BUKH solutions on your LM

[dolac]

I have BUKH DV20 on my 1985 LM28. Last summer I had a not typical problem. Anyway, there is a hose that goes from thermostat into Y part and from that Y part one hose goes back to exhaust pipe and another goes all the way to exhaust hose just where exhaust hose ends. The Y part number is 008E1267 and it got broken and all the salt water went into engine room, lucklu i was following engine temperature and suddenly saw how it drops down.. I had pure luck cuz salt water was just near air filter.... Then after I made DIY Y part and connect hoses, suddenly on part no. 008E68 start leaking as well.. Anyway on the internet I see DV20 engines without those parts at all, there is one single short hose that goes from thermostat straight into exhaust pipe without that Y part and 3 different hoses. Can you please let me know how does it look like in your boats because I am looking forward to remove those parts (BUKH in Denmark told me how they don't even supply part no. 008E68) and connect the hose directly from thermostat into exhaust pipe.

Here are some photos for better understanding. My boat

Picture on the internet

And this is the place just 10cm from the end, between two black exhaust hoses is part no. 008E68

[dolac]

Here are catalog numbers for the parts I am talking about. How does it look like on your boats?

[Sula]

I believe it is a syphon break arrangement (also known as an anti-syphon fitting). Perhaps others could confirm or otherwise my thinking?

You can easily and fairly cheaply replace this with a non-Bukh fitting (see below).

Such a syphon break is needed unless the point where the water is injected into the exhaust elbow is significantly above the waterline. It is usually between the engine and the exhaust (like yours), but sometimes is between the water pump and the engine.  

A syphon break is to allow air into the cooling water circuit at its highest level when the engine is stopped. This allows the water level in the system to fall either side of the anti-syphon fitting, leaving air in the middle, and this stops water being able to syphon back into the system (from either the intake or the exhaust) and eventually rising high enough to spill into the engine through the exhaust manifold and valves.

In your case I believe the Y piece is where the air is allowed in to the cooling water circuit (when the water is not under pressure because the engine is stopped), and it draws that air in from near the end of the exhaust. (Another boat of mine (not LM) with a Bukh engine had a somewhat similar arrangement.)  When the engine is running water will be dribbling out into the end of the exhaust.

You can do away with the Y fitting you have by running the hose from the outlet from the engine block upwards to a point higher than the top of the engine (in a nearby locker if the engine compartment does not go high enough) to a plastic (or metal) syphon break fitting as shown in the links below.  You then run another hose from the other side of that fitting to the exhaust elbow (near the engine).  I will link below to Vetus diagram that shows the arrangement. 

The syphon break fittings come in two different basic types.  In both types the air inlet is usually on top of an inverted U shaped fitting.
 
The simplest type is similar in principle (if not appearance) to the one you had: it just has a plain opening in the top.  A little water flows out when the engine is running, and air is down in when the engine is stopped.  You connect a thin hose or tube to the top, and this can either go to near the end of your exhaust, as you have at present, or through a small fitting to exit outside the hull, or some people favour it draining into the cockpit, so you can see instantly if the cooling water is flowing or if it stops at any time.

The slightly more sophisticated type has a simple little rubber valve in the top, which prevents water coming out when it is under pressure (when the engine is running) but opens to allow air in when the engine stops and the pressure falls.  This does away with the need for an outlet hose or tubing.  With this type it is important to take the top off the fitting periodically (e.g. once a year) and rinse it off with water, as salt crystals can gradually form inside it and prevent it from working properly.

This page shows a variety of different types, sizes and brands of anti-syphon valves:    
www.asap-supplies.com/fittings-valves-strainers/valves-spares/siphon-break-valves

Page 85 of this (English Language) Vetus catalogue has a diagram and good advice about the correct arrangement. (It may be  different page number in other language versions of that catalogue):  
viewer.zmags.com/publication/6afeb8e9#/6afeb8e9/84

p.s. I have just looked again at your photo, and I think the fitting you have is incorrectly installed and was doing nothing to protect your engine!  It is not high enough, and this is important.  

