External breather emissions
Road Master
Joined: Dec 2012
Posts: 848
Likes: 30
From: CO
Harley's are only a dry sump in the fact that the oil is not stored in the crankcase. A Softail has it in the bag above the transmission. Dynas and the large cruiser in the tank below the transmission. All Harleys run with some oil in the crankcase that is being constantly dumped in and pulled off by the two stacked suction and pressure oil pumps The suction return is larger than the pressure one but the pickup for it leaves oil in sump.
This oil left is spun by the two large crank rotors (sort of like flywheels) . This is the main lubrication for the inner cam needle bearings. In the older engines before the cooling piston jets that are in are twin camshaft engines for cooling, the spinoff was what cooled the inside of the pistons. Note that the jets do not operate at idle oil pressure and in hot parts of the country, modifying the oil pressure for pressure above 12lbs at idle will cook the oil.
You can overfill a Harley but it is truly hard to get too much oil in the crankcase. On a Softail, you really cannot and it will come out the tank plug if you do. However, they will sometime drain down into engine if left sitting for a long time. Know mine does but it does not go far even after 3-4 months. On a big cruiser or Dyna with a screw in oil cap, guess you can but it is a small amount simple since there is only so much room above full. Unlike a car, the oil should be checked right after you turn it off (especially on a Softail) and unless it's hot, should be at the middle between the low and full line. If it's truly hot, it can be at the full mark. That does not cause problem.
This oil left is spun by the two large crank rotors (sort of like flywheels) . This is the main lubrication for the inner cam needle bearings. In the older engines before the cooling piston jets that are in are twin camshaft engines for cooling, the spinoff was what cooled the inside of the pistons. Note that the jets do not operate at idle oil pressure and in hot parts of the country, modifying the oil pressure for pressure above 12lbs at idle will cook the oil.
You can overfill a Harley but it is truly hard to get too much oil in the crankcase. On a Softail, you really cannot and it will come out the tank plug if you do. However, they will sometime drain down into engine if left sitting for a long time. Know mine does but it does not go far even after 3-4 months. On a big cruiser or Dyna with a screw in oil cap, guess you can but it is a small amount simple since there is only so much room above full. Unlike a car, the oil should be checked right after you turn it off (especially on a Softail) and unless it's hot, should be at the middle between the low and full line. If it's truly hot, it can be at the full mark. That does not cause problem.
Road Master
Joined: Dec 2009
Posts: 843
Likes: 43
From: Louisiana
I swung by my local dealer and bought 2 replacement breather valve assemblies and 2 rocker box gaskets. IIRC right around $50 all in. A couple hours later problem solved. I hate to see folks jury rig around the breather system before they've actually attempted to fix it. I think sometime in late 2011 Harley upgrade the breather assembly bodies from plastic to stamped steel. Once the top rocker box cover is off it only 2 bolts to remove the breather assembly.
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From: Honah Lee
I'm on my 3rd twin cam bike and have always kept the oil level at or near the full mark when hot. I've never had oil pukeing out of the air filter on any of the bikes until about 3 weeks ago. Current bike has just under 35k miles on it. I pulled the filter and cleaned everything up. Got it good and hot and held the engine speed at around 3,000 rpm for several minutes while watching the breather holes in the backing plate. Sure enough oil started to weep out of the rear cylinder breather hole. The oil pressure is normal, meaning no big change up or down that might signal something may be going south.
I swung by my local dealer and bought 2 replacement breather valve assemblies and 2 rocker box gaskets. IIRC right around $50 all in. A couple hours later problem solved. I hate to see folks jury rig around the breather system before they've actually attempted to fix it. I think sometime in late 2011 Harley upgrade the breather assembly bodies from plastic to stamped steel. Once the top rocker box cover is off it only 2 bolts to remove the breather assembly.
I swung by my local dealer and bought 2 replacement breather valve assemblies and 2 rocker box gaskets. IIRC right around $50 all in. A couple hours later problem solved. I hate to see folks jury rig around the breather system before they've actually attempted to fix it. I think sometime in late 2011 Harley upgrade the breather assembly bodies from plastic to stamped steel. Once the top rocker box cover is off it only 2 bolts to remove the breather assembly.
All twin cam Harleys run with about 20-24 ounces of sump oil in the crankcase/cam galley area. The return side of the pump leaves this much due to the pickup point. This splash is what lubricates the inner cam bearings. This splash gets with some of the air that vents up thru the pushrod outer tubes into the rocker arm area and out that baffle you rebuilt. If you run Harley's full air filter box, you will not see oil outer than in the box. An open SE filter will get some to the outside especially if it has sat for a while.
