How Does the Twin Cam Engine Venting System Work?

[Ohio HD]

It's a super simple system. Just not always super good at what it does. oil level too high, it effects the breather output by mixing oil that's being blown around the rocker box assembly, then making it to your catch can, or TB.

Some motors have a very clean vent system. Mostly that's due to that motor having an extremely good ring seal.

The attached images are just a walk through the system, as to how the crank case introduces the pressure to the heads, and then how the breather system evacuates the crank, now head pressure.



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[Ohio HD]

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[billbuilds]

     Good explanation and photos. I was just check out the breather layout in the SM the other day. Almost installed the umbrella valves incorrectly using the stamped steel units. No, they don't go the way they come packaged.       
     Did those Vulvan rocker arm supports come chamfered like that or is that your work? They're very pleasant to the eye.

[Ohio HD]

No, not my doing. They make them as you see them. All of the Vulcan parts that I've used (parts they made) are very high quality.

[Wookie3011]

Thanks Ohio HD, I am still trying to memorize oil flow and paths as well as pressure paths in the TwinCam engine. If I understand how it works and can visualize it, then working on and trouble shooting is easier. It really helps when it's all laid out like this. The shop manual has it all in several pages in a way that makes it hard to visualize. Vulcan has outstanding performance parts. Super nice guy to. 

[FLDavetrain]

So with all installed correctly and still copious amounts of oil pouring out once at full temp implies rocker boxes are overwhelmed w oil that's not draining

[Don D]

Lifters, oil pressure, and volume play roles in how much oil is delivered to the top. Drain back holes in both the rocker supports and heads are in the mix getting this oil back to the sump / tank. Ring seal, if compromised, adds to crankcase pressure and if excessive interferes with the oil separation process which is done under the umbrella valves.

[Thermodyne]

The breather system works reasonably well, so long as the engine is mechanically sound.  There is actually a slight vacuum on the crankcase when all is working well.

But if you lose ring seal and the blow by increases, the increased volume of gases being vented will carry more oil out too.  And the engine is going to lose ring seal over time, no way to stop that.

Another issue that increases oil carry over is raising the oil pressure.  Higher oil pressures increase the amount of oil in the upper and lower areas of the engine. And that can easily overwork the simple little oil separator set up in the breather as well as exceed the capacity of the drains in the rocker supports.

If it only slobbers out on the big slab, it's usually fixable by drilling out the drain holes.  But when they get to slobbering all the time, it usually requires more work.       

[60Gunner]

Thing is,it's a compounding issue. The stock setup is marginally good enough...for a stock bike.
There's way better alternatives. Crankcase breathing has never been a strong suit for Harleys.
Use a good external reed valve. They close quicker and don't allow ANY air back in that builds pressure. They also don't dry out and fail to seal at all.
I don't get a drop of oil out of mine. My umbrella valves are removed. The stamped housings are still there, empty, to aid in oil separation.

Drill the return holes under them to 1/8".

[Ohio HD]

This is what comes from my catch can on my 124" TC. I'm running a stone stock breather system, and see no oil coming from the breathers. I also have extremely good ring seal, which has more to do with excessive oil expulsion than the breather mechanism. Put more oil into the rocker box than the oil drains can keep up with, you'll see oil expulsion no matter what you use as a breather valve.

This is after a weekend of hard riding, some moisture from condensation, and a minuscule amount of oil trace from oil mist that is generated by high RPM running.

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The breathers in my current 124", stock late model OEM.

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[Ohio HD]

This is the breather system that I'll use in the 124" TC I'm building now. The OEM style assembly removed, and will use an S&S 50-8122 breather valve connected to the upper rocker box, then fed to the catch can. Of course one valve on each head.

This motor will see a lot of high RPM use. This setup was recommended to me by the guy that just did my heads. He knows a lot more about high performance HD's than I ever will. Inexpensive and works.

The Vulcan breathers I have will go into the old 124" motor.


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[cheech]

Are you plugging what you call the "pressure exit hole" in the head or rocker bridge or just at the OEM breather holes where the air cleaner mounts?

[Ohio HD]

Actually this AM I decided to use parts from the early TC breather, the cast aluminum parts. Strip the valve and foam out. Drill and tap the drain hole with a 1/4-18 NPT tap and use a flush plug to block off the exit port all together. I'll use green Loctite to insure it never movies.

But I can't believe I don't have a 1/4-18 NPT tap. I have to get one, and will pick up the flush plugs in aluminum just to keep the materials the same.



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[jsachs1]

This is the breather system that I'll use in the 124" TC I'm building now. The OEM style assembly removed, and will use an S&S 50-8122 breather valve connected to the upper rocker box, then fed to the catch can. Of course one valve on each head.

This motor will see a lot of high RPM use. This setup was recommended to me by the guy that just did my heads. He knows a lot more about high performance HD's than I ever will. Inexpensive and works.