In my LM27 the pipes are taken aft to get the height, and the anti-syphon valve is up under the aft deck.

In a previous boat of mine (non-LM) the pipes are taken to the side and up through holes into a cockpit locker to get the height.    


p.p.s.  If your new arrangement does not have a pipe to your existing fitting near the end of the exhaust hose (it will depend on the type of valve - see above) you must either remove or block off that, otherwise you may poison yourself with exhaust fumes, and/or get water spilling out of it and filling your boat.


 

[chrismunson]

My LM 32 engine box nearly flooded when the thermostat hose popped off. The mechanic had not tightened the clamp, and I got 6 inches of nasty water in the box before a $10 water alarm saved me a flooded engine. It sounds like a smoke detector. These are made to put near your home water heater to detect a leak. They use a 9v battery, and last forever! I'll do a full post on these soon.

[dolac]

Mar 10, 2020 18:52:03 GMT Sula said:

I believe it is a syphon break arrangement (also known as an anti-syphon fitting). Perhaps others could confirm or otherwise my thinking?

You can easily and fairly cheaply replace this with a non-Bukh fitting (see below).

Such a syphon break is needed unless the point where the water is injected into the exhaust elbow is significantly above the waterline. It is usually between the engine and the exhaust (like yours), but sometimes is between the water pump and the engine.  

A syphon break is to allow air into the cooling water circuit at its highest level when the engine is stopped. This allows the water level in the system to fall either side of the anti-syphon fitting, leaving air in the middle, and this stops water being able to syphon back into the system (from either the intake or the exhaust) and eventually rising high enough to spill into the engine through the exhaust manifold and valves.

In your case I believe the Y piece is where the air is allowed in to the cooling water circuit (when the water is not under pressure because the engine is stopped), and it draws that air in from near the end of the exhaust. (Another boat of mine (not LM) with a Bukh engine had a somewhat similar arrangement.)  When the engine is running water will be dribbling out into the end of the exhaust.

You can do away with the Y fitting you have by running the hose from the outlet from the engine block upwards to a point higher than the top of the engine (in a nearby locker if the engine compartment does not go high enough) to a plastic (or metal) syphon break fitting as shown in the links below.  You then run another hose from the other side of that fitting to the exhaust elbow (near the engine).  I will link below to Vetus diagram that shows the arrangement. 

The syphon break fittings come in two different basic types.  In both types the air inlet is usually on top of an inverted U shaped fitting.
 
The simplest type is similar in principle (if not appearance) to the one you had: it just has a plain opening in the top.  A little water flows out when the engine is running, and air is down in when the engine is stopped.  You connect a thin hose or tube to the top, and this can either go to near the end of your exhaust, as you have at present, or through a small fitting to exit outside the hull, or some people favour it draining into the cockpit, so you can see instantly if the cooling water is flowing or if it stops at any time.

The slightly more sophisticated type has a simple little rubber valve in the top, which prevents water coming out when it is under pressure (when the engine is running) but opens to allow air in when the engine stops and the pressure falls.  This does away with the need for an outlet hose or tubing.  With this type it is important to take the top off the fitting periodically (e.g. once a year) and rinse it off with water, as salt crystals can gradually form inside it and prevent it from working properly.

This page shows a variety of different types, sizes and brands of anti-syphon valves:    
www.asap-supplies.com/fittings-valves-strainers/valves-spares/siphon-break-valves

Page 85 of this (English Language) Vetus catalogue has a diagram and good advice about the correct arrangement. (It may be  different page number in other language versions of that catalogue):  
viewer.zmags.com/publication/6afeb8e9#/6afeb8e9/84

p.s. I have just looked again at your photo, and I think the fitting you have is incorrectly installed and was doing nothing to protect your engine!  It is not high enough, and this is important.  

In my LM27 the pipes are taken aft to get the height, and the anti-syphon valve is up under the aft deck.

