By 
PWL216
				
					
						I was the winning bidder on a pump powered by a Kohler K91R engine. Based on its specs it’s a 1961. I don’t really have a need for it at the moment, but couldn’t pass it up. Here’s what I found about the K91…
	 
	
		Model: Kohler K91
	 
	
		Spec Number: 31504A
	 
	
		Serial Number: 3019680
	 
	
		Horsepower: ~4 HP
	 
	
		Shaft Orientation: Horizontal (most likely, based on spec)
	 
	
		Year of Manufacture: 1961
	 
	 
	About Spec Number 31504A
	 
	Kohler’s spec number identifies the exact configuration of the engine — including shaft size, PTO options, mounting patterns, and whether it’s for a tractor, generator, or industrial use. While full public spec decoding guides are rare, the “A” suffix usually designates a factory revision or minor configuration changes.
	 
	Spec 31504A is known to have been used on early Wheel Horse tractors, most likely models like:
	 
	
		RJ-58
	 
	
		RJ-59
	 
	
		Suburban 400 or 550