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Rh and set up on the engine in a similar manner to that for a new engine in the erecting shop. Slide valves are re-faced, or if they are worn too thin or are otherwise defective they are renewed. Piston rods and valve spindles require re-turning and re-grinding, as they wear unevenly in the glands, and are often found to be badly scored and grooved. Screw threads and cotter holes in them are examined for flaws, which if found, cause the rods to be condemned.

The various pins in the valve gear wear slack in their holes, and the holes in the links through which they pass are found to be enlarged. The metal being case-hardened these holes cannot be re-bored, but they may be made true by lapping them out with a lead mandrel using emery and oil. An alternative and more rapid method now generally employed is to use a special grinding machine with a very small wheel. If the enlarged holes be used as they are, new pins are required, but in many cases the holes are bushed with hardened steel bushes. The wearing surfaces of the quadrant links are re-ground or lapped out. Great care should be taken that all oil holes are in their proper positions and thoroughly cleaned out.

The brake-gear is overhauled and adjusted and new cast iron brake blocks are provided. There are various other details too numerous for description in this primer, and it remains only to be mentioned that the putting together again, of the engine is very similar to the erection of a new engine as described in Chapter VIII.