So-called matched parts
I’m repeating myself, I know. A lot of people think that certain Honda parts are matched and cannot be separated and mixed. Cam bearing caps, for example. The discussion inevitably includes the term, “line boring”, a term that conjures up images of the 1940s rebuild tech of honing cam or crank journals while rebuilding a cast-iron V8 engine, or resizing the connecting rods in the same engne. However, this is not how Honda engines are manufactured. Honda’s machining is so precise that the parts can indeed be interchanged with those from another identical engine, and this is true whether the parts are assigned part numbers or not. Hondas have always been like this. And regarding the specific case of the cam bearing or holder or plate, many people are not aware of the kind of clearance they are made with. It’s huge—as in 0.005”-0.007”. Thus there is even more freedom to swap parts. Bottom line—the ability to swap Honda cam bearings has been there from the beginning. It has not only legitimately and successfully been practiced by generations of professional mechanics, Honda themselves has endorsed it.

The same is true of carburetor parts that many seem to think are matched, when in reality it is only the arrangement Honda has made with the parts vendors that results in some parts being sold only as sets. It’s marketing. It has nothing to do with engineering.

Marvel Mystery Oil
Let’s cut to the chase. Marvel Mystery Oil is almost one hundred percent mineral oil. Baby oil, in other words! Is that some kind of magical ingredient? That alone should stop you in your tracks. But there’s more. Any first-semester mechanics school student knows the danger of adding oil to a four-stroke engine’s combustion. It’s a fast track to detonation. At least one technically archaic piston airplane engine manufacturer has issued warnings about Marvel Mystery Oil, it being a perversely enduring apocryphal practice in private aviation that is demonstrably harmful to their engines. And Marvel Mystery Oil’s use persists in powersports for the same reason—folks just have to feel like they’re doing something meaningful while at the same time cheap and easy. If they knew how rapidly Honda cylinder heads carbon up and what the consequences are, they wouldn’t. But “snake oil” continues to entice.