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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: pdg on February 14, 2013, 07:52:51 PM
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Just something that's popped into my head.
The crankcase breather hose ('z' hose, 's' hose, whatever) on my 75S is quite perished/cracked and probably leaky... I can't get a new one in a hurry so am thinking of an 'alternative' as it must be letting air in (unmetered) which can't be helping the mixture.
I can probably find a bit of straight hose that'll fit the stubs, but I'm not sure if it'll clear the bottom of the airbox - so my multipart question is:
Can this be removed and the inlet stub blanked? Is the crankcase designed to be pressurised or could I fit a small filter to the stub to stop random crap getting in the casings? Either temporarily or as a permanent thing.
Cheers.
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Just tape up the hose you have with cloth surgical tape or duct tape. A new "Z" hose should cost you about 15 bucks.
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Just tape up the hose you have with cloth surgical tape or duct tape.
To do that well enough so that I'm satisfied will require removal, and I don't think it'll survive that! It's split all the way round where it goes on the stubs, with cracking on the corners... I'll have a better look when it's not dark and raining.
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It sould be possible to re-route the crankcase breather to the outside venting it through a K&N style filter, and block the inlet on the air chamber. It has been done in the past. I'm sure there are write ups on this forum or others but you can get an idea of what needs to be done from this series of Youtube videos: BMW K75 Air Filter Timing cover 1of4 (http://www.youtube.com/watch?v=EnNEsM3nGyw#)
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Have my 85RS apart and also have seen the sticky residue in the air box, even on the inside of the ram tubes. And guess it's the cause of residue build up on outside of a couple TB. So, as previous posters have wondered, why is this oily crankcase air going into the air box anywho? Obvious answer, laws.
However, why not run it through a trap of some kind first? Angled so as to drip back onto the crankcase? As my old volvo? Or, is there a trap in the crankcase already that can't be seen, and maybe overfilling the sump causes the mess? Guess I'll have to experiment after I get this beast screwed back together. Anyone take a K motor down to see if there is an internal baffle or trap of some kind in the crankcase?
Just want to stop the residue from coming back after it's all cleaned up. Cheers
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This never crossed my mind before, but what's the worse that can happen if the crankcase breather hose is permanently removed and the two ports are blocked?
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Google "oil catch can"
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Thanks!
http://oilcatchcan.com/
Seems necessary.
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The K motor has an almost remote oil reservoir in that it resides well below the crank, nevertheless the spinning crank will mist some oil into the crankcase atmosphere. And this should be strained before it get sucked into the air box. Space being the main problem.
Ring blowby is another consideration for crankcase breathing as the engine ages. So, another thing to tinker with in the spring. Guess the German tinkerers tinkered plenty before making that Z hose routed into the air box. It was simple, direct, took little space, stopped global warming and laid the framework for the cracked crankcase hose syndrome. Whoopee. Thanx for the info.
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Thanks!
http://oilcatchcan.com/
Seems necessary.
I suppose it answers both why positive crankcase ventilation is important and also addresses the oily residue though I actually intended to just address the residue :riding:
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Definitely going to do something about this. Got a good idea, see ya down the road.
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Still mulling this over before fabbing a catch can. Most available are for cars, 750ml and up, which is huge.
AFAIK, which isn't much, the four pistons in a K100 move up and down in pairs causing, at most, a sloshing of air inside the case to and fro. With some, at most, getting kicked around. And some ring blowby that increases with age.
Intro a rubber crankcase tube connected to low pressure chamber, the air box. In a perfect world the AMM, the ignition and fuel metering computers, using various signals, would be perfectly telling the system how to function, barring any unmetered air leaks within the system. I think, so far.
Now along comes a variable, the crankcase air, unmetered, whether the Z hose is cracked a little, the rings are getting tired or the oil filler O-ring is old/cracked.
Anywhoo, it seems to make more sense to have no unmetered air from anywhere getting into the air box. Not to mention the gooey mess inside the air box eventually smearing itself over the top of the cylinder head gumming up the throttle bodies.
So, am still thinking about this, fabbing hoses, whatever, it's a Sunday, snow tomorrow, oh the horror, no news crews in town yet.
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I'm in the process of tearing apart my 75RT. Had a peek inside the air box and saw the oily residue referred to in this thread. Nine80seven, you referred to the ram tubes. Are those the (in my case) three white vertical tubes inside the air box directly above the injectors? If so, what is their purpose and is it worthwhile, or even wise, to try cleaning them off? I had thought that perhaps they are some kind of final filter but they don't look porous.
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They are just tubes that optimize the air flow and velocity going into the TB's. They are needed.
I just took my airbox out. Tubes were clean. Very little oil residue inside the airbox.
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Clean the tubes if you have the opportunity.
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As winter progresses work also continues on KRS '84 and thinking about the weird no crankcase ventilation on the 84 to 89 Ks. There is no fresh air introduced to the crankcase?
The only thing I can figure is, blowby exits the crankcase because one, it is slightly pressurized, and two, the crankcase is connected to a sporadically negative pressure area, the air intake plenum. Since there is no cyclonic or other trap of some kind to remove oil from blowby, plenum eventually gets the smeared insides.
Strange that this is how things were German engineered? No fresh air to the crankcase? Guess the pressure vacillates, vibrates as cylinders rotate in pairs. Sort of a pulsing of blowby gases. Some of which go up through the z-hose. No PCV valve. No maze through which the oil,can be separated.
