I'm not trolling anyone. I'm being dead serious after looking at my engine up close. It was ran with air filters it's whole life (30,000 miles). Still there's some light scratching on the insides of some of the bearing surfaces. Some worse than others. Where would an abrasive material come from that could do that? CLUTCH
That's where you misunderstand- the engine bearings are not affected by dirt through the intake tract. Scratches in the main bearings could be caused by a bad clutch, but they could also be caused by infrequent oil changes over the life of the bike. It's true that oil gets dirty as a result of temperature, wet clutch environment, etc, but that's also the reason for the 1500 mile oil change interval.
On the intake side, not running filters will result in wear on the top side- carbs, valves, guides, rings, top part of the cylinder bore, etc.
Also, you vastly underestimate the "tiny amount" of dirt present in the air on the road. Have you ever looked at a dirty air filter before? It didn't collect all that stuff just sitting.
Intake and oiling are two different systems. To say dirt in one is better or worse than the other seems pretty irrelevant to me. Keep your oil changed and your air filter clean and you'll run a lot of miles without issue.
+ one. Very good post.
I will only add that filters are only useful/needed when they actually have something in the supply to collect.
Small particulates are just are wearing as large ones that the naked eye can see. Just because you can't see it, does not prevent it from being harmful.
Air quality makes a big difference. Seldom do allergy sufferers see what effects them, but they sure feel it.
I expect if you live near large bodies of water, like the ocean, your air will be cleaner than if you live out in the dry windy desert. And that will make a big difference in what your engine ingests into the cylinders and blasts onto cylinder walls and valve seats while the engine is running.
So, the engine's metal erosion rate is tied directly to the quality of the air source for the engine. Air filters just make what the engine ingests predictable, rather than dependent and random chance, weather patterns, and dumb luck.
If you live or operate the bike only in an area that has no allergy sufferers being sensitive, no flying insects, and generally clean air quality, a filter is not strictly necessary. But, that leaves few places on the planet where your engine is risk free. The filter removes the risk/gamble, and is why no machine manufacturer on the planet will honor their warranty if the air filter is removed from an internal combustion engine. However, if YOU become the engine manufacturer, it is you that pays for warranty service.
Personally, I can't see any valid comparison to the engine oil supply and filter, unless you are putting in used, dirty oil into it routinely, and NOT using a oil filter.
Just how fast do you want to wear out and/or damage a 30 year old engine? And, what are you willing to do to guard against that eventuality?
