I'm assuming he is referring to the manufacturer's recommendations and not what is required to keep the engine airworthy. You can write in basically anything a

I'm assuming he is referring to the manufacturer's recommendations and not what is required to keep the engine airworthy. You can write in basically anything as a manufacturer, doesn't mean it is binding unless it is an official communication. For example, I have a dirt bike that states to replace the piston every 10 hours of operation.