High Fenders: Is Gravel Spray Blasting Your Engine?

How are the air cooled engines of motos with high fenders being protected from destruction by gravel spray? The delicate fins and even the engine cases themselves, I mean. For instance, if you're doing something like traversing the looooooooong gravel roads of Alaska what's to keep your engine from being sandblasted into powder?

This TW200 has a high fender conversion; you can see from the immense volume of mud, and the spray patterns thereof, that while the high fender keeps the front wheel from locking it's also completely exposed the fins and cases.

Air cooled dirt bikes and enduros have been using the high-fender-exposed-engine design for decades, so maybe blast from gravel spray really isn't an issue like I think it is, or is it genuinely an issue that the OEMs decided just isn't their problem?

I would only worry about mud on the engine blocking the air from keeping it cool. I have the stock low fender and a mud flap on my 2013. I just try to keep mud from building up on the front of the motor and clean it off if it does.

Mud, mud, glorious mud,
Nothing quite like it for heating the blood . . . when your front wheel keeps locking up.

Some gravel rash is preferable to frequent sudden "naps".

I have used a piece of "garden border" black plastic (stiffish but mildly flexible ~ and very cheap per multi-yard roll);
cut and shape with tin-shears;
use your own ingenuity with placement & attachment.
No beauty prizes, of course.

As a general rule, the plastic strip needs be only slightly wider than the front tire, to block 90% of the unwanted rubbish.
If the strip is about 6 inches or more ahead of the cylinder, then the oncoming air flow will eddy around both sides, and maintain fair cooling.

This. That is all.

I've never had mud be an issue with an air cooled motor. My ninja 250 on the other hand would pack the radiator full of mud and boil over in a couple minutes. That was with the stock fender.

I don't know about high fenders, but every ride starts and ends on gravel for me, so I have bash plates on my bikes, and they look like they've been peppered with birdshot. I have to believe an unprotected engine, given enough gravel miles, would suffer, no?

That bike has a short fender that looks more like an aftermarket supermoto fender. I say that because my friend's 225 has a similar fender and that is what his was.

A short flap can always be added at the back to reduce the spray up into the engine without adding a bunch of weight and still being flexible if it contacts something. I had them on my trials bike when I ran a custom high fender on the front.

By the way, ever look at the spray of gravel and crap that hits the engine of a flat tracker running no fender? Motocrossers as well, get a lot of spray on them. High fenders have been on most all off roaders since the late 60s.

It's not the issue you think it is. End of story.

As your own picture illustrates, the skid plate and the header pipe (at the curve) receive the clear majority of mud and other detritus. The same outcome is evident on my DR650, with its [properly] high fender. The underside of the skid plate on my bike is rough from miles of gravel and such, but that simply means it's doing its job.

You already have a skid plate fitted, and I'd guess that you clean your bike after rides such as what is evident here. You're good to go.