Oily Airbox

Anyone else have any experience of oil in the front part of the airbox. When I pulled the plug on the drain pipe loads came out so I opened up the airbox and found it very gooey with oil. Any ideas where it's coming from or why?

I guess I can epoxy a piece of plastic over the crack, but that seems very odd to me. It's on the vertical front panel of the box nearest to the engine.

My understanding:
Its oil vapours from the cylinder heads, not legal to be vented to the enviroment, probably toxic? They are collected at the box under the main switch, whatever condenses ther due to the lower temp (than the heads), is routed back to the engine, the rest (vapour) is routed to the airbox to be drawn in the comustion chamber to be burned. Some of this vapour gets condensed in the airbox, maybe 'couse of the low pressure, so it needs to be drained out by the drain pipe. According to my owners manual, this has to be done every 5000 km.

Cracks on the lower part of the airbox, or the drain pipes (mine has 2), or a missing drain pipe plug, will allow very litle amount of air and dirt to get in, bypassing the filter... the real problem is that the incoming airs velocity will not allow the liquid oil to drain, and it will end up as more dirt on the throttle butterflies and even as more carbon on the valves/piston...

It's best to keep the oil level between the min mark and the midpoint between min and max on the stick. If you fill it to max, it's way too much and it will continue to blow out, make a mess and will crud up the throttle bodies as well.

No idea why the airbox is cracked but they are one of the things you'll find a few of readily available on the bay of fleas for not very much.

As for oil in the airbox? It's evidence usually of over filling. Never fill any big block Guzzi to the 'Full' mark on the stick, it will simply expell lots of it through the breather system. Start off with it half way between the 'Add' and 'Full' marks and don't add any unless it drops off the end of the stick. Most of the find their own level and then stop expelling it. That point is usually somewhere between the halfway mark and the low mark. There is lots of oil in the motor. It doesn't need to be kept at the 'Full' mark.

Pete

As Pete says, it's all about oil level and not oil vapourization. If you high fill the sump, the internal design & dynamics create more mist (bulk oil, irrespective grade) that gets en-trained with the blow-by gas and thrown into airbox where centrifugal forces drop it or stick it to butterflies.

Vapourization (boiling off the oil light ends) less likely to causes the air box problem because a) 10W60 doesn't have much light ends b) oil vapours aren't droplets so usually flow and burn with the blow-by rather than condense or separate in oil box/on inlet flaps and c) oil level doesn't impact vapourisation much.

The blow-by is there to handle oil vapour, resulting from both vapourization and evaporation.
I dont think that the factory, made it to route the exesive engine oil to the airbox (when the engine runs) - and marked the stick in a way that encourages overfilling...

Oil vapour will be there, always, and it will condensate on various surfaces (hopefully inner), and its expected to have *some* oil in the airbox, even withought overfilling.

Cracks, holes or any openings at the airbox drain area (sidewalls-botom-pipe) are a bad thing, as even if a single droplet of liquid oil gets in front of this oppening, will be spitted (actualy sucked) in the main airstream to the butterflies or idle valve.

Petros, there are a variety of things that will effect how much oil an engine will happily accept in its crankcase and unless they are run in very well and/or never taken above 5,000rpm there will, if you fill the sump to the 'Full' Mark on the stick, expell oil through the breather system until there is sufficient volume of gas in the crankcase to lower the amount of pressurisation to the point where the condensor box can work properly.

There is always blow-by past the rings to a degree which means that the crankcase is always pressurised. This is exacerbated by the pumping action of the Pistons and each revolution of the crank the case will change in volume by roughly 2/3rds of its swept volume which causes that much gas to try and be expelledut the faster the engine is spinning the less time there is for that to happen but the number of firing cycles and the amount of blow-by increases.

Inside the crankcase it is not just hot gas moving about. It's an absolute maelstrom with streamers of oil being thrown off the crank and gushing back down the return galleries from the heads. Windage from the crank whips the surface of the oil in the sump into a froth and the under piston sprays will produce a further fog of oil droplets. It is this particulate matter that will overwhelm the condensor system and if ring seal is poor there may even be oil forced back up the oil condensate return line due to crank case pressurisation and that will also end up getting pushed into the airbox.

By dropping the oil level in the sump not only do you reduce the effects of windage on the oil surface as it is physically further away from the crank but the added gas volume reduces crankcase pressurisation, (Gas being compressible whereas oil being a liquid is, to all intents and purposes, not.)

If you run your engine oil level at the 'Full' mark on the stick and ride the bike normally it will, with almost 100% certainty, expell oil through the breather system and into the airbox. As long as you keep topping it up it will keep expelling it! Start off with it half way between the 'Add' and 'Full' marks and it will probably expell a little bit and then stop. As long as the level is still visible on the stick you're all good. With Guzzis it has always been thus, as the swept volume of the engine has increased though so has the propensity for oil expulsion.

