2. If a coolant leak is detected with a clean cylinder head, check the head for deformation. For this purpose, use a ruler and probes or mirror glass. If the surface curvature exceeds 0.08 mm, resurface the head by grinding. Make sure that the minimum distance between the valve disc and the gasket surface is within specifications.
3. Clean the pistons and the top of the cylinder bores. If the pistons are still in the block, be careful not to let carbon particles get into the cylinders, as this can scratch their walls, damage pistons and rings. Turn the crankshaft and clean the rest of the pistons and cylinder bores from carbon deposits.
4. Carefully remove carbon deposits from the cylinder bores, and then pour some liquid oil around the edges of the pistons to lubricate the piston rings.
5. Inspect the valve discs (especially graduation), make sure that they are not chipped or burned. At the same time, inspect the valve seats. If the seats are only slightly burned, defects can be eliminated by simultaneously grinding the valves and their seats, first with a coarse and then with a fine grinding paste. If the valve seats are heavily chipped, they must be regrinded to a seat cone angle of 45°. Valves usually wear and burn a lot, so they need to be replaced and lapped to the seats.
6. To lap the valves, apply some coarse silicon carbide to the valve seat and install «lap» with suction cup on the valve head. rotating «lap» alternating 180°, lap the valve disc against the seat, lifting the valve from time to time to redistribute the lapping compound. When a smooth matt line appears on the valve and seat, remove the compound and repeat the lapping with a fine carborundum compound, turning and lifting the valve as above. When an even continuous light gray strip appears on the valve and on the seat, the lapping operation can be considered completed.
7. Remove all carbon deposits from the valve head and stem. Clean them completely of lapping compound, being careful not to leave any traces of it in the channels and in the valve guides. Clean the valves and seats first with a rag soaked in kerosene, then with a dry rag and blow off the valves, guides and passages.
8. To check for valve guide wear, insert a new, unworn valve into the guide and check for side to side wobble. If it wobbles, remove the guide bushing from the cylinder head with a drift. The outer diameter of the guide is slightly larger (by +0.012 mm), to maintain its interference fit in the cylinder head. Before installing the guide, heat the cylinder head to 80-90°, and cool the guide in liquid nitrogen or dry ice, if possible. Insert the guide so that the spring split ring rests smoothly against the top surface of the cylinder head.
9. Check the free length of the valve springs against a new spring and replace if necessary.
10. Check up crackers of plates of springs where they are available, and if it is necessary, replace them.