Arm yourself with a 28mm socket, small extension rod & breaker bar so you can hand rotate the motor. Also get a set of feeler gauges. Ideally one that's calibrated metric.
Remove the rocker cover (three bolts on the top). The hose from the power brake booster should be in the way. remove the connection on the booster.
There's a permanent gasket on the bottom of the rocker cover that you'll put back on later. If you don't have an oil leak dripping on the garage floor, the gasket is probably fine. But now's the time to take a look at it.
You should see the row of rockers, some pointing left and some pointing right. Each one should have a coiled spring holding it down. See if one is missing or disconnected from the retaining clip that holds it to the rocker stud. A pair of needle nose pliers can be used to reattach one that popped off.
You'll see some rockers are pushed down by the cam and others are not. The ones pushed down by the cam will be solid. The ones not pushed down will have a little bit of wiggle room, but not much. While you're looking, is there a bad cam lobe?
Now you can rotate the motor through a full revolution. Do the turning so that the chain comes up past the chain tensioner (it's on the side with the exhaust manifolds).
Do it a bit at a time and wiggle the rockers that are not pressed by the cam. This is not at all a rigorous test; get out the feeler gauge. Find the right feelers for valve clearance and also one that's the next larger size. They should be a bit oily. Also they should be free of grime.
As the cam rotates the time/place to check the clearance is when the pointy part of the cam lob is pointed away from the pad on the rocker it rotates through. Also, you need to figure out which ones are intake and which ones are exhaust. Eyeball where the rocker is relative to the ports on the intake and exhaust (That's easier than remembering EII EEII EEII E; something you yell when you bust a knuckle
).
To actually change the valve clearance, you need a special open-end wrench. That's not the kind of thing you pick up on a Sunday, so don't worry about it. Also, don't rely on memory, write down the clearances on a piece of paper.
To put the rocker cover back on, wipe the mating surface of the head a bit to clean up any grime/oil that got in. Lay the gasket on the head then put the rocker on the gasket. Some wiggling is required to get it to slip in the grove and then seat.
Don't over-tighten the bolts that hold it down. When you reattach the brake booster line, don't over-tighten that one either.
-CTH