Lister Engine Forum

How to / DIY => Everything else => Topic started by: Doug on February 22, 2007, 04:25:00 AM

Title: Crank case vapours
Post by: Doug on February 22, 2007, 04:25:00 AM
Interesting ( I use that word a lot because I can spell it correctly... ) technical stuff on seperating oil mist from crank cse vapours.

I don't have a vent tube for the spare head on Gus and this seems like a better way to deal with the problem any ways rather than blow gasses directly from the rocker box into the intake port.

Title: Re: Crank case vapours
Post by: jtodd on February 22, 2007, 07:34:27 PM
I'm sure that there have been other threads on this elsewhere on the board, but keyword searching has been a bit hazy on the forum so maybe I'm asking questions for which there are already answers...

I don't know why it wouldn't be OK just to create some sort of tube arrangement to pull air/vapor out of the existing crankcase vent and suck it into the intake.  Seems like a pretty good solution and would keep to a minimum the amount of gunk floating around the generator shed (oil vapor, etc.) by simply re-burning that vapor.  Am I missing something?  I don't think there'd be enough oil in that air to create any sort of unintended fuel run-away, so I can't really see a downside to machining a flange/hose that leads from crank vent into the intake or air filter area...  Is it really necessary to filter it on a Lister?

Title: Re: Crank case vapours
Post by: dkwflight on February 22, 2007, 07:40:30 PM
I remember reading about a home made oil seperater for the oil mist from the crankcase. It consisted of a can full of the copper kitchen scrubbers (Chore boy). The can had a connection for the crankcase breather and a small hose from the can that carried any oil-water residue to a can the hold the waste oil gunk.

This should be easy to make. Maybe use a small pressure cooker for the can
Title: Re: Crank case vapours
Post by: binnie on February 22, 2007, 08:26:08 PM
Anyone remember this fix by "wwiprops"...easy solution. I do like Jtodd's suggestion for anyone who doesn't have easy access to vent.
Title: Re: Crank case vapours
Post by: Tom on February 22, 2007, 09:15:47 PM
Though a bit smaller (3/8" NPT) the engine in my IH Scout has a small can screwed into the valve cove with copper mesh in it to vent blow by fumes into the air cleaner. The other advantage to this is that it also functions as a flame arrestor should the gas engine backfire through the carb.
Title: Re: Crank case vapours
Post by: jtodd on February 22, 2007, 09:20:05 PM
OK, maybe it was that picture from wwiprops that I was remembering.

Looks fine, but I guess I wonder why you'd vent it outside, when it seems like it would be an easier thing to just pipe it back into the intake.  I think it would have to be somewhere near the "open" end of the intake, so that there was little or no suction applied to the vent tube (don't want to put a vacuum in the crank to try to pull things past the rings, or through the bearing seals) but that shouldn't be so tough.  Just close enough that any smoke or mist will always waft towards the intake.

There seem to be plenty of smaller check valves available on eBay, so plumbing one in to replace the "reed valve" would probably do a reasonable job.

Title: Re: Crank case vapours
Post by: dkwflight on February 22, 2007, 09:50:29 PM
Back inthe '60s all engines vented over the side. When PCV came along the engines got dirtier. The oil neede changing more often. More acid in the oil etc.
Title: Re: Crank case vapours
Post by: ronmar on February 22, 2007, 11:36:37 PM
Because of the nature of the beast, you want the crankcase of a diesel kept under a slight vacume.  Unburned diesel fuel gets by the rings and into the oil.  Under the right conditions(hot engine), this diesel and oil mist can re-vaporize and you can achieve a combustible air/fuel mix in the crankcase which can result in a crankcase explosion.  All the large marine diesels I have operated had crankcase exhaust blowers that kept the case under a vacume.  This pressure was monitored and we would get alarms in the control room if it was not great enough.  You couldn't start an engine without the blowers running and the engines would auto shutdown if a vacume was not maintained.  The last ship I was on had bypass switches on the ships service generators to allow a startup with no electrical power.  Someone had to hold this switch till a generator was up and running and connected to the main buss to power the electric blowers that provided the vacume. 

It does happen and is a real threat.  We used to drill regularly on this scenario and possiblity of a followon enginroom fire from the hot oil blown all over the enginroom from the relief ports.  These are large spring loaded check valves in the crankcase which open and vent the overpressure from an explosion which keeps acces panels from being blown off and killing someone.

Google "Crankcase Explosion" and you will find plenty of information on the subject.
Title: Re: Crank case vapours
Post by: snail on February 23, 2007, 01:29:08 AM
    some engines of comparable age to the Lister do re-breathe their crankcase fumes. I have a 1936 southern cross diesel which breathes via the rockerbox into the inlet tract. the rockers at least make some use of the oil before it gets burned.
    On the other hand,the lister(oid) twins run positive crankcase pressure.I intend to vent the breather to the inlet and hope to get as much vacuum as possible to imitate the singles. The main reason for this is to reduce oil leaks.I know that there's not much available on a diesel but every little helps. :)
    Wandering off topic for a moment,would a slight restriction in the intake do any harm? I've read elsewhere on this forum that getting extra air into the cylinder is detrimental to efficiency. I'm not entirely happy with that statement, but I'm happy to defer to people who know more than I do about engines. :) If it's true, then it seems logical that reducing the air slightly would not be detrimental, providing that you don't need full power from the engine.
    Any comments?



Title: Re: Crank case vapours
Post by: phaedrus on May 07, 2007, 08:56:17 PM
I think that Ron has more experience with big diesels than I do, but I would add that they used "explosion doors" on the Enterprise engines I've worked on. (They were inline 8's, making 6000 hp at 450 revs, turbocharged and intercooled nuclear power standby emergency generators) Anyway the explosion doors were designed to allow release of gas from a crankcase explosion, but deny air getting in. Seems that crankcase explosions are sort of two step, first a fairly minor explosion that blows the doors loose and lets air get back in as the temperature drops, then a second and more serious explosion triggered by all that air making a nice explosive mix around a (red) hot bearing or whatever. Those Enterprise engines used pneumatic instrumentation that exhausted inside the case, making a continuous air purge.

