Honda Valve Clearance (Tappet) Adjustment

Obtain the intake and exhaust clearance specifications for your exact engine and do not mix them up. Examples quoted in the discussion (all cold): B16A and all DOHC VTEC B-series including B18C variants - intake 0.15-0.19 mm, exhaust 0.17-0.21 mm, measured at the camshaft; B18B - intake 0.003-0.005" (0.08-0.12 mm), exhaust 0.006-0.008" (0.16-0.20 mm), measured at the camshaft; H22A1 - intake 0.15-0.19 mm, exhaust 0.17-0.21 mm; D15B7 - intake 0.18-0.22 mm, exhaust 0.23-0.27 mm, measured at the valve. The engine must be stone cold - leave it unstarted for several hours, ideally overnight. Do not attempt the job without the correct specifications, the correct tools, and a clear understanding of the whole procedure.

Unplug the spark plug leads and disconnect the PCV tube from the rocker cover. Undo the five rocker cover bolts and lift the cover off. Optionally remove the spark plugs as well - this greatly reduces the effort needed to turn the engine over by hand.

Undo the two 10mm bolts securing the upper timing (cam) belt cover and remove the cover so you can see the camshaft sprocket markings.

Fit a 17mm socket to a long 1/2" bar, connect a breaker bar, and fit it to the harmonic balancer (crankshaft pulley) bolt. You can reach it through the inner guard without removing anything: either jack up the front of the car, support it on jack stands and remove the wheel, or keep the car on the ground with the steering turned to full left lock for access.

Turn the engine over counter-clockwise with the breaker bar until the UP mark on the cam sprocket points up and the TDC mark on the harmonic balancer lines up with the pointer on the timing cover. The TDC mark is the single (usually white) mark on the circumference of the larger ring of the balancer; the ignition timing mark is a red one sitting between two other marks - do not confuse them. At TDC on the compression stroke for cylinder 1, the cam sprocket markings also align with the cylinder head's flat surface. Confirm cylinder 1 is on its adjustable stroke by lifting the tops of its tappets - they should move up and down slightly.

Insert the correct feeler gauge for your specification between the adjusting screw and valve tip (SOHC) or between the camshaft lobe and rocker arm (DOHC). Push and pull the gauge a few times to get a feel for the clearance: it should feel snug - the gauge should slide out with slight resistance, neither jammed tight nor loose. On DOHC engines the original author inserts the gauge from the outside of the head and then re-checks from the inside to make sure the setting is not too tight.

Place the 10mm ring spanner on the tappet locknut with the feeler gauge in position and a flat-blade screwdriver on the adjusting screw. Crack the locknut just enough that the screw can turn. Turn the screwdriver counter-clockwise to increase (loosen) the clearance or clockwise to reduce (tighten) it. Make an adjustment, hold the screwdriver firmly so the screw cannot move, and nip up the locknut - snug enough that nothing moves, but not fully tight. Re-check the clearance and repeat until it is correct; expect up to 10 attempts at first, dropping to 3 or fewer with practice. When the clearance is right, hold the screwdriver firm and tighten the locknut properly - do not overtighten it (it will snap) and do not leave it loose (the adjustment will drift and can damage the valvetrain). Check the clearance one final time, then repeat for the other exhaust valve, then the intake valves (remember the intake specification is different). Before moving on, confirm all four locknuts on the cylinder are tight and re-check each clearance once more.

Turn the crankshaft 180 degrees counter-clockwise (the cam sprocket turns 90 degrees - the original post initially said 90 degrees at the crank and was corrected in the replies). Check the cam sprocket markings, then adjust cylinder 3 intake and exhaust exactly as for cylinder 1. Turn the crank a further 180 degrees counter-clockwise so the balancer TDC mark lines up again, and adjust cylinder 4. Turn a final 180 degrees counter-clockwise (sprocket markings as they were for cylinder 3) and adjust cylinder 2. As a sanity check, the tappets of the next cylinder in the sequence should feel slightly loose when that cylinder reaches its adjustment position.

Refit the upper timing belt cover and tighten its two 10mm bolts. Clean the head surface where the rocker cover gasket sits and clean the gasket itself on the cover. Apply Ultra Grey (or Hondabond) to the gasket, concentrating on the corners, the cam seal area and around the distributor - these spots leak most readily. Refit the rocker cover and torque the bolts to the manufacturer's specification in a criss-cross pattern. Tighten the spark plugs if you loosened them, and reconnect the leads and PCV tube.

Before starting, remove the socket and breaker bar from the harmonic balancer bolt - a forgotten bar will spin with the crank and tear the front guard open. There is no need to let the sealant cure: refit the cover and start the engine. The valvetrain should be noticeably quieter.