Thorough cleaning of the cylinder head and related valve train components, followed by a detailed inspection, will enable you to decide how much valve service work must be done during the engine overhaul. Clean the combustion chambers with a wire brush to remove all carbon residue, and scrape away old gasket material and sealing compound from mating surfaces, being careful not to gouge the cylinder head. Remove scale build-up from coolant passages, use a stiff wire brush to clean oil holes, and run an appropriate size tap into threaded holes to eliminate corrosion and thread sealant. Clean the threads of the exhaust and intake manifold studs, then clean the cylinder head with a soft brush and solvent, ensuring thorough drying, possibly using compressed air. Clean valve springs, shields, keepers, and retainers with solvent, taking care to clean one valve set at a time to avoid mixing parts. Scrape heavy deposits from the valves and use a motorized wire brush for the valve heads and stems, ensuring not to mix up the valves. Inspect the head surface, intake and exhaust ports, and combustion chamber for cracks, replacing the cylinder head if any are found. Check the cylinder head and manifold mating surfaces for warpage using a straightedge and feeler gauge, and examine valve seats for pitting, cracking, or burning, which would require valve reconditioning. Since checking valve guide clearance requires specialized tools, it is advisable to take the head to a machine shop for this. Inspect each valve face for wear, deformation, and cracks, and measure the margin width, replacing any valve with a narrower margin than specified. Inspect valve springs for wear and pitting, measure their free length, and check for squareness; any distorted or sagged springs should be replaced. Any damaged or excessively worn parts must be replaced, and if the inspection indicates that the valve components are in poor condition, reassemble the valves in the cylinder head for further servicing recommendations. If no excessively worn parts are found and the valve faces and seats are in good condition, the valve train components can be reinstalled without major servicing.
Posted by ToyotaPartsDeal Specialist 
