Diesel fumes from breather cap
Printed From: Laser 28 International Class Association
Category: Laser 28 General
Forum Name: Maintenance
Forum Description: All the things to care for your boat
URL: http://www.laser28.org/forum/forum_posts.asp?TID=674
Printed Date: 28 April 2024 at 10:21am
Software Version: Web Wiz Forums 11.03 - http://www.webwizforums.com
Topic: Diesel fumes from breather cap
Posted By: Mad Max
Subject: Diesel fumes from breather cap
Date Posted: 03 July 2014 at 12:25pm
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For years we've been suffering from the bypass fumes of the engine in the boat. I considered putting in a fan to vent the engine fumes outside but hesitant about cutting a hole in the boat. I found a simple solution to the problem similar to emission controls in our cars. I removed the oil filler cap and fitted a radiator hose with plug to fit over the tube and allow the attachment of a 3/8 ID rubber hose. I ran the hose over the engine and inserted into the air breather allowing the engine to remove the fumes. After a 5 day race including a 13 hours of running the engine for delivery the boat was finally free of fumes. I have not seen nor could find where this issue has been addressed on the forum. For me it was an easy solution for an annoying problem. Happy Sailing ------------- Dick #122 |
Replies:
Posted By: Mike V
Date Posted: 03 July 2014 at 10:37pm
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Good tip. Many cars have used the system. Any chance you would consider racing in the Can Am Challenge. We have 6 boats registered. Contact me if you need help to get there or some information. We would love to have another boat to race with. ------------- Sparkplug Hull #182 NYC |
Posted By: George S.
Date Posted: 04 July 2014 at 4:14pm
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Could you post some photos of your installation, please.
I am wondering if you drilled another hole in the air intake rather than just stuff the 3/8 hose in the existing intake opening. That would restrict the amount of air going to the engine and diesels like a lot of air..... Sounds like a good fix though... cheers, George WarBird |
Posted By: Winner
Date Posted: 04 July 2014 at 8:29pm
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Yes I'd also appreciate seeing pics of the installation. The fumes on my boat are not too bad, but none is better than any when it comes to this smell!
------------- Chris Eclipse #240 Thunder Bay, ON |
Posted By: frfletch
Date Posted: 05 July 2014 at 4:03am
| I agree these fumes in the boat are annoying. I'm just wondering about the method, however. The oil-fill cap is sort of made special with a reed valve on the top. I presume this allow has something to do with the internal oil pressure inside the crankcase. The modification you describe basically leaves the top of the oil-fill tube open to atmosphere preventing any internal pressure from developing at all. While I have actually re-built my Bukh myself, I admit to not knowing whether it relies on internal crankcase pressures or not. Bill? Somebody? If it works and does no harm, I will go with it for sure. |
Posted By: Mad Max
Date Posted: 05 July 2014 at 7:54am
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I know the old Mercury outboards required crankcase pressure to operate the diaphragm in the fuel supply line. Don't know why pressure would be required in a diesel. The motion of the piston creating pressure and vacuum has to be equalized, but I'm no diesel mechanic. My thinking on the reed in the cap is to trap oil residue. Will take pictures of setup today and post. Will also bring home the oil cap to see if it will hold pressure. Temporarily the hose is stuck inside the air intake. Plan to attach hose to the outside further down the air horn so it won't rob air to the engine. Thanks for feed back. Dick ------------- Dick #122 |
Posted By: Bill Layton
Date Posted: 05 July 2014 at 8:54am
| Crankcase pressure is equal and opposite to compression so when the piston hits BDC the crankcase has to be able to release that pressure and does so thru the vented oil fill cap. My observation anyways. |
Posted By: frfletch
Date Posted: 05 July 2014 at 10:48am
| So ok on releasing at BDC through open oil filler tube as vent, but does the engine require the vacuum created in the crankcase by the piston's rise on the way to TDC. If one places one's hand over the oil fill tube with the cap off and engine running, the air suction and discharge can be felt as very pronounced. If it doesn't matter, why is the cap built with a one-way reed-valve? |
Posted By: Bill Layton
Date Posted: 05 July 2014 at 11:02am
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That's the shortcoming in it's design I suppose. I just tested a filler cap (nice clean dry one in my basement) and it allows crankcase pressure to exit out the cap but does not allow air into the crankcase. So this explains the engine smell we have when motoring. Looking closely at what Dick did makes sense except I'm not sure how you dealt with the baffling that's part of the oil fill cap. The baffling fins on the cap prevent oil from getting out the filler neck. This is a problem when motoring when healed. Any stock engine will spew out oil thru the cap if motoring when healed..... most of us have experienced this at some point. With the baffling removed and just a hose installed and led to the air cleaner. I would suspect you may be burning some of that escaping oil. Just a thought.... I would watch your oil level closely. |
Posted By: Mad Max
Date Posted: 05 July 2014 at 11:16am
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The hose coming off the filler tube is sticking up so the oil has to travel vertical another 6" or more up the tube. Will run the engine today and check the hose for oil afterwards although it won't be running on an angle. Another thought is any oil coming through would collect at the bottom of the air filter. After a week of running hard I would think some would appear there if its a major problem. Will report back tonight. ------------- Dick #122 |
Posted By: Bill Layton
Date Posted: 05 July 2014 at 11:24am
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It doesn't take much healing for the oil to get past the baffles in the cap and spray the entire engine compartment with oil. I've seen it many times. Is there a way to use the cap so you can retain the baffling? Perhaps modify the cap to fit the hose. Just thinking out loud. You don't want to lose engine oil to the air filter for any reason if you can help it. |
Posted By: Mad Max
Date Posted: 05 July 2014 at 11:30am
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Excellent idea. It would be very easy to clamp the fitting onto the cap rather than remove the cap and clamp to the tube. Just a matter of modifying the jury rig. All bases would be covered. Thanks Bill ------------- Dick #122 |
Posted By: frfletch
Date Posted: 05 July 2014 at 11:48am
I love it! Thanks people! 
