Crankcase breather


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cross
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Crankcase breather

Post by cross »

Hi Guys,
I'm curious as to how some of you took care of crankcase breather.

I did eliminate this as it was recommended while back and I bypassed the air box and routed hose straight into the catch tank however, I didn't think of making a vent along the line.
I'm thinking of the following

1. Keep the hose from the crankcase attached to the drain tank and somewhere midline add T and breather filter.
2. Eliminate drain tank, attach a hose upward, somewhere between the carbs and attach breather filter on the top to vent so that the oil drains back into the crankcase.
3. Attach breather filter straight on to the crankcase outlet.

Which would you suggest
In the case of #3, What would happen with oil that gets out of the crankcase?
As I do get some oil in the drain tank.

Thanks
Sasha

'82 Honda CBX
'99 Triumph TBS
'01 Honda Valkyrie

:auto-sportbike:

daves79x
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Re: Crankcase breather

Post by daves79x »

Who suggested taking the crankcase breather from the airbox and doing anything else with it? On a bike with a stock airbox, the stock plumbing is neat and does the job just fine. On bikes with individual filters, then accommodations have to be made. Think you're trying to solve a non-existent problem.

Dave

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cross
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Re: Crankcase breather

Post by cross »

I think it's one of the Mike Nixons recommendations so that the carbs don't get dirty from the oil.
I do get oil in the catch tank.
So you say that I should just keep it connected to the air box?
Sasha

'82 Honda CBX
'99 Triumph TBS
'01 Honda Valkyrie

:auto-sportbike:

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Re: Crankcase breather

Post by daves79x »

Yes, keep the vent stock. There won't be any issue with oil from there on the carbs if the hose is intact. Problem now is that the hose is NLA from Honda if you need one. Easy I suppose to adapt something else.

I think Mike will agree that the vast majority of grimy carbs comes from valve cover bolt grommets that leak. Oil just gets funneled right back over the carbs.

Dave

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cross
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Re: Crankcase breather

Post by cross »

Thank you Dave
Sasha

'82 Honda CBX
'99 Triumph TBS
'01 Honda Valkyrie

:auto-sportbike:

EMS
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Re: Crankcase breather

Post by EMS »

I believe a concern would be that you get oil INSIDE the carbs, not "over" them. :?

The fact that the breather goes into the airbox has another reason: The scavenging effect. Of course, all is based on EPA and pollution requirements, that's why manufacturers have to vent the crankcase back into the engine. And if you scavenge the crankcase actively, theoretically, you have less pumping losses. Many combustion engines used to route the breather tube back into the valve cover. In recent years, the EPA is toying with a mandate to use more "force" to "evacuate'" crankcase vapor.
This would mean the application of a "vacuum" pump, similar to the designs used for brake vacuum on Diesel and Direct Injection engines.

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Re: Crankcase breather

Post by cross »

So keep it stock or disconnect it and have it vent?
Sasha

'82 Honda CBX
'99 Triumph TBS
'01 Honda Valkyrie

:auto-sportbike:

daves79x
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Re: Crankcase breather

Post by daves79x »

The crankcase has to vent somewhere. I can't imagine how much oil could possibly be blowing out your vent to cause harm. The airbox has internal baffling to prevent the possibility of any oil actually ever getting to the carb intake. Maybe oil fumes, but not oil. The venting system, if clear, will drain any oil to the catch tank. If you are blowing noticeable oil in all the longer you've run the bike, then you have other issues.

Again, I think we're talking about a non-existent problem. Everyone I know with a stock airbox runs the stock crankcase vent system.

Dave

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Re: Crankcase breather

Post by Mello »

My original breather tube was cracked, so I had to replace it with a rubber hose. I didn't notice that the las time I fiddled with the carbs, I managed to kink the tube, effectively cutting off the venting back to the carb. Last Friday, I went for a ride with a mate of mine only to find another oil leak! Looking for the source, I noticed the kinked tube. I managed to work the tube off and was amazed at the built up pressure that was still in the crankcase despite the bike standing for around an hour while we had breakfast.

W continued our ride with the tube disconnected. At time I pushed the old girl up to 200 kph (around 130mph) and no further leaks and no oil from the crankcase. To get in to replace the tube is virtually impossible without tilting the engine, so I've just run a tube from the crankcase between the carbs, over the airbox and back down past the collector box. I also blocked the airbox "intake". So far seems to have done the trick.
"Aerodynamics are for people who can't build engines." - Enzo Ferrari

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Re: Crankcase breather

Post by daves79x »

The stock Honda vent hose might be available over there. It's not here. Anyway, you found out what happens when a crankcase can't vent. Oil is forced out lots of places due to high crankcase pressure.

Dave

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Re: Crankcase breather

Post by cross »

That's exactly what happened to me.
I bypassed the air is and run hose straight from the crankcase into the drain tank.
And I guess to the vacuum that got created, after I shut the engine off, after few minutes some oil got sucked out of the drain tank and back around the crankcase hose over the engine. This happened after hwy run at higher speeds.
I was thinking that my engine my not be good as there is so much oil coming out.
I kept things same only I added a breather filter midway and have been riding this weekend and no problems, there is no oil in the drain tank at all.
Lucky me that I didn't blow a gasket or seal.
But I'm definitely going to reconnect it back into the air box as there is smell coming out of he breather filter.
Sasha

'82 Honda CBX
'99 Triumph TBS
'01 Honda Valkyrie

:auto-sportbike:

daves79x
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Re: Crankcase breather

Post by daves79x »

Running the crankcase vent directly to the catch tank still results in a closed system with no vent - if the plug is still in the drain hose from the tank. So you had no crankcase vent that way either, as I guess you found out. You're doing the right thing by going back to the stock location. On these things, most of the time, you can't reinvent the wheel.

Dave

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Re: Crankcase breather

Post by CBX-Six »

The crankcase breather seems still to be sold out.
Does any one have another workable solution, as installing just a standard rubber hose will bend and close the breathing.

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Re: Crankcase breather

Post by tevan »

There was a solution on Facebook about that last year. I will check when I get home this afternoon on that information. Pm me

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Re: Crankcase breather

Post by Louis »

CBX-Six wrote:The crankcase breather seems still to be sold out.
Does any one have another workable solution, as installing just a standard rubber hose will bend and close the breathing.
Have plenty NOS ones in stock as well as a few used one. If you decide you still need one just email me at usedcbxparts@hotmail.com or thru my web page www.usedcbxparts.com

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