Engine Crankcase Breather

[Paul75]

Guys I'm looking for a neat solution for the breather tubes. As you can see I've got the K&N's and obviously lost the stock metal air boxes. From reading previous threads on this I understand the spent oil form the engine is turned into mist and redirected into the air box.

So my question is basically what different options do I have for redirecting this after the twin outlets? I'm not interested in sending this down to the chain as I think it could look pretty ugly, I want as neat as possible! I see some have used a small filter, I guess to catch spent oil?

If it helps I did actually buy the two brand new tubes, the copy of the original wire bound type, with wire, which I was thinking of using somehow....hmm......

Any ideas for peeps who have insight into this (I'm sure there are many!!) Would help enormously,

Paul

 

[Paul Sutton]

Perhaps we need a full explanation as to what the breather is meant to do? Does the engine run under a slight vacuum to cut down on air drag? Do we have 650cc of air being constantly pumped up and down those pipes? What would happen if we just plugged the pipes? What if there was a check valve so air only flowed out?

I see no sign of oil in my air boxes.

 

[Bob Kelly III]

I believe there is already a check valve in the breather arangement that lets air out and none in....
a person could re direct the tubes into the Pods but I doubt that would be a good idea as they barely have enough capasity for clean air as it is
..... my prefrence would be to use it as a chain oiler.... but barring that the bikes of Old just went over the back of the engine and vented infront of the rear tire.... which is a very bad idea... it should be to one side of the tire or the other.....
a filter on it is probably a good looking alternative but probably unnessarry....
grab a manual and check out the breather if your interested in it's make up....
My air boxes are oil free mostly...so I can't see any advantage of using the breather pipe as a chain oiler ! perhaps in 20,000 miles that will be diferent
but right now she's purty tight.
....
Bob.......

 

[Paul Sutton]

Check out the thread "Crankcase Breather". It has several ideas.

 

[Paul75]

Bob, if there is already a check valve in the breather arrangement why do people bolt on brake check valves?

 

[Max Midnight]

The purpose of the breather is to allow blow-by gasses to escape from the crankcase.
In doing so it will also pick up some oil vapour which contains un-burnt hydrocarbons which in the good old days (whenever that was) were vented to atmosphere.

The simplest way of dealing with this in the absence of an air-box would be to run a tube to the back of the bike. Not ecologically friendly but that is what Triumph did on my 1972 Bonneville.
As suggested above you could route the breather hoses into the rear of the K & N's which would mimic the OE set-up.
Lastly you could make an air-oil separator which would collect the condensed oil at the bottom of it which could then be fed back into the RH clutch cover with the fumes either going to atmosphere or routed back through the K & N's.
The advantage of the latter system is that oil consumption will be reduced as it is re-used rater than being dropped on the road or burnt.

 

[retiredgentleman]

Simple solution. Put your stock air boxes back on. Any crankcase vapours are drawn into the cylinders and burnt, the same as cars and trucks. Your CV carbs will work better as well......................imagine that! This was all designed by automotive engineers that knew what they were doing. Pods were designed by people that did not know what they were doing, and their only motive was to make profit at your expense. Strange how the world works

 

[fredintoon]

Guys I'm looking for a neat solution for the breather tubes. As you can see I've got the K&N's and obviously lost the stock metal air boxes. From reading previous threads on this I understand the spent oil form the engine is turned into mist and redirected into the air box.
So my question is basically what different options do I have for redirecting this after the twin outlets? I'm not interested in sending this down to the chain as I think it could look pretty ugly, I want as neat as possible! I see some have used a small filter, I guess to catch spent oil?
If it helps I did actually buy the two brand new tubes, the copy of the original wire bound type, with wire, which I was thinking of using somehow....hmm......
Any ideas for peeps who have insight into this (I'm sure there are many!!) Would help enormously,
Paul

Hi Paul,
FWIW, later model XS650s only had one vent tube and that unit will bolt straight onto your engine.
And all the Britbikes I ever owned ran their vent hoses to where they'd pant oil mist onto their drive chains.
Which is what I did after I swapped my stock airboxes for Unipods.
BTW your engine photo shows tapered pleated pods.
That style of pod does not play well with stock carburettors even if they do say XS on their ends.
But what to do with your vent tube if you don't want to oil the chain with it?
Run it to a catch-pot with an air vent hole in the top?