Post 31 statement is based on misinformed information. Sadly even kept going by Harley mechanics trying to justify why some people see a few oil drops on their new $20,000 bike. Study the design and read the oil system in the service manual. On a Softail, the oil bag is actually above the the engine and it does not get too much oil in engine. If you do overfill it cold, it will however pop the plug out. On a Softail, the oil can run into the engine if the oring in the pump is bad and sits a long time.
The dual rotor oil pump pulls the oil in and the return side which is larger pushes it out. It does not run in. This applies to all Large Cruiser, Dynas and Softail TwinCams
Last edited by Jackie Paper; Sep 14, 2018 at 11:10 AM.
Road Master
Joined: Dec 2009
Posts: 843
Likes: 43
From: Louisiana
Just a thought. I certainly agree filling to the top hot on the stick has nothing to do with the amount of tramp oil in the crankcase let alone the head area. It had probably sat for a few and the little collected on the internal passageways and had ran down. What you saw was this and it would have stopped. The one way poppet valves are one way out and do not stop oil. They prevent the upward motion of the pistons from pulling air in. The baffle box and that screen shave off most oil as the pressure waves from the driving down pistons blow out.
All twin cam Harleys run with about 20-24 ounces of sump oil in the crankcase/cam galley area. The return side of the pump leaves this much due to the pickup point. This splash is what lubricates the inner cam bearings. This splash gets with some of the air that vents up thru the pushrod outer tubes into the rocker arm area and out that baffle you rebuilt. If you run Harley's full air filter box, you will not see oil outer than in the box. An open SE filter will get some to the outside especially if it has sat for a while.
Post 31 statement is based on misinformed information. Sadly even kept going by Harley mechanics trying to justify why some people see a few oil drops on their new $20,000 bike. Study the design and read the oil system in the service manual. On a Softail, the oil bag is actually above the the engine and it does not get too much oil in engine. If you do overfill it cold, it will however pop the plug out. On a Softail, the oil can run into the engine if the oring in the pump is bad and sits a long time.
The dual rotor oil pump pulls the oil in and the return side which is larger pushes it out. It does not run in. This applies to all Large Cruiser, Dynas and Softail TwinCams
All twin cam Harleys run with about 20-24 ounces of sump oil in the crankcase/cam galley area. The return side of the pump leaves this much due to the pickup point. This splash is what lubricates the inner cam bearings. This splash gets with some of the air that vents up thru the pushrod outer tubes into the rocker arm area and out that baffle you rebuilt. If you run Harley's full air filter box, you will not see oil outer than in the box. An open SE filter will get some to the outside especially if it has sat for a while.
Post 31 statement is based on misinformed information. Sadly even kept going by Harley mechanics trying to justify why some people see a few oil drops on their new $20,000 bike. Study the design and read the oil system in the service manual. On a Softail, the oil bag is actually above the the engine and it does not get too much oil in engine. If you do overfill it cold, it will however pop the plug out. On a Softail, the oil can run into the engine if the oring in the pump is bad and sits a long time.
The dual rotor oil pump pulls the oil in and the return side which is larger pushes it out. It does not run in. This applies to all Large Cruiser, Dynas and Softail TwinCams
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From: Honah Lee
My SE filer which is the oil soaked one does that for about a month after cleaning and re oiling. I just wipe the drool off the old girl's chin. My bike with 50k will get a few oil spots on the dust on the Chrome oil bag in a 200 mile run above 55 mph.
Road Master
Joined: Dec 2009
Posts: 843
Likes: 43
From: Louisiana
Mines is the factory CVO filter that is dry and doesn't get oiled.
Outstanding HDF Member
Joined: Aug 2012
Posts: 3,217
Likes: 90
From: Detroit
Post 31 statement is based on misinformed information. Sadly even kept going by Harley mechanics trying to justify why some people see a few oil drops on their new $20,000 bike. Study the design and read the oil system in the service manual. On a Softail, the oil bag is actually above the the engine and it does not get too much oil in engine. If you do overfill it cold, it will however pop the plug out. On a Softail, the oil can run into the engine if the oring in the pump is bad and sits a long time.
The dual rotor oil pump pulls the oil in and the return side which is larger pushes it out. It does not run in. This applies to all Large Cruiser, Dynas and Softail TwinCams
Excess oil can be pushed into the engine if the oil level in the tank is too high. The third connection between the tank and the engine is an air vent line. When the pump returns oil from the engine, it is a mixture of oil and air, so it also pushes a lot of air into the tank. If the tank wasn't vented, pressure inside the tank would continue to rise. Harley vents this air back to the engine, where excess eventually exits out the breathers.