The Vulcan breathers I have will go into the old 124" motor.


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I started using a set up like that in 2000 on some of my customer builds. I mounted a rt. angle adaptor over the center of the intake rocker arm. I put a PVC valve into the adaptor, a length of hose and let it work. There is a very
small amount of power gained. I run this system on my Buell.
John

[Ohio HD]

I started using a set up like that in 2000 on some of my customer builds. I mounted a rt. angle adaptor over the center of the intake rocker arm. I put a PVC valve into the adaptor, a length of hose and let it work. There is a very
small amount of power gained. I run this system on my Buell.
John

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    Jim said the same, a little insurance that you're relieving the pressure.

[turboprop]

Actually this AM I decided to use parts from the early TC breather, the cast aluminum parts. Strip the valve and foam out. Drill and tap the drain hole with a 1/4-18 NPT tap and use a flush plug to block off the exit port all together. I'll use green Loctite to insure it never movies.

But I can't believe I don't have a 1/4-18 NPT tap. I have to get one, and will pick up the flush plugs in aluminum just to keep the materials the same.



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I think you plan to run the AC from HPI. Have you considered hunting it with button head bolts (not center drilled) and a piece of aluminum round stock instead of the vented standoffs from HPI? 

[Ohio HD]

That's correct, The V2 is still the plan. I have the original internal and the external breather standoffs. I'm going to use the standoffs for internal vent to TB and those bolts. They're hollow, but by blocking the breather inside the rocker box, I don't have to deal with sludge coming out the backing plate bolts when I have the need to remove them.

That's what made me decide to go that direction this AM, seal it from the inside. Just to eliminate the need to clean and dry the threads in the head when I remove the air breather. Then I can apply blue Loctite and put it back together without getting the threaded hole dried out so the Loctite adheres.



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[kd]

I started using a set up like that in 2000 on some of my customer builds. I mounted a rt. angle adaptor over the center of the intake rocker arm. I put a PVC valve into the adaptor, a length of hose and let it work. There is a very
small amount of power gained. I run this system on my Buell.
John

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    Jim said the same, a little insurance that you're relieving the pressure.

If you are using an automotive PCV valve test it first.  For the most part, they are not a positive seal and will actually breath both ways. (one way is more like a leak)  If you want to hold negative crankcase pressure it may not perform the way you want.

[Ohio HD]

If you are using an automotive PCV valve test it first.  For the most part, they are not a positive seal and will actually breath both ways. (one way is more like a leak)  If you want to hold negative crankcase pressure it may not perform the way you want.

S&S one way check valves.


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[kd]

Yeah, I just dropped into the thread and it looked like PCV valves were on the menu too.  rbabos did some testing a few years and ran a bit of a thread.  They were not all the same.  I am sure the S&S units are called one way check valves for a reason.

[Ohio HD]

Yep, you can only get flow through the white side to the black side. The other direction they flat close.

[Ohio HD]

A really positive point to using these valves, if one does get gunked up for some reason. You can change it in five minutes. The OEM valves you have to open the rocker box, buy gaskets, etc....  just to look at it.

[rigidthumper]

Are you going to drill & tap the head, or the rockerbox?

[turboprop]

If you are using an automotive PCV valve test it first.  For the most part, they are not a positive seal and will actually breath both ways. (one way is more like a leak)  If you want to hold negative crankcase pressure it may not perform the way you want.

S&S one way check valves.


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How do you intend to route the lines and what are they going to?

Have you seen the video by Tom Reiser on using the oil tank as a catch can and then venting the tank? He wants to drill the trans case (M8 application) for the oil return. There are other ways to do this. For example on an earlier TC the trans case has a plugged hole on top right behind the engine. The vent line could go into that and then drill/tap the oil spout for a vent line. I have been thinking of leveraging this against the Torque-A-Hoe bike and eliminating the external catch can. Only drawback I see is not being able to monitor what is coming out of the vents, but it should result in a much cleaner exterior, specially after extended high speed touring.

[Ohio HD]

If you are using an automotive PCV valve test it first.  For the most part, they are not a positive seal and will actually breath both ways. (one way is more like a leak)  If you want to hold negative crankcase pressure it may not perform the way you want.

S&S one way check valves.


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How do you intend to route the lines and what are they going to?

Have you seen the video by Tom Reiser on using the oil tank as a catch can and then venting the tank? He wants to drill the trans case (M8 application) for the oil return. There are other ways to do this. For example on an earlier TC the trans case has a plugged hole on top right behind the engine. The vent line could go into that and then drill/tap the oil spout for a vent line. I have been thinking of leveraging this against the Torque-A-Hoe bike and eliminating the external catch can. Only drawback I see is not being able to monitor what is coming out of the vents, but it should result in a much cleaner exterior, specially after extended high speed touring.

That concept of taking the discharge from the heads to essentially the oil pan via the transmission case has me thinking. It would be a nice clean system regarding making it a closed system as it really should be. I agree about being in the blind as far as being able to see what happens at times. Currently I planned to go from heads to catch can.

