crankcase (and other) vents

[fossilrider]

Hey folks,I need some input from anyone who has been through this.I'm currently getting two T3s going,one I am cafe-ing the other will be stock.Problem is I want to simplify the tangle of hoses that vent everything.I have two of the vent canisters off 850Ts,which are much smaller and neater than the unit for the T3.I am modifying the "Y" tube where the vents from the valve covers connect so the hoses can run straight from the outlet on the valve cover to a "T attached where the "Y" was cut off(the "Y" was pointed in the wrong direction so the hoses had to sweep way around to line up or they would kink).This is going to work fine for the stock bike and it will tidy up the area between the carbs.(Forgot to mention,I'm useing K&N pods on both bikes).For the cafe,though,I would still like to do away with more since I am useing a smaller battery and have moved the electrics up under the seat and will use no side panels.Has anyone found small individual"pod-type" breathers that would work for this? Any help greatly appreciated.Steve

 

[WCGuzzi]

Depending upon the local climate and you riding style, you might consider ditching the valve cover breather hoses altogether. Maybe in a cold climate with a lot of short hops they are justified, but it is a cluttered fix to a non-problem for many. A short bolt ans sealing washer handles the valve cover. I got thread protectors from the local Ace hdwre to cap off the engine/tranny phase separator.

 

[Rafael]

hey fossil

I used the 850-T crank breather as well on my T-3 and SP. On the T-3 I used a internally reinforce fuel lines. On the SP the same till I bought an Agostini breather box. It cleaned up the hose layout nicely. Haven't seen an Agostini BB for sale in a while though. I've seen K&N breather filters on tontis, did't get the model #, but they do make one with a hose fitting, it just may need an adapter.

 

[john zibell]

If you block off the valve covers as suggested above, you can use an Eldorado breather that doesn't have the connections for the valve cover lines. http://www.mgcycle.com/product_info.php?products_id=246 I believe Pete Roper is pretty up on crankcase venting and if he doesn't post here in a day or two ping him with a PM for a definitive answer.

 

[Chris R]

The 'breather box' is really an oil-air separator. A bigger box helps as the air has more time for the oil to drop out - which is all the 'Agostini' racing box is. Putting baffles in the box so the air has to change direction also helps. Putting stainless steel wool in the box really helps increase its efficiency as a separator. So if you want to use the smaller box do that.

The valve cover vents are essential on the square blocks as they are used as returns but not on the round heads where they are just additional venting.

If you want you can get rid of the sump return and use the valve cover vents as returns - which reduces the possibility of oil leaking on the clutch and increases oil flow to the cam (but may also aerate the oil more). Of course this is probably not as tidy!

Where Guzzi got it completely wrong is where they stuck the PCV valve (actually two: one in the tube that connects the crankcase to the breather box and one in the box itself) which is there to stop mayonnaise. Being a 90 degree V twin, the pressure in the crankcase is a synusoidal wave with part of the curve being vacuum - which means the cold and damp outside air will get temporarily sucked into the crankcase. The mayonnaise happens when hot oily crankcase blowby meets cold moist air. If you are in the desert you won't notice but if you live in the UK you will. In the guzzi setup the oil air separates where the cold atmosphere air can get at it.

The valve should be AFTER the breather box and to atmosphere. Remove all PCV valves and stick one where it should be. I use a generic nice stainless steel valve as used as a check valve for feed air to catalytic converters. They should be available at any parts store. Something like this: http://www.summitracing.com/parts/SMP-AV7/ (the one I use has swaged tubes on either end and cost like $8). It is nice and big and has metal petal valves which have more than enough flow capacity.

Ta,

 

[fossilrider]

Thanks for the info,Guys.I am assuming the smaller tube that the breather box sits on would be for the "engine/tranny phase separator"? So,if I understand this correctly,the only thing I really need to be concerned with is venting the crankcase to atmosphere with a check valve in the line? I just didn't want to close off anything that might cause crankcase pressure to build and push past seals,cause leaks,etc.. Back in my hot rodding days,I saw guys do that by blocking off vents arbitrarily.I live in SE Tn.and,though the humidity is high,it gets plenty hot during most of our riding season and I usually ride long enough that I think it would burn off accumulated moisture/condensation.If that is all there is to it,this should be an easier fix than I thought.Thanks again,Foss

 

[john zibell]

Thanks for the info,Guys.I am assuming the smaller tube that the breather box sits on would be for the "engine/tranny phase separator"?

