Removing the breather box?

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low-side
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Re: Removing the breather box?

#16

Post by low-side »

If the engine is running remotely close to well, oil won't be hitting the road. Oil vapor will condense on the wall of the tube and stick there or even soak in. Most folks spill more oil during an oil change than a road tube would drop in a decade. If you look at a pre '77 CB750, it has 2 breather tubes. 1 from the crankcase to the oil tank and a road tube that runs from the valve cover down to a space between the engine and the swing arm. Catch cans are an emissions control device, not a safety device. If it's working well or can be readily repaired I'd keep it; if it's beyond repair you can certainly work around it. I have 2 '78s; one's a bagger and the other is more of a cruiser. The bagger has a functioning catch can so I kept it. The cruiser had a road tube when I bought it. Both run very well and neither leave a puddle.
wannabridin
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Re: Removing the breather box?

#17

Post by wannabridin »

On my 77, the stock breather catch can was shot, so I have the engine output running to an automotive PCV valve w/ a one way valve in it (airbox bypassed).

Is it recommended to run the hoses back to the airbox? Or could I simply plug the airbox holes and use the existing setup?
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Sidecar Bob
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Re: Removing the breather box?

#18

Post by Sidecar Bob »

There will always be some blowby, especially when the engine is cold and the rings haven't expended enough to close their end gaps so the crankcase must be ventilated to keep the pressure from building up inside it. Any moisture that is in the combustion air and gets past the rings will be expelled through the breather system too and it often carries a bit of oil with it. The canister is actually a separator that is supposed to allow vapours (including unburned fuel) to be drawn back into the carbs for a second chance to be burned while the liquids settle out in the form of an emulsion of oil & water that smells of burned hydrocarbons.
BTW: If the engine isn't run long enough to warm thoroughly some of the moisture will condense when the engine cools again and pool at the bottom of the oil until the engine is run long enough for the oil to get hot enough to boil off the water, which is one of the main reasons it isn't good to start the engine and let it idle every week or so during the winter.

If pressure is allowed to build up inside the crankcase it will force the oil out through the weakest oil seal. I learned about that when I arrived home on the GL1000 that was my winter bike one day several decades ago and discovered that the right leg of my snowmobile pants was covered with oil. I couldn't see where the oil had come from so I washed it off with of hot, soapy water, topped up the oil and fired it up hoping to see where the leak was but I saw nothing. I called a friend who is a Honda trained mechanic and he told me what probably happened was the hose from the canister was dragging in the snow and some condensate froze in it so the pressure built up until oil sprayed out from the tach cable seal. He said to cut an inch off of the hose and it would probably never happen again and he was right.

Many years later I was experimenting with the breather system on my CX650E based winter machine and tried installing a PCV valve between the crankcase and the separator in hopes that it would stop any condensate that was in the line from running back into the engine when I shut it off. Unfortunately, when it got cold enough the condensate that the valve stopped froze and kept the valve from opening. This time the weakest oil seal was the shift shaft so my left leg got soaked. I also noticed it soon enough that I was able to stop every few minutes and open the oil filler to let the pressure out.
When I got home I removed the valve.

Speaking of moisture in the crankcase (& this the condensate), I noticed a long time ago that there is always more condensate when the weather is wet. The CX/GL500/650 family of bikes (like my winter machine) have the separator hanging below the airbox with drain tubes that hang below the separator and caps in the tubes that have to be removed when condensate is visible in the tune to drain it. I got fed up with having to crawl under the bike & sidecar to get to the the drain tube on the winter machine, most often when the garage was cold and the bike was dripping from a trip home in the wet so I replaced the cap in its drain with an old fuel filter (& later figured out that the wind between the bike and sidecar was siphoning oil out through it so I moved the outlet to the left side of the bike).
It is not uncommon to find a quarter sized spot of condensate on the garage floor after a half hour ride in the rain.

BTW: I removed the catch can on the GoldWing and put a filter on its drain line too. One less job to have to remember to do...
Mr. Honda ('83 GL1100/Dnepr) summer How a motorcycle evolves thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
wannabridin
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Re: Removing the breather box?

#19

Post by wannabridin »

wannabridin wrote: Mon Apr 19, 2021 11:19 am On my 77, the stock breather catch can was shot, so I have the engine output running to an automotive PCV valve w/ a one way valve in it (airbox bypassed).

Is it recommended to run the hoses back to the airbox? Or could I simply plug the airbox holes and use the existing setup?
I've changed my design to use a Uni breather filter, some 1/2" hose and I ran it straight up under the airbox. It's tidy and doesn't interfere w/ the carb linkage, so it should be nice and simple. Gravity will let everything drain back simply.
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Sidecar Bob
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Re: Removing the breather box?

#20

Post by Sidecar Bob »

See my comments above about the moisture &c exiting. Letting that stuff drain back into the engine is like swallowing snot to stop your nose from running.
Mr. Honda ('83 GL1100/Dnepr) summer How a motorcycle evolves thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
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dontwantapickle
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Re: Removing the breather box?

#21

Post by dontwantapickle »

Crankcase vent tube to up under the tank, gravity drain back......
just like my BSA B50 race bikes were. It worked good.
I modified a B44 Victor to vent the same way.
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Sidecar Bob
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Re: Removing the breather box?

#22

Post by Sidecar Bob »

It's up to you but I'd rather get that stuff out of the crankcase even if it meant adding oil a bit more often.
Mr. Honda ('83 GL1100/Dnepr) summer How a motorcycle evolves thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
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dontwantapickle
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Re: Removing the breather box?

#23

Post by dontwantapickle »

That's how the factory did it back then.
My Norton Commando crankcase vented right back into the oil tank.

Both are IMHO better options than blowing oily crap out onto the road,
(or all over your back tire).
wannabridin
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Re: Removing the breather box?

#24

Post by wannabridin »

Appropriate care of your motor includes appropriate warming cycles and PCV inspection/cleaning. Lots of shot trips, not getting to temp will cause excessive moisture. If you get your motor hot and keep it there, more moisture will escape the oil.

So lots of quick jaunts around town require more frequent oil changes to free the un-liberated moisture. Makes sense to inspect the PCV hose at this time too, won't take much time to do so while the oil is draining.

And of course, some nice "italian tune ups" are always good for keeping things in running order...
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