with Jim Cambron
When Rocker Arm Cap Screws Turn Up Missing
When you remove the valve cover to inspect the valve train, be sure to check the flat-headed Philip head screws that hold down the rocker arm shafts for tightness. Occasionally, one of these flat-headed screws come loose -- especially after work has been done involving these screws. If you notice a screw is missing, a careful examination of the top of the head assembly is in order. If you are lucky, you'll find that the errant screw is in the bottom of the oil pan. It got there by being "rinsed" down one of the two oil passages indicated in the picture. The red circles indicate the return passages from the head as viewed through the block from bottom.
A distant second place is in a remote corner of the top of the head where the screw is waiting to move to the worst place -- under a cam lobe! If a screw falls under a cam lobe, it can jam the camshaft causing the timing belt to snap. Fortunately, because most stock pistons have indentations in their tops to provide clearance for stuck open valves, there is little chance for damage to the valves or pistons to occur. Your timing belt, the belt tensioner mechanism and the camshaft itself may not be so lucky.
Here is a picture of a screw that was fished out of the bottom of the oil pan on an engine I am rebuilding. Fortunately, it didn't cause any damage while getting there...
It is important to note that while rocker arm cap screws do occasionally work themselves loose, it is usually due to improper torqueing in a previous repair. Be sure to tighten down these screws to factory specification.
According to the 1988 Samurai Shop Manual (Page 3-46) the torque specification is:
- 9-12 N-m,
- 0.9 - 1.2 kg-M
- 7.0 to 8.5 lb-ft. (for the metrically impaired)