| Author | Message | ||
     Midknyte |
Ok, several threads have passed on catch cans. I have a vague understanding of what's goin on, but need clarification. I do minimal wrenching. My old bike had a clear puke tube that was plugged at the end and ran to the bottom of the bike near the kickstand so you could periodically drain it. I believe that this is analogous. From what I've read here, I take it that there is no puke tube or catch system on the XB's and it is instead routed in to the airbox(?). If this is the case, I don't understand why. What's the sense of having an air filter and being concerned about proper care and feeding (of air intake) if this gunk is going to be dumped in there? 1) So, question one - just what is this mucous? Where does it come from and why? 2) Is it indeed being feed back in or dumped in the airbox? Edumacate me please. Pictures always welcomed and helpful. Thanks. | ||
| Patrickh |
The idea behind feeding the vent into the airbox is that oil vapor enters the intake tract and is burned during the course of normal combustion. This is supposed to be environmentally friendly. The reason why is is a pain is that (at least on my tuber) if you over fill the oil tank a little bit you will get a signifigant amount of oil blowing-by into your filter making a mess. Personally my bike dosen't blow a ton of oil, but some people's rides blow by more than others. You need to vent your crankcase so the oil can "breathe" with the pulses of the crank and cons, but an unfortunate side effect of this is occasional oil blow-by. A catch can keeps it tidy. | ||
| M1combat |
As Patrickh said... On my bike... After 14K miles I have a thin layer of oily residue on my throttle plate. I have to assume that it's the same with the intake manifold, intake ports (although I'm sure by the time it sits there for a little while it turns to a carbon layer and the same for the intake valves). It's not pretty and after many miles it starts to reduce the output of the engine. It makes the intake tract a little smaller in effect. The EPA doesn't want this blow-by and occasional squirt of oil to be placed in the atmosphere (I can't really say as I blame them... Look at LA. So, you take the puke tubes (that normally puke into the filter) and re-route them to a catch can so the blow-by and "extra" oil go there. You can then drain it at your leisure and put it in with your used oil. At that point, you can take it to wherever you take your used oil for disposal. Still environmentally clean (assuming where you take it disposes of it properly) and it also keeps your engine running properly for a longer period  . A win/win situation if you ask me . | ||
| Midknyte |
So where exactly does this blow-by come from? Blow-by sounds like you are talking about oil making it past the pistons along the sidewalls, and wouldn't that be burned? | ||
| Howieshotrods |
My understanding is the blow by is coming from the oil vents in the heads, the oiling system...not the pistons. | ||
| Midknyte |
Ok, now I know less...  | ||
| M1combat |
The blow by is spent combustion chamber by-product that gets blown by the rings into the crank case. It then works itself into the cam cover and up the pushrod tubes into the heads. There is a PCV valve in each head. The reason to get it out of the engine (as I understand it ) is because the burnt/unburnt fuel mixture that is blow-by will break down the oil faster. I'm sure there are other benefits. /EDIT - It's not JUST blow-by though... If there is any water vapor in the crank case, it will get vaporized at operating temp and will be expelled by the breather system. Same thing if you put too much oil in the bike... It'll heat up and puke out the breather system. In the EPA compliant design, that oil would be blown into your intake AFTER the filter and would be run directly through the combustion chamber... UGLY!!! (Message edited by m1combat on June 27, 2005) | ||
| Firebolt1203 |
The way I understand the Vacuum tubes and the whole PCV sustem (positive crankcase ventilation) is to put the crankcase in a vacuum. Oil will fall faster in a vacuum and rings seat better when the only pressure is form the combustion chamber side. -my 2 cents | ||
| Joele |
If blow by is left un-vented it can combine with water vapor to form an acid that is bad for oil and other parts of the crank case. | ||
| Blake |
The EPA's concern with PCV is that unburned fuel get re-routed back into the engine rather than released into the atmosphere. It ain't about the oil, it's about the volatile hydrocarbons in the gasoline. So the EPA mandates that said blow-by be recirculated through the combustion process to see that it gets another chance to ignite and burn thus ideally transforming into water and CO2. That is the EPA part of the PCV equation. There is also the engine performance/integrity part of the PCV scenario in that without an outlet for blowby, the crankcase becomes pressurized and will over time in almost all cases cause seals and gaskets to commence leakage. And as already mentioned above by someone wise and knowledgeable, the existence of pressure in the crankcase hurts engine performance, both by impeding ring seal (thus exacerbating the blowby output) and by fighting against the intake and power stroke. Here's an interesting scenario to consider: Imagine someone riding their bike a few miles to work and back each day, never getting it up to operating temperature, thus much if not virtually all the water vapor that enters the crankcase after blowing-by the rings condenses inside the crankcase and is born by the engine oil. If this goes on for maybe a month until the weather warms and/or the bike hits the road for an extended journey, what will then happen on a hot day, riding hard where the engine and oil temperature quickly climb well above the boiling point of water? Can you say... "My boiler done busted a seam!"? It really is darn near like an explosion of steam bursting out of all possible orifices connected to the crankcase. That happened to my primary cover once. While pressure washing my Cyclone, I inadvertently sprayed water into a poorly fitted clutch adjuster boot effectively funneling it straight into the primary case. Apparently the tranny breather vent was overwhelmed and unable to accomodate the volume of steam produced in the primary. Maybe the circuitous route from primary case through the clutch area and into the tranny was too restrictive. Anyway the result was that all manner of nastiness was compelled to spew forth with great vigor from the front of the primary cover where gasket meets the engine case and all around the chain inspection cover and clutch cover. Upon achieving the boiling point, the primary was pressurized by steam thus pushing the covers up off their gaskets and allowing the steam to escape along with lubricant making for an alarming mess which I discovered at the next fuel stop. Freaked me out until I figured out what had happened. I cleaned up the mess and never had any further problem with it. Imagine if that same scenario were to play out not in the primary/tranny, but inside the crankcase. No matter if there is a purpose-built vent or not, when water turns to steam in the crankcase, it WILL find a way out. Thus we have positive crankcase ventilation. That the byproducts of combustion can combine with water in the crankcase and form harmful acids is not much hindered by the PCV system. The PCV does not prevent formation of water in the crankcase. The PCV only prevents the build up of pressure in the crankcase. Thus, use a good oil and change it often when operating in scenarios where the engine might not achieve operating temperatures adequate for boiling off any residual moisture. Really interesting stuff. | ||
| Blake |
So in conclusion, the engine absolutely needs PCV (positive crankcase ventilation) in order to function reliably and efficiently, but engine operational concerns do not require the reintroduction of PCV system exhaust to the combustion process via engine intake; that characteristic of the PCV system configuration is mandated by the EPA. Even lawn mowers are configured with their PCV exhausting to the intake. Bzck on topic: A catch can will help sequester any oil mist that might be born along with the blow-by/PCV exhaust. I agree, it is not a good thing to feed engine oil to your Buell intake. I recall a dyno test once that showed that removing the PCV exhaust from the intake added a not insignificant amount of power to the engine. Not sure if that would hold true of all engines or only those exhibiting significant blow-by. Ever since I had the Nicasil plated all aluminum cylinders installed in my Cyclone, I've had virtually zero blowby. And in over 10,000 miles my catch can has yet to register any accumulation. | ||
| Brucelee |
I took off my catch can about 5000 miles ago. Was that a bad thing? | ||
| Natexlh1000 |
Vent that crap to the road where it belongs. |