 

[grizld1]

No, Bob, there is no check valve in the OE assembly. There's only a baffle. Now let's get to the point. When the pistons rise, air is pumped into the crankcase. When the pistons fall, the air in the crankcase is pressurized and must be released; otherwise the crankcase seals will blow out, usually starting with the clutch pushrod seal. A one-way valve lets air out but not in, so that the pistons drop into low pressure in the crankcase instead of pushing against high pressure. A good one-way valve will eliminate oil loss through the breather almost entirely and will reduce seeping elsewhere. I use a purpose-built valve from Krankvent. It costs an arm and a leg and it's very effective; no oil mess anywhere and no oil loss between changes. A Google search will take you to it. Others report good results with an inexpensive power brake booster valve; I haven't used one, so I can't comment beyond saying that the thing is going to cycle more times in a few minutes of operation on a bike motor than it would in a year of its intended application. Mike's XS offers a Chiwanese reed valve. I haven't used it and don't trust the vendor.

 

[grizld1]

RG, we're in complete agreement on retaining the still air box with vacuum carbs. Pods are for carburetors with mechanically actuated slides, and it's usually not the manufacturers' fault that the unknowing use them where they don't belong. I say usually, because Mike's XS will take advantage of the stylin' buyer's ignorance at every opportunity. Bottom line on the breather issue, though, is that oil does the most good when it's kept where it belongs, which is in the crankcase.

 

[fredintoon]

Simple solution. Put your stock air boxes back on. Any crankcase vapours are drawn into the cylinders and burnt, the same as cars and trucks. Your CV carbs will work better as well......................imagine that! This was all designed by automotive engineers that knew what they were doing. Pods were designed by people that did not know what they were doing, and their only motive was to make profit at your expense. Strange how the world works

Hi RG,
and I always reckoned that the stock airboxes were designed by an evil co-operation between the EPA Nazis and the Bandaid manufacturers.
And I got the frustration issues and the scar tissue to prove it.
& BTW, Unipods work fine on CV carbs, it's those tapered pleated pods that eff up CV carbs although they are OK with normal ones.

 

[mrtwowheel]

My question ??????, and to help out Paul75. If tubes are attached to the breathers and just routed towards the ground, will these tubes suck dirt into the engine? Is a cover/screen/filter necessary to keep grit from entering the engine?

The breather also expels moisture/condensation that is warmed up, evaporated, in the engine. Without a closed system, will moisture be able to enter through those open tubes?

In general, WHAT IS THE DOWNSIDE OF JUST USING OPEN HOSES? Sorry for raising my voice.

Scott

 

[grizld1]

Scar tissue? Bandaids? Fred, with respect and all the compassion I can muster: How the hay did you manage to cut yourself on a late plastic airbox?!

 

[grizld1]

The downside of open hoses? Pistons fall into high pressure, pushing on seals and pushing oil mist out the hose. Run your bike that way at 70 to 80 mph on the highway for a day, then check your oil level. I don't care where you started on the dipstick, you'll be quite a lot lower. If the open hoses are long enough, alternating positive and negative pulses will keep garf from reaching your motor.

 

[mrtwowheel]

The downside of open hoses? Pistons fall into high pressure, pushing on seals and pushing oil mist out the hose. Run your bike that way at 70 to 80 mph on the highway for a day, then check your oil level. I don't care where you started on the dipstick, you'll be quite a lot lower. If the open hoses are long enough, alternating positive and negative pulses will keep garf from reaching your motor.

