Use a razor blade or thin, sharp knife to cut carefully through the center of the impression made by the intake valve.Īny number of factors or changes to an engine will influence piston-to-valve clearance, such as decreasing the piston deck height or angle milling the cylinder heads–both of which will boost the compression ratio but require disassembling the engine and machine work. Now you can observe the distinct impressions in the clay on top of the piston. There’s a chance the clay may adhere to a valve, so carefully remove the cylinder head so that the clay is not disturbed. Remember, it takes two crankshaft rotations to completely rotate the camshaft once. With a ratchet and crank socket-or in our case, the timing wheel-rotate the crankshaft in the normal direction several times to ensure that the valves make a good clean impression in the clay. Regular valve springs can be used for the clay method, but it’s much tougher to rotate the crank. Finger-tight is okay for securing the rocker arm. Install the rocker arms and zero the valve lash. A solid lifter must be used for measurments. Hydraulic lifters will bleed down and corrupt the measurements using both the clay or indicator methods. If the engine is to be built with hydraulic lifters, they cannot be used for checking clearances. Position the cylinder head on the block and use enough head bolts to tighten snugly. 030 to each valve if the engine is equipped with aluminum rods as they tend to stretch more than steel. 100-inch for exhaust, which requires a little more clearance because of the increased heat factor. So, how much clearance is enough? A safe rule of thumb is. Once you determine the difference, you can subtract that number from your measurement, and this total should still be within. Otherwise, you’ll need to measure the thickness of your new gasket, then check with the manufacturer to find the compressed thickness. A head gasket with the proper thickness is required to ensure accurate clearance measurements. Avoid excessive amounts of clay on the edge of the piston to keep clay off the cylinder wall during measurement.Įach valve receives a light oil treatment to help keep the clay from sticking to the valve face as the crankshaft is rotated. Press a generous piece of clay into the two valve reliefs on top of the piston. This is non-hardening clay that molds very easy when it's warm.īefore placing clay on the piston, apply a thin coating of either WD-40 or light engine oil on the cylinder wall to help keep the clay from sticking during the measurement process. Modeling clay can be purchased at a local craft store. After attaching the timing wheel and pointer, set true top dead center (TDC). A simple crank socket and ratchet can be used in place of the wheel for turning the engine over while using the clay method. The clay method doesn’t require a timing wheel, but we’re setting up in preparation for demonstrating the dial-indicator method. The valves are installed on the cylinder head for the corresponding cylinder using checking springs (more on those later). Make sure the cam is degreed for the intended setup as the cam position will affect piston-to-valve clearance. The short block is set up with the camshaft, timing set, crankshaft and at least the Number 1 piston and connecting rod with the proper bearings. Shown are the main tools needed to check piston-to-valve clearance: modeling clay, machinists scale, dial-indicator and base, timing wheel, pointer and checker springs.
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