LETTERS


| November/December 1960



Chippy

THAT MARSH VALVE GEAR AGAIN

Since the Advance is one of my favorite engines and I like the Marsh valve gear, the recent articles by LeRoy Blaker, Edward Hutsel and Joseph May were very interesting to me. I have engineered two different Advance engines with Marsh gears a total of six threshing seasons, also several different engines with Woolf and Link gears, and I certainly will not agree that the Marsh is the 'worst' valve gear.

I agree with Mr. May in that I do not think a clear exhaust or 'bark' is an indication of economy or efficiency. I think engines with a short distance from exhaust port to nozzle such as the Advance simple or Avery under-mounted will 'talk' louder than where the exhaust steam has to travel farther and maybe thru a heater. The tandem-compound Advance engines have a soft, muffled exhaust, this means to me that the expansive force of the steam has been used in the cylinders to produce power instead of making a bark up the stack. Advance engines are usually considered as very economical so the Marsh gear must not be too bad. I understand Advance Rumely tested other valve gears on their new engine, before deciding to use the Marsh gear.

I have found the Marsh gear easy to care for and keep snug. I believe the small number of joints and the short, easy motion accounts for this. And in spite of the lack of extra notches for the reverse lever the Advance seems to handle as easy or easier than most engines, running slow 'stiff-geared'.

The large, heavy strap and arm of the Woolf and other single-eccentric gears, with considerably more throw than the travel of the valve-stem, along with the sliding block, guide and pivot all add up to many joints with possible lost motion and noise. I am not trying to say that the Woolf is the 'worst' gear, I like the sound of a well-adjusted Case as well as the next man, but I will not agree that the Marsh is the 'worst' valve gear either.

I agree with Mr. May, that a properly designed valve seat will not wear uneven from 'hooking up'. When the valve opens to 'lead' at one end the other end slides off the raised edge of the valve seat, if not made this way it could possibly wear shoulders on the seat even with fixed cut-off gears. I would be inclined to believe that with reasonably good water and good lubrication it would take a long time to wear a shoulder even if the valve stopped short of the edge of the valve seat.

O. R. ASLAKSON, New Rockford, North Dakota