I had always planned to drill and tap the oil inlet opening at the transmission oil filler neck while everything is apart. That way if I did decide to vent from the transmission case, I just remove a cap and connect a hose.

I have a few questions about what I can do with and around the transmission case. To the point I bought a damaged six speed case to learn from. I should have that on Tuesday next week. Pinwall Cycle is in Ohio, and ships pretty quick.

Updated: they already shipped yesterday, and it should be here today.

I'm going to look for the TR video, thanks for the heads up.

[kd]

If you are using an automotive PCV valve test it first.  For the most part, they are not a positive seal and will actually breath both ways. (one way is more like a leak)  If you want to hold negative crankcase pressure it may not perform the way you want.

S&S one way check valves.


You cannot see attachments on this board.

How do you intend to route the lines and what are they going to?

Have you seen the video by Tom Reiser on using the oil tank as a catch can and then venting the tank? He wants to drill the trans case (M8 application) for the oil return. There are other ways to do this. For example on an earlier TC the trans case has a plugged hole on top right behind the engine. The vent line could go into that and then drill/tap the oil spout for a vent line. I have been thinking of leveraging this against the Torque-A-Hoe bike and eliminating the external catch can. Only drawback I see is not being able to monitor what is coming out of the vents, but it should result in a much cleaner exterior, specially after extended high speed touring.

That concept of taking the discharge from the heads to essentially the oil pan via the transmission case has me thinking. It would be a nice clean system regarding making it a closed system as it really should be. I agree about being in the blind as far as being able to see what happens at times. Currently I planned to go from heads to catch can.

I had always planned to drill and tap the oil inlet opening at the transmission oil filler neck while everything is apart. That way if I did decide to vent from the transmission case, I just remove a cap and connect a hose.

I have a few questions about what I can do with and around the transmission case. To the point I bought a damaged six speed case to learn from. I should have that on Tuesday next week. Pinwall Cycle is in Ohio, and ships pretty quick.

Updated: they already shipped yesterday, and it should be here today.

I'm going to look for the TR video, thanks for the heads up.



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Here's a consideration.  Rocker box to catch can, catch can vent to filler neck.  Best of both worlds.  The catch can is a mid flow monitor station but doesn't vent to atmosphere. I would even guess you could split the return line to the filler neck to fit a gauge to read crankcase pressure for OCD checks of engine conditions.

[turboprop]

If you are using an automotive PCV valve test it first.  For the most part, they are not a positive seal and will actually breath both ways. (one way is more like a leak)  If you want to hold negative crankcase pressure it may not perform the way you want.

S&S one way check valves.


You cannot see attachments on this board.

How do you intend to route the lines and what are they going to?

Have you seen the video by Tom Reiser on using the oil tank as a catch can and then venting the tank? He wants to drill the trans case (M8 application) for the oil return. There are other ways to do this. For example on an earlier TC the trans case has a plugged hole on top right behind the engine. The vent line could go into that and then drill/tap the oil spout for a vent line. I have been thinking of leveraging this against the Torque-A-Hoe bike and eliminating the external catch can. Only drawback I see is not being able to monitor what is coming out of the vents, but it should result in a much cleaner exterior, specially after extended high speed touring.

That concept of taking the discharge from the heads to essentially the oil pan via the transmission case has me thinking. It would be a nice clean system regarding making it a closed system as it really should be. I agree about being in the blind as far as being able to see what happens at times. Currently I planned to go from heads to catch can.

I had always planned to drill and tap the oil inlet opening at the transmission oil filler neck while everything is apart. That way if I did decide to vent from the transmission case, I just remove a cap and connect a hose.

I have a few questions about what I can do with and around the transmission case. To the point I bought a damaged six speed case to learn from. I should have that on Tuesday next week. Pinwall Cycle is in Ohio, and ships pretty quick.

Updated: they already shipped yesterday, and it should be here today.

I'm going to look for the TR video, thanks for the heads up.



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There is a piece of the puzzle in each of these three videos. Can certainly be done with hardware sourced elsewhere but he does a god job of explaining everything.

[Ohio HD]

Are you going to drill & tap the head, or the rockerbox?

The upper rocker box, high as I can on the intake sides. over the rocker arm.

[Ohio HD]

If you are using an automotive PCV valve test it first.  For the most part, they are not a positive seal and will actually breath both ways. (one way is more like a leak)  If you want to hold negative crankcase pressure it may not perform the way you want.

S&S one way check valves.


You cannot see attachments on this board.

How do you intend to route the lines and what are they going to?

