CHECK VALVES

VALVE TIMING TROUBLES? With fuel and sparks arriving in the right place and on cue, the only thing left to check is the valves. Start by checking the valve timing if the engine is overhead cam and has a timing belt. Remove the belt cover and turn the engine so the timing marks of the camshaft pulley(s) line up. Now look at the timing marks on the crankshaft pulley. The TDC mark should be lined up exactly. If it isn’t, the timing belt has jumped.

BELT TIMING If the belt has jumped, find out why (wrong belt tooth profile, failed tensioner, seized water pump or idler). Replace the belt. Check the idler and fit a new one if it’s anything less than perfect.

CHAIN DRIVE? Such mayhem is less likely on a chain-driven OHC or OHV engine, but it’s worth checking. Turn the engine until cylinder one is at TDC and the rotor arm points to the cylinder one segment of the cap.

CHECK CAM POSITION Both valves of cylinder one should be on the back of the cam, with some clearance between the rockers and valves. You can also check the cam pulley timing marks on a chain-driven OHC engine.

CHECK CLEARANCES If the timing’s OK, check the valve clearances. If there’s no clearance and the valves can’t shut, the engine will struggle to start when it’s stone cold. A telltale is a suspiciously fast cranking speed.