Nope, it is for oil return to the crankcase. Take a look at a parts manual and you can see where it goes. If you aren't going to use a "breather box" you could just seal it off at the top.

 

[georgemii]

Chris R - I think I understand what you're saying; just want to double-check. Am I correct that you're
suggesting (for my Tonti/big block with pods) to move the check valve from it's original location
to the atmosphere/outlet of the separator? Am I also correct that the check valve would be
oriented to open from separator to air, and close from air into separator? This would prevent
cold/humid air entering separator (hold the mayo, please) and as the crankcase pressure goes
below ambient, will also reduce pressure in the box, perhaps helping to scavenge oil/vapors?
Might I use the original check valve; just relocated? I'm NOT trying to pick a fight. I like your
idea; just trying to understand what it'll look like before I start into remodeling the plumbing.
Thank you.

 

[Chris R]

Chris R - I think I understand what you're saying; just want to double-check. Am I correct that you're
suggesting (for my Tonti/big block with pods) to move the check valve from it's original location
to the atmosphere/outlet of the separator? Am I also correct that the check valve would be
oriented to open from separator to air, and close from air into separator? This would prevent
cold/humid air entering separator (hold the mayo, please) and as the crankcase pressure goes
below ambient, will also reduce pressure in the box, perhaps helping to scavenge oil/vapors?
Might I use the original check valve; just relocated? I'm NOT trying to pick a fight. I like your
idea; just trying to understand what it'll look like before I start into remodeling the plumbing.
Thank you.

Yes to all. The check valve should be oriented to let air out of the crankcase and not in. There is a small performance benefit in it as the greater the vacuum in the crankcase the better the rings work and there is less losses due to windage. In real race engines the scavenge pumps of the oiling system do this - the crankcase is under pretty considerable vacuum. Cosworth have some very nice pumps that de-areate the oil.

You can re-use the check valve - it is basically a ball bearing that rest against a seat so it has to be oriented so that gravity can do its thing. It is not the best design - it is prone to sicking/can't handle the flow when the rings go bad. Guzzi has redesigned it a couple of times. That's why I ditch it for a reed type valve.

As plumbed on the round heads if it sticks shut or is overwhelmed, the crankcase will pressurize and push oil out of the return line until the oil falls below the level of the return line which is conveniently located below the oil level in the sump. I have had arguments with a few people who refuse to believe this happens - you can check it very simply by plugging the large crankcase vent with your thumb and watch what happens. This is the only engine I have ever seen with this arrangement.

In the lemans they have a nice bracket for the breather box line that directs it right at your rear tire - a nice feature as it tells you definitively and immediately that your rings have gone south/the valve has stuck shut!

 

[Rafael]

thanks Chris R, for the tip on the check valve. I'm going to try it on my SP. I don't like the OE check valve much, a ball bearing banging against a circlip does't make much sense.

I think resusing the OE check valve at the discharge hose is too problematic, you'd have to lift it up so that the valve is oriented correctly and you'll end up with a P trap in the hose or the hose discharging up high somewhere.

 

[georgemii]

Chris R,
I like your idea, have modified my Tonti breather box and collected an example
of the valve you suggest. As I put this together, one question comes to mind: upon
shutdown, as the engine cools, the case is looking to "inhale" (for lack of a better word).
As the check valve should be now closed, how - or where - is air admitted into the case?
I do intend to use this setup, but inquiring minds.......
T.I.A.
George

 

[Chris R]

As the check valve should be now closed, how - or where - is air admitted into the case?

If you could keep the crankcase at a negative pressure that would be a good thing - as F1 engines do by having a big scavenge pump. Less friction, better ring sealing, better de-atomization of the oil etc.

In the case of the guzzi, it is likely to be slightly above atmospheric as blowby will pressurize the crankcase. The pressure will change in a sinusoidal pattern as the pistons go up and down and the engine fires.

The effect of the engine cooling is only likely to bring it to atmospheric. Even if you do crate a vacuum it will be short lived - nature abhors a vacuum - the valve or crankcase will invariably leak. Either way it doesn't affect the engine function.

 

[kinkajou]

Hey Guys,

Im planning to do the same thing on my eldo as the breather box was smoking like an exaust before I rebuilded the engine....

But I cant quite get the explanations....Anybody have pictures?

I think I should plug the return line
use the valve vent as a return line and install a pcp on the other pipe....

Correct?

Thanks

 

[bumati]

Twin motorcycle crank case breather kit.