Have you seen the video by Tom Reiser on using the oil tank as a catch can and then venting the tank? He wants to drill the trans case (M8 application) for the oil return. There are other ways to do this. For example on an earlier TC the trans case has a plugged hole on top right behind the engine. The vent line could go into that and then drill/tap the oil spout for a vent line. I have been thinking of leveraging this against the Torque-A-Hoe bike and eliminating the external catch can. Only drawback I see is not being able to monitor what is coming out of the vents, but it should result in a much cleaner exterior, specially after extended high speed touring.

That concept of taking the discharge from the heads to essentially the oil pan via the transmission case has me thinking. It would be a nice clean system regarding making it a closed system as it really should be. I agree about being in the blind as far as being able to see what happens at times. Currently I planned to go from heads to catch can.

I had always planned to drill and tap the oil inlet opening at the transmission oil filler neck while everything is apart. That way if I did decide to vent from the transmission case, I just remove a cap and connect a hose.

I have a few questions about what I can do with and around the transmission case. To the point I bought a damaged six speed case to learn from. I should have that on Tuesday next week. Pinwall Cycle is in Ohio, and ships pretty quick.

Updated: they already shipped yesterday, and it should be here today.

I'm going to look for the TR video, thanks for the heads up.



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There is a piece of the puzzle in each of these three videos. Can certainly be done with hardware sourced elsewhere but he does a god job of explaining everything.

Thanks, just got back home. I'll view these shortly.

[Ohio HD]

 Well, the case arrived already. My UPS woman just shakes her head at me and laughs. She a really good person, always takes care of my packages if rain or snow is in the forecast.

She'll shake ammo boxes and say, you get some nine's  ?   


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[Ohio HD]

If you are using an automotive PCV valve test it first.  For the most part, they are not a positive seal and will actually breath both ways. (one way is more like a leak)  If you want to hold negative crankcase pressure it may not perform the way you want.

S&S one way check valves.


You cannot see attachments on this board.

How do you intend to route the lines and what are they going to?

Have you seen the video by Tom Reiser on using the oil tank as a catch can and then venting the tank? He wants to drill the trans case (M8 application) for the oil return. There are other ways to do this. For example on an earlier TC the trans case has a plugged hole on top right behind the engine. The vent line could go into that and then drill/tap the oil spout for a vent line. I have been thinking of leveraging this against the Torque-A-Hoe bike and eliminating the external catch can. Only drawback I see is not being able to monitor what is coming out of the vents, but it should result in a much cleaner exterior, specially after extended high speed touring.

That concept of taking the discharge from the heads to essentially the oil pan via the transmission case has me thinking. It would be a nice clean system regarding making it a closed system as it really should be. I agree about being in the blind as far as being able to see what happens at times. Currently I planned to go from heads to catch can.

I had always planned to drill and tap the oil inlet opening at the transmission oil filler neck while everything is apart. That way if I did decide to vent from the transmission case, I just remove a cap and connect a hose.

I have a few questions about what I can do with and around the transmission case. To the point I bought a damaged six speed case to learn from. I should have that on Tuesday next week. Pinwall Cycle is in Ohio, and ships pretty quick.

Updated: they already shipped yesterday, and it should be here today.

I'm going to look for the TR video, thanks for the heads up.



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There is a piece of the puzzle in each of these three videos. Can certainly be done with hardware sourced elsewhere but he does a god job of explaining everything.

Thanks, just got back home. I'll view these shortly.

I may select a spot in the transmission case to drill and tap for hoses coming from the top end. If I don't use that method, I can always just put two pipe plugs in the transmission. Well and a third tapped hole near the oil fill for the new breather outlet. It can also be plugged if not used.

The only issue I can see with dumping the vents into the oil pan is you're potentially dropping water droplets into the oil if you get a lot of condensation in your area. I can park mine after a hot days ride. If it cools off overnight, I get more condensation in the rocker covers. When I start the motor it starts sending water droplets to the catch can, what doesn't burn off as the motor warms up.   

Think about the PCV valve system in cars. Some end up with the milky brown oil gunk in the valve and valve covers. That's water and oil mixing, or trying to mix.

[Hossamania]

My thought as well, I'm not a fan of running the vents back into the oil pan, I've seen what can come out of those hoses.

[kd]

It is fairly common to run a can to catch the sludge and acidic discharge then pass the gasses back into the crankcase (or in this case oil reservoir).  The bad part is because it is then a truly closed system condensed air that carries moisture stays in the sealed atmosphere and becomes acidic. 

My can is from a 5.7 Hemi and it works like that but the fumes eventually got delivered to the intake without the oil sludge load. Venting it high after the can makes more sense to me to keep the pistons clean of carbon but the EPA doesn't think so.

I have a low mounted can and a stainless vent line up and then down.  Any residual moisture leaves as a gas vapor and moisture runs back down until it becomes vapor and leaves on its own.  The line doesn't drip.

[Ohio HD]

I'm pretty sure I'm going to stay with the conventional catch can like I have on the current 124". No chance that anything gets back into the motor. I don't loose any oil through the vents anyway.

I expect the same behavior with the new 124".


