Valve clearance

[nat]

     When I put my, (1924), car on the road I adjusted the valves to .003" and .004" hot and drove it many miles that way.  

     Last week I checked them cold, wrote down the clearances and rechecked them when it was good and hot.  Cold, all the intakes were .002" wider and the exhausts .001" to .0015" wider.

     The intake valves have a cast iron head and steel stem and the exhausts are "Silchrome" which at that time was a martensitic stainless steel.  The difference in those materials may be the reason that the, (colder), intake valves expand more than the exhausts.

     Dodge Brothers and Graham Brothers used identical engines, (correct me if I'm wrong), but specified different valve clearances.  That may have been because the trucks engines would likely work harder than a passenger car and/or be a difference in opinion between Dodge and Graham.    The tiny clearance specified by Dodge suggests that all is well as long as some, (no matter how slight), clearance always exists.  Lack of clearance will burn the valves in a jiffy.   Excess clearance will only cause harm if it's enough to batter the cam and lifters.

     Having recently done it several times, I can have the necessary tools ready, park where the lighting is best and adjust the valves before the engine has much chance to cool.  Even then it seems there will be a difference in temperature between the first and last valves that are adjusted.  I'm inclined to add .002" to the desired hot clearance and adjust them cold.  It's easy enough to check them hot and running.

     It also dawned on me that if the ignition timing is set when the exhaust valve just closes, the Graham clearance will cause the timing to be a little more advanced than it will be if the smaller Dodge clearance is used.

[MikeC5]

I don't have MIM handy but I thought the valve clearances in it were given cold (I can't remember the values).  I'll try to dig it out and confirm.  Where did you find the hot clearances?  I'm a believer in giving a bit more clearance to ensure no valves are burned.  A relevant link:  https://forums.aaca.org/topic/200946-25-db-valve-settings-cold/#comment-1021999

Edited April 16, 2023 by MikeC5 (see edit history)

[Mark Gregush]

1914-1927 Mechanics' Instruction Manual, bottom page 134, hot. Under "Valves" in the Engine section. 

[MikeC5]

The grey matter ain't what it used to be...