In a previous boat of mine (non-LM) the pipes are taken to the side and up through holes into a cockpit locker to get the height.    


p.p.s.  If your new arrangement does not have a pipe to your existing fitting near the end of the exhaust hose (it will depend on the type of valve - see above) you must either remove or block off that, otherwise you may poison yourself with exhaust fumes, and/or get water spilling out of it and filling your boat.


 

[dolac]

first of all thank you for your explanation!! second, I am so sorry for late reply....

unfortunately you cannot see well how is installed on my boat as I don't have better picture yet.. the pipes go down as you can see and then go all the way behind the table up.. it is above the engine level and the engine exhaust elbow is above water line.. it is like this since my dad bought the boat in 1998.... yes, it is kind of syphon but the old part was just a hose without any valve or something in it.. then I was searching for BUKH engines and found all the pictures on website like i posted in first post. with the hose directly from thermostat housing int exhaust elbow.. I gave to do home made syphon and after I installed it, the hose that is connected just near the end of the exhaust (part no. 008E1268) broke too and as I cannot find that part I was thinking about removing all those things and connect the hose from thermostat housing direct into exhaust elbow.. now I don't know should I do it or not even the exhaust elbow is above the water line....

[chrismunson]

Please, whatever you do, do not make a direct connection from the thermostat to the exhaust. You risk flooding the engine if it does not immediately start, as water could backflow through the exhaust manifold into the cylinders. Suggest you consult a local specialist, as a marine engine has very a specific cooling scheme based on the engine model and its installation as it relates to the water line. It sounds like your system is old and may have been modified outside of the manufacturer's specifications. There are one way valves and restrictors in marine systems, these may have been removed or failed. In my boat, some components were missing and one had been installed backwards relative to flow. It's a wonder it worked at all. Hope this is helpful.

[Sula]

Hello again Doolac. I now think I have better understanding of the problem.  

As I understand it, your Y piece (also called anti-syphon valve or air vent, Bukh part 008E1267) failed but you have, I think, managed to repair it.  Your Y piece is well above the waterline behind the table (under the aft deck) if I understand you correctly (so I was mistaken before in thinking I could see it in your engine box).

Your T piece (Bukh part number 008E1268) has also failed, with the inlet spigot broken off, as shown in your third photograph. 

First of all, unless you are certain that your exhaust elbow (where the main cooling water flow goes into the exhaust) is at least 15cm above the waterline you must (as Chrismunson says) have an anti-syphon Y piece - as shown in the second diagram below from the Vetus catalogue I linked to before.  (I would prefer to have one even if my exhaust elbow was higher above the water line.)


 

You can easily buy a new Y piece (anti-syphon valve/airvent).  It does not have to be a Bukh part.  As I said before, these come in two different types, one (like the original Bukh part) with a tube and hose to let the water out when engine and air in when it is stopped (Vetus type ASDH is this type).  The other type has a valve which prevents the water coming out when the engine is running, but allows the air in when the engine is stopped (Vetus type ASDV is this type).  

If you have the hose type, the outlet does not have to go into the end of the exhaust. Usually these days it will go through a small skin fitting to the outside of the boat well above the waterline, as shown in the Vetus diagrams.  (Some people prefer them to drain into the cockpit so that they know that the cooling water is flowing.) 



The T piece is not something you can buy off the shelf, as far as I am aware.  I don't think this sort of arrangement is common now.  You could have your existing T piece repaired, or a new one made, by an engineering workshop; or (and I think this would be better) you could remove it altogether. 

If I were you I would -
(a) remove the T piece completely and replace the exhaust hose (especially as yours looks quite old) with a new piece of hose that goes directly to the exhaust through-hull outlet; and
(b) buy a new valve type Y piece - e.g. Vetus ASDV, but other brands are available. (If you get a valve type, note that it is possible for the valve to eventually be held open by salt crystals forming and leak water out, so (i) fit a tube to the valve outlet and run it downhill to somewhere you can see if it starts to leak (it must be able to let air in, but normally no water, or only a drop or two, will come out), and (ii) take the valve off once a year and rinse it with fresh water to remove any salt crystals.)