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[Wookie3011]

When I had the motor out, I considered tapping the top trans cover to run my breathers into it. I found a gasket inside of the cover. I wasn't sure exactly what the gasket was for? Was it to keep a certain amount of pressure or just a oil seal? I backed out of doing it. My current vent system is 3/8 out the breather bolts. I bored out the breather bolts and opened up the holes hair more. With the venting system, how can I promote good vacuum for ring seal and to prevent ring flutter while still releasing pressures? Is this the primary purpose of the S&S valve? Does venting to atmosphere hurt vacuum potentially in a open system without this valve?

[Ohio HD]

The S&S valve is used when you remove the OEM breathers internal to the rocker box on top of the head. I won't be using the OEM breathers.

My head porter recommended that I use the S&S valves and place the oil lines as high as possible in the rocker box. He knows much more than I do.

[Ohio HD]

Permanently blocked off the lower breather plate of early style Twin Cam breathers.

Tapped for 1/4 NPT, plug was liberally coated with high Strength Sleeve Retainer. I doubt you could get it out 24 hours from now. If you did, the part would be warped from the heat.



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[turboprop]

As a result of this thread, I had a look at the two TC124s in my FXRs to see if this setup could be leveraged against them. Not needed at this point, but curious. I did not lift the tank and hold hardware in place, just sort of eyeballed it (VROM?). Seems that if one were to use the fittings and location shown earlier, that both lines would be obstructed by the mount for the upper link. Maybe not. I have a bunch of 6AN fittings to include some 90s and 220s(?) that might work better. I have a TC bagger but have never looked under the tank. Go figure.

[Ohio HD]

As a result of this thread, I had a look at the two TC124s in my FXRs to see if this setup could be leveraged against them. Not needed at this point, but curious. I did not lift the tank and hold hardware in place, just sort of eyeballed it (VROM?). Seems that if one were to use the fittings and location shown earlier, that both lines would be obstructed by the mount for the upper link. Maybe not. I have a bunch of 6AN fittings to include some 90s and 220s(?) that might work better. I have a TC bagger but have never looked under the tank. Go figure.

Yeah, your setup has different restrictions as far as rocker box access. Is there room above the rocker box and the gas tank? You could use an AN6 x 1/8 pipe with a 90°. That would keep the required access height lower under the tank. Or send the AN6 connection to the right of the bike.


 

[Ohio HD]

When I had the motor out, I considered tapping the top trans cover to run my breathers into it. I found a gasket inside of the cover. I wasn't sure exactly what the gasket was for? Was it to keep a certain amount of pressure or just a oil seal? I backed out of doing it. My current vent system is 3/8 out the breather bolts. I bored out the breather bolts and opened up the holes hair more. With the venting system, how can I promote good vacuum for ring seal and to prevent ring flutter while still releasing pressures? Is this the primary purpose of the S&S valve? Does venting to atmosphere hurt vacuum potentially in a open system without this valve?

I'm going to drill and tap the transmission case for venting to the oil pan, and for venting from the oil fill. I'll plug them for now, but they'll be there if I need or want to use them.

[turboprop]

When I had the motor out, I considered tapping the top trans cover to run my breathers into it. I found a gasket inside of the cover. I wasn't sure exactly what the gasket was for? Was it to keep a certain amount of pressure or just a oil seal? I backed out of doing it. My current vent system is 3/8 out the breather bolts. I bored out the breather bolts and opened up the holes hair more. With the venting system, how can I promote good vacuum for ring seal and to prevent ring flutter while still releasing pressures? Is this the primary purpose of the S&S valve? Does venting to atmosphere hurt vacuum potentially in a open system without this valve?

I'm going to drill and tap the transmission case for venting to the oil pan, and for venting from the oil fill. I'll plug them for now, but they'll be there if I need or want to use them.

A 90 degree adapter fitting into the top cover would certainly work. I am stupid sometimes. I had a 90 degree hose end sort of held in place and thinking it was too tight. But duhh, a 90 degree adapter and a straight hose end would work very well. Based on your results, I might give this a try.  Thanks. Learning has occurred.

[Ohio HD]

When I had the motor out, I considered tapping the top trans cover to run my breathers into it. I found a gasket inside of the cover. I wasn't sure exactly what the gasket was for? Was it to keep a certain amount of pressure or just a oil seal? I backed out of doing it. My current vent system is 3/8 out the breather bolts. I bored out the breather bolts and opened up the holes hair more. With the venting system, how can I promote good vacuum for ring seal and to prevent ring flutter while still releasing pressures? Is this the primary purpose of the S&S valve? Does venting to atmosphere hurt vacuum potentially in a open system without this valve?

I'm going to drill and tap the transmission case for venting to the oil pan, and for venting from the oil fill. I'll plug them for now, but they'll be there if I need or want to use them.

