GMC 12520274 Cylinder Head & Stud Kit, 4.3Z

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Do not assume that the heads are clean enough for reassembly just because they were serviced by a valve machine shop. Start by greasing up and putting in the first valve, apply moly-base grease or clean engine oil to the valve stem. In such cases, there are three types of valve stem oil seals, depending on the year, size and model of the engine; 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. Make sure new valve stem seals-especially round O-ring or umbrella types-are seated properly over each top of their respective valve guides. Drop these spring seats or shims over each guide and then set the valve spring(s), shield, and retainer (or rotator) into place. Using a valve spring compressor compress springs before positioning with lower groove seal only if it is a flat o-ring ensure it is lying flat without any twist to it. Put keepers in place at upper groove after releasing compressor making sure they really seat properly. These keepers can be stuck with grease if necessary. Take care not to mix up parts when doing other valves in this manner. After having placed all of your valves in both heads, check these vacuum pump operated special adapters for leaking on each head's O ring seals which can be done by either service department, repair shop or automotive machine shop. The adapter should be attached to every valve retainer or rotator while vacuumed using hand pump upon them. If vacuum cannot be maintained, it indicates a leaking seal that must be checked and replaced before installing the head on the engine. Now measure installed spring height using either ruler or dial caliper ensuring it meets specified height measurements accordingly. However, this measurement should be accurate if servicing was done elsewhere but it's better to check again-it is essential though. You should measure the distance from the top of each spring seat or shims to the top of oil shield or bottom of retainer/rotator which are the same points. In case this height is more than prescribed, add shims under springs to bring it down with precautions not to lower it below. From here, apply moly-base grease on both rocker arm faces and pivot balls then install rocker arms and pivots on cylinder head studs threading the nuts just a few times.

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.