Chevrolet 12520274 Cylinder Head & Stud Kit, 4.3Z

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Ensure the heads are clean before reassembly, regardless of whether they underwent valve servicing at an automotive machine shop. Begin by lubricating and installing the first valve, applying moly-base grease or clean engine oil to the valve stem. Depending on the engine's year, size, and model, three types of valve stem oil seals may be used: a small O-ring around the valve stem above the guide boss, a flat O-ring in a groove below the valve stem keeper groove, or an umbrella-type seal that extends over the valve guide. Ensure that new valve stem seals, especially round O-ring or umbrella types, are properly seated on top of the valve guides. Drop the spring seat or shims over the valve guide, then set the valve spring(s), shield, and retainer (or rotator) in place. Compress the springs with a valve spring compressor and install the lower groove seal if using the flat O-ring type, ensuring it lies flat and not twisted. Position the keepers in the upper groove and release the compressor, making sure the keepers seat correctly. A small dab of grease can be used to hold the keepers in place if needed. Repeat this process for the remaining valves, taking care not to mix up components. After installing all valves in both heads, check the valve stem O-ring seals for leaks, a procedure requiring a vacuum pump and a special adapter, which can be performed by a service department, repair shop, or automotive machine shop. The adapter is attached to each valve retainer or rotator, and vacuum is applied with a hand pump. If vacuum cannot be maintained, it indicates a leaking seal that must be checked and replaced before installing the head on the engine. Next, measure the installed valve spring height using a ruler or dial caliper, ensuring it matches the specified height. If the heads underwent service work, this measurement should be correct, but it's essential to verify it. Measure from the top of each spring seat or shims to the top of the oil shield or the bottom of the retainer/rotator, as these points are the same. If the height exceeds specifications, shims can be added under the springs to correct it, but avoid reducing the height below the specified value. Finally, apply moly-base grease to the rocker arm faces and pivot balls, then install the rocker arms and pivots on the cylinder head studs, threading the nuts a few turns only.

Chase the threads in the head bolt holes with the appropriate tap and clean the threads thoroughly.

Cylinder head disassembly involves the removal of intake and exhaust valves and related components.

Scrape off heavy deposits from the valves and use a motorized wire brush to remove deposits from the valve heads and stems.

Begin by lubricating and installing the first valve, applying moly-base grease or clean engine oil to the valve stem.

Complete the installation by following the remaining steps in reverse order.

Once the valves and related components have been removed and stored, the head should be thoroughly cleaned and inspected.

Inspect the cylinder head for cracks, coolant leakage, and warpage.