How to set timing on the head

Timing the Cam to the Crank

There are several ways to time the cam to the crank. Be sure to check the manual before you install the timing chain or belt.

• Some timing sprockets are properly timed when the marks face each other.
• On others, there must be a certain number of chain links between the marks.
• Sometimes chains have colored links that must be aligned with the marks on the sprockets.
• Some overhead cams have a mark on the cam gear that lines up with a mark on the cylinder head when the timing mark on the damper is at the TDC mark.

If the old parts are available, carefully compare the new gears or sprockets with the old ones. Check the keyway and timing marks just in case there might have been an error made in manufacturing. Sprockets are sometimes stamped backward. Its much better to find the problem during assembly, rather than waiting until problems show up after reassembly and reinstallation.

Maintaining Valve Timing

During a valve job, it is essential to keep the timing chain or belt in place to maintain correct valve timing. Position the number one cylinder at TDC. Some overhead cam engines use a single long chain for a cam drive. The chain can be wedged against its guides with a tapered block of wood.
the chain tensioner on some ohc engines must be wedged to keep the chain in position during cylinder head removal. courtesy of nissan motors.

Some engines have a lower and upper chain. These engines do not require special attention to wedging the chain. Be sure to look for hidden head bolts and check the repair manual before removing the OHC head.