Good luck, and let us know how you get on.

  

[Brian & Glenda]

Bukh Exhaust-compressed.pdf (379.41 KB)

If I did this right: Attached is a copy of the pages in the Bukh DV36/DV48 Workshop Manual, offering a description of the Exhaust System.

In my LM32, I have a freshwater cooled DV36SME with an aftermarket heat exchanger rather than a Bukh heat exchanger, but I don't think that matters in this discussion...)

The seawater coolant discharge hose runs from the engine coolant heat exchanger to the bottom aft end of the engine compartment, where it passes out of the engine compartment and runs aft along the bottom of the hull in a depression that forms the top of the skeg for the rudder, up the aft end of the boat to a point just under a small shelf that is hidden behind my steering quadrant, where the vent/airlock is located, than back alongside this hose, back into the engine compartment where it enters the exhaust elbow. (The vent/airlock is Bukh Part 008E5435 in these drawings) - but as Sula mentioned ... you are not limited to the Bukh parts for this.) My airlock/vent is plumbed into the Bukh Water Lock System (Bukh part 008E5433) as noted in the third drawing. Both the outbound and return runs of this hose are enclosed in the same, what appears to be fiberglass insulated, plastic covered, approximately 4" diameter sleeve that runs from the opening at the bottom aft end of the engine compartment, to just shy of the aforementioned shelf leaving the airlock visible. This sleeve protects these hoses from chafing or damage by the shifting goodies stored under the cockpit sole.

These are the drawings that I was referring to in the thread: 'Exhaust Route on LM28' created by JohnC on July 25, 2019.

www.dropbox.com/s/npnbkrk5faby13o/Bukh%20Exhaust.pdf?dl=0

Hope that helps!
Cheers, Brian.

[dolac]

guys, thank you for your explanations.. Unfortunately I don't have better pictures at the moment and currently I am in Taiwan.. because of covid-19 not sure when I will be able to go back..

the system is all original since 1985, my dad bought this boat in 1998 from 1st owner who was crazy meticulous and didn't allow even to his son on the boat to sleep in it.. I still have LM original plates, glasses etc.. never mind, the point is that all those hoses and design is from the factory..

I think I will do as Sula said, will remove T part completely and yes, I will do change exhaust hose which I already have new ready to change..

About Y piece, the one I had was just a metal (i think copper) pice without any valve inside (I am 100% sure). First i say water leaking there, then after I made new Y pice part and replace and then that day I say that T piece is broken as well.. The point I wanna say, I could easily connect two hoses as I will remove T piece, am I right? Because even now there is just Y piece, like piece of metal hose, no valve inside, nothing, I made it as I planned to fix it with the third hose which goes into T piece but now as I will remove T piece I am not sure do I need Y pice at all, I could just connect those two hoses, at the same place behind the table, quite enough high from water level and job could be done..

And pretty confused how other BUKH DV20 what I can find when google, all of them have hose straight from thermostat housing into exhaust elbow.... (just write "bukh dv20" into google and you will see, all of them have that short hose, connected to exhaust elbow directly from thermostat housing..)

[Brian & Glenda]

Hello Dolac,
I get more than a little confused in the discussion of T pieces and Y pieces, and I have a DV36 instead of a DV20 ... My waterlock itself is more of a U shape although the fitting where the vacuum breaker hose joins the exhaust pipe is T shaped; but I have never seen a DV20 or an LM28 or the manuals for either!

That said: I believe that only the raw/sea water cooled Bukhs have a hose straight from the thermostat housing into the exhaust elbow. If yours is raw/sea water cooled ... I expect that may be acceptable provided that it meets the criteria quoted below, as copied from the Bukh DV36/48 workshop manual (and included in my previous post), which states:

"When choosing exhaust arrangement, find out first whether the placing of the engine in proportion to the water-line requires installation of Water Lock system.

