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Crankcase Vent Tube

PostAuthor: TheBeast » Thu Sep 19, 2019 4:35 am

Greetings. My first forum post...
Just purchased a very sick Virago 125 1997 which I plan to rebuild over the coming months.
Some dodgy DIY has been done on the bike that I need assistance with please.

The Crankcase vent pipe coming out of the back of the rear crank (just behind the oil filler cap), is run behind the 'mock' exhaust pipe and then leads down the frame in front of the rear wheel pointing towards the ground...

I have no idea where this is supposed to run and vent to, but there is another pipe (same diameter pipe that is connected to the frame at the back of the air box on the frame that leads to nowhere and has been plugged with a bolt?
Is the crankcase vent pipe supposed to be joined to this pipe and lead back in to the frame?

Any advice would be greatly appreciated...
Last edited by Jake on Fri Sep 20, 2019 10:38 pm, edited 1 time in total.
Reason: Topic from XV250 merged with XV125

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Re: Crankcase Vent Tube

PostAuthor: Arjay » Thu Sep 19, 2019 8:23 am

This sounds like AIS (air injection system) but dont know the 250. The AIS is part of the anti pollution system of years ago. Quite like the catalytic converter in principle, injecting air into the exhaust to burn off excess gas fumes in the stock exhaust chamber.

Many people get rid of the ais but usually (on xv1100) they stuff an empty brass 38 shell casing in the hole where ais tubing was removed from head. So two of them. There are youtube viddoes shows how.

But, I don't know the 250, only guessing.

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Re: Crankcase Vent Tube

PostAuthor: TheBeast » Fri Sep 20, 2019 3:14 am

Thanks Arjay

Appreciate the feedback.
I think this is different on the 125 and 250...
As mentioned, the venting tube is currently routed from the crankcase to the back wheel, but I don't think this is where it is supposed to vent as it does potentially dispel oil, so not great to have oil mist venting on to the back wheel!
There is a pipe coming from the frame that has been blocked off, so I am trying to work out if the crankcase vent tube is supposed to be connected to this to push the crankcase air back in to the frame?
The research continues...

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Re: Crankcase Vent Tube

PostAuthor: mark75 » Fri Sep 20, 2019 4:29 pm

re. 125 all I can add is this post with pdf manuals (owner & service) >>> viewtopic.php?f=88&t=30767

hope that helps until someone more knowledgeable chimes in.
"Over the Mountains of the Moon,
Down the Valley of the Shadow,
Ride, boldly ride" ... E.A. Poe


Time flies >>> whether you're having fun __ :bike: or not :fan: ---

Any day above ground is a good day.
so Laissez les bon temps roulez. just roll safely --- Semper Vigilans...always watchful

"I hear and I forget, I see and I remember, I do and I understand." ... Confucius*

If you don't read the news you are not informed.
If you read the news you are misinformed.
... Mark Twain


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Re: Crankcase Vent Tube

PostAuthor: mark75 » Fri Sep 20, 2019 4:46 pm

all new posts show in the same place, so posting the same issue in 2 forums wont help much to get more attention - mostly it only clogs an already challenged system.

I am more analog than digital, but I shall attempt to merge your 2 threads.
"Over the Mountains of the Moon,
Down the Valley of the Shadow,
Ride, boldly ride" ... E.A. Poe


Time flies >>> whether you're having fun __ :bike: or not :fan: ---

Any day above ground is a good day.
so Laissez les bon temps roulez. just roll safely --- Semper Vigilans...always watchful

"I hear and I forget, I see and I remember, I do and I understand." ... Confucius*

If you don't read the news you are not informed.
If you read the news you are misinformed.
... Mark Twain


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The views, opinions, and experiences expressed in this post are mine and may not necessarily represent views and opinions of other VTF members, so feel free to agree, disagree, or ignore them.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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Re: Crankcase Vent Tube

PostAuthor: Arjay » Fri Sep 20, 2019 5:19 pm

I read somewhere that early harleys used lots of oil and one reason was a deliberate steady drip was dedicated for the chain.

Fill er up and It'll need a quart of oil...

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Re: Crankcase Vent Tube

PostAuthor: Jake » Sat Sep 21, 2019 6:14 am

I deleted your post in XV250 and merged all replies to the one in XV125.

You only need to post one topic per issue/problem. Multiple threads on the same topic will not get you faster or better answers, most likely just duplicate answers. If different solutions should be offered, it's better to have them on one thread.

If you don't get an answer in a reasonable time, reply to your own thread with "bump".
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Re: Crankcase Vent Tube

PostAuthor: Jake » Sat Sep 21, 2019 6:40 am

TheBeast wrote:same diameter pipe that is connected to the frame at the back of the air box on the frame that leads to nowhere and has been plugged with a bolt?
Is the crankcase vent pipe supposed to be joined to this pipe and lead back in to the frame?