I'm not seeing why there would be an increase in crankcase pressure with the open hoses versus hose routed to an air box. I've never been convinced of a definitive solution for doing this without using the airbox on any thread.

So, that breather is pulling in air, and pushing air out?

Am I right that this is very comparable to an automotive engine breathing through the hole in the valve cover that must use a filter to keep grit out of the engine?

Scott

 

[fredintoon]

Scar tissue? Bandaids? Fred, with respect and all the compassion I can muster: How the hay did you manage to cut yourself on a late plastic airbox?!

Hi grizld1,
most of the blood, bandaids and bad language was from my battles with the stock airboxes on my XS11.
I guess that experience predisposed me to ditching the XS650 airboxes the first time they frustrated me.

 

[Paul75]

That's s good question Scott, it's something I don't fully understand either. It's made the more interesting because people on here are sometimes fitting a Brake booster check valve which as I understand it, does NOT let any air in, only oil mist out.

This check valve is something I want to explore as it MAY eliminate the use of the two tubes? I have (I'd sell them if it did!). If someone has done the check valve is there a 'how to' or is it too simple for one ?? An explanation would be great please. I'm looking on eBay and there is one available in the UK, I'll post a link up separately and hopefully someone can tell me if it's the correct type..

Regarding using the stock air boxes, that's not an option, I'm building a custom bike. The above does however make for painful reading as mine has the K&N's which look lovely but they are gonna cause me fueling issues right? This is quite a bummer, if I struggle they'll have to go I guess :-(.

Cheers guys

 

[grizld1]

Scott, I didn't claim that long open hoses would cause a difference in crankcase pressure vs. routing the hoses to the air box, opening the breather straight off the head, or whatever; they won't. You asked why the one-way valve was beneficial. I told you why. You asked if an obstructive filter was needed on an open hose in the absence of a valve, routing to air box, etc.. I gave you my experience there. Please don't attribute statements to me that I didn't make. Thank you.

 

[figure8]

Simple solution. Put your stock air boxes back on. Any crankcase vapours are drawn into the cylinders and burnt, the same as cars and trucks. Your CV carbs will work better as well......................imagine that! This was all designed by automotive engineers that knew what they were doing. Pods were designed by people that did not know what they were doing, and their only motive was to make profit at your expense. Strange how the world works

I thought it was common knowledge that these bikes came lean from the factory. When I put Uni's and rejetted my carbs my bike ran better than ever.

 

[Max Midnight]

I'm not seeing why there would be an increase in crankcase pressure with the open hoses versus hose routed to an air box. I've never been convinced of a definitive solution for doing this without using the airbox on any thread.

There won't be any difference in crankcase pressure assuming they both vent into ambient atmospheric pressure. Mr grizld1's post (#9) explains what is happening.

So, that breather is pulling in air, and pushing air out?

As you say the breather will suck and blow.
To surmise, the volume of the crankcase is not fixed; it will increase as the pistons move from bottom dead centre (bdc) to top dead centre (tdc) and air will be sucked in from the breather (nature hates a vacuum). From tdc to bdc the volume will reduce and air will be displaced. As the piston rings are not a perfect seal there will also be some blow-by from the combustion process. Additionally the rotating parts in the crankcase will cause some of the oil to mist.
It is a combination of the air sucked in as the pistons rise, the piston blow-by and oil mist that is expelled as the pistons descend.

This is why over time an open vent will expel oil.

Am I right that this is very comparable to an automotive engine breathing through the hole in the valve cover that must use a filter to keep grit out of the engine?Scott

Yes, although manufacturers haven't done this for many years as emission regulation have become more severe.

The picture below shows the arrangement I have on my V Max. The OE CV carbs have been replaced with flat slides and the air-box removed.
What you can see is an air/ oil separator which collect the crankcase fumes and allows the oil to condense and return to the crankcase whist any fumes are fed back into the carbs.
A similar system is described in the XS650/ 750 Engine Modification Guide.

The internals are shown here.