"The water-line must under no loading or inclination conditions come over or flush with the point where the hose from the thermostat goes down into the exhaust bend without using the BUKH Water Lock Exhaust System which protects against penetration of water in the cylinders of the engine because of the pipette effect whiech (sic) may arise, if the placing of the waterline is as described above.

"The fitting of exhaust system with dimensions for fitting of BUKH Water Lock system is shown on the sketches overleaf. Please note the difference of the vacuum hose for freshwater cooling and sea-water cooling functions as by-pass for the sea-water besides functioning as pipette breaker.

"If it is not necessary with the Water Lock system, fit the exhaust pipe so that water cannot be gathered in it, i.e. it must not hang in a curve downwards.

"At the same time the exhaust should be lead out astern and attention should be paid to the stern wave, and therefore the measure "C" on the sketch should be observed in any case (see page Y 9)." (Page Y 9 is the third page of the above attachment, and the measure C is the distance of the center of the exhaust outlet above the waterline, and that measure is "min 50mm")

The next paragraph discusses the Sound Deadening Functions and Components, and the paragraph following that offers that "The dimensioning of the exhaust system (for DV36/48) is 1 3/4" in contrast to 1 1/2" for DV10 and DV20." Thus I suspect that the above is applicable to DV10, DV20, and DV36/DV48. A copy of the above, and these following paragraphs are page one of my attachment above.

I hope the link in my preceding post works. I was expecting to see the documents themselves posted in the forum, not a Dropbox link; but perhaps you were able to access them? Please DO let me know if the above link does not give you access, and I'll make another attempt to post them. I can see the attachment when I click on the link, but it is my Dropbox and don't know if other viewers can extract documents from it unless I give them explicit permission to do so. I didn't give any such explicit permissions for viewing, but I don't know if that means everyone can see that document, or no-one can!

Hope you get home safely soon,
Stay healthy,

Brian

[dolac]

Dear Brian,

sorry if I confused you. So lets go once again, I am a second owner and I am pretty sure that the previous owner didn't do any modification on those hoses.. As I can't reach my boat soon, I would like to know what are my options before I go on the boat next time, I did some drawing, not the best but guess you all might understand better as I don't have pictures of the engine in my phone

On my LM28 with BUKH DV20 there is direct sea water cooling, there is impeller that suck the water and push it through the engine and out on exhaust of course. Suddenly, last summer, both Y and T part (small, I even don't know how would I explain that thing but small tiny part on what I have to attach hose) got broken at the same time (I guess when I was fixing Y part and was moving the rubber hose, suddenly I broke the tiny part on T part as well)

Engine on LM28 is way above the water line.. Anyway, now I am thinking about other option, so here are my pictures and please help me to understand better what is the purpose of the hose that goes from Y part to T part. In case I don't need that hose, I would leave hoses that go from thermostat into Y part (even then there will not be three exits anymore but just connection between those two hoses) and remove the T part and its hose.


I really wish this drawing can help you to better understand how does it look like on my boat.. And mostly what I google about DV20, all of them have direct hose from thermostat housing into exhaust elbow.. I don't need to do it directly if I can remove third rubber hose that goes from Y part into T part.

T part is metal cylinder with that tiny thing on which I attach rubber hose, and on the pictures in my previous posts you can find how does it look like.. New idea (if I can't make direct hose from thermostat int elbow exhaust) is to remove T part completely, and put new exhaust hose. Instead of Y part just put connector to connect those two hoses. Anyway, there is no any vacuum or some valve there.





This is the picture of original Y part I have found on my phone, it is the simplest part made from brass.. Here I have found leaking and as soon as I touched, it just fell off..





Hope so this COVID-19 will finish soon, so I will be able to fly back to Croatia, I need to clean the hull and put new antifouling as soon as possible.... But cannot move the boat until i repair this problem so that is why I am trying to find best solution before I go there..

