Q: What steps should be taken for thorough cleaning and inspection of the cylinder head and valvetrain components during an engine overhaul on GMC Jimmy?
A: When you remove the cylinder head for cleaning, it is advisable to clean also the other valvetrain related parts and then inspect them so that you determine how much work has to be done on the valves during the overall engine rebuilding process. To prepare the surfaces, first remove all matted deposits of gasket and sealing compound from the head gasket, intake manifold and exhaust manifold contacting surfaces with a dull scraper for the gaskets and gasket removal solvent; do not attempt to use power tools or old-fashioned metal scraper that can scratch the surface of the machined parts. Scrape off the deposits formed round the coolant passages and scrub the oil holes by using stiff wire brush. Small threads allow for a suitable size tap to be fitted in each threaded hole to remove rust and the thread sealant; use compressed air to blow any debris if available. Use die to clean all the threads of the exhaust and intake manifold studs and use wire brush on all the rocker-arm stud threads. Wash the cylinder head with the solvent and make sure that you dry the parts properly, use a compressed air to help you hasten the process. The concept of decarbonising chemicals may be relevant but has to be approached cautiously. With solvent, clean rocker arms, pivot ball and push rods. Wipe off dry then proceed to clean each and every valve spring, keepers, retainers, rotators, shields and spring seat one valve at a time so as not to mix them. Remove thick and thick rust from the control valves and use a motor wire brush for the heads and stems of the valves, but should not mix them. Check the head and the block for cracks, leaks of the coolant, and other mechanical problems; if necessary, change the head. To determine if this surface is warped beyond limits, place a straight edge on the face of the gasket mating surface and use feeler gauges to measure the warp, and if yes resurface. Intensively check valve seats for pitting, crack out, burnt area so it may require professional service. It is essential to check the inside diameter of the valve guides then measure them to compute valve stem-to-guide clearances with a view of defining where reconditioning or replacement is necessary. A study of the rocker arm faces will reveal excessive wear, the ends of the push rods for scuffing while rolling them over a flat surface will reveal bending. For each valve face look for the cracks, pits, burned spots, the condition of the valve stem and the neck must be checked for the cracks and excessive wear. Check the width of the valve margin and compare it to the recommended width and supply broader ones if the valve margins are narrow. Take measurements on the valve stem to establish the valve stem to guide bore to ascertain if the steps of reconditioning the valve will be necessary or not. To do this look for wear and pitting on the lower ends of the valve spring, examine their free length prescried by the manufacture's manual and lastly make sure they are at right angles to the cylinder head. Check spring retainers and keepers for signs of wear or cracks and replace any worn out part. If an inspection reveals that they are in rather poor condition and show signs of excessive wear, then reinsert the valves in the cylinder head and operate them in accord with recommendations on valve maintenance. Unless certain of greatly worn valve and guide contact areas or valve faces and their seats are found to be worn, the valvetrain components should not require major service but the valve could be had recooked up, for new-like specifications, if engine has high mileage and is being build up to new standards at automotive machine shops.