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Posted By: Mad Max
Date Posted: 05 July 2014 at 8:57pm
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Here are the pictures. There was no oil in the air cleaner from the hose. Pic with filler cap apart you can see the rubber gasket which keeps air from getting sucked in as Bill mentioned. New attachment for hose is brazed onto air breather. Will need to make trip to auto parts store for new hose to go over filler cap which is a hair over 1 3/4". I hoping it won't touch fly wheel when installed. In the last picture you can see a hose which comes from lower housing unit and sits just below the flywheel. Is there something missing or does it just sit there open? Looks like a dip stick tube or is it just a vent? https://flic.kr/s/aHsjYNW4kF ------------- Dick #122 |
Posted By: Bill Layton
Date Posted: 05 July 2014 at 10:19pm
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The hose from the saildrive leg is it's oil fill hose. It came with a plastic plug on that end. You could always ty-rap and screw the 3/8" hose to the underside of the cockpit and drop it down by the air filter, leaving some wiggle room. Keeping that hose vertical until it hits the cockpit is probably desirable should oil ever get into it. |
Posted By: frfletch
Date Posted: 06 July 2014 at 3:52am
| Ok! I think I will machine a new metal cap for the oil filter such that it preserves the current reed-valve assemble, but the cap can have an outlet on it to which we can connect a small breather tube. I'm thinking 3/8" silicone hose that is easy to bend and route anyway we want. I'll send some photos when done. |
Posted By: Mad Max
Date Posted: 06 July 2014 at 8:56am
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After sleeping on it I decided to go the Bondo and Aluminum tape route to finish out the summer. Did not remove the oil residue from filler cap so Bondo can be easily removed. I like Frank's idea. Winter project. https://flic.kr/s/aHsjZs5rqb ------------- Dick #122 |
Posted By: George S.
Date Posted: 06 July 2014 at 3:00pm
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hi Dick,
It looks to me from your photo of the drive leg filler hose that you have the plastic plug there already. It looks hollow from the top, but is actually a plug at the other end. Slacken the hose clamp holding it and it should pull out of the hose for re-filling drive leg after draining. (might be time) Nice to see that extra fitting brazed on the air intake so as not to restrict amount of combustion air to engine. Good work... George WarBird |
Posted By: frfletch
Date Posted: 29 August 2014 at 11:37am
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Hi All. I finally got to the project of the re-breather for the oil cap and tested it earlier this week. It works. http://s1124.photobucket.com/user/ratbagg/media/BUKH%20Breather%20modification/utf-8IMG_1025.jpg.html">  http://s1124.photobucket.com/user/ratbagg/media/BUKH%20Breather%20modification/utf-8IMG_1015.jpg.html">  http://s1124.photobucket.com/user/ratbagg/media/BUKH%20Breather%20modification/utf-8IMG_1021.jpg.html">  http://s1124.photobucket.com/user/ratbagg/media/BUKH%20Breather%20modification/utf-8IMG_1020.jpg.html">  http://s1124.photobucket.com/user/ratbagg/media/BUKH%20Breather%20modification/utf-8IMG_1013.jpg.html">  http://s1124.photobucket.com/user/ratbagg/media/BUKH%20Breather%20modification/utf-8IMG_1019.jpg.html">  http://s1124.photobucket.com/user/ratbagg/media/BUKH%20Breather%20modification/utf-8IMG_1014.jpg.html">  |
Posted By: Bill Layton
Date Posted: 01 September 2014 at 4:09pm
| Nice work Frank! |
Posted By: fatjohnz
Date Posted: 18 July 2017 at 9:46am
| Good info here gentlemen. I was pulling my hair out trying to figure out where the fumes were coming from and poof(!), a solution in the forum. Thanks, John |
Posted By: fatjohnz
Date Posted: 25 July 2017 at 12:59pm
| I'm surprised by the amount of air flowing from the vent tube now that it's captured in a hose. Does back pressure on this vent pose a problem for the engine operation? js |
Posted By: bal149
Date Posted: 01 August 2017 at 8:39pm
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i agree , nice work. The drawback is that you must now check your air filter more often as that oil mist will clog it up. Running the lines into the filter housing downstream from the filter would avoid this, but should the Buhk take a big gulp of oil that has pooled in the bottom of the housing the con rod will suffer (hydraulic lock). The reed is there to generate negative pressure in the crankcase so that the seals are not blown out. Pollution controls on cars plumbed this back into the air intake as you have done -PCV valve. They do not heel like a laser so there are no big discharges that could cause problems. Cars that sustain high G forces pump their oil into a tank to avoid this (Dry Sump). This was on a lot of classic motorcycles in the past but now internal baffles prevent large losses of lubricants. You can't make a silk blanket from a sow's ear but you have greatly improved what is at best a very old design.