[Sula]

Doolac,

As I've tried to explain before, the purpose of the Y and T parts, and the hose between them, is to ensure that water cannot syphon back into the exhaust when the engine is at rest. (If it can syphon in from the exhaust or the seawater inlet, it can get into the engine through the exhaust valves and cause very expensive damage.) That is the reason that manufacturers install such arrangements.  

It does not make any difference whether the engine is direct (seawater) cooled or indirect (freshwater) cooled.   It does not make any difference whether it is a Bukh or other make of engine.

When the engine is running the water is being pumped through the big hoses, through the Y part, and some of it escapes down the thin hose and out through the T part into the open end of the exhaust 

When the engine is stopped, because the Y part is high up the water tries to drain downward, and sucks in air through the T part, the hose and the Y part. With air inside the big hoses, there is no continuous column of water and therefore water cannot syphon in to the exhaust and risk the engine.

If you were sure the point where the main water flow is injected into exhaust elbow was at least 15cm above the water line then you do not need the Y and T part. (But I would fit something similar anyway.)  Like this -

lmowners.proboards.com/attachment/download/519

If the water injection point into the exhaust elbow is not at least 15cm above the waterline (or you are not sure it is) you must fit the Y part (or an equivalent, such as I've linked to above).  You do not need the T part, as instead of having outlet of the thin pipe in the exhaust, you could run the thin hose instead to either outside the hull (but well above the waterline) or inside the cockpit, similar to left hand version in the picture below; or alternatively with a replacement for the Y fitting with one that has a one-way valve in it, like the right hand version in this picture  -

lmowners.proboards.com/attachment/download/518


Looking at the following drawing it seems that the exhaust elbow water injection point is not much above the waterline.
lmowners.proboards.com/attachment/download/542

 

[Sula]

Apr 22, 2020 19:58:46 GMT Sula said:

Doolac,

As I've tried to explain before, the purpose of the Y and T parts, and the hose between them, is to ensure that water cannot syphon back into the exhaust when the engine is at rest. (If it can syphon in from the exhaust or the seawater inlet, it can get into the engine through the exhaust valves and cause very expensive damage.) That is the reason that manufacturers install such arrangements.  

It does not make any difference whether the engine is direct (seawater) cooled or indirect (freshwater) cooled.   It does not make any difference whether it is a Bukh or other make of engine.

When the engine is running the water is being pumped through the big hoses, through the Y part, and some of it escapes down the thin hose and out through the T part into the open end of the exhaust 

When the engine is stopped, because the Y part is high up the water tries to drain downward, and sucks in air through the T part, the hose and the Y part. With air inside the big hoses, there is no continuous column of water and therefore water cannot syphon in to the exhaust and risk the engine.

If you were sure the point where the main water flow is injected into exhaust elbow was at least 15cm above the water line then you do not need the Y and T part. (But I would fit something similar anyway.)  Like this -

lmowners.proboards.com/attachment/download/519

If the water injection point into the exhaust elbow is not at least 15cm above the waterline (or you are not sure it is) you must fit the Y part (or an equivalent, such as I've linked to above).  You do not need the T part, as instead of having outlet of the thin pipe in the exhaust, you could run the thin hose instead to either outside the hull (but well above the waterline) or inside the cockpit, similar to left hand version in the picture below; or alternatively with a replacement for the Y fitting with one that has a one-way valve in it, like the right hand version in this picture  -

lmowners.proboards.com/attachment/download/518

 
Looking at the following drawing it seems that the exhaust elbow water injection point is not much above the waterline.

Attachments:

[dolac]

Thank you Sula, I do understand your explanation better and I will start to find someone who can make me new T part as rest of the parts I have, even in the links you sent me it is different in the pictures and what do I have.

But need to say again, when I am thinking, even there is T and Y part, the water still can go to the exhaust/muffler while engine is at rest, right?

Anyway I will go try to find someone who can make new parts and replace it as soon as I will be able to go back to the boat