High Zinc (ZDDP) Engine Oil: My 2 cents
Just my 2 cents, exchange rates may vary.
The engine oil additive package often called "Zinc", refers to the compound ZDDP which is an abbreviation for a much longer scientific set of names for Zinc and Phosphorus that I am not going to try and type out. Apparently, this compound does a number on catalytic converters and has been reduced in most typical automotive engine oils.
Per the literature, the ZDDP is a clingy particulate that works to prevent metal to metal contact under high load, and makes a big difference with flat tappet camshafts.
After getting my first Walk behind Gravely, a 1968 model L, I started to dig around about oil types and came to the conclusion that the High ZDDP should make sense for these older engines, and in particular the bronze gear in the differential.
My search first landed me on the Valvoline VR-1 Racing Oil, and I've tried that in my L with no issues so far.
Digging around some more, I find that the Lucas Hot Rod and Classic Motor Oil has about twice the ZDDP of the VR-1, So I ordered a case of 3 of the 5 Quart jugs.
I put the Lucas in the Kohler engine and gearbox of my Commercial 10A and will see how it goes.
Lucas also has a Marine Engine Oil with even more ZDDP, but I was able to find the Hot Rod stuff much easier.
Just looking to pass along my thoughts, but I am far from an expert on this stuff, just a guy looking to protect his old beaters