A 90 degree adapter fitting into the top cover would certainly work. I am stupid sometimes. I had a 90 degree hose end sort of held in place and thinking it was too tight. But duhh, a 90 degree adapter and a straight hose end would work very well. Based on your results, I might give this a try.  Thanks. Learning has occurred.

I've always liked that phrase.

[JSD]

Thing is,it's a compounding issue. The stock setup is marginally good enough...for a stock bike.
There's way better alternatives. Crankcase breathing has never been a strong suit for Harleys.
Use a good external reed valve. They close quicker and don't allow ANY air back in that builds pressure. They also don't dry out and fail to seal at all.
I don't get a drop of oil out of mine. My umbrella valves are removed. The stamped housings are still there, empty, to aid in oil separation.

Drill the return holes under them to 1/8".

A picture of external reed valve please. 

[60Gunner]

Thing is,it's a compounding issue. The stock setup is marginally good enough...for a stock bike.
There's way better alternatives. Crankcase breathing has never been a strong suit for Harleys.
Use a good external reed valve. They close quicker and don't allow ANY air back in that builds pressure. They also don't dry out and fail to seal at all.
I don't get a drop of oil out of mine. My umbrella valves are removed. The stamped housings are still there, empty, to aid in oil separation.

Drill the return holes under them to 1/8".

A picture of external reed valve please.

This is the actual reed valve used in the BMW twins.




This is the machined housing the valves are in. It can used in line or as a case mount by changing the fittings. I'm working on the best case mount location. I'll drill/tap a hole once I come up with the best location but for now this works really well. I've actually got it shortened up more and they're barely visible behind the AC. The case mount version of this is used on Norton twins. I never cared for breathing from the heads. My sporty build was from the cam chest. Drill/tapped a hole in the cam cover at the 2 o'clock position. Totally hidden by the front pipe.

[Don D]

Harley goes to great trouble (and expense) to also provide oil separation from the vented air. The system works fair at best but we push it's capabilities with modified engines. A one way valve just controls the backflow of the vented air. Oil carryover must be controlled and that can be accomplished by the choice where to tap which is out of the windage or Harleys method by employing separation. Let the pressure out and keep the oil in.

[60Gunner]

If you are using an automotive PCV valve test it first.  For the most part, they are not a positive seal and will actually breath both ways. (one way is more like a leak)  If you want to hold negative crankcase pressure it may not perform the way you want.

S&S one way check valves.


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How do you intend to route the lines and what are they going to?

Have you seen the video by Tom Reiser on using the oil tank as a catch can and then venting the tank? He wants to drill the trans case (M8 application) for the oil return. There are other ways to do this. For example on an earlier TC the trans case has a plugged hole on top right behind the engine. The vent line could go into that and then drill/tap the oil spout for a vent line. I have been thinking of leveraging this against the Torque-A-Hoe bike and eliminating the external catch can. Only drawback I see is not being able to monitor what is coming out of the vents, but it should result in a much cleaner exterior, specially after extended high speed touring.

I'm not sure I'd want to return all that nasty crud to my oil tank/pan. It should burn off but...

That S&S valve looks like a copy of the one used by the Mercedes kompressor engines before the turbo. It's my understanding they're quick acting enough to work well for this application and can be had for under $10. Just not sure how well they hold up. Most automotive breather valves, especially PCVs, have an extremely short life expectancy. They can't handle the rapid pulses.
I'd like to see the actual valve in those S&S breathers.

Harley goes to great trouble (and expense) to also provide oil separation from the vented air. The system works fair at best but we push it's capabilities with modified engines. A one way valve just controls the backflow of the vented air. Oil carryover must be controlled and that can be accomplished by the choice where to tap which is out of the windage or Harleys method by employing separation. Let the pressure out and keep the oil in.

This is why I haven't vented from the cases...yet. I had a good location on my sporty and had 1/8npt X hose barb 90° baffled inside the cam cover. It worked quite well for oil separation. I just haven't given it enough thought on this twin cam...yet. But I will.

A visit to some other twin forums with giant air pumps like our engines and you'd see they pretty much laugh at Harley's umbrella valves.
Reed valves are way better at keeping a slight vacuum. 
The location (heat) doesn't do umbrella valves any favors tho.

The benefits are obvious. Better ring seal which means less pressure in the first place is a good enough reason for me tho.
These reed valves are obviously getting it done as my ring seal is outstanding. Did a compression test last week and while the calculators say my ccp should be around 207, it's just short of 215psi cold. I'll call it 212. Both cylinders are identical.

The best location for crankcase venting is closer to the source of the pressure imo. That would be the cases like they use to be before the EPA bs and venting back to the intake became mandatory. It would aid in oil return from the heads too.

[Ohio HD]

That S&S valve looks like a copy of the one used by the Mercedes kompressor engines before the turbo. It's my understanding they're quick acting enough to work well for this application and can be had for under $10. Just not sure how well they hold up. Most automotive breather valves, especially PCVs, have an extremely short life expectancy. They can't handle the rapid pulses.
I'd like to see the actual valve in those S&S breathers.

