Thanks for the response valve lash is a little above my pay grade but the oil cooling fins are blown out after every mowing as is the whole machine and under the deck is cleaned as well. The engine is a 32hp vanguard big block, I went with factory filters and HD30 Castrol. The reason I was asking about oil is my dealer recommended 10-40, knowing there is not a huge difference between that and 10-30.... Not sure why, called several other dealers and got a wide variety of different oil weights up to and including synthetic. All fluid levels are checked before every use as well as tire pressures.
Oil is sold on volume basis.
The more I buy the less it costs
I get my mower oil in 44 gallon drums @ $ 500 to $ 900 a drum
Thus I only keep 2 grades
SAE 30 & SAE 10W 40
Same with bottled oil
Buy 10 bottles = full price
buy 100 bottles = 1/2 price
Thus you tend to recommend what you have a lot of in stock.
Mower engines are cheap so they are simple and will happily run with a wide range of oil grades without any problems
About 20% of mechanics actually understand oil .
About 0.5% of the general public actually understand engine oils.
Thus a lot of total BS gets spread about by advertising agencies to make you believe one oil is substantially better than another.
The rule of thumb is the more something is advertised the less value it is.
If there was a "magic" oil out there then professionals would use it.
Just because something works better in F1 race cars does not make it better for your mower.
Now the big problem is the "armchair experts" go & use some super dooper oil that claims it will work for 10,000 hours and actually expect that they will never have to change it cause they never will do 10,000 hours on their mower ( invented number )
Thus they run on dirty contaminated oil and end up buggering their mower.
Even worse is because this "super oil" is 10 x the price of Walmart oil they expect it to last 10 x as long.
For most average home owners, (about 50 hours mowing a year ) a single oil change every years at the end of the season will keep their mower running fine.