused the knock to not be so loud and potentially damaging to the engine internals, and pulled into the first driveway i could find. i shut it off and pulled the valve cover to check for loose nuts and they were all fine so i put it all back together and started it again, just let it idle for a bit. it idled fine for about 30 - 45 seconds and then the knock came back, and as i gave it gas it just sounded awful.

is there anything else to check besides the timing chain? maybe one of the valves may be adjusted slightly too loose, and the cam is slapping the lifter creating the knock?