Whether Mercedes, S&S or whom ever uses these one way check valves, you can be sure they're made for industrial and medical use as a common type of valve. Neither Mercedes or S&S manufacture these valves.

They're commonly available with extremely low cracking pressure, as low as 1 to 3 PSI to seal them. Seal materials are commonly Viton, Buna or Silicon. They respond extremely fast due to the free floating diaphragm seal and seat design.


Coming from an industrial facilities background, as well as automation machine tool manufacturer, I've seen these types of valves work in poor factory conditions for many years before replacement.

What data do you have on life expectancy of these valves in cycles, and the actual cause of failure? By the way these are not automotive PCV valves.

[60Gunner]

That S&S valve looks like a copy of the one used by the Mercedes kompressor engines before the turbo. It's my understanding they're quick acting enough to work well for this application and can be had for under $10. Just not sure how well they hold up. Most automotive breather valves, especially PCVs, have an extremely short life expectancy. They can't handle the rapid pulses.
I'd like to see the actual valve in those S&S breathers.

Whether Mercedes, S&S or whom ever uses these one way check valves, you can be sure they're made for industrial and medical use as a common type of valve. Neither Mercedes or S&S manufacture these valves.

They're commonly available with extremely low cracking pressure, as low as 1 to 3 PSI to seal them. Seal materials are commonly Viton, Buna or Silicon. They respond extremely fast due to the free floating diaphragm seal and seat design.


Coming from an industrial facilities background, as well as automation machine tool manufacturer, I've seen these types of valves work in poor factory conditions for many years before replacement.

What data do you have on life expectancy of these valves in cycles, and the actual cause of failure? By the way these are not automotive PCV valves.

I wasn't implying those WERE pcv valves.
Extensive testing by several of us sporty guys 6 or 7 years ago is my experience with a variety of one way breather valves. No automotive PCV valve ever held up, at least not for long, in this application. The springs don't hold up. Others are not fast acting and can't keep up with the rapid pulses and allow air back in.
 An automotive application is far different and less demanding when there's just as many pistons going up, basically canceling out the ones going down at any given time,  as opposed to 2 going up and down at nearly the same time or in the case of a BMW twin at exactly the same time.
The XL forums has a huge database of all the testing we did, including slack tube testing and tutorials with pics on how to install the ultimate crankcase vent. My Sporty mod that a lot of them are running in one variation or another is there in detail.
No one that has done it has ever gone back to breathing from the heads. But twin cams are a different animal.
I could kick myself for not going gear drive cams tho. The DT cam plate I'm running has a labyrinth that separates air from oil. It's why this pump/plate eliminates aeration of the oil as I understand it.  R&R also has a cam cover that integrates with the plate and has a built in breather location that ties into this and solves the air/oil separation issue breathing from the cam chest. This cover only works with gear drive cams tho as it uses all the same bolt holes as the cam plate. How well it all works I don't know but I sure would've liked to have found out. According to one of the guys at R&R it works well.

This particular reed valve has been tested in street and track BMWs and why I chose it and its used in Norton twins now as well.
It's not cheap tho.

[Ohio HD]

That S&S valve looks like a copy of the one used by the Mercedes kompressor engines before the turbo. It's my understanding they're quick acting enough to work well for this application and can be had for under $10. Just not sure how well they hold up. Most automotive breather valves, especially PCVs, have an extremely short life expectancy. They can't handle the rapid pulses.
I'd like to see the actual valve in those S&S breathers.

Whether Mercedes, S&S or whom ever uses these one way check valves, you can be sure they're made for industrial and medical use as a common type of valve. Neither Mercedes or S&S manufacture these valves.

They're commonly available with extremely low cracking pressure, as low as 1 to 3 PSI to seal them. Seal materials are commonly Viton, Buna or Silicon. They respond extremely fast due to the free floating diaphragm seal and seat design.


Coming from an industrial facilities background, as well as automation machine tool manufacturer, I've seen these types of valves work in poor factory conditions for many years before replacement.

What data do you have on life expectancy of these valves in cycles, and the actual cause of failure? By the way these are not automotive PCV valves.

I wasn't implying those WERE pcv valves.
Extensive testing by several of us sporty guys 6 or 7 years ago is my experience with a variety of one way breather valves. No automotive PCV valve ever held up, at least not for long, in this application. The springs don't hold up. Others are not fast acting and can't keep up with the rapid pulses and allow air back in.
 An automotive application is far different and less demanding when there's just as many pistons going up, basically canceling out the ones going down at any given time,  as opposed to 2 going up and down at nearly the same time or in the case of a BMW twin at exactly the same time.
The XL forums has a huge database of all the testing we did, including slack tube testing and tutorials with pics on how to install the ultimate crankcase vent. My Sporty mod that a lot of them are running in one variation or another is there in detail.
No one that has done it has ever gone back to breathing from the heads. But twin cams are a different animal.
I could kick myself for not going gear drive cams tho. The DT cam plate I'm running has a labyrinth that separates air from oil. It's why this pump/plate eliminates aeration of the oil as I understand it.  R&R also has a cam cover that integrates with the plate and has a built in breather location that ties into this and solves the air/oil separation issue breathing from the cam chest. This cover only works with gear drive cams tho as it uses all the same bolt holes as the cam plate. How well it all works I don't know but I sure would've liked to have found out. According to one of the guys at R&R it works well.

