When your valves need to be adjusted some of the symptoms can be excessive valvetrain noise, smog fail HC, a small drop in performance, driveability, and fuel economy. If your valve lash is too tight it can cause you to wear down the cam resulting in a costly repair (not to mention lots of metal shavings circulating through your engine).
According to the manual, you should adjust the valves every 12 months or 20,000 miles. You will also need to perform a valve adjustment if you loosen the head bolts for any reason (ie mini-me or headgasket change), change the cam, or disassemble the valvetrain.
For the feeler gauges I suggest Craftsman 40802 approx $10 from Sears. For the Valve Adjustment Tool I suggest Alltrade/Powerbuilt 648827 approx $13 from Amazon.com.
The engine must be stone cold. Let the car sit overnight. Note - you can't do a valve adjustment on a head before you install it on the block because torquing it down will change the thickness of the head.
Verify the VIN number on the emissions label on the underside of your hood against the VIN stamped on your firewall. Then verify that the engine type the label refers to is the same engine you have in your bay. Trust the specs on the emissions label above all else, but if the hood or engine aren't original to the car, download the repair manual for that particular engine.
Pull the ebrake, put the car in neutral, chock a rear wheel, jack up the front end, put a jackstand under the driver's front jack point, let the car down, pop the hood. Remove the driver's front wheel (loosen lugs before you lift the car if you don't have an impact).
Pull the spark plug wires out of the valve cover and set them aside (mark them with a sharpee, one closest to the crank pulley is #1). Removing the spark plugs makes it much easier to rotate the engine by hand.
Remove the breather hose and ground wire from the valve cover. I prefer to remove the distributor cap, put all the wires in their respective holes in the valve cover, then flip the whole thing over and out of the way. Later I wont have to think about which post on the distributor goes to which cylinder.
Remove the bolts holding down the valve cover and gently pry it up at a point that isn't critical to sealing - or tap it with a rubber mallet.
Remove the 10mm bolts holding the upper timing belt cover and remove it.
Put a socket on the crank pulley bolt, run an extension through the access hole in your wheel well, set your ratchet to loosen, and crank the engine counterclockwise until the "UP" etching in the cam is pointing straight up indicating cylinder 1 is at tdc on its compression stroke. Watch the rocker arms as you rotate the engine. They must be completely at rest when you adjust the valve clearance. All the valves for a particular cylinder will be at rest when that cylinder is at tdc on the compression stroke.
Check the valve clearance on cylinder 1 (closest to crank pulley). Use your .007 feeler gauge on the intake side and the .009 on the exhaust side.
The .007 should slide in with a slight drag on the intake side. But the .008 should not be able to fit. If it does, insert the .007, loosen the lock nut with the jam nut tool and turn the screw gently using two fingers. When you feel it contact the feeler gauge, gently pull back on the gauge. It should be locked in place. Loosen the screw just a hair until you can barely free the gauge (it should drag). Be careful not to press down on it with the jam nut tool. Now try inserting the .008 again. It should not fit (don't force it).
Repeat this using the .009 and .010 on the exhaust side.
Next is #3. The firing order is 1, 3, 4, 2. Turn the crank pulley until the cam pulley turns 90 degrees counterclockwise. The "UP" etch mark will face the front of the vehicle. Check/adjust the valves.
Next is #4. The "UP" etch mark will face downward. Check/adjust the valves.
Next is #2. The "UP" etch mark will face the rear of the vehicle. Check/adjust the valves.
Go through the cycle a few times until you are comfortable that each valve is consistent. Then torque the lock nuts and check it one last time.
Clean the gasket mating surface. Put the upper timing belt cover in place. Put the valve cover gasket into the valve cover and apply the liquid gasket at the sharp corners where the distributor and cam pass through the valve cover. Set the valve cover in place and install the bolts in a swirl pattern starting in the center. First torque them by hand and then with the torque wrench according to the spec. If you over tighten these bolts they break very easily.
I don't exactly index the plugs as that would require special washers. But I mark them with the sharpee so I can make sure the ground strap doesn't face the intake ports.
Hold the wheel in place and hand tighten the lug nuts so the wheel fits evenly. Then tighten them as much as possible before putting the car on the ground and torquing them to spec.
The rest of the installation procedure is the reverse of removal.
On most Civics you simply unplug the battery or remove the 7.5A fuse under the hood and flash the brights to remove any residual charge.
Don't wait until Monday morning to find out if you did something wrong! Make sure no oil is leaking from the valve cover and that there's no excessive valvetrain noise or other obvious problem.
In most cases you'll notice the car is more peppy, the idle is smoother, and you'll pick up some mpg.