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12425 - Established June, 2013 - all GRiSO, all the time...
 
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 1400 project update.

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beetle
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beetle

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PostSubject: Re: 1400 project update.   1400 project update. - Page 5 Icon_minitime1Sun Jun 07, 2020 5:02 am


The point is to maintain a closed system, so that crankcase gases get fed into the airbox sans oil. Letting air out is naughty.


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bahamazoo
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PostSubject: Re: 1400 project update.   1400 project update. - Page 5 Icon_minitime1Sun Jun 07, 2020 6:09 am

mmm not sure on the GRiSO, but the Sport sure vents out to the world...

the standard plastic MG catch can receives spoil from the rockers and the front plate, and then supposedly drains oily fluids back into the sump... and it feeds the airbox, presumably to recycle oily fumes back into the intake mix...
but airbox isn't a sealed unit and so it farts and dribbles out into the environment (which as we all know is over there, outside the 12 mile limit   scratch ).

all that ditch pumping pressure beneath the pistons has to go somewhere   Razz  Razz



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beetle
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PostSubject: Re: 1400 project update.   1400 project update. - Page 5 Icon_minitime1Sun Jun 07, 2020 4:49 pm


No, that's exactly how all the CARC bikes standard breather system works. Since the oily fumes are only created when the engine is running, they all get sucked into the throttle bodies. Unless your Sport runs differently? Sure, some will leak out into the environs, but we're not supposed to let it all out...


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Pete Roper
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PostSubject: Re: 1400 project update.   1400 project update. - Page 5 Icon_minitime1Sun Jun 07, 2020 5:43 pm

Pat, if your bike is dribbling oil into the environment it has a problem. The whole point of the 'Catch Box' is to act as a separator where the amalgam of air and oil can separate from one another. The oil then drains back to the sump but the air, with whatever residual oil in it, is fed to the airbox where it is recirculated back through the combustion chambers thus reducing hydrocarbon emissions.

Certainly by the time the engine had grown to 1200cc it had really started to push the friendship of the relationship between crankcase volume and swept volume and that is why it is important to not fill the crankcase to the full mark on the dipstick. If you do the 'Compressable volume' within the case becomes too small, the oil is in too close proximity to the spinning crank and windage picks it up and keeps it in suspension in the gas within the case.

Because there is always positive pressure within the case due to blow-by there is a constant outward flow of gas through the breather system and if the gas is heavily saturated with oil particles it will overwhelm the condensor system and the still 'Too Oily' gas will pass on to the airbox. This is the reason one needs to drain the hose from the airbox at service time as there will usually be some oil in the hose as people on the whole tend to over-fill their bikes. The airbox ends up as a 'Secondary' condensor.

This over-filling is readily understandable. I mean the factory instructs us to put in too much! This is why I tell people never to fill higher than halfway between the 'Add' and 'Full' marks on the stick. In reality though, depending on how the bike is ridden and how it was broken in when new, the oil should stabilise somewhere between the 'Add' and 'Half-way' mark on the stick but if it is closer to the bottom it's very easy to be paranoid and think "I'd better top it up." when in fact this is most likely completely unnecessary! Don't worry, that is perfectly normal psychology. Laughing I used to do it myself until I got my oil temperature dipstick which I had to calibrate myself and I 'Cured' myself of my overfilling addiction by simply riding the bike for 1,000km without checking the oil at all and then marking the new stick, with the bike on its sidestand at the level the oil was at. That is now my 'Full' mark and it never uses a drop! I also don't have any issues with oily airboxes or full drain hoses! Ever!

The problem with Mark's 1400 is a bit more complex but the majority of the issues I believe are simply down to the ratio between swept volume and available crankcase volume being too great. Why designing a breather system that prevents this has been such a problem for Guzzi I don't know? I mean BMW twins have approximately 1/3rd more discrepancy between maximum and minimum crankcase volume than the Guzzi engine and they don't, as far as I know, have oil expulsion issues. Nor do a host of other large 90* twins. It seems to be a uniquely Guzzi problem. In reality I think the only real, permanent, fix for the 1400 is a bigger crankcase and that is a bit difficult.......
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