I must say I find the apparent lack of servicing manuals or an online parts site for Honda very irritating. For ten years I had a Mercury 4str. There are third party service manuals available and mine was very good. The Mercury parts web site is really, really good, with drawings of every bit of the engine and all parts numbers listed. Through it I gained an understanding of the working of the engine as well as problem areas to look out for. This allowed me to decide whether I was capable of servicing/fixing things, or best to leave it to a service engineer.
My new Honda is a mystery, full of bits I don't understand and hardly dare touch for fear of damage or 'negating' my six year warranty. It's not yet two years old, so my local dealer is still servicing it. This doubles, at least, the cost per hour of running the engine. I somehow doubt that I shall be able to continue to pay for all the dealer servicing for the full six years of warranty, thus that warranty will be void. Then, apart from oil and filter changes, the engine will go unserviced unless I can find a reasonably priced service manual and a parts list.
I must say that I am very pleased with my Honda engine. My local dealership and service department are excellent and most helpful and I have every confidence in them and in the engine.
But, my next engine will be from a manufacturer that doesn't, apparently, keep its service information and manuals secret - or for dealer use only. I am sorry to say that, from my current understanding, that engine will not be a Honda. Which is a pity.