And all this happens with no metering through the AMM. This assuming the FICU can adjust to this air. Which it cannot. As said earlier, still thinking about this setup. Or have I missed something? Is there a trap buried somewhere in the crankcase?
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There's only so much engineering that can be done before a product has to go to market and still have attractive price tag. It met USA standards, that was enough. It's only a motorcycle, after all, and it works pretty good if ridden plenty, lubed regularly and given clean fuel.
As far a German engineering goes, how about that VW diesel pollution control?
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Just trying to understand how, with the early Ks, the only way blowby is handled is at high vacuum in the intake plenum. Which is at idle and closed throttle deceleration. The engine is the crankcase vacuum pump.
No PCV, no fresh air into crankcase and no oil/air separation. Seems like this is what's going on with these engines. Is what it is. I get it. Sticky stuff in plenum, ram tubes, throttle bodies and on down the line. Guess I can live with that, maybe. Guess all four cylinder UJMs of the era were the same. Thanx.
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the only way blowby is handled is at high vacuum in the intake plenum. Which is at idle and closed throttle deceleration.
At idle and deceleration you have low vacum in the plenum chamber, highest is at WOT.
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Not according to my vacuum gauge. Take foot off accelerator, deceleration, vacuum pegs. Idling, vacuum over 20 inches. Floor it, vacuum drops way down, five or thereabouts. When throttle plates close the cylinders really get sucking hard. When wide bleeping open, the gas is flying free.
Nevertheless, either way, there's no way to control the egress of uncontrolled AMM unmeasured crankcase air into intake plenum. Which is the way it was designed. Still conflicted as to if I'll experiment. Easiest just to hook up new Z-hose and gum up another 80 thou. miles. Thanx
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Inge is correct.
Your vacuum is being measured downstream of the throttle butterflies. Opening the throttles allows more air flow through the plenum. Mr. Bournelli says that increased airflow lowers the pressure in the plenum.
It's not a good idea to argue with Mr. Bournelli. He's been right for a couple hundred years.
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Don't know where Bernoulli principle applies here, but take off for gauge is on motor side of throttle plate. What we know is blowby is inside the plenum. Also blowby must be very small to not throw off the ratio of fuel to air because it is not metered. A cracked Z hose can let in more air.
Motor vacuum drops when air velocity increases on plenum side of throttle plates. Two different zones. Second low pressure area probably right at the entry to the plenum from the Z hose as the air flys by. My mistake. Or was that backwards? Doesn't matter. Cheers Bro.
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This never crossed my mind before, but what's the worse that can happen if the crankcase breather hose is permanently removed and the two ports are blocked?
If blocked the gasses will find the easiest way out of the engine, ie weakest point. Usually a seal or gasket will start leaking.
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Actually fabbed aluminum catcher, new elbowed hose on engine pipe, followed by PCV, got it all positioned, capped plenum inlet. Then the nagging problem of the crankcase pressure not being high enough to vacate any blowby. So, gonna scrap the project as a useless foray, install Z hose, forget it, and wash out plenum every 80K. Thanx for comments.
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One other thing, sucking crankcase air into plenum even though very small, creates and keeps a lower pressure in the crankcase, which is easy on engine seals. Expecting the crankcase to evacuate itself by blowby pressure only may raise all sort of seal issues.
The engine guys way back in '80-82 likely tried lots of different approaches and this little Z hose is likely the best way to air the gases out of the crankcase. Cheers, gotta go get a couple shims.
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I'm new to this particular bike, but the breathing is a big topic on the British bike forums. With those big twins, both pistons rising and falling together, crankcase breathing is very important.
In any case, I have some cracks in my breather tube. Sealed them with silicone, but I'll be looking to replace that tube. Had a look, and it seems like a bit of trouble to get to the thing. I am tempted to just put a filter on a short tube and block off the entry to the air box. Anybody tried this?
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I am tempted to just put a filter on a short tube and block off the entry to the air box. Anybody tried this?
This thread seems to have covered many reasons why that may not be a good strategy but nobody wrote that they tried it—you read all that, I guess. How about you do it and report back, BlitzenGruv? It would be a significant contribution to the body of knowledge here.
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Will do.
Before '74 Triumphs just vented the crankcase to the air. Starting in '74 they ran the vent back into the air cleaner to meet emissions standards. Absent a PCV valve, I can't see why routing the vent to air would cause any problems with this engine.
I will report back.
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Try this thread: http://k11og.org/forum/viewtopic.php?t=11285&highlight=crankcase+breather
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I'm new to this particular bike, but the breathing is a big topic on the British bike forums. With those big twins, both pistons rising and falling together, crankcase breathing is very important.
In any case, I have some cracks in my breather tube. Sealed them with silicone, but I'll be looking to replace that tube. Had a look, and it seems like a bit of trouble to get to the thing. I am tempted to just put a filter on a short tube and block off the entry to the air box. Anybody tried this?
New hose is cheap and it is simple to replace. Just do it.
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New hose is cheap and it is simple to replace. Just do it.
Not on a 4V.
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Oops! Missed the 4v part. Still not all that hard. Good time for a bunch of other maint while in there. Fuel hoses, intake boots, fuel injector cleaning, etc.
Still think it should be replaced. Good for another 10yrs.
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Thank you!
The link and the pictures are very helpful. It appears that it would be just as much trouble to modify as it would be to just replace the hose. I need to inspect the air filter anyway.
Now I just need to figure out how much needs to be removed just to get the airbox open. The factory manuals are a bit difficult to follow.