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1940 LaSalle Flathead Valves - Hardened Exhaust/ Stock Intake

Started by csearider, November 26, 2012, 03:50:12 PM

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csearider

I am rebuilding my 1940 322 flathead. I will not run ethanol blends in it but will be using regular non-ethanol fuel. I will be replacing all 8 exhaust valves with hardened valves due to the hot exhaust gasses (2 of the exhaust were bent and no good) . I am planning  to use the original intake valves on the intakes ( all 8 in good shape and seat properly)
Below is a 2005 article in Engine Builder written by Larry Carley as follows: http://www.enginebuildermag.com/Article/1171/valve_selection_hot_valve_materials_for_hot_engines.aspx

The bottom line here is that intake valves and exhaust valves both require different types of alloys. The same alloy can be used for both intake and exhaust valves (say 21-2N or 21-4N, for example), but the best results are usually obtained when different alloys are selected for the intake and exhaust valves. Why? Because an exhaust alloy that has good high temperature strength and corrosion resistance really isn't needed on the intake side, and it may not have the hardness and wear resistance of an intake alloy at lower temperatures. Even so, some companies sell the same alloy for both intake and exhaust valves while others offer different alloys for intake and exhaust valves.
Intake valves run cooler and are washed with fuel vapors which tend to rinse away lubrication on the valve stem. So for intake valves, wear resistance may be more important than high temperature strength or corrosion resistance if the engine will be involved in any kind of endurance racing. Exhaust valves, on the other hand, run much hotter than intake valves and must withstand the corrosive effects of hot exhaust gases and the weakening effects of high temperatures. Consequently, a premium valve material is an absolute must on the exhaust side.

Would appreciate technical comments appropriate to keeping the original intake valves

Wayne Womble 12210

Frankly, I wouldn't worry one bit about the valves on a 40 flathead.  They are not subject to enough abuse to cause any recession problems. Just not enough compression and spring pressure for any concern at all. 

csearider

Thank you so much...that is exactly what my machinist said (43 years on engines with many a flathesd). The reason I am going with hardened on the exhaust is that 2 are not useable so instead of just replacing the two will do a set of 8 on the exhaust only. I really appreciate the added backup and will proceed with ordering the valves.....thank you.