crankcase vent on 85 k100 with 138 k miles

[gard]

The Z shaped crankcase breather is once again cracked with oily crap all over the place. I suspect I have some combustion gas getting past the rings, thus pressurizing the crankcase, causing oil leaks everywhere. I hate to think what the inside of the manifold looks like.

So what is wrong with just venting the crankcase to the atmosphere and blanking off the tube into the manifold?

I have done this on old diesel tractors and they stopped leaking oil. There is now a slight oily mist that is directed towards the ground. I intend to reattach the crankcase vent system to the intake manifold after replacing the rings on the tractor. I know this does not meet current emission standards but am not sure if a little oil mist is that much worse than combustion gasses into the environment. On the tractor there was enough ring blow by to overwhelm the crankcase ventilation system and pressurize the crankcase, causing oil leaks everywhere and sometimes popping off the oil filler cap. I simply replaced the oil filler cap with a U shaped section of old radiator hose directed at the ground.

What problems might I be creating by doing something similar on the K bike? I would have to figure out how to direct it away from the tires, brakes and my shoes.

[Laitch]

You seem to have answered your own question, gard, including mentioning the general air pollution created by open venting. You could install a removable filter on the stub or install a catch can; only time would tell you how often replacement or cleaning would be.

Consider doing a compression test and a leak-down test for further information. Try posting a photo of your Brick here. Many of us might be curious. How long have you had this relic?

Welcome to Motobrick.

[daveson]

Welcome gard

Well I thought I could be rough as guts but this one blows me away.

I think you want to do these modifications to avoid replacing worn rings, but you haven't done tests like Laitch mentions to find out if they are worn. How many miles on your brick? The hose should cope with the blow by, I think that's one of the reasons it's there.

I'll say it's not good. After you replace the rings on your tractor you're going to reattach the hose, so I'd say replace the rings on your brick if they're worn. Can you feel a lot of blow by, was the replacement hose new and cracked in a short time? Is the oil level too high? Maybe consider some other things first.

[gard]

Thanks for the replies, I have had the bike since it was new in spring of 1986. It now has 138,000 miles. It recently started having a nasty knocking noise at idle so I replaced plugs and did a compression test for the first time, 115, 111, 115, 122 cold. This was with the throttle open and what I later found to be a dirty air filter in place, so air flow valve also closed. I may yet attempt this again with air filter removed and I understand the valve should be removed or held open somehow without damaging the air flow sensor? I also may try a leak down test. I also replaced one of the ignition wires that looked like it had been chewed by a mouse. I cleaned some electrical connections, including the ground below the battery but there must be some other ground screws someplace? I blew out the air filter and it seems to be running much better now.

I also think I will attempt to measure the pressure inside the crankcase, if it is positive with the new Z tube installed perhaps I will think more about trying the "road tube" idea, I was amazed at how well this fixed all the engine oil leaks on the old tractors (David Brown, 1958 DB900 and 1967 DB990).

It has had service over the years (intake manifold rubber, hall sensor, water pump), but I am not convinced I want to put rings in it, the local shop said it would be considerably less expensive to put in a lower mileage engine. Putting rings in the antique tractor seems way easier and less expensive.

I am embarrassed to say I do not seem to have a good photo of the bike, I will attempt attach a couple of photos

[Laitch]

I replaced plugs and did a compression test for the first time, 115, 111, 115, 122 cold.

Was Frank's the local shop? If it was, they weren't kidding about expensive.    That isn't to say it's simple, as you well know. The cylinders are tough and probably not worn. New rings might do the trick. Used engines come up occasionally on eBay.

In BMW's service manual here on Motobrick, all the compression values in your engine are in the Poor category but they're relatively balanced so it's running ok. If it were mine, I'd do a leak-down test for more exacting information. Did you try squirting oil into each cylinder and repeating the test to determine if the rings were the main cause? If the numbers jumped some, that would be telling.

Thanks for the photos. 

