Crankcase pumping losses

[Steptoe]

Questioning - is the act of asking questions, is it not?

I

Also questioning others opinions, thoughts = i.e. why they did it in a certain way.

As opposed to your question ( not questioning). HOW does it work.

?

Now that is clear, does anybody have any answers?

Remind me, what was the question, i've forgotten .

 

[cral]

i guess i was wrong then

 

[Engineer]

Also questioning others opinions, thoughts = i.e. why they did it in a certain way.

As opposed to your question ( not questioning). HOW does it work.







Remind me, what was the question, i've forgotten .

It should have been plain from the context of my original post that my 'questions' were of the simple 'inquiry' type. I will repeat them here for the benefit of those unskilled in the art of reverse scrolling


Crankcase pumping losses
Excuse my ignorance but....

Does the boxer engine suffer from a relatively high level of crankcase pumping losses (due to both pistons moving up and down together) compared to a 4-cylinder engine or a twin with the pistons moving out of phase?

How much is the torque reduced by these losses?

Is anything done to reduce or control these losses?

Does my 1200GS have crankcase breather and filter, or is the crankcase sealed?

I'm just curious about how these things work.

 

[Engineer]

i guess i was wrong then

Both pistons are at TDC and BDC together. So they are always moving in opposite directions, hence the forces are equal and opposite and cancel, gving primary balance.

 

[alimey4u2]

Not an expert on this engine at all Engineer but this may answer one of your questions......

 

[Rob Farmer]

Any positive crankcase pressure is vented into the airbox using a simple read valve. It's anybodies guess what pressure this actually vents at, I don't suppose it really matters as long as the cases can vent.

 

[alimey4u2]

Found this too........

Well-conceived and effective solutions are also to be found in – seemingly insignificant – details such as the crank cavity air purge: To minimise undesirable pressure pulses within the cavity, with air pressure going up and down as a result of piston motion, a valve complete with membrane openings fitted here opens and closes the air purge outlet automatically as a function of pressure conditions in the crank cavity and at the same time provides a large air purge cross-section whenever required. This serves to reduce pressure fluctuations and air flow in the crankcase to a minimum, with an advantageous effect on engine output, internal efficiency (reduction of ventilation loss), oil foaming, and oil consumption particularly at high speeds.

 

[Engineer]

Found this too........

Thanks - where did you find that?

Sounds like they are trying to maintain a near constant pressure in the crankcase - guess that sort of makes sense, it won't matter if the air presssure is reduced when the pistons go 'up' as you will get most of the energy back when they go down again - probably better than letting lots of air rush in and out all of the time.

 

[Blackal]

Christ, but some of you guys can really kick the arse out of a thread

Why not make a resolution to try to answer someone's genuine query without taking the pi55 - It'll make you a nicer person

Back to the subject..........................

There are obviously losses due to the constant movement of air between the crankcase and airbox, in much the same way as pumping losses on multi-cylinder engines within the crankcase (i.s. from the underside of cyl 1 to the underside of cyl 4). I suspect the losses on the boxer engine will be greater, but that is just gut feeling on my part.

The pumping losses should not affect torque, only power output.

Al

 

[(RIP) Kaister]

from the underside of cyl 1 to the underside of cyl 4

...errr. nope - cyl 1 and 4 go up and down together - and they move the air displaced into the gap caused by 2 and 3 moving

 

[Blackal]

from the underside of cyl 1 to the underside of cyl 4

...errr. nope - cyl 1 and 4 go up and down together - and they move the air displaced into the gap caused by 2 and 3 moving

Oops - true, for a 4 cylinder engine - you are correct - I was more intent on illustrating the movement of air within the crankcase and the power required to do that.

"Multi-cylinder engines" gives me a bit of a get-out, however. - I've worked extensively with 12 and 18 cylinder engines


Al

 

[MikeP]

Right as a result of this thread I've been in to my local police station to report the loss.

If anyone finds any of my lost crankcase pressure please contact Ivybridge police station on 01752 692628 and quote Register 'A' Ref: 26553478, they will contact me and I'll pop around to collect it.

 

[alimey4u2]

Thanks - where did you find that?

Here but ensure your popup blocker is on......

http://www.totalmotorcycle.com/photos/2004models/2004models-BMWR1200GS.htm

 

[alimey4u2]

Christ, but some of you guys can really kick the arse out of a thread

Why not make a resolution to try to answer someone's genuine query without taking the pi55 - It'll make you a nicer person

I also really don't understand this..... There are people here much more knowlegeable on the subject/s that spend more time "trying" to be funny. The thread was in the technical section & not the bollox, joke, pub humour etc. section & should have been treated as such.

In my book, the only stupid question is one that is not asked, it "seems" that others more qualified disagree......

In saying that, I'm not one to shun a good laugh but lets get the business of sharing knowledge over with first......

 

[Steptoe]

I also really don't understand this..... There are people here much more knowlegeable on the subject/s that spend more time "trying" to be funny. The thread was in the technical section & not the bollox, joke, pub humour etc. section & should have been treated as such.

In my book, the only stupid question is one that is not asked, it "seems" that others more qualified disagree......

In saying that, I'm not one to shun a good laugh but lets get the business of sharing knowledge over with first......

 

[Engineer]

Christ, but some of you guys can really kick the arse out of a thread

Why not make a resolution to try to answer someone's genuine query without taking the pi55 - It'll make you a nicer person

Back to the subject..........................

Al

One would think it would be easy - However communication in Internet Forums is limited to the written word and so is far more susceptible to misunderstandings than face to face conversations.

On the otherhand maybe GS owners are more likely to be 'Grumpy Old Men' than owners of types of motorcycles. (A little humour nearly always helps)

Bright idea! - How about a 'Fossil' forum where the 'Grumpys' can whinge away to each other about anything or everything - I might even join in occasionally.

P.S. Thanks for all the intelligent replies, along with a bit of research of my own I now have better understanding of what goes on inside the Boxer engine.

 

[Engineer]

Here but ensure your popup blocker is on......

http://www.totalmotorcycle.com/photos/2004models/2004models-BMWR1200GS.htm

Thanks for that - see what you mean about the pop-ups!

 

[rokraider]

This is an interesting thread. It is a pity that it has been sidetracked by a few people spouting bollox about questioning and asking questions.

I thought that the general principle on most 4 strokes was to try and run a negative air pressure in the crankcase (not a full on vacuum) on the basis that minimal air pressure is easier for the pistons to push through than simply breathing it in and out into the airbox. It also enables the engine to consume its own crankcase fumes by sucking them into either the airbox or the inlet manifold.

 

[Blackal]

This is an interesting thread. It is a pity that it has been sidetracked by a few people spouting bollox about questioning and asking questions.

I thought that the general principle on most 4 strokes was to try and run a negative air pressure in the crankcase (not a full on vacuum) on the basis that minimal air pressure is easier for the pistons to push through than simply breathing it in and out into the airbox. It also enables the engine to consume its own crankcase fumes by sucking them into either the airbox or the inlet manifold.

Humble apologies if I have reduced your reading pleasure in some way

I don't see how a consistant negative pressure can be achieved in a crankcase without some sort of scavenge pump. Additionaly - the vacuum required to make a difference to piston movement is way in excess of any vacuum achievable.

Al

 

[(RIP) Kaister]

I don't see how a consistant negative pressure can be achieved in a crankcase without some sort of scavenge pump.

theres a set of pistons going up and down pulling a constant vacuum through the air box - its basically an air pump scavenging out of the air box.

the crankcase is one way vented to there - so all positive pressure is dissipated into the engine.

thinking about it - its probably what causes low speed surging.. ?