Crankcase explosions are not limited to diesels. Dresser Rand had one not too long ago in a hydrogen compressor. Crankcase vent was clogged (but they didn't know that) and she had a bad pistonrod seal (a crosshead type double-acting pump). The door blew off, clear off, and flew into a man. Shattered the pelvis... bummer! Takes two guys to pick up one of those doors. The crew were wearing all their PPE and nomex clothing, so the other injuries were limited and the burns were minor. Now, they say, they vent these by purging N2 through the case and there's supposed to be instrumentation to verify continuous purge. Maybe. I decline refinery work these days - too many guys get hurt.

As to re-breathing the crankcase vapors, uummmm, I have some doubts. The vapor ought to be mostly air, so it can't do much harm, but it also can't do much good, can it? Some water vapor ought to be in the crankcase vapor stream, wouldn't want to condense that back into the lubeoil. Ditto the fuel oil. Seems to me that one ought to simply dispose of these vapors to atmosphere by exhaust venting the engineroom, perhaps by "gas-phase thermosiphon", eg a nice fat stack on the roof...I have my eye on a nice oil drum that'd make a purty stack. Enginroom make-up air can bring in dust and dirt though, so it can be counter-productive.

The question Snail posits, eg slight restriction, well, an intake filter results in just that, a slight restriction. Perhaps more significantly, the nature of the l'oid, the large displacement sucksucksuck cycles, create momentary below atmospheric pressure events at a rate proportional to engine speed. These don't cause any harm either, and might be valuable in getting oil up to the top rings and so forth.
Title: Re: Crank case vapours
Post by: hotater on August 18, 2007, 01:49:56 PM
My solution for crankcase vapors is to wrap a doubled paper tower over the CC breather and hold it there with a rubber band.  It takes about a week for the towel to become oil soaked.  I use those for starting trash fires.
Title: Re: Crank case vapours
Post by: mobile_bob on August 19, 2007, 01:11:07 AM
crankcase explosions,, hmmm :)
i got a story!

many years ago, back in my youth hotrod days and after getting numerous tickets for speeding
i found myself unable to afford high risk insurance on a new el camino that i had just bought,,, (not a hotrod, just a nice car)

so i sold the elcamino and bought for cash
a little 67 chevy nova ss with a 327 and 4 on the floor,,, pretty fast and i could buy plain old liability for it.

well the previous owner had put a  highrise and holley,, headers  and a set of M/T valve covers with the nice twist off breathers

the highrise also had the old style oil fill pipe common on the old smallblocks as well with the push on breather that had "oil"
embossed in the top of it.. nice steel unit, with wire wool inside.

well one day i stopped at my favorite station and the kid comes out to fill me, and asked if i needed my oil checked,, i said sure!
he did and allowed how it was a quart low

so i told him to put in a quart,, he grabbed one of the old style quart can's and removed the valve cover breather
stuck the quart can down it one of those nifty units that was a pistol grip thing that had the funnel and can stabber all in one
he then dropped it over on the fenderwell which was a common thing to do to let it drain... but....


a huge exposion and lots of smoke,,,
smoke cleared and no kid!

i went around to find him and found him laying on his back out cold
with a big red mark right in the middle of his forehead

he came too and had a lump that was growing by the second with the mark "LIO" (the reverse of the standpipe filler cap!!)

when he dropped the filler funnel it inadvertantly hit the positive cable clamp on the battery and shot sparks down the valve cover...
and being a hotrod with a holley that always boils over down the intake when you park it , past the rings and into the crankcase
with the fumes of hot oil and gas the mix was perfect for a huge explosion.

he had a lump for about a week

and i had a car that every seal leaked oil from then on
i suspect every seal had been turned inside out!

i know it pushed out the valve cover gskts :)

looking back it was funny as hell,, at the time i thought he was dead!

bob g
Title: Re: Crank case vapours
Post by: hotater on August 19, 2007, 01:55:37 AM
It said  '710'

emailed 'joke'?
A few days ago I was having some work done at my local garage. A blonde came in and asked for a seven-hundred-ten. We all looked at each other and another customer asked, 'What is a seven-hundred-ten?' She
replied, 'You know, the little piece in the middle of the engine, I have lost it and need a new one..' She replied that she did not know exactly what it was, but this piece had always been there. The mechanic gave her a piece of paper and a pen and asked her to draw what the piece looked like. She drew a circle and in the middle of it wrote 710. He then took her over to another car which had its hood up and asked 'is there a 710 on this car?' She pointed and said, 'Of course, its right there.'


It's like that 'eleven oh nine' welding rod thats' so popular.
Title: Re: Crank case vapours
Post by: mobile_bob on August 19, 2007, 04:14:27 AM
mark my business partner had a auto shop before we joined forces

one day when he came to work there were several messages on his answering machine

message 1:  hello mark,, my car has a red light on,,, it looks like a magic gennie lamp! oh well i don't know i will stop in after work

(he was 50 miles away)

message 2:  hello mark,,, the car is making a funny noise,, i am turning around and heading to your shop

(still about 50 miles away)

message 3:   mark!  the car is squealing!!! i am on my way!

message 4:  MARK! the noise is aweful!

anyway,, mark stops the answering machine as the car rolls in
the guy pulls up to a stop with alot of smoke, steam and knocking
before he shuts the engine off,, it seizes

go figure!

magic gennie light... funniest thing i ever heard :)

bob g