Topic: What does a breather seperator do?

[Bradyn13]

I was trying to fix a vaccuum leak the other day by installing some new carburetor boots, and while doing that I noticed a bunch of extra tubes that don't seem to do anything.  I found a picture of them on this forum that I have attached.  Can someone explain in depth what these tubes actually do?  I can't find mention of them in my owners manual.  Can I remove them, or cut them short?

[Jerry Rxman Griffin aka MuthaF'er]

IN THEORY it helps separate the oil from the air and the air with or without the oil vapors returns to re-burn. Early emission control. Necessary for function, no. Good idea (in 1977), yes.

[evinrude7]

my guess is it's an emissions thing.  notice it says on bikes after dec 31st 77.  i'm sure someone more knowledgeable will pipe up. 

[TwoTired]

The engine rebreather has several attributes.
It evacuates gases from the crankcase, such as oil vapor, water Vapor, and piston ring blow by. Water vapor in particular is best removed forcibly from the crankcase, rather than be allowed to languish inside.  The other gases are mostly hydrocarbons, with some debate about whether oil contamination is a concern, or not, for engine benefits.  However, it is very well known that hydrocarbons in our once breatheable atmosphere is decidedly a bad thing for the lungs of all mammals on the planet, and is best burned in the engines combustion chamber.

The vapor separator is primarily to prevent or reduce water vapor condensate from being inhaled by the engine.  Water and engine metals are far less likely to corrode without water ingestion.

Hope this "clears the air".   😷

[Bradyn13]

Those gasses would escape on their own though if the tube just vented to atmosphere correct? The only downside is it is worse for the environment.  So the vapor separator is basically a catch can where water can condense and run out the bottom tube, and the air/gasses can go back into the cylinders if I understand correctly. If I remove the system, any ideas on how best to plug the hole that would be in the cylinder head? I'm sure I can find a way to plug the one in the airbox, but the head is a little more worrying. 

Thanks for the reply btw.

[TwoTired]

Those gasses would escape on their own though if the tube just vented to atmosphere correct?

That's the dream.  But there is no positive flow or movement with a simple hole to the outside.  Gases can linger and contaminate the oil supply.
I suppose if you did more frequent oil changes the effect would be reduced.

The only downside is it is worse for the environment. 

Not entirely, see above.  But, some feel that lung cancer is a rather severe downside.  Not really fair to require everyone else to stop breathing, IMO.

So the vapor separator is basically a catch can where water can condense and run out the bottom tube, and the air/gasses can go back into the cylinders if I understand correctly. 

In essence yes.   All the tubes are in fact ducting devices.

If I remove the system, any ideas on how best to plug the hole that would be in the cylinder head?

Do NOT plug the crankcase hose vent.  It is the only way piston blow by gasses and pressure can be relieved or equalized with the barometric pressure of the atmosphere.  You can blow seals and cause oil leaks.

Most devil-may-care operators just let the tube vent to atmosphere, and/or put a small air filter on the tube to keep crawling/flying critters out of the engine internals.

My opinion is these folks ought to run the tube up to exit at the gauge cluster.  So, they can experience the full benefit of the mods they made.
(Only half joking there.)

[flybox1]

Those gasses would escape on their own though if the tube just vented to atmosphere correct?

That's the dream.  But there is no positive flow or movement with a simple hole to the outside.  Gases can linger and contaminate the oil supply.
I suppose if you did more frequent oil changes the effect would be reduced.

The only downside is it is worse for the environment. 

Not entirely, see above.  But, some feel that lung cancer is a rather severe downside.  Not really fair to require everyone else to stop breathing, IMO.

So the vapor separator is basically a catch can where water can condense and run out the bottom tube, and the air/gasses can go back into the cylinders if I understand correctly. 

In essence yes.   All the tubes are in fact ducting devices.

If I remove the system, any ideas on how best to plug the hole that would be in the cylinder head?

Do NOT plug the crankcase hose vent.  It is the only way piston blow by gasses and pressure can be relieved or equalized with the barometric pressure of the atmosphere.  You can blow seals and cause oil leaks.

Most devil-may-care operators just let the tube vent to atmosphere, and/or put a small air filter on the tube to keep crawling/flying critters out of the engine internals.

My opinion is these folks ought to run the tube up to exit at the gauge cluster.  So, they can experience the full benefit of the mods they made.
(Only half joking there.)

^^^This.

[drumstyx]

*sigh* alright TwoTired, you've convinced me, I'll run the rebreather. What sizes are the hoses used?

[TwoTired]

My parts lists are 700 miles away at the moment.  But, if fallible memory serves, it's 12 mm.

Cheers,

[SKTP]

Sort of on topic...I have always assumed that the oil-tank vent and the case vent hooked into the re breather...but after seeing that diagram, they don't...I ran hose connecting the two...is that wrong? How are those 2 "vents" supposed to go?....I did this (not my picture)

[flybox1]

Top of the valve nipple cover goes to the breather at the bottom of the battery tray
From there, the gasses get circulated to the top of the airbox and the moisture drains to the ground along the inner right side of the frame near the swing arm.

The rear crank case nipple is the oil tank overflow inlet.
These should not be interchanged.

[SKTP]

The rear crank case nipple is the oil tank overflow inlet.
These should not be interchanged.

I am slow after the long weekend...so that picture is correct. Correct?

[flybox1]

The rear crank case nipple is the oil tank overflow inlet.
These should not be interchanged.

I am slow after the long weekend...so that picture is correct. Correct?

Yes

[TwoTired]

What airfilter element do you use?

For the 750s, I use K&N.
For the 550s,  I use either the Uni foam or the Honda paper.  My 78 runs better with the paper, I assume slightly more restriction .  The rest don't care.
The 78 has a lower rebreather stand pipe in the box than earlier models.  Still in cold temps and wet humid weather it needs more frequent cleaning as the sponge saturates with condensate.  The telltale for service is the brown mayo showing up on the dipstick.  Time to clear the breather sponge.  Very easy on the 550.  And run the engine hot for 20-30 minutes to vaporize the crankcase water accumulation.  I'd rather the water condensate collected outside the engine crankcase.

I don't think the 750s have that sponge filter, though.  It's a screen isn't it?  Argh, documents 700 miles away.

Cheers,

[flybox1]

@TT...yes.  Its a sponge.  NLA IIRC. 
I just trimmed down a standard absorbent kitchen sponge.

[TwoTired]

@TT...yes.  Its a sponge.  NLA IIRC. 
I just trimmed down a standard absorbent kitchen sponge.

  Open cell foam you can breathe easily though, should work just fine, provided it is oil and gas impervious.  You could put it in some gas to test it.  If it doesn't dissolve, should work fine.
I suppose the thickness should be mentioned.  It should fit the space for it without any compression .

Cheers,