When the oil level in the tank becomes too high, there is a greater tendency for the oil to slosh into the air vent line, and be pushed into the engine. This excess oil creates more oil mist inside the engine, and in the air which goes out the breathers.
Last edited by Warp Factor; Jul 5, 2015 at 10:12 AM.
Seasoned HDF Member
Joined: Mar 2010
Posts: 38,586
Likes: 6,435
From: Honah Lee
I'd say that post 31 is more correct than incorrect.
Excess oil can be pushed into the engine if the oil level in the tank is too high. The third connection between the tank and the engine is an air vent line. When the pump returns oil from the engine, it is a mixture of oil and air, so it also pushes a lot of air into the tank. If the tank wasn't vented, pressure inside the tank would continue to rise. Harley vents this air back to the engine, where excess eventually exits out the breathers.
When the oil level in the tank becomes too high, there is a greater tendency for the oil to slosh into the air vent line, and be pushed into the engine. This excess oil creates more oil mist inside the engine, and in the air which goes out the breathers.
Excess oil can be pushed into the engine if the oil level in the tank is too high. The third connection between the tank and the engine is an air vent line. When the pump returns oil from the engine, it is a mixture of oil and air, so it also pushes a lot of air into the tank. If the tank wasn't vented, pressure inside the tank would continue to rise. Harley vents this air back to the engine, where excess eventually exits out the breathers.
When the oil level in the tank becomes too high, there is a greater tendency for the oil to slosh into the air vent line, and be pushed into the engine. This excess oil creates more oil mist inside the engine, and in the air which goes out the breathers.
Your are correct that both the Softail oil bag upper pipe and the oil bag below the transmission on the large cruiser and Dynas do have a vent line heading to the engine. Even looks like it more so on the Softail since you can see it. However, if you study the service manual, you will see it is a sealed passageway to the transmission where it is truly vented.
The primary is also vented to the transmission thru the clutch push rod cavity. Oil bag and primary share the down tube on the transmission.
Breather valves are vented to the clean side of the air box. Most oil there falls out since it's too heavy to be carried into engine since air is only rushing in under 15 lbs of atmospheric pressure filling the vacuum in the cylinder going down. That fall out is what we see.
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So what good does that do? Doesn't the oil just collect inside the filter and eventually drip out?
I've been meaning to swap out my intake for a dk one with the external breathers, I run the bike pretty hard and it doesn't take much for the air filter to start dripping oil. I have a maintenance plan with the dealer so they do all the oil changes so it's right under the full line when hot. I was gonna get this http://www.tt-motorcycles.com/catalo...VERFLOW_CA.htm and see if I can rig it up to use as a catch can.
I've been meaning to swap out my intake for a dk one with the external breathers, I run the bike pretty hard and it doesn't take much for the air filter to start dripping oil. I have a maintenance plan with the dealer so they do all the oil changes so it's right under the full line when hot. I was gonna get this http://www.tt-motorcycles.com/catalo...VERFLOW_CA.htm and see if I can rig it up to use as a catch can.
Everytime you wash the bike (or at least every 5000 miles) spray the filter with some soapy water, let it sit a couple of minutes, then spray it off. The oil will come out and the filter is ready to absorb another 5000 miles of oil with no dripping.
This is the filter on one of my bikes after several thousand miles-
You can see the different breathers and filters at this LINK.
WF and a few others are correct about oil level, and shame on some HD techs that don't know what they're talking about, directly contradicting the manual that comes with each of our bikes.
This is straight from the HD owners manual-
"The correct oil level should register midway between the FULL and ADD marks on the dipstick.
If oil level is at or below the ADD mark, add only enough oil to bring the level to the middle of the two marks on the dipstick."
More info on oil carryover can be seen in this thread-
https://www.hdforums.com/forum/oil-a...f-my-bike.html
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Last edited by DK Custom; Jul 6, 2015 at 01:28 AM.
Outstanding HDF Member
Joined: Aug 2012
Posts: 3,217
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From: Detroit
Your are correct that both the Softail oil bag upper pipe and the oil bag below the transmission on the large cruiser and Dynas do have a vent line heading to the engine. Even looks like it more so on the Softail since you can see it. However, if you study the service manual, you will see it is a sealed passageway to the transmission where it is truly vented.