Bukh Exhaust question .

So I'm wondering is the diameter of the pipe off the exhaust flange critical or would it not matter if it was increased to go over the ss elbow rather than inside it as before?

A small difference in the diameter of the exhaust should be no problem. If you are talking about a larger dia of pipe to slip over pipe that is already in the system, go for it. Most of the older engines allow a fair bit of flexibility when installing.

And while on this subject does the length of the rubber exhaust pipe from the blue water mixer to the transom outlet affect engine power or economy? On mine there seems to be around 3 meters which goes up in a loop above the waterline, then down to floor level again and finally up again the the outlet? Does this seem a lot or normal?

If that is how much exhaust hose is needed to get from the engine to the exhaust outlet in the hull, then it's normal.
If the above waterline loop was fitted by a previous owner I would accept it as a necessary modification.
You have a small engine that is pretty economical as it is and 10 HP is all you are ever going to get out of it.
Reliability is the number one factor to be looking for in a yacht engine. Not speed or power.

gary

I just figured out how to insert photos...

The stainless water in elbow looks good.
You could buy a new iron flange or get one made in s/s with a bit of pipe zapped into it to which you could weld that elbow. The first bit of flex pipe is after exhaust cooling.
Stick with the blue plastic water trap.

As the main square part with the bolt holes is absolutely solid I thought I would just cut off the round pipe section and have a new piece welded on. I just wasn't sure whether to try and keep the same diameter and go inside the ss elbow or have it made larger to go outside...

Looks like it was a threaded joint and the steel part has completely rusted out and the ss thread has also coroded away. I would cut both old threaded parts off and weld new ones on. Commonly found plumbing fittings. Keep the mild steel part mild steel if stainless it might eat the manifold.

I would just make a new flange from stainless and insulate it from the motor with a gasket.

If your installation allows the fitting of a one piece unit,, do away with the thread.

Ok, so I got the pieces welded up and they look fine.
I put them on today but am still getting an issue.
There has never been a great deal of water coming out the exhaust on idle but now is even less but still a bit. If I give it some revs in neutral it spurts plenty of water out initially then a bit less.
I wasn't happy with how it looked but temp was still ok so I took her out just around the marina and basically when she is under load most of the water stops coming out the exhaust and there is some dark grey smoke, not a huge amount and there seems to be plenty of pressure behind it (it doesn't come out in a cloud, more straight out and it's not thick smoke).
The temp was also rising, again not a lot but getting just over half and she would always be just over a quarter before this issue. It could have continued to rise I am not sure as I brought her back in.

Any ideas from the Seabreeze diesel mechanical team?
thanks

Raw water cooled so no heat exchanger, new impeller and I think gear driven pump?
I read that maybe dark/black smoke can be caused by overloading like maybe something wrapped around the prop but would overloading cause lack of water flow?

I am also trying to think if we have used the boat since we hauled her out last and could anything have happened during or after the haul out to give these symptoms?

Hi Cockpit
Cograts on the exhaust fix.

As to the cooling water flow problem.
Water in- water through- water out.

Water in.
Check inlet cock for blockage by plastic bag or sea life. Remove hose from cock and open.
Check line to strainer. remove at strainer and open cock.
Check strainer. Clean strainer and with top off open cock.
Check line from strainer to cooling water pump. Remove line at pump and open cock.
Water through.
As Ramona suggested . Remove line from pump and run engine.
Remove line into block and run engine.
Remove thermostat and check. A stuck closed thermostat will cause the engine to warm up excessively. (warm up!)
A stuck open thermostat will not show any real symptoms. But it is worth pulling it and having a look. New gasket can be made from corn flakes packet cardboard.
Water out.
Remove water outlet line (from block to exhaust inlet) run engine and check flow.
Check inlet nipple on exhaust is not blocked or restricted. Remove hole and poke nipple interior with a screwdriver.

If all of those things are clear , the only other thing that would restrict cooling water flow would be calcium/grunge buildup in the internal cooling passage of the engine block and head. That does not happen suddenly as seems to be your case.

You say" just over half and she would always be just over a quarter before this issue."
How many degrees are we talking about?

I would suggest that the cause, if not a blockage is, somehow , the impeller.
Wrong size?
Not fitted properly?
Slipping on shaft?

And lastly, hopefully , as you said, "There has never been a great deal of water coming out the exhaust on idle"
you don't really have a problem and are overthinking it.

All the best
gary

Cocky...My old engine was a 10hp Bukh. There was never much of a water flow, it just used to spit really,
but I didn't get an overheating problem. I did however get smoke blowing every time I throttled up, even
a gentle rev increase. The smoke only lasted until the engine got to the desired revs then disappeared but
that was coupled with slow starting ( it had to build revs before firing ) so I knew the compression was failing.
Ultimately I replaced the Bukh with a Beta 14hp twin. Everything increased dramatically, exhaust water flow,
power, revs. speed. No smoke of course and instant starting. The old Bukh had just got too tired.

Cockpit
I too have a raw water cooled Buhk DV10.
I have been told they don't pump much cooling water. This becomes obvious when you remove the outlet line from the pump and see the orifice size is a lot less than the 1/2" id skin fitting, hose etc.
I checked everything as per the previous replies. I don't have an overheating engine. Only thing left to do is clear the buildup in the water jacket. When I replaced the zinc I had to chip away salt build up as instructed by the tech at Buhk to fit the new anode.
Next time I'm on the boat I will try and remember to video my water discharge and upload if my computer skills allow.

Success! (I think).

Thanks again for all the help especially Greg on the phone.
I managed to get on the boat today and after a bit of detective work found this:


This is the hose after the impeller pump which goes to a metal Y piece to the block and thermostat housing.
Obviously a build up of salt or calcium which would have taken some time to get like that I think as the plug was over 1 cm long and as can be seen was only letting through a tiny amount of water. The metal piece it went onto was the same. I'm amazed that I had decent water flow at all up to the current problem...
Anyway, a quick clear out and now she throws water out better than ever
I ran her on the dock in neutral and in gear (but didn't go to normal cruising revs in gear) and she seems great, no smoke at all. I will try and take her out tomorrow just to make sure she is good under load and normal revs but am keeping fingers crossed all is good now.
I am going to replace the water hoses with new while I am at it.

So if anyone is getting restricted water flow check your hoses...

Cheers

Well done Sherlock!!

So I took her out today and gave her a good run around the Marina and all is good.
Not a wisp of smoke, perfect temp and Niagara falls out of the exhaust (well not quite ).
I enjoy learning new things and this is just one more thing that makes me more confident on the boat.
Cheers

OK Ramona I understand. I didn't get Cockpits problem but I did get a build up of zinc around the the engine
anode which I had to chip off to get the anode in. So now I've got a fresh water cooled engine where am I
likely to get a calcium build up and what do I do about it ??.