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ROAD and WORKSHOP by
Page 61
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Handyman Hard facing exhaust valves
WHETHER burnt in a petrol engine VV or hammered in a heavy diesel, many thousands of otherwise sound valves are thrown away each year when at least 50 per cent could be reclaimed with a little extra care. Quite often the repairer scrubs the idea of reclaiming valves by building up the face because of poor results arising from a wrong approach to the job, yet with the aid of one or two "tricks of the trade " profitable recovery is easy. Every one in the repair trade is well versed in valve refacing, and many deal quite successfully with replacing the worn or burnt .valve seating. Yet all too often their approach is not all it might be, and the result does not somehow justify the effort. Add a' little method to the job and valve recovery -can be well worth while. Let us see how the job should be tackled. step. by step. • First of all, the worn valve. This must be clean and clear of carbon, and any cracks, burnt areas or lips should be ground out. Next, the working platform, stand or jig. This is most important. A vice, anvil or any old brick will just not do, otherwise the thin area of the valve seating will overheat, burn or melt. A suitable jig can be made quite easily, as follows. Use an old taper roller hub race (still reasonably smooth running), position this on the work bench and, with the back of the outer track at the bottom, secure the outer edge of inner cone to a block of copper 3 to 4 in. in diameter and at least 0-5 in. thick. This is the trick often missed, as the copper block will take care of excess heat and prevent damage to the valve rim.
Drill the edge of the copper block and insert six 3-in.-long pegs of 0-25 in. welding rod and the turntable jig is now ready for use. Ii you are clever enough to power drive the jig at one rev, per minute, so much the better. Now, the rod; Stellite has had the answer for a long time, and their 0-125 in. or 0.1875 in. grade 6 rodis very suitable. Your local B.O.C. man can advise and usually supply. Use oxy-acetylene equipment, and remember that you are not welding steel. therefore a somewhat
cooler flame is necessary. To obtain this, a 225-litre nozzle is used at gauge settings of 8-lb. acetylene, and not more than 10 lb. oxygen, with the flame adjusted to a 0-25-in.-long inner cone, and the longer white cone to just under I in.
Place the valve on the copper turntable, and warm the head gently. To start the deposit, hold the torch with the flame directed all the time at the valve centre and slightly downwards, bringing the inner cone just in contact with the valve seating, warming the rod at the same time. The next step is important. Watch for the valve seat steel to " sweat ", not melt, and at that moment begin to feed on the rod, rotating the jig by a ,touch of the rod, and continue until the circle is complete. Where it is necessary to build up the outer edge of the valve, place a 0-125 in. copper washer below the valve, and the deposit will then flow round the edge smoothly. The final job before machining is to remelt the deposit to smooth out the finish and clear any scale, then allow to cool slowly in dry sand.
Remember, before machining, that any grinding wheel will not do, and when obtaining a wheel make sure that the supplier understands that it is to be used on Stellite.