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Diesel fumes from breather cap

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Mad Max View Drop Down
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    Posted: 03 July 2014 at 12:25pm
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
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Mike V View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike V Quote  Post ReplyReply Direct Link To This Post Posted: 03 July 2014 at 10:37pm
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

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Post Options Post Options   Thanks (0) Thanks(0)   Quote George S. Quote  Post ReplyReply Direct Link To This Post Posted: 04 July 2014 at 4:14pm
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Winner Quote  Post ReplyReply Direct Link To This Post Posted: 04 July 2014 at 8:29pm
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote frfletch Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mad Max Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2014 at 7:54am
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
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Bill Layton View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bill Layton Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote frfletch Quote  Post ReplyReply Direct Link To This Post 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?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bill Layton Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2014 at 11:02am
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mad Max Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2014 at 11:16am
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bill Layton Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2014 at 11:24am
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mad Max Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2014 at 11:30am
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote frfletch Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2014 at 11:48am
I love it! Thanks people!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mad Max Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2014 at 8:57pm
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
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Bill Layton View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bill Layton Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2014 at 10:19pm
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote frfletch Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mad Max Quote  Post ReplyReply Direct Link To This Post Posted: 06 July 2014 at 8:56am
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 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote George S. Quote  Post ReplyReply Direct Link To This Post Posted: 06 July 2014 at 3:00pm
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote frfletch Quote  Post ReplyReply Direct Link To This Post Posted: 29 August 2014 at 11:37am
Hi All. I finally got to the project of the re-breather for the oil cap and tested it earlier this week. It works.  










Edited by Bill Layton - 29 August 2014 at 4:05pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bill Layton Quote  Post ReplyReply Direct Link To This Post Posted: 01 September 2014 at 4:09pm
Nice work Frank!
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