Timing Belt? Top Dead Center?
 

ok guys so I just bought a 98 civic that had some vent valves. I took off the whole cylinder head to
replace the valves. everything went smooth. the problem is that I didn't know I had to do the "top dead center"
part. My question is, since I can see 4 cylinder holes, can't I just turn the crankshaft with a wrench until
cylinder 1 is at top dead center? and then when I'm ready to put back the whole cylinder head, put the camshaft
pulley with the "up" mark up and the belt back on and everything will be fine. I've read that if cylinder 1 isn't at tdc
a piston could strike an open valve (usually an intake) and you have a mess. also, can someone tell me the clearance
for the intake and the exhaust valves? I'll be ajusting them in a couple of days. Thanks in advance!:)

Yes, you can TDC the crank by looking at the pistons, but you should not turn the cam while the crank is at TDC because the valves need space. So TDC the cam first then the crank then put the timing belt on.

One of the teeth on the small timing belt pulley on the crank has a dent in the end. This should be lined up with the arrow on the casting at about 1:00 to TDC the crank. Do not use the key slot in the crank for this purpose. You can also use a suitable wire or rod to probe through the spark plug hole in cylinder #1 with the head on and feel when the piston is all the way up.

When you have the belt on, loosen the tensioner pulley bolt so the spring can move the tensioner down. Turn the crank slowly counterclockwise by hand to pull the front of the belt tight, the tensioner should take the slack out of the belt. While the front is tight, tighten the tensioner bolt. It needs to be tight. Then turn the engine through a few complete revolutions by hand to make sure the marks are still in time and the valves don't crash.