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enigmas
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340 Posts
Discussion Starter #1
I've been repairing some small irritating oil leaks on the rear rocker cover of my 2004 Vrsca. I decided to take a look at the method the engine breathers hook up to the airbox. There's a funny little tower in the middle of the airbox. There's one outlet at the top and it's about a 1/4" hole perhaps smaller. Considering that both breather feeds from the front and rear of the engine are considerably larger 1/2" to 3/8" this is one hell of a constriction. Remove the top from the tower and there are 2 pieces of foam wedged in the top most portion creating a further restriction. This seems like a great way to pressurize the inside of the engine and perhaps load up some of the gaskets (eg. rocker cover gasket).

Here are some pix.










(I've removed the top from the tower and will leave it off for the time being. If you run the engine with the air filter box off there's quite a bit of internal pumping of air occuring...and this is only at idle.)
 

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durata membro
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17,603 Posts
that is supposed to be the positive crankcase case vent.I never understood this at all because negative pressure in the crankcase helps performance.
Anyway,there are other filters around and I think they work like an automobile engines vent system that trys to keep the pressure equal,and maybe creates a few inches of vacuum by using manifold vaccum,which again,only works when the engine torque is low.
A thermactor pump from a Jap car works great and has shown a 15 rwhp gain on the small V-8's I've worked with.15 hp could be make the difference of the race at the end of the day!

I use a drain back catch system on my mini bikes because at over 14,000 rpm's,it's hard to contain oil in the crankcase.I make them from Toyota dehydrator tanks from the A/C system.Sorry for the nastiness,but I've lost interest in this particular bike and it's been sitting for a few years.it still runs good.
The Revo should have a checked drain back system,instead of letting the oil flood the filter area like it does when used at 7 grand and higher for miles at a run.
 

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enigmas
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340 Posts
Discussion Starter #5
The Doherty's thing looks nice but it's quite easy to also cobble up something using an automotive PCV valve for $10.

ElrodontheV-Rod,
I've never had any pooling of oil in the filter box as yet, although I've read quite a few posts on this forum with Vrods experiencing this problem...perhaps the big inch motors cause more internal pumping.
(As an aside, if you've ever had an early SVHD motor apart there's a gear driven timed port , when timed incorrectly will cause all the gasket areas to weep due to internal pressure.)
 

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durata membro
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17,603 Posts
The Doherty's thing looks nice but it's quite easy to also cobble up something using an automotive PCV valve for $10.

ElrodontheV-Rod,
I've never had any pooling of oil in the filter box as yet, although I've read quite a few posts on this forum with Vrods experiencing this problem...perhaps the big inch motors cause more internal pumping.
(As an aside, if you've ever had an early SVHD motor apart there's a gear driven timed port , when timed incorrectly will cause all the gasket areas to weep due to internal pressure.)
I've heard of the leak you're talking about.There isn't anything in the Revo like this,that will cause this,that I know of.
My 1250 does it when I get into high altitude.The 1130 has completely stopped.That was many thousands of miles ago.
 

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Registered
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2,103 Posts
I've been repairing some small irritating oil leaks on the rear rocker cover of my 2004 Vrsca. I decided to take a look at the method the engine breathers hook up to the airbox. There's a funny little tower in the middle of the airbox. There's one outlet at the top and it's about a 1/4" hole perhaps smaller. Considering that both breather feeds from the front and rear of the engine are considerably larger 1/2" to 3/8" this is one hell of a constriction. Remove the top from the tower and there are 2 pieces of foam wedged in the top most portion creating a further restriction. This seems like a great way to pressurize the inside of the engine and perhaps load up some of the gaskets (eg. rocker cover gasket).

Here are some pix.










(I've removed the top from the tower and will leave it off for the time being. If you run the engine with the air filter box off there's quite a bit of internal pumping of air occuring...and this is only at idle.)
i agree with you about the stock setup ..i put doherty power vents,basically a well made one way check valve on our breather lines on our 1450 v-rod.. i was suprised to pick up 3hp but i would think that if they lowered the crankcase pressure even slightly the ring seal would improve so maybe 3hp wasn`t suprising..our motor is due a rering and has more blowby than it should .. i am not sure if they would make as much difference on a motor with good ring seal ,, i wll test them back to back after we rering it but that will be this spring sometime..
 
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