Among the literally hundreds of important things you won't see advice about on sohc4.net is the issue of Honda's early four cylinder bikes' chrome plated rocker arms. In an obvious effort at minimalizing costs, Honda on certain models including the sohc fours, hard chrome plated their engines' rocker arms ("followers"), instead of hardening them through heat treating as was done on the rocker arms on for example the 60s-70s 450 DOHC twin. They almost got away with it. I have seen enough 350/400, 500/550, and 750 sohc engines during my more than fifty years at this that I would estimate that around a third of them hadn't failed. Whether through low mileage or studious oil changes I can't say. But most of these rocker arms will and have failed. Of course the hardened ones do also, but in a different way. The chrome on the plated rocker arms eventually breaks open and begins stripping off. This in fact is why aftermarket camshaft manufacturers refuse to warranty the cams they supply for Honda sohc fours and other Hondas that have plated rocker arms.