Crancase breather on a listeroid twin

[jens]

removed

[Grael]

If nothing else works. I'd go for your plan B, but why put the filter? I can't possibly think of any crap getting into the intake. Heck, most engine crank cases are vented into the intake to burn up any volatile vapors, and I have yet to see any engine with a filter to remove junk; save for the TDI which has a 'filter' of sorts, that condenses tiny oil droplets, so as to not have them go into the intake and make it oily.

[Grael]

I wouldn't imagine that there would be too much incoming outside air. Most of it would probably be blow by. And even if there was dirt/dust in the air going into the engine, I would imagine that it would be mostly caught by the oil.

[Tijean]

Sounds like the right conclusion about the twin not being able to create a vacuum by the same check valve method as the single. Any piston blowby would be a constant imput to the base. Some engines did have a rather filtered air intake/oil filler cap to let air in that was pulled out by the road draught tube in the days before positive crankcase ventilation, but that was auto engines in the 50s and 60s that I cut my teeth on.

I see a possible problem with some unusual failure causing a large oil intake causing a runaway condition on a diesel engine. How about using a venturi effect opening into the exhaust stream and suck the blow by away without putting it through the engine?

Frank

[M61hops]

I think you have the right idea Jens!  I think you should have some sort of filter between the crankcase and the intake to filter out drops of oil and return them to the crankcase.  I'd try a fuel filter first though it might not be big enough to flow the volume of blowby you might have.  You could rig up something larger later if it seems nessecary.  As there isn't much intake vacuume caused by the main air filter you might need more like a 1" breather hose to get any suction in the crankcase.  Maybe you could use something salvaged from the automotive world?                          Leland

[Grael]

Well, if you want some way to condense the oil vapors, you could have the plumbing going through some sort of box like dealie (technical term) that is stuffed full of those copper scouring pads. There is something similar to that on a little antique engine I have, except it is vented to the air.

[SHIPCHIEF]

The device is called an air maze, or oil maze. It needs to be pretty big, so the air velocity will be low. The oil will condense into the copper wool or whatever and slowly drip out the bottom so it can return to the crankcase. Some have a separate drain line, but if you ran a 3/4" hose straight up from the existing vent into the maze, the condensed oil would run straight back down the sides of the hose returning to the sump.
The line from the maze to the intake can be smaller, but needs to be a steady upward slope so any additional oil to condense out can flow back to the crankcase too. It should enter the intake manifold at the lowest possible point so there is no chance that oil might puddle in the intake manifold.
That should create a minimal crankcase vacuum, and keep oil from slobbering out, yet not suck in dust to increase wear.

[Tom]

A simple copper or stainless steel kitchen scrubber in a small stuffed in a small can will work extremely well to recondense any oil in the crank case gases. Run a hose into the bottom from the crankcase and out the top to the intake manifold and you are good to go.

[oliver90owner]

If you have little blow-by why not do as has been done on countless engines before.  Put an atmospheric breather on the oil filler and feed any blow-by into the inlet system at atmospheric pressure (virtually if your filter is adequately sized?) so there is no real draw from the vent by the engine. 

Simply venting it to atmosphere would enable you to check out the effect on your leaks.  If they pesist this thread is just about totally irrelevant.  Take one step at a time. KISS!  Why complicate things before you know whether it would solve the problem?

Regards, RAB

[Stan]

I'm sure more experienced diesel guys than me can comment on this but isn't it prudent to be careful that if you vent a crankcase into the intake of a diesel, you could potentially get into situation where the engine is sucking in "fuel" and presents a runaway situation?  I know this happens on briggs and scrapem engines where the engine sucks in the lube oil and runs the engine dry, thereby toasting the bearings. 

Just musing.
Stan

[1958steveflying]

Covered earlier in the thread Stan.

[ronmar]

RAB, I hate to admit it but I never considered the possibility of the crankcase being pressurized by blow-by. I am pretty sure I checked that the vent on the inspection cover is free to move. I can however just pull that little steel disk that does the venting and see if that changes anything. I assumed I was running at atmospheric and would need to apply a bit of negative pressure to hold the oil in.
Thanks!

Jens

Yes Jens the blowby will pressurize the crankcase.  You can also run into issues of a combustible mixture building up in the crankcase and causing a flash fire/explosion inside the crankcase.  On the ships I have been on, this was a frequent practiced drill as it was a real threat.  The engines had electric crankcase exhaust blowers that maintained a certain level of vacume on the case.  This vacume was monitored, and the engine would automatically shutdown if vacume was lost.  Under certain hot conditions such as steaming across the equator, the ammount of blowby at full load coupled with other case leaks would exceed the vacume available from the blowers and the engines would shutdown at full power.  This was a limiting factor sailing thru warmer waters.  You are right in that a little vacume will help a lot in keeping the oil inside the engine.

[Tom]

The scrubie in a can I mentioned is essentially what is screwed into the valve cover of my Scout to prevent a carb back fire from blowing up the engine. It will also condense the oil and allow it to drain back into the crank case. I used to sell similar units in a stainless steel case for $100's of dollars. You can make your own real easy.

[Stan]

Sorry about that Steve...I was in Ottawa for a couple of weeks and didn't get a chance to read all the posts on the forum as carefully as I should have,  as computer time was at a premium at my daughter's place.
Stan

[ronmar]

Yes, splash lube is very effective.  I replaced the metal flapper plate breather valve on my 6/1 crankcase breather with a in-line 3/4" brass check valve commonly used in plumbing applications.  I made a new steel plate that goes on the existing breather elbow and welded a 3/4 NPT pipe nipple to it.  I removed the spring from the check valve and screwed it to the welded nipple.  I will eventually plumb this outside, but for now, I have a old rag sock pulled over it.  At load, you can see the blowby gasses exitiing thru the materal weave, and the sock gets soaked with oil.  This from a port that has a splash shield over it on the inside of the case cover.

Small droplets and blowby gasses will exit thru a small port at rather high velocity.   That is where the scrubbie in a can that Tom mentioned comes in.  The gasses expanding into the can allow the flow to slow down.  The surface area of the scrubber material(metal/machine tool shavings/large steel wool) catch the oil droplets and condenses them into larger drops that can flow back into the case without being carried back out in the airstream.  However used, the crankcase exhauster port should use something like this to capture the droplets and redirect the oil back into the case.

A small open hole like a dipstick port would be capable of blowing out quite a lot of oil droplet spray as the velocity thru the small opening would allow droplets to be more easilly carried.