If one insists on keeping the oil above its chosen level the expulsion can cause all sorts of problems with gummed up TB's and stepper's leading to all sorts of high and erratic idle issues and permanently soggy Airboxes full of oil. If the level is left at the engine's 'Happy Place' all you'll end up with is a barely detectable greasiness on the walls of the airbox! Rather than having to remove and clean the TB's every 10,000 Km as suggested by the factory they can be left alone for multiples of that figure! I tend to clean mine every 30,000 or so.

Pete

I hope its not anoying that I keep up with this topic, exhanging thoughts, even debating, improoves my (at least) understanding for my bike... I realised how the blow-by system works (I think)

Pete Roper wrote:

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There is always blow-by past the rings to a degree which means that the crankcase is always pressurised.
........

Was not surre about that, crankase beeing pressurized, suspected it trying to figure flow directions, thx for explaining it...

I don't get the "piston pumping"... When the piston moves towards the crank, it pressurises the crankcase, so fluid tends to leave it, but the next moment, the piston moves away from the crank, so the previus pressurization should be negated, as should be whatever fluid flow resulted from the previous piston movement, leaving the pressure build up due to ring blow-by, being the only one affecting constantly outgoing fluid flow.

Pete Roper wrote:

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It is this particulate matter that will overwhelm the condensor system
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My perspective, being "condensor system" is suppossed to receive vapour and turn it to liquid.

So presence of oil vapour is normal, is expected, and included in the bike design. The temperatures, even at the heads, may or may not be high enough for vaporization (boiling) of the oil, but surrely, everywhere in the motor, especialy at the heads, are high enough to accelarate evaporation (absorption of it by the surrounding air). Its also normal and expected, those oil vapours to be turned to liquid, and routed to the airbox, as its normal, expected and instructed to drain oil from the airbox. I'm not commenting quantity, *some* (whatever this means) quantity of oil is expected in the airbox.

Pete Roper wrote:

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may even be oil forced back up the oil condensate return line due to crank case pressurisation and that will also end up getting pushed into the airbox.
........

I'm thinking, its not only getting pushed but also sucked by the airbox. The airbox sucks from the condenser box, with the same force that sucks air from the filter.
So, overpressure in the crankcase plus suction from the airbox, the pressure difference may be significant, as the crankcase leaving fluid flow, gas or liquid....

At least for the 1200.

The 1100s blow by system, has one difference to that of the 1200, the 1100 has a "breather pipe", that connects the condenser box to the belt frame. At 1200, there is no "breather pipe", both box and frame have the pipe connecting points but are closed off.
Looks to me that, this pipe cancels the suction of the airbox to the crankcase, and provides a hudge buffer (the atmosphere) for any crankcase pressure pulses.
Of course I don't know why this pipe was abolished for 1200, I can suppose that at the factory realised that the 1100 draws unfiltered air through this pipe, or figured out that oil may flow out of it when the engine is stopped, or, more probable, it was a mean of releasing *illegal* vapours to the atmosphere...
Anyway, the 1200 does not have it, looks to me that missing it, the fluid flow leaving the cankcase is multiplied.
These are just thoughts, have no idea how close they are to reality, as I have no idea how prone to oil expuslion from the crankcase is the 1100 compared to 1200... (yes, luring)

Hey Petros,

Evaporation is a phase equilibrium effect - Entrainment is a physical bulk liquid effect

You are 100% correct that pressure in the crankcase is due only to blow-by that comes from what is basically controlled explosions of fuel/air the other side of the pistons. The blow-by consists partially burned fuel, N2, CO, CO2, NOx etc and not much but maybe a bit of 'engine oil' as either vapour or droplets in the gas phase (obviously there's plenty of oil being scraped down and up the bore in the oil control ring to lubricate it all).

The engine oil doesn't boil or even evaporate much (the NOACK for 10W60 is 6% which is lowest of almost all oils on market; and NOACK runs at 250C for 1 hr under air flow which isn't a temperature your oil is seeing anywhere near - even around pistons it is flowing fast and high volumes so not sitting there long enough to get as hot as the metal it touches so not much evaporating). Some light ends may evaporate initially when oil is fresh but that is buttons in the scheme of things.

So relatively there isn't much engine oil vapour in the gases going to the air box (there is lots of other lighter stuff that could condense like unburnt or partial burnt gasoline); but as Pete already pointed out there is a f*cking lot of entrained oil droplets.

The PHYSICAL effects in the engine create foams, droplets, etc which get much worse at high oil levels 'cos it creates more likelihood of oil getting thrown around more. These foams and droplets are bulk oil (additives and all) which get carried along in the gas phase (stokes law) until they hit something in the way or get centrifuged out when gas changes direction (like in the airbox). Once the oil is expelled and the level drops, the effect will reduce until you top it up.

So there isn't much evaporation and condensing (vapours) going on compared to the physical process.

