Clickin in the engine?

[240_two_fast]

ok this is the deal. i just bought a 1990 240sx for 1500. there is a clicking in the engine. it gets fast when you rev it up. a machanic said it was in one of the valves. one of my friends said it was the lifters. then another friend said it was the timing chain. who is right, what do you think it could be, and is it bad to drive it like this.

[slipnfall]

use a socket extension as a ghetto stethoscope. Put the extension on the valve cover in various spots. If it's loudest at the very front of the engine, it's likely the timing chain.

[240_two_fast]

ok now it does it for about 10 min. and then will stop for a wile and do it again. it does this over and over.