Crank case breather

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What would be the best crank case breather set-up (with part#s please) to achieve a vacuum in the crank case?
 

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Hi,

I've read a fair few postings on using a breather valve but I'm not fully understanding the reason why?

I have a 75 MK3 ES which has a breather pipe etc. Does this not just let the 'pressure' out? Why do you need a valve?

Sorry if this seems very basic but sometimes I can be a bit slow :D


Kevin
 
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If you have a checkvalve that lets the pressure out but not back in then after the downstroke when the pressure is released, the upstroke will then reduce the internal pressure as the air cannot return back down the breather. The lower internal pressure will tend to suck oil back in instead of excess pressure forcing it out. The check valve has to cope with up to 7000 rpm changes in internal volume so a reed valve copes better than a spring loaded seat.
 
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PJL said:
Or, alternatively, a Ducati Paso breather valve, which contains a pair of reeds...

http://i476.photobucket.com/albums/rr12 ... 1239550036

http://i476.photobucket.com/albums/rr12 ... 1239550247

Is this breather valve very expensive?

I have looked at how CNW does it, they use a "common" reed valve block from the engine of a pocket bike along with a custom made housing, custom machined crankcase as well as plugging a number of holes from the timing chest. Their kit is not cheap though.

Jean


Crank case breather

Crank case breather

Crank case breather

Crank case breather
 

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kommando said:
If you have a checkvalve that lets the pressure out but not back in then after the downstroke when the pressure is released, the upstroke will then reduce the internal pressure as the air cannot return back down the breather. The lower internal pressure will tend to suck oil back in instead of excess pressure forcing it out. The check valve has to cope with up to 7000 rpm changes in internal volume so a reed valve copes better than a spring loaded seat.

Doh!!, should have sussed that one myself :roll:

Many thanks for the explaination.

Looks like a read valve is on the shopping list, any good suppliers out there?

Kevin
 

PJL

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I got the valve for a few pounds off eBay, second hand. Then found some used hoses at a Ducati dealer nearby. The reeds inside are just like those you show.

There are some very nice machined from billet reed housings for later Ducatis, but they are expensive. They are also screwed into the crankcases so are not too suitable for the Norton (though they would be neat). The one I have is off a 906 Paso.

When I visited Pete Lovell in Smethwick (B'ham UK) last summer he showed me a very nice inline reed unit he was manufacturing for British twins, including the Commando. Perhaps give him a call?

http://petelovelldevelopments.com/home.cfm

Phil.
 

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PJL said:
I got the valve for a few pounds off eBay, second hand. Then found some used hoses at a Ducati dealer nearby. The reeds inside are just like those you show.

There are some very nice machined from billet reed housings for later Ducatis, but they are expensive. They are also screwed into the crankcases so are not too suitable for the Norton (though they would be neat). The one I have is off a 906 Paso.

When I visited Pete Lovell in Smethwick (B'ham UK) last summer he showed me a very nice inline reed unit he was manufacturing for British twins, including the Commando. Perhaps give him a call?

http://petelovelldevelopments.com/home.cfm

Phil.

Hi Phil,

Thanks for the info.

Kevin
 
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Thanks Phil,

I will look into it, either th Ducati side or making my own. I stopped by a scooter shop ( http://www.scootart.com/ ) yesterday and the owner gave me a kevlar reed, making my own housing should not impossible and I may just put it on the back of the timing chest instead of modifying the crankcase like CNW does.

Jean
 

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Jeandr said:
Thanks Phil,

I will look into it, either th Ducati side or making my own. I stopped by a scooter shop ( http://www.scootart.com/ ) yesterday and the owner gave me a kevlar reed, making my own housing should not impossible and I may just put it on the back of the timing chest instead of modifying the crankcase like CNW does.

Jean

Hi Jean,

I just realised I hi-jacked your thread :oops:

Sorry about that :D

Kevin
 
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hi jean, keep us informed, the back of the timing chest seems a better idea than the back of the crankcase,(utiliseing the timing chest volume)
 

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+1 for the CNW reed breather.

For $265 they will clean and machine your case, they also block off all the obvious holes that communicate between the crankcase and the timing chest, short of the main bearing. The beauty of this implementation is that it is fitted at the very bottom of the sump, directly where the force of the down stroke pressure is felt; CNW claims a small (4-5) RWHP gain and, if assembled correctly, an enngine with no leaks.

I'd call that pretty elegant, and all I had to do was drop the cases at UPS; I wish I could solve all my problems for $265... :D

RS
 
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I tried to install one of the xs650 units but for some reason - it's been too long - I couldn't get it to fit/work. So I use a Harley "KrankVent" - it works fine. Pricey, although not in CNW modification territory (and probably doesn't work as well) - I think it was $90 or so.
 
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I installed the Motormite one. I believe it was about $6 at the auto parts store. I installed it at the transition from the large hose to the small one, and it hides at the top front of the oil tank, under the seat.
 
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Dang, Bill. Lemme assure you that was less than the frickin' KrankVent. That's what you get for buying parts sourced for Harleys!
 
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Here's a pic of the $16 Yamaha reed valve mounted on my 72 Combat. It won't pull fourth gear wheelies, but it mysteriously cured the crankshaft main seal leak.

Crank case breather
 
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chris plant said:
hi jean, keep us informed, the back of the timing chest seems a better idea than the back of the crankcase,(utiliseing the timing chest volume)

Will do. Old Brits use a $6 plastic valve inserted in a cool looking machined housing ($$) and bolt that to the back of the timing chest, so there is more than one way to skin a cat. The way CNW does it is worth it to some, I find it pricy since I am not really looking for the most powerfull engine, only an oil tight one. BTW, $265 is only for the crankcase machining, there is an extra $200+ for the $10 reed valve and the machined housing, but CNW has a right to make a living and recoup his development costs.

Jean
 
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'CNW claim a modest 4-5 RWHP gain'! That's more than you'd get from a hot cam and a gas flow, I think I'll but two and go racing!
 
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