[gard]

Yes it was Lester at Franks that said the compression test on these bikes is not very useful unless the throttle is open, air filter removed and air valve opened. I did not try the oil in the cylinder and or leak down test, may still do that. It is running much better now so think we will go for a ride instead.
The first compression test I did before visiting Franks was with the throttle closed and I got values between 70 and 97psi hot but running like crap. That was kind of depressing, Then I got back from Franks and measured with throttle open, got much better but still poor as you note.
Then took off lower fairing, checked air filter and other stuff...
Sorry about the upside down picture.
The wife says perhaps it is time for a newer bike, hard to argue with that one.

[Laitch]

It is running much better now so think we will go for a ride instead. The wife says perhaps it is time for a newer bike, hard to argue with that one.

[The Mighty Gryphon]

The wife says perhaps it is time for a newer bike, hard to argue with that one.

Gotta listen to the better half.  A low mileage K100 0r K11 might keep her happy.

[gard]

As an update, I put on the new air filter and Z tube crankcase vent. I found a tight fitting cork to replace the oil filler cap and measured a negative pressure (in other words vacuum) inside the crankcase of about 2 inches water at about 2000 rpm. So I guess the ventilation system can handle whatever ring blow by there is for now and no need for some kind of road tube extra ventilation contraption as on the tractors.
Anyone know what the pressure is supposed to be inside the crankcase when running?

I guess I will live with the small amounts of oil leaking from various places for now. Now I just need to clean things up and reinstall all the lower fairing bits.

[beemuker]

ride on, but check the oil level.

[Laitch]

Anyone know what the pressure is supposed to be inside the crankcase when running?

[daveson]

I didn't try the cork and bottle thing, but put my hand over the oil filler cap opening and also tried with a piece of paper. At idle I'd say there was compression and vacuum in equal amounts. At 2,000rpm I'd say the compression was more dominant. I'm wondering if your air inlet is restricted somewhere. I can't make out if you checked the snorkel type thing that feeds air into the air filter box.

[gard]

When I did the test the new Z shaped crankcase vent hose that goes into the bottom of the intake manifold was in place and tight. I found a cork that fit into the top of the oil fill opening. The cork has a small hole that I attached to a simple home made U tube manometer. This showed a small vacuum inside the crankcase that varied some with engine speed.

It seemed to me it is kind of hard to tell what's going on when you pull the oil filler plug out with the engine running, flow is coming in and out with each engine cycle. Once you plug it with a cork and pressure gauge, it takes a few seconds for the pressure or vacuum to stabilize.

I also noted in a separate test, that if the Z shaped vent hose is temporally pinched close, the pressure in the crankcase quickly rises to a couple of psi and oil starts leaking from various places, I would not recommend this but it did show the capability of the crankcase to become pressurized if the vent is not working properly. This also matched my experience with the old tractor engine where the crankcase vent is only about 1/4 inch in diameter and pressure would build up enough to occasionally send the oil filler cap across the room. It will be interesting to see what the pistons and rings look like.

I found the hose clamps on the 4 rubber boots that go between the engine and throttle bodies were all a little loose. The Bike is all cleaned up and running better now than it has in a couple of years. Not sure why a new coat of wax makes it run better.

I still do not know if there is a spec, someplace for crankcase pressure.

[daveson]

At the moment I'm too far from my brick to repeat the test with the z hose clamped, I'm thinking it's to be expected that the pressure builds with the hose clamped. I'm thinking maybe there's nothing wrong except maybe some seals aren't as pliable as when they were new. Maybe fix some of the leaks.

[gard]

Just to be clear, I am not proposing that pinching off the vent hose is a good idea, I do not know if the pressure build up might damage something.

I think measuring crankcase pressure or vacuum with the vent tube unobstructed and normally connected may be of diagnostic help and is easy. Again, I measure a vacuum pressure of 2 inches of water column or around 0.1 psi

I wish I had thought of the propane trick when the lower fairing was off.

[daveson]

I just measured one and a half inches vacuum of water column at idle and from 2,000 to 2,500rpm got two inches, same as yours. This was on a 1984 RT with 157,000 miles on it, and wants a bit of TLC. Your David Browns reminds me of a Fiat bulldozer I once had, I'd have to hold on the filler cap tight when I removed it.

I think your rings are good, your engine is good and it probably just wants a good service.