The crankcase vent pipe is supposed to be connected to the frame so the blow by is recirculated with the intake air and burned. The air intake for the Virago is funneled through the frame, that is the reason for the vent pipe attachment, on automobiles there is a PCV ( positive crankcase ventilation ) that performs the same function.

It would not hurt to leave it vented the way it is, it’s up to you.


Please add your location to your profile so no one has to ask in the future. With members all over the globe, some info is geographically specific.

Add your location at this link to your User Control Panel

This concerns the XV125 because most of the members of this forum are in the US, and the XV125 was never sold here.
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It’s what you know for sure that just ain’t so.”

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Re: Crankcase Vent Tube

PostAuthor: mark75 » Sat Sep 21, 2019 1:55 pm

Arjay wrote:I read somewhere that early harleys used lots of oil and one reason was a deliberate steady drip was dedicated for the chain.

Fill er up and It'll need a quart of oil...



most very early internal-combustion engines had nothing to collect/reservoir the oil, it ran in one end and out the other via gravity.
simple, elegant design, but very messy.
"Over the Mountains of the Moon,
Down the Valley of the Shadow,
Ride, boldly ride" ... E.A. Poe


Time flies >>> whether you're having fun __ :bike: or not :fan: ---

Any day above ground is a good day.
so Laissez les bon temps roulez. just roll safely --- Semper Vigilans...always watchful

"I hear and I forget, I see and I remember, I do and I understand." ... Confucius*

If you don't read the news you are not informed.
If you read the news you are misinformed.
... Mark Twain


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The views, opinions, and experiences expressed in this post are mine and may not necessarily represent views and opinions of other VTF members, so feel free to agree, disagree, or ignore them.
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Re: Crankcase Vent Tube

PostAuthor: Flyingdog » Tue Sep 24, 2019 4:51 am

Arjay wrote:I read somewhere that early harleys used lots of oil and one reason was a deliberate steady drip was dedicated for the chain.


OK? And there for what? Chain drive vs shafty.... How does this help the OP?

Beast..don't know bout the 125 or 250 vent setup..diagrams kinda vague, but like on the Gen 1 750s, there's a vent hose that's pretty hidden, coming off air filter box and squeezed between the tool box/frame.. Actually has a foam filter element, the pipe terminates to open air. Like I said..wasn't sure if yours has something like this. Both of my bikes had something like this and mounted a cheap, external "vent filter" inline of this hose. Acts like a catch-can, for these crank case fumes. Other wise it just drips to the ground.
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Re: Crankcase Vent Tube

PostAuthor: Jake » Tue Sep 24, 2019 6:06 am

Flyingdog wrote:
Arjay wrote:I read somewhere that early harleys used lots of oil and one reason was a deliberate steady drip was dedicated for the chain.


OK? And there for what? Chain drive vs shafty.... How does this help the OP?

Beast..don't know bout the 125 or 250 vent setup..diagrams kinda vague, but like on the Gen 1 750s, there's a vent hose that's pretty hidden, coming off air filter box and squeezed between the tool box/frame.. Actually has a foam filter element, the pipe terminates to open air. Like I said..wasn't sure if yours has something like this. Both of my bikes had something like this and mounted a cheap, external "vent filter" inline of this hose. Acts like a catch-can, for these crank case fumes. Other wise it just drips to the ground.
DSC_0001.JPG


ummm.....the XV125 is chain.
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It’s what you know for sure that just ain’t so.”

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Re: Crankcase Vent Tube

PostAuthor: Flyingdog » Tue Sep 24, 2019 8:46 am

Yea..ok..still wouldn't terminate to a drive chain. Specially not vent fumes. Was pointing out, if OP could find if there was a (open) venting nipple somewhere (possibly off the air filter box?)..the whole thing (crankcase venting) could be terminated to a filter and not wonder where all this other stuff was. Besides..and pretty lame excuse..broke a tooth on a frikk'n apple, of all things. Spent 6hrs in the chair of a guy I think was a graduate of " Steve Wonder/Jigsaw school of Dentistry". :cl: Still seeing triple.
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Re: Crankcase Vent Tube

PostAuthor: Cusstout 1100 » Tue Sep 24, 2019 10:32 am

As an aside, and just to confirm Arjay's comment: Yes, my '75 XLCH Sportster 1000 has a drip oiler for the chain from the back of the crankcase. I have it shut off (it is somewhat adjustable) but she still profusely marks her territory in the garage. A friend said he had one years ago, and if she wasn't leaking oil he was afraid there was none in it. :-)
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