Here is the article I read concerning the routing of the oily air. Look at page 9 of the article and you will see that Harley did indeed route the oily mist to the transmission.

www.cycleworld.com/harley-davidson-motorcycles-new-milwaukee-eight-big-twin-engine

 

I read the following:

"Small details are important. In the past, if the oil was overfilled, excess oil could wet the air filter via the breather. This has now been rerouted through the transmission case."

I am not sure what they are talking about. There may be some sort of additional relief system...or they could just be wrong. Sometimes magazines get it wrong. I read in one magazine that the M8 has solid lifters. But when I actually checked out the lifters, they are not solid, they are hydraulic.

In any case, the M8 uses the same breather bolts the Twin Cam does. Those breather bolts route hot, oily, oxygen depleted air from the crankcase up thru the breather bolts directly into the air cleaner.

Again, there may be an additional relief system, but the breather bolts are still there, and they are still routed into the air cleaner.



Below are a couple of photos of an M8 with the air cleaner cover removed.

You can see the breather bolts with the hoses coming off of them, and the T together and then dump into the back of the filter element.

 

In that same article in the photo of the motor on page 11 you can see the two breather bolts very clearly. Like mentioned before by DK, maybe there is some other routing also. Or the writer misunderstood and or didn't get the complete story.

 

I couldn't understand why Harley would route that crap into the transmission either.
You are most likely correct about the writer not knowing what he was talking about; sort of like the news media on the 5:00 pm news.

 

"Small details are important" True that, it says "This has now been rerouted through the transmission case." Not to the transmission case. Which makes even less sense?

If you think about it, a crankcase cannot be sealed, the piston ring blowby gasses have to go somewhere or it would pressurize. So you vent the crankcase at the highest point to keep as much oil mist in there as you can. Cars use a PCV valve; Positive Crankcase Ventilation for when there's positive pressure route it to the intake, but don't let air suck back in when there's not. The high places on a V-twin, like in a car engine, are in the area above the cylinder head under the valve covers, and they are connected to a couple of drain paths. Oil comes in to the rocker assemblies via the pushrods, and drains back down a drain path; gasses come up through the pushrod covers.

Are the drains now somehow routed through the transmission case on the way back to the pump? Or maybe the transmission is vented to the same drains, and any excess overfill oil backing up into it? I don't know, just some thoughts. The writer might have got the why wrong, but he must have seen that something was done to mention it.

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Edit:

For comparison, I looked at the manual on my '14 Rushmore; about the oil return, it says "Oil flows through the upper passageway in the crankcase, enters a passageway at the front of the transmission housing and empties into the oil pan onto the front of the baffle plate." Maybe they just drilled a hole there? Ha, doubtful! Maybe it's still the same but the writer took that the wrong way?

Here is the vent path:




As for the drain path on the Rushmores:



Anybody got a manual for a '17 to see how it's different?