The simple truth is all engines can benefit from a crankcase ventilation system that vents to the atmosphere, the level of benefit is debatable. Since production engines very on ring seal, the amount of blowby introduced back into engine will very from bike to bike. It comes down to how much blowby (oil) you think is too much. If your bike is saturating the air filter between maintenance intervals, install an external breather. If its not, then there is little benefit from modifying the factory system.

 

Agree with sixguns.... Find out what the limitation is, where you are pushing or pulling air from based on your seals, worn, overuses parts, and vent accordingly. Running head breathers out the back isn't venting. Venting the oil tank, in my opinion isn't solving the pressure issue. Its the breathers in the rockers and the current flow of air from crank to cam to oil tank

 

Actually, the current air flow vents crank pressure, over the transmission into the oil tank via the transmission cover. That is exactly where the Trask Check M8 transmission cover is installed to vent the crank case pressure to the atmosphere.

A seal has been installed on late model 2019 and subsequent M8's to prevent crank pressure from pressurizing the oil pump and cam chest limiting crank pressure to the crank case and oil tank via the transmission cover.

 

Blowby is produced in the Crankcase and flows to the Cam chest. It used to do that through two paths - the cam bearing and the crank bearing.
Before the seal, the crankcase, cam chest, oil pan and heads all shared the same airbody - think of it as one big balloon. They are all connected with pathways with little restriction to each other.

High speed widely swinging pressure oscillations in the engine could occur as the pistons move up and down creating alternating vacuum then pressure, plus the added blowby, all in this unregulated large air body...
It was believed that those pressure oscillations de-primed the oil pump. [That's the theory]

To fix this, HD introduced the new Seal.
The new seal (behind the oil pump) closes off the crank bearing path leaving only the smaller cam bearing path and thus SLOWS the flow of pressure into the Cam chest - it retains pressure - it isolates the crankcase - it makes the balloon smaller...
This was done to keep the crankcase at a more stable/even pressure level, which aids in keeping the oil pump primed.
So the business end(s) of Team No-Sump are this Seal and the Isolated crankcase.

Getting to it... the blowby/pressure that is slowly bleed off the crankcase enters the cam chest.
The cam chest shares air space with the oil pan and the heads through pathways - they are all at the same pressure. The head breathers (2) vent off this pressure as normal.

So... adding a third vent to the trans cover/dip stick etc is only releasing pressure in the cam chest/oil pan/heads - not the crankcase.
It does nothing for sumping and not much for performance - the air body doesn't care what the air pressure is (the business end is the crankcase).
It does however, aid in slowing the flow out the head breathers which has the added benefit of keeping the intake track cleaner... which you could do just the same with a bypass.

So is a cleaner intake worth 300+ bucks or even 100 bucks? Not sure, but you can get the same effect as mentioned by venting the head breathers to atmosphere or catch can and you can do that for 20 bucks depending on the mod.

Sorry for the wall of text.

 

I am not disaggreeing with you. But if you take the cam chest off and crack the transmission cover open and turn the motor over by hand, pressure builds from the crankcase and pushes and squeezes into the cam chest. You can hear it the air. Cracking the transmission cover or venting it doesn't help relieve the pressure. If you pull the crankcase sensor it does relieve the pressure.

 

If the cam plate is off and the crank bearing is sealed, could that air be leaking through the cam bearing?

 

It is. That's where the crankcase vents - into the cam chest. There is no pathway directly from the crankcase to the oil pan.
The way any air "gets to" the oil pan is via the tunnel molded through the trans case that connects the oil pan to the cam chest.

The reason that tunnel through the trans case is there? To eliminate a pressure build up in the oil pan.
The oil pump returns oil to the pan, actually pumps it, and if it were not vented, it would build up pressure that could restrict the oil flow.
Thus the oil pan vents to the Cam chest as well. Cam chest collects all venting (blowby from the crank, pressure from the oil pan), and sends it up the pushrod tubes to be vented to atmosphere (intake) by the breathers in the heads.

The trans cover vent mod is like putting a vent on the "tunnel" to atmosphere and since the oil pan, cam chest, and heads are the same air body, it's exactly like putting a third vent on the heads... same job, same effect.

 

I've been thinking of this also. Here is an interesting opinion from Doc Harley:

 

Thanks for that explanation. I only stumbled across this thread because I am having an overpressure in my cam chest and its pushing oil through the lower pushrod tubes. Yes, they are installed correctly. Seated firmly in the O-Rings.

My plan is to install T-Man breathers, and use the transmission cover vent. The Harley breathers are garbage. I had a similar issue on my Twin Cam and just vented to the atmosphere. I am running the headbreather bolts to atmosphere currently. Hopefully the Tman breathers help, as well as the Transmission breather mod.

S&S also believes the piston rings may be off, which I doubt because of the pressure build up in the crankcase.

Wish there was a way to just vent the crankcase.

 

FWIW, when all things are properly installed there should not be pressure buildup in the crankcase causing oil to be “pushed” out the breathers.
By simply venting the crankcase you may have eliminated an oily mess your abnormal crankcase pressure issue still remains.
IME its always best to identify and fix the blow-by issue rather than bandaid it.
Bob