Technical Tips no 42 – Austenitic valves
Some years back I was the proud ownerof a 1938 Packard 120. Unfortunately this particular car had a reputation for being a bad starter especially when hot. It was assumed the problem lay in the ignition or timing as the engine had been rebuilt by experts some years previously and over the years had had very little usage.
As a youngster I was brought up with this type of car and to my memory they started without a problem even in icy conditions. I recall our family car (6 volt) starting without serious problems even when covered with ice and snow.
Speaking to an expertwho had worked on these engines in his youth,he warned that the problem most likely lay with the exhaust valvesas the car had stood for long periods between being used, and when rebuilt, it was most likely fitted with NOS (new old stock) valves. On the strength of his advice and with the results of a compression check we pulled the head off and found he was correct. The exhaust valves were covered with very fine pitting and therefore leaking. Strangely enough, the compression check showed the compression was within acceptable limits.
I was advised that rather than “lap” the valves “in”to rather replace them with austenitic valves. It was explained that austenitic meant the valve would be manufactured out of a non magnetic material typical of most diesel engine valves.Evidently these valves are made out of a material which has much better resistance to rusting or pitting.
After scratching around numerous engine part suppliers we eventually found austenitic valves of a similar size to the Packards that needed the minimum of machining. Once fitted, the result was incredible. Never again was there a starting problem, hot or cold.
The bottom line is not to fit NOS valves or valves made from an early softer type of material but rather find equivalent size valves made out of a more modern material.