All Crop Cylinder Tach?

They are for cylinder speed yes, are they common, no.  I would say they are borderline rare.  I am not near ours, to be able to say for sure where they connect to, but I think it is on the rotor shaft at the drive belt connection.

When we sold them a small counter was included with the combine.  We used those to measure the proper PTO speed.  We had set the cylinder speed so many times we - don't laugh - did it by sound.  In fact, we did not check it with the counter - only the PTO speed and the separator speed. 
Thinking back when the 60 first came to us we used spacers to set the cylinder speed.  We put a certain number in for wheat and certain ones for other grains.  It was later that the crank for setting speed came out.  Needless to say we were delighted.
As far as the tack shown above we never installed on non did we have the demand.
Good Luck!
Bill Long

ps:   Please don't laugh but we sold and set up so many 60's that we could listen to them and tell what was working right or was wrong.  In fact when I look back and think about it they were an easy machine to work with.  Once you had them set up unless the machine was physically damaged or a part wore out they were trouble free.

ours had a little rubber tipped hand held tach, that you checked the cyl speed with, would fit in the palm of your hand, came with the combine...

DiyDave wrote: ours had a little rubber tipped hand held tach, that you checked the cyl speed with, would fit in the palm of your hand, came with the combine...

looked something like this.

I still have the hand held one from my Dads Allcrop, Still in the Stewart Warner can.

There is an older one, that is spring loaded, has a scale, on a tube, that has markings, reads like a ruler, lowest speeds on left or bottom of the tube, higher  speeds to the right, or top of the tube.  About the same diameter as the S-W gage, bit the tube sticks out the top.  Kind of looks like a dredel toy...

Not exactly pertinent to the thread, but a memory has been recalled. I have many memories of my Grand Dad. Some are in my mind as if a quick video clip. In the '53 to '54 time frame, Pop Pop had just traded his Allis combine to Mr. Long's dealership for a new Allis combine. He was using a revolution counter that was pushed against the end of the shaft and his watch to determine the rpm's. I crowded in too close while watching and received the only scolding that I can still remember from him. I heard all about the dangers of exposed belts and pulleys. I have never learned the models. The old unit required a rider that filled bags and then slid them down the chute onto the ground. The new combine stored the grain and then unloaded into the truck when the bin was full.
Thanks for helping to recall the good times.
Jim

The Prigel farm is in Baltimore county, Maryland. I don't factually know the source of the combine, but uncle Bob remembers dealing with your family business until it closed. Hence, I assumed that it came from the Longs. If I'm off on the timing, the memory could be from as late as 1957.