This particular reed valve has been tested in street and track BMWs and why I chose it and its used in Norton twins now as well.
It's not cheap tho.

Lets keep the discussion to what we're "using" then and not confuse everyone with "automotive PCV" that no one is using in this post.

At the end of the day the valve style has nothing to do with oil expelling from the head. The valves job is to stop reverse flow of air from entering the head, and then allowing air to exit when the internal direction of flow changes in the motor. You get oil expelling when the head can't drain fast enough, or is being over loaded by internal motor issues or components. In those cases the valves become exposed to more oil than they should. 

S&S started using these check valves several years ago with their cylinder heads and with their crate motors. They however use one valve for the entire motor.






 

[Don D]

"You get oil expelling when the head can't drain fast enough, or is being over loaded by internal motor issues or components."

The location of where venting is tapped matters. There are many places that have a lot of oil windage that are not suitable to use to relieve pressure without guarding or other means of oil separation. These conditions are prevalent all the Harley big twins even on motors that have no issues.

[Ohio HD]

The location of where venting is tapped matters. There are many places that have a lot of oil windage that are not suitable to use to relieve pressure without guarding or other means of oil separation. These conditions are prevalent all the Harley big twins even on motors that have no issues.

We're assuming valving is connected using the OEM flow location. What I plan to do is not how the OEM system was designed. Hence at the beginning of the post I show the OEM system function and flow path.

[Don D]

I read all of that but in my opinion there is a lot of oil splash out of the top of the covers, your proposed connection point , right? This is probably why sachs drills the heads, he can comment on that.

[Ohio HD]

I read all of that but in my opinion there is a lot of oil splash out of the top of the covers, your proposed connection point , right? This is probably why sachs drills the heads, he can comment on that.

I started using a set up like that in 2000 on some of my customer builds. I mounted a rt. angle adaptor over the center of the intake rocker arm. I put a PVC valve into the adaptor, a length of hose and let it work. There is a very small amount of power gained. I run this system on my Buell.
John

Pretty sure that John and I are on the same page as far as drilling the connection into the rocker cover.
This also recommended to me by Jim Libonati. Both who have been involved with racing HD motors and building them. Both for over 40 years.


My purpose is not to better the OEM system for oil control, rather to insure all pressure in the rocker box is relived. This is why I said "We're assuming valving is connected using the OEM flow location" for the discussion of valve types.

The motor I'm building is not a highway cruiser. I expect to have less than perfect "cleanliness" when running this motor hard. 

[Don D]

All makes sense, appreciate tye clarification.

[60Gunner]

"You get oil expelling when the head can't drain fast enough, or is being over loaded by internal motor issues or components."

The location of where venting is tapped matters. There are many places that have a lot of oil windage that are not suitable to use to relieve pressure without guarding or other means of oil separation. These conditions are prevalent all the Harley big twins even on motors that have no issues.

This is right on what I was getting it. It DOES matter.

The breather system works reasonably well, so long as the engine is mechanically sound.  There is actually a slight vacuum on the crankcase when all is working well.

But if you lose ring seal and the blow by increases, the increased volume of gases being vented will carry more oil out too.  And the engine is going to lose ring seal over time, no way to stop that.

Another issue that increases oil carry over is raising the oil pressure.  Higher oil pressures increase the amount of oil in the upper and lower areas of the engine. And that can easily overwork the simple little oil separator set up in the breather as well as exceed the capacity of the drains in the rocker supports.

If it only slobbers out on the big slab, it's usually fixable by drilling out the drain holes.  But when they get to slobbering all the time, it usually requires more work.       

Not entirely true either. My DT pump and plate has adjustable oil pressure as I'm sure you know and it's set up currently to 42psi or roughly 10psi higher than stock. I don't get a drop out of my breathers partly because of the improved crankcase vacuum of the reed valves and no oil pooling in the heads or rocker boxes but mostly because of the dual port scavenging of the pump and a plate which also maintains a constant vacuum on those scavenge ports.
Another thing I noticed the other day changing oil. It took an extra 6+oz to get to the full mark than it use to because I drained 6+oz more. Oil that is no longer being left in the sump for the crank to swim in. Yes I fill my oil to the full mark now.
And a benefit of improved pressure is setting my idle to 920rpm when engine temps reach 250 to he!p with cooling without fear of starving the top end of oil.