ENGINE 87 Fig. 14 Fig. 15 Fig. 16 REMOVAL OF VALVE SEAT INSERTS For both inlet and exhaust valves, valve seat inserts are standard fitment. They are shrunk and then pressed in cylinder head. Therefore, removal of valve seat inserts should be done only if they are damaged beyond repair or worn out beyond specified limits. 1 For removing seat inserts from cylinder head, use suitable boringmachine. Bore old insert thin (about 0.5 mm thickness) and then try it out. 2 Alternatively, use a suitable turning tool to cut an angular groove into seat insert and then pull it out with a suitable puller. In order to avoid damaging of machined cylinder head parting surface, place copper or any other protective sheet-metal under puller supports. 3 Measure basic bores for valve seat inserts with bore gauge. If the boring and prying is done carefully without damaging the parent bore of the inserts, fitment of an oversize insert will normally be not necessary. However, if the parent bore dimensions deviate from the values specified, enlarge bore to the next repair size. This should done on a suitable fine boring machine. 4 Re-machined bore must exactly be at right angles to the cylinder head surface and the bore size should be strictly within specifications so as to ensure proper interference fit of the inserts. 5 Clean basic bores in cylinder head and seat inserts thoroughly before fitting. INSTALLATION OF VALVE SEAT INSERTS 1 Place valve seat inserts in liquid oxygen for about 20 to 30 minutes to bring their temperature down to - 195 deg C (when liquid oxygen stops no longer producing 'vapour' and stops spurting, valve seat inserts have a temperature of approximately - 195 deg C). If liquid oxygen is not available, keep inserts in ice and salt mixture for about 6-8 hours. CAUTION Do not touch liquid oxygen or chilled valve seat inserts with your fingers. Use a pair of tongs. 2 Heat cylinder head to approx. 80 deg C in a water bath. 3 Take seat inserts out of liquid oxygen by using tongs and place on bore of heated cylinder head (Fig. 15). Install them quickly by slight hammering with the help of a drift. Fig. 16. 4 After inserting seat inserts, check distance between parting surface of cylinder head and face of valve seat insert. If necessary, re-machine the face with an end mill/suitable cutter. 5 Machine valve seats as per specifications.
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