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Milwaukee Eight (M8) 2017 and up M8 Air and Liquid Cooled discussion

Anyone doing the breather bypass on your M8?

 
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Old 11-28-2016, 06:25 AM
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Originally Posted by SWThomas View Post
Can someone educate me? How does the oil level in the pan dictate whether or not there will be oil coming out of the head breather bolts? I mean, the oil is pumped up to the heads and drains back down, so in theory no matter how much oil is in the pan the same amount is going to be pumped to the heads, where the breather bolts are. I just don't see how running the oil level lower would reduce the breather issue.
Now you've done it Marine!

Put your steel pot on and hunker down
 
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Old 11-28-2016, 07:38 AM
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Originally Posted by SWThomas View Post
Can someone educate me? How does the oil level in the pan dictate whether or not there will be oil coming out of the head breather bolts? I mean, the oil is pumped up to the heads and drains back down, so in theory no matter how much oil is in the pan the same amount is going to be pumped to the heads, where the breather bolts are. I just don't see how running the oil level lower would reduce the breather issue.
I don't have the answer but owning and flying aircraft for 30 yrs if its filled to the top level mark it will blow out 2 qts in 6-8 hrs everytime leave it at 2qt low mark stays there for next 30 hrs .Now it holds 12 qts of oil. Also air cooled engine. Not saying it relates but I know for fact with those engines it made a difference
 
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Old 11-28-2016, 09:46 AM
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Originally Posted by SWThomas View Post
Can someone educate me? How does the oil level in the pan dictate whether or not there will be oil coming out of the head breather bolts? I mean, the oil is pumped up to the heads and drains back down, so in theory no matter how much oil is in the pan the same amount is going to be pumped to the heads, where the breather bolts are. I just don't see how running the oil level lower would reduce the breather issue.
I'm not sure if the M8 has the affliction but it was common for Twin Cams to blow a little out the breather if running the oil level near full. I suspect that it stems from the savenge system and the pressure pulses in the case from both pistons roughly going up and down at the same time. The scavenge pump has a flow rate that greater than the feed pump so oil scavenged from the motor is aerated when returning to the oil tank. Lowering the oil probably helps to keep the system in balance.. Once out of balance the air in the crankcase likely sees a heavy oil mist that is hard to separate at the breathers. Running the motor at higher Rs for long periods of time makes them bleed more but lowering the oil level in the tanks definitely helps. It wouldn't surprise me that the M8s have the same issue as the scavenge system is close to TCs.

One of the features of the M8s was supposed to be a less misting at the breather due to a better separator but HDs have been blowing a little out of the breathers ever since they started making big twins..
 
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Old 11-28-2016, 01:30 PM
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I run the breath bypass on mine the day I brought home. Pretty simple and cheap mod.
 
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Old 11-28-2016, 02:13 PM
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Originally Posted by bwoltz View Post
I'm not sure if the M8 has the affliction but it was common for Twin Cams to blow a little out the breather if running the oil level near full.
they still do, despite some of the claims it's a thing of the past..already changed air filters on both our M8's at 3K miles..same rules apply as always...midway on the dipstick HOT is prudent
 

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Old 11-28-2016, 02:50 PM
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Originally Posted by cr3999 View Post
i run the breath bypass on mine the day i brought home. Pretty simple and cheap mod.
how ??
 
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Old 11-28-2016, 05:28 PM
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Originally Posted by bwoltz View Post
I'm not sure if the M8 has the affliction but it was common for Twin Cams to blow a little out the breather if running the oil level near full. I suspect that it stems from the savenge system and the pressure pulses in the case from both pistons roughly going up and down at the same time. The scavenge pump has a flow rate that greater than the feed pump so oil scavenged from the motor is aerated when returning to the oil tank. Lowering the oil probably helps to keep the system in balance.. Once out of balance the air in the crankcase likely sees a heavy oil mist that is hard to separate at the breathers. Running the motor at higher Rs for long periods of time makes them bleed more but lowering the oil level in the tanks definitely helps. It wouldn't surprise me that the M8s have the same issue as the scavenge system is close to TCs.

One of the features of the M8s was supposed to be a less misting at the breather due to a better separator but HDs have been blowing a little out of the breathers ever since they started making big twins..
And add to this good explanation, at some rpm/load, range, the top piston ring will lose seal with the piston and more blow by, than the designers hoped would blow, will leak some pressure into the crankcase and blow oil out, into the breather system.
 
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Old 11-28-2016, 06:56 PM
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Originally Posted by fourburgs View Post
how ??
I have some pictures to upload, but the little picture button is not working for me. What's up with that?
 
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Old 11-28-2016, 07:00 PM
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bwoltz might be right that it's because of the scavenge system plumbing


I'm betting that pressure plays a role too. The more oil you have in the pan means the less air space you have on the supply side of the pump. As oil temp increases the pressure inside the chamber will increase faster with the restricted space. All the pumps I've worked with react to an increase in supply side pressure with a corresponding increase in output pressure.


In any case it's got me curious. I'm probably going to spend a little time with a pressure gage on the breather output and see how it changes with oil fill level.... once riding season is actually over that is.
 
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Old 11-28-2016, 08:32 PM
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Pull the stock hoses off and throw away.



Drill a hole in the location of your choice in the air box.



route to ground or install a catch can. Looking at the SE AC there will be some drilling the backing plate as they they reuse the same bolts as the stock air box. Also the air box is a lot closer the jug. There's not enough room do install like the twin cams, as there isn't enough room.

This is the way I did the by pass. Your plan my vary.
 
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