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PCV valve location and routing for VN heads


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#1 Cook

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Posted 10 May 2019 - 01:06 PM

Hi all,

 

I've read a number of posts from a few forums and starting to get a bit confused (not difficult) as to what is the correct routing of pcv lines on a VN headed 308.  I believe one side runs from the underside of the air cleaner to the rocker cover, and this would be to allow drawing of clean air into the crank case.

 

The line from the other rocker is where I am getting mixed info.  Some people run this to a vacuum port on the carby and others to vacuum on the intake manifold.  Which is correct or is either acceptable?

 

Lastly, which line should the PCV valve sit in, drawing or venting?

 

Thanks in advance as always.  Cheers Ron


Edited by Cook, 10 May 2019 - 01:09 PM.


#2 Dr Terry

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Posted 10 May 2019 - 02:31 PM

Yes, the vent hose connects to the air cleaner base. The 2nd hose which draws vapour from the other rocker cover must connect to full manifold vacuum. 

 

But you can't just connect it to any fitting, it must get its vacuum from all cylinders equally, not just a few of them, which is why they use a common vacuum fitting at the carby base. The PCV valve itself fits into this line.

 

Dr Terry



#3 Cook

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Posted 10 May 2019 - 02:42 PM

Thanks for that Dr Terry.  So this is why some people are running it to the carby to take the guess work out of ensuring all cylinders are getting equal vacuum.  Maybe a question for another day but if you tapped the manifold, how would you know where to do so to achieve the right result? Cheers Ron 



#4 Dr Terry

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Posted 10 May 2019 - 03:17 PM

If you your carby doesn't have a PCV fitting, you will need to drill & tap the manifold just beneath the carby so you get the vacuum from the correct area.

 

Dr Terry



#5 Cook

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Posted 10 May 2019 - 04:03 PM

Thanks.  In my case I have a threaded PCV and I am getting one of the rocker covers tapped where the elbow normally fits and run it from there.  I did contemplate tapping the manifold but that was just for looks.  Not going to bother now.  Cheers Ron



#6 Dr Terry

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Posted 10 May 2019 - 05:06 PM

Be careful of the orientation of the PCV valve, it only flows one way.

 

Dr Terry



#7 Cook

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Posted 14 May 2019 - 06:28 PM

Thanks again Dr Terry for the heads up.  I suspect the PCV valve I have bought with a threaded end is only good if it is fitted to the inlet manifold, as opposed to the rocker cover. Take 2.  Is there a straight line, threaded PCV valve that is fitted to the rocker cover? Cheers Ron.  






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