Crankcase Venting 101

Re: crankcase venting,duh

skully said:

sounds like i just dont know anything about bikes,ill be darn must have spent the last 40 years as a certified cycle tech and factory suzuki and yamaha race mechanic for nothing.but i guess they do it different down under,good luck my friend maybe you should get a job for husaberg and help them out,and please post more smart ass remarks bushwacker

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Sometimes when your a n00b it is better to sit back and learn the players before jumping in with both feet.
Its so easy to sit in your living room and be an on line persona.
Now where is the Taffmiester when we need him?

RE: Re: crankcase venting,duh

well he does have a point about the simplicity of an open breather really so I can't be too grumpy with him, its his comments about factory engineers "knowing more than him" (and us) and everything being ok because his bike is "just fine" that i have an issue with.

I can also understand his viewpoint and being a certified factory race mechanic is usually impressive but cmon usually the factory don't certify anyone to think the factory is wrong.

But that is not to say a certifed guy doesn't know anything and Im sorry to have offended you Skully, i'm looking forward to anything useful you may be able to contribute. I just hope you can back it up with some sound reasoning rather than "i'll be darned" and certificationals.

Bushmechanic has plenty of certificationals and has no issue with being called a bushwacker, over here all that means is he gets to whack a lot of bush... sometimes its called horizontal dancing.

for whatever it may be worth I believe that "reinventing the wheel" with regard to husaberg crankcase/gearbox pressure differential is more along the lines of adding a scavenge pump to the crankcase which interestingly is commonplace in the yamaha and suziki bikes mentioned above and (also just FWIW) ads a new dimesion of potential problems.

http://ktmtalk.com/index.php?showtopic=357789

Argh! there is another 'ole to the crank case that doesn't have a reed on it?=! :shock:
Didn't get it until now... Totally uncertificated I am...

But then what happens to the vacuum?, you probably don't have any much of that! Instead you have an open 'ole that sucks in air and very likely sucks in splashes of oil as well when the piston is going aloft.

But hey, maybe this is what is needed to get pressure pulsations to the rocker box so that there is something to shake around the oil mist?

It also explains, maybe, why people would ever consider a high speed check valve for their breather hoses. The old stuff, at least up to the 2000 model, that didn't have the open crankcase holes, don't produce much pulsation at all and it is just as good to just use a hose, run it over the frame and down, done. With the open hole to the crank case it makes sense to use a check valve on the breather hose, it minimizes pulsations through the breather and thus the oil coughing out of it.

Rocket engineering is simple in comparison, flame shoots out of rocket one way, rocket goes the other.

But hey, maybe this is what is needed to get pressure pulsations to the rocker box so that there is something to shake around the oil mist?

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tis also the reason the high speed air valve perks up the 628 engine quite nicely, something I don't want to give up, hence the idea of adding a reed valve to the extra ole. the power output tests Lineaweaver did were perhaps on bikes without the second ole in the case

on the oil mist and pulsations, besides simply not having a check valve on the breather pipe I believe there would also be a lot to gain from having the 2 breather pipes in the rocker cover positioned more effectively or a drip line feed to the cam or at least to the exhaust rockers.

its like they added the second breather on later models to make use of the huge amount of oil being thrown up off the chain, catch some of it in the foam and have it come down the other original breather. it is a pity that they did not move the original breather to the centre of the rocker cover directly over the cam so it could spray the oil around. there are also some cutouts in sprocket region of the rocker cover on the later models to direct oil to the cam.

there have been pics on here of an oil line running an overhead drip to the cam (lineaweaver) and others specifically to feed the rocker arms. lots of ideas, seems even the factory took a while to decide whats best not surprisingly almost every change they've made is to increase the amount of oil available to the top end and also to increase the pulsations through the breather.

the exception being adding, then removing the oil pressure feed to the head, it seems the bottom end needed more oil, bottom line is the oil pump is struggling to do enough for both, increasing the pressure differential across the oil pump can't be bad. I could also weld the counterbalancer jet hole closed.

heres another Ktalk thread that popped up recently

http://ktmtalk.com/index.php?s=b3f797b9 ... pic=360023

2 reed valves, works good.

yes but which would you push out the way if you were the crankcase compression? you'd push the one with no oil behind it wouldn't you?

regards

Taffy

the one I added is only over an existing open hole so i don't think anythings changed exept the rockers aren't under a vacuum

or did you mean summink else Taffy?

second reed valve 02 650





free HP no blowby and still allows oil mist lube where it is needed

FWIW

there is a relatively new KTM 990 part that can be used as a check valve

KTMTalk RFS thread Link



thread is a bit confusing but it seems like the correct number is 60030090344

Hi

What's the int diameter of the pipe that goes it to this check valve ?

Thanks

ZAGA

dunno Zaga

you'll have to buy one and let us know

ZAAGA

Way too small, only some 8mm...

Hmm, but after a few revolutions enough air has escaped to make the CC in a vacuum, would it not matter at that point that it's only 8mm id?

Certainly enough for the blow-by flow, but the pulse from the down moving piston needs to be vented too.

Yep. I installed a too small valve and blew the gasket in the top cover.

it does look too small .. thanks Dr_C

the thread says they were using it up to 540cc

FWIW this is my breather filter on my 700, car fuel filter, quite restrictive and the ID of the fittings is 8mm



I don't have any problems with excess pressures but i have 2 reed valves between the main crank cavity and the gearbox. where there are 2x 8mm holes in total.

on my "new" engined 628 there is so little blowby it is hard to discern any outward flow at all even at 7 - 8000 rpm, it also has the 2 reed valves.

Dr_C said:

Way too small, only some 8mm...

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Yep, I ordered one too . . . and immediately thought "there's no way this is gonna work". Ok, lesson learned, gonna find one Lineaweaver specified.

you might be surprised Goose

internally there are only 2 small holes between the engine crank case proper and the gearbox, on the older bikes there is only 1 hole .. its smaller than the ID of that valve

the ktm dudes reckon it works

once a vacuum is created there isn't any air with which to transmit any pressure waves. on both my bikes (running the crankcase proper under a vacuum rather than the whole engine) I find the crankshaft seals actually get sucked inward with such great force that I have to make special retaining lips to stop them being chewed up by the bearings.

With my automotive check valve, on start-up I get a couple chuffs of air, then nothing. Even at high revs there is no air escaping asfaras I can tell.

There is no oil residue anywhere. Fwiw, I'm running 1100 ml of oil, (halfway up the sight glass cold)

A good way to test what's going on would be to put a ballon over the outlet, affix it with some tape then start it up.

If it's already warmed up, crack the oil filler to zero out the pressure first.