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Posted By: Mad Max
Date Posted: 02 August 2017 at 6:30am
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I've been thinking about adding a catch can to Mad Max so solve (avoid) this very problem. People have been adding these to cars to cut down on repairs to direct injection vehicles where the intake valve is being fouled after thousands of miles. Here is an article explaining the problem with autos. http://tinyurl.com/ydf8slph I'm thinking a metal can with screw on lid containing heavy steel wool acting as the separator would eliminate the problem. Mounted in a convenient location for easy access, simply duct the breather hose in and out before entering the air intake. Looking for input. ------------- Dick #122 |
Posted By: Bill Layton
Date Posted: 02 August 2017 at 7:08am
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The air filter in the snorkel is actually only a wire mesh screen so oil won't clog it. I keep my snorkel vertical. If your worried that your collecting too much oil in it you could drill a hole in the bottom outside of the wire screen and this would allow it to drain in to a catch can.. or even on to a rag. I haven't collected any oil in my snorkel in the 2 years it's been installed. If you do not use your engine with the boat heeled it won't be an issue. And if you do you should be wise enough to check it out occasionally. This device isn't meant to compensate for using the engine when heeled. It's only to keep the crankcase fumes separate from the air you breathe down below. Catch cans on cars are meant to drain automatically back into the engine. To do this on this engine it would have to be mounted above the oil filler neck of which there isn't much space between the cockpit floor and the top of it.
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Posted By: frfletch
Date Posted: 02 August 2017 at 10:36am
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I have been running with this re-breather for over 3 years now and we race 12 months per year plus do some cruising in the summer. I haven't had any problems to date. My observation is that because my tube mounts vertically to the top of the fill cap, the oil fumes condense as they rise and cool coming out of the cap and into the hose. Then, any condensed oil probably runs back down into the engine via the same route it came out of when the engine is not running. No idea how it gets past the reed valve, however I can see some oil residual in the clear hose up to about 100mm above the attachment to the cap, but none beyond that, so I'm guessing that is what happens. I think it never makes it to the air filter. I took my cap off the other day and neither was there any accumulation of oil between the top of the cap and my re-breather cap. If one makes one of these gismos, I can advise that if you use that clear reinforces plastic hose that is on Voila, it may look upon installation that it stands up nicely to bridge between the oil fill cap and the air filter. However when the engine compartment heats up, the plastic goes temporarily soft and will sag onto the flywheel. I support mine by suspending it from the bottom of the cockpit sole, or the top of the engine compartment. Finally, I am not afraid of engine damage at this point and the arrangement keeps my boat smelling fresh when running and also keeps my engine compartment much cleaner that having the oil fumes condense all over the place at large after escaping the original oil cap into the atmosphere. |
Posted By: fatjohnz
Date Posted: 18 September 2017 at 6:44pm
| Hi Frank, Nice work! You have a PM with my address. John |
Posted By: Winner
Date Posted: 22 October 2017 at 8:11pm
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I'll be doing this modification as a winter project. Two questions: 1) The pictures that Frank posted a few years ago no longer seem to be active. Frank are you able to repost them or email them to me? 2) I removed my oil filler cap and air intake to bring home and noticed that the wire mesh of my air intake is pretty sooty. Can I just clean it with diesel fuel or is something else better? ------------- Chris Eclipse #240 Thunder Bay, ON |
Posted By: Bill Layton
Date Posted: 23 October 2017 at 6:49am
| You can wash the air cleaner screen in just about anything. From Lacquer thinner to Kerosene, even paint thinner works. |
Posted By: Mad Max
Date Posted: 23 October 2017 at 9:08pm
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Unable to view pictures, what am I missing? ------------- Dick #122 |
Posted By: Winner
Date Posted: 10 March 2018 at 4:25pm
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I'm shamelessly bumping this. Frank by chance do you still have those pictures of your setup for the rebreather cap? The ones you posted a few years back have a broken link now. ------------- Chris Eclipse #240 Thunder Bay, ON |
Posted By: frfletch
Date Posted: 10 March 2018 at 6:51pm
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Hi Chris, Sorry. I made this item up for you and then moved my shop. I will find it and send it. Please send me your mailing address. Frank |
Posted By: John Mills
Date Posted: 29 April 2018 at 7:14am
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Did this upgrade , easy to do . will let you know if it worked . I note that I was surprised that the crankcase is sealed and the reed valve seems to be there to let presure out but there is no "intake" so the air does not seem to flow through . I guess you are just catching the blowby ? ------------- Unplugged # 164 NOTL |