PS I spent 10 years developing crankcase engine oils including running blow-by condensation rigs under the bonnet of cars; and pretty much the only things that condense are water & fuel !

paulbrice wrote:

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So there isn't much evaporation and condensing (vapours) going on compared to the physical process.

I never believed that its supposed to be "much", although I do believe that there is, as I wrote, "*some* (whatever this means)". This NOACK test, confirms that there is *some* evaporation even at 100C - probably way less that 6%, still, there is *some*. The ring blow-by should have almost no oil at all, unless the ring is damaged. I also believe that *some* evaporation happens at the top of the heads, not inside the combustion champer but above it - under the rocker arm cover. The highest temperatures are there, oil is there, spread over a large surface... If there is no evaporation/condensation that means that either Guzzi (and Piaggio) spent money to install something that was not needed (unlikely), or that they had foreseen the oil foaming issue (not likely either) and spend those money to install the system that would route it to the airbox (most unlikely)

Anyway, I re-entered Gheto to write some thoughts about the other parts of the blow-by system...

There is one part, I'm not sure what its function is: the "reduction" at the point that the pipe from the condensor box connects to the sump. It reduces what? The pressure/flow from the sump to the box? The opposite would be... well, not smart.

If that is the case, and the pressure diference between sump and box through this pipe, is reduced (adequately), so will be the flow... The alternative route left, is through the galeys of the heads, of course not those that feed the heads with oil, as those are part of the oil pump closed circuit, but through some other openings like the cam chain space...

I tried to find a photo, and coinsidentaly, this posted by paulbrice at the "tappet inspection" post, is very good...
the cam chain galey, can very well provide a route for the crankcase pressure to be reliefed, unrestricted, in the rocker space, and through it to the condensor box...

Looking at this photo, I think that whatever fluid flow (gas, liquid or foam) is relieved from the crankcase, among with whated is carried by the cam chain, would be throun directly on the nosle of the pipe that conacts the rocker space to the condenser box - and has the airboxe's suction pressure.

If the sump pipe "restriction" does actualy restricts, having this pipe at that position, how possible it is, the oil in the aibox, gramars or tons, to be getting there from the heads?

paulbrice's photo, above the cam chain, the pipe having the airbox suction pressure:
[You must be registered and logged in to see this image.]

One more thought: If the "restriction" actualy restricts, and the cam chain passage is not adequate to relief the crankcase pressure to the rocker space (and throu it to the box), then the crankcase pressure will be relieved through the return oil galeys (maybe it does anyway). Vapour or foam from the crankcase, flowing against the normal liquid oil flow. Mess.

There is no such thing as 'Suck'.

The pressure within the entire engine, top end and bottom end, is effectively identical. This pressure is vented through the pipes at the back of the heads to the condensor box and separation of the particulate matter is encouraged by the Flingers on the back of the camshafts outboard of the sprockets. They push the gas flow outward so particulates of oil will be thrown into contact with surrounding parts of the head and rocker cover where surface tension will grab them and they will then drain back to the sump. This is a means of minimising the stress on the condensor system.

As Paul says there is no real evaporation of oil, it simply doesn't get that hot, not even under the piston crowns or in the galleries around the exhaust valves, simply because of the flow rates and time it spends in contact with pieces that are hot.

The reason you get the 'Panting' effect is because as the crank spins the crankcase volume changes. As the crank speed increases time becomes the governing factor as there simply isn't enough of it for the volume of gas change to be exhaled and inhaled every revolution due to the size of the pipes in the breather system and the inertia of the gas, consequently the pressure rises and falls but overall the crankcase pressure is always positive and is equal everywhere within the engine.

If there is no evaporation/condensation that means that either Guzzi (and Piaggio) spent money to install something that was not needed (unlikely), or that they had foreseen the oil foaming issue (not likely either) and spend those money to install the system that would route it to the airbox (most unlikely)

Petros

1) the system is there to recycle emissions (unburned fuel, partial burned fuel, NOx & other junk) back into the combustion chamber to avoid dumping them in the atmosphere; so the only way out the engine is through combustion then exhaust.
2) They clearly DID foresee oil droplets in the gas flow 'cos they stuck a separator box at the front (it's not a condensor) to disengage oil droplets and drop them down the pipe to the sump
3) It not a fecking restrictor. Because the liquid returning to the sump from the separator is much lower flow (in volumetric terms) than the gas flow; it doesn't need such a big pipe & it will flow very slowly down under GRAVITY because the liquid head of the oil in the sump is above it - ie there will be a 'leg' of returning fluid backed up the pipe that ultimately will balance the height of oil in sump (once dynamics settle).

Note there is water & emulsion dropping back into the sump here as well (especially when bike is cold); hence you will often find emulsion in the pipe & sump at the return point.

I think we've done this to death !

Me too. Yes, in contrast mm on parlance it is known as a condensor box but as Paul says it's a separator, designed to get the oil droplets to settle out of the gas flow. Ist effectively a box stuffed with wire wool.