Dan that makes sense, so would the rotators not do the same for carbon biuld-up?
Sure, but there's a lot less of that with unleaded fuel and today's oils, too. Basically, the problems that Rotocaps were installed to stave off, are no longer problems.
The lead used to cushion the valves
Not quite "cushion", more like buffer. See
here for what the lead actually did in terms of valve protection.
but it built up and caused problems?
Leaded gasoline made a mess inside engines. The lead salts and associated scavenger chemistry coated the combustion chamber & valves, built up under valve seats and in ring lands, fouled spark plugs, and crapped up the engine oil. In extreme cases it attacked valve metal (dished/necked valves are virtually never seen any more now we don't burn lead any more). Once out of the engine, it formed compounds that aggressively ate exhaust systems from the inside out. A longtime engine engineer I know, who spent many years designing many of the Chrysler engines we know and love, told me about a decade ago the popular perception that gasoline lead was some kind of engine-saving wonder is exactly backwards: "It was more like we had to design engines to give good service
in spite of the lead in the gasoline".
Leaded gas remained on the market as long as it did because it was a cheap way of obtaining octane ratings, it was made by an industry that bought a lot of lobbyists, and with its widespread availability there was no incentive for automakers to spend the few cents extra to upgrade the exhaust valve and seat materials. Once we figured out leaded gasoline was
turning our kids into brain-damaged criminals and
poisoning us, about the same time we figured out we
needed catalytic converters, gasoline lead went away and a bunch of stuff got better (and Rotocaps became obsolete).
Unfortunately, a bunch of other stuff got worseprimitive emission controls made cars run poorlyhence the popular misconception that unleaded gas spoiled everyone's fun. Today's cars wouldn't run nearly as well as they do if we still had leaded fuel.
I'm just tryng to get a handle on why they would be bad, my thinking is like rotating tires, you would get more milege from a part rotating verses one wearing the same spot constantly?
Metal thing repeatedly sitting on metal thing: less wear than metal thing constantly rotating against metal thing.
