Technical Paper
EXHAUST-VALVES AND GUIDES FOR AIRCRAFT ENGINES
1924-01-01
240033
Trouble with the exhaust-valves of the Type-J air-cooled cylinder caused an investigation to be made of valve-cooling and of valve and guide wear. A temperature of 1300 deg. fahr. invariably caused fractures of the exhaust-valve stem at the junction of the stem and the neck. A file-hard tungsten-steel valve with a shallow hole and no filling eliminated breakage but scaling was apparent. The same valve, using a hard tungsten-steel guide, when tested with salt filling, gave improved cooling; the area of the hot zone was reduced in size and the stem remained dead-black. Scaling was reduced and the wear of the valve-stem and guide that appeared was overcome by substituting a roller tappet for the solid tappet previously used. Tests showed that extreme hardness is of advantage even for inlet-valves. Experiments with a Type-K air-cooled cylinder gave excellent results with a salt-cooled valve in spite of a very high head-temperature; with an unfilled valve the results were not so good.