Piston Valve Clearance - Keep 'Em Separated - CHP Step By Step

Once the clay was pressed into the valve reliefs, Shoemaker set the head onto the block. You know the rest of the drill: Lifters, pushrods, and rocker arms must be in place on the cylinder being tested. Checking springs are still a good idea here. The test can be done with or without head gaskets-just be sure to add in the gasket thickness if you test without.

With the head bolts snugged down and the valvetrain in place, Shoemaker again turned our test subject through a full rotation. With the heads removed, the impression left by the valves on the No. 1 cylinder is readily apparent. Take note that the marks left in the clay by the valves match the reliefs in the piston, both in shape and size. If they don't, the pistons will need to be cut-or replaced-to work with your chosen cylinder heads.

Of course, the main goal here is to determine just how close the valves are coming to the piston. Shoemaker carefully cut through the clay impression with a razor blade. The idea here is to create a sharp cross section that will provide an accurate depth reading. Note that Shoemaker is carefully cutting the intake side without disturbing the exhaust side.

The clay depth can be measured in several ways; Shoemaker prefers a dial caliper that allows for depth measurements. For accuracy's sake, it's important to measure the clay impression without digging into it with the caliper.

In this case, the tale of the clay shows that we have 0.080 inch clearance between the intake valve and the piston. Add in the thickness of a gasket, we'll say 0.039 inch in this case, and we've got a more-than-safe 0.119-inch clearance for this hydraulic-roller motor. If you're curious, the exhaust valve in came in at 0.090 inch, providing for 0.129 inch clearance. In a solid-roller motor, we'd also add 0.020 inch hot-lash clearance. And with that, we can assemble this engine without worrying about Mr. Valve meeting Mr. Piston. CHP