2. If a coolant leak is detected with a clean cylinder head, check the head for deformation. For this purpose, use a ruler and feeler gauges or a mirror glass. If the surface distortion exceeds 0.08 mm, restore the head surface by grinding. Make sure that the minimum distance between the valve plate and the gasket surface complies with the 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 the cylinder walls and damage the pistons and rings. Turn the crankshaft and clean the remaining pistons and cylinder bores of carbon.
4. Carefully remove any carbon deposits from the cylinder bores, and then pour a little liquid oil around the edges of the pistons to lubricate the piston rings.
5. Inspect the valve plates (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, the defects can be eliminated by simultaneously grinding the valves and their seats, first with a coarse and then with a fine lapping paste. If the valve seats are heavily chipped, they must be ground again until the seat cone angle is 45°. The valves usually wear out and burn heavily, so they must be replaced and ground to the seats.
6. To lap the valves, apply a small amount of coarse carborundum compound to the valve seat and fit the lapping tool with a suction cup to the valve head. Rotate the lapping tool alternately 180° to lap the valve plate to the seat, occasionally lifting the valve to redistribute the lapping compound. When an even matte strip appears on the valve and seat, remove the compound and repeat the lapping with fine carborundum compound, rotating and lifting the valve as described above. When an even, continuous light-grey strip appears on the valve and seat, the lapping operation is complete.
7. Remove all carbon from the valve head and stem. Clean them completely of lapping compound, making sure that no traces of it remain 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 channels.
8. To check the valve guide for wear, insert a new, unworn valve into it and check for wiggling. If it does, remove the guide from the cylinder head using a drift. The outside diameter of the guide is slightly larger (+0.012 mm) to maintain a tight 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 snap ring fits smoothly on the top surface of the cylinder head.
9. Check the free length of the valve springs against the new spring and replace them if necessary.
10. Check the spring retainer crackers, where present, and replace them if necessary.