Bukh DV20 Exhaust elbow

[Mistroma]

Ok. As I said there were no washers when I undid my flange nuts but there clearly are in the Parts manual exploded view.

I am now in the process of trying to build a dam around the thermostat housing to fill with diesel to soak the bolts. I am using an old wheelbarrow inner tube. It wont be possible to seal off the bottom to get diesel into the bottom gasket, but will at least allow diesel to possibly get down the bolts and the middle gasket. If this doesn't work then there is room to get the manifold off sideways thankfully as long as the nuts want to move.

It will be difficult to get diesel down to the threads. The bolts have a 60mm unthreaded section before the 20mm threaded part which actually screws into the manifold. Have you already tried localised heat on the manifold close to the base of the thermostat housing?

At least manifold removal is a quick and easy job and taking the manifold home to complete the job isn't a big deal.

Head removal is a lot more time-consuming but I can't see any reason to do that unless you were planning that work for another reason. I couldn't understand why others suggested it.

 

[Poignard]

As I suggested before, your pentrating oil or diesel would stand a better chance of arriving where it is needed if you scraped away the rust, dirt and paint around the joint between the thermostat tower and the cylinder head and around the hex-headed screws.

 

[rotrax]

As I suggested before, your pentrating oil or diesel would stand a better chance of arriving where it is needed if you scraped away the rust, dirt and paint around the joint between the thermostat tower and the cylinder head and around the hex-headed screws.

Waste of time if it is like the one I removed from our Kiwi boat.

After a week in a bucket of diesel, totally submerged the threads at the manifold end WERE wet.

But the long shanks of each cap screw were completely dry. The reason was simple - the shanks, top quality HT Steel were rusted into the grey cast iron thermo housing.

It was the aplicacation of substantial heat with a big gas torch - oxy-acetylene would be favourite if available - to the full length of one corner of the thermo housing/cap screw while moving gently back and forward with a half inch drive ratchet, 1/2 inch to 3/8 adaptor and a top quality 3/8 drive allen key socket that got it moving.

There is NO WAY I would ever use such heat/gas torch in the confined area of a yacht engine space.

But with the manifold screwed tight with coachscrews to a 6X6 beam as I had no firmly fixed large vice, it was an easy job.

Penetrating liquid WILL NOT travel down 60mm of red rust. 50 years of fixing antique vehicles means I know that for a fact. Heat, however, WILL break down the bond between the long screws and the thermo housing. Well it worked for me. When the thread was clear on each screw, they could not, even with the head clamped in a vise grip, be pulled from the thermo housing.
They had to be punched out with a 5mm pin punch from the bottom and the holes cleaned out with a 7mm drill bit turned by hand in a vise grip.

1mm of solid rust between screw and housing!

Grey iron and HT Steel have different melting temps, dull red did it for me! Screws stayed good, rust released its grip.

Good luck.

 

[joyfull]

Waste of time if it is like the one I removed from our Kiwi boat.

After a week in a bucket of diesel, totally submerged the threads at the manifold end WERE wet.

But the long shanks of each cap screw were completely dry. The reason was simple - the shanks, top quality HT Steel were rusted into the grey cast iron thermo housing.

It was the aplicacation of substantial heat with a big gas torch - oxy-acetylene would be favourite if available - to the full length of one corner of the thermo housing/cap screw while moving gently back and forward with a half inch drive ratchet, 1/2 inch to 3/8 adaptor and a top quality 3/8 drive allen key socket that got it moving.

There is NO WAY I would ever use such heat/gas torch in the confined area of a yacht engine space.

But with the manifold screwed tight with coachscrews to a 6X6 beam as I had no firmly fixed large vice, it was an easy job.

Penetrating liquid WILL NOT travel down 60mm of red rust. 50 years of fixing antique vehicles means I know that for a fact. Heat, however, WILL break down the bond between the long screws and the thermo housing. Well it worked for me. When the thread was clear on each screw, they could not, even with the head clamped in a vise grip, be pulled from the thermo housing.
They had to be punched out with a 5mm pin punch from the bottom and the holes cleaned out with a 7mm drill bit turned by hand in a vise grip.

1mm of solid rust between screw and housing!

Grey iron and HT Steel have different melting temps, dull red did it for me! Screws stayed good, rust released its grip.

Good luck.

Ok. I think I am in the same position. Everything I have looked at on the engine so far is completely seized. I will try the rubber dam soak insitu for a couple of days, then go for attempt to remove the manifold. At least I have access to a decent torch with a nice tall bottle of gas.

 

[joyfull]

"Grey iron and HT Steel have different melting temps, dull red did it for me! Screws stayed good, rust released its grip."

Does dull red refer to the glow of the thermostat housing after applying plenty of heat?

 

[Malish]

this thread is making me want to ease and then copper grease in turn all my DV24 thermostat bolts next time I am on the boat doing some maintenance. I had them off 3-4 years ago without issue but I am starting to feel paranoid about the next occasion ;-) Yes I know to take care on retightening with grease on the threads but I suspect Bukh have built in a wide torque tolerance.

 

[rotrax]

"Grey iron and HT Steel have different melting temps, dull red did it for me! Screws stayed good, rust released its grip."

Does dull red refer to the glow of the thermostat housing after applying plenty of heat?

Yes. I bought the full length of a screw hole to dull red, turned off the torch and set to with the allen key socket. On one I had to heat a second time, the other three came out OK.

 

[James_Calvert]

Yes. I bought the full length of a screw hole to dull red, turned off the torch and set to with the allen key socket. On one I had to heat a second time, the other three came out OK.

Just curious,

did the thermostat survive this treatment, or were you replacing it anyway?

 

[rotrax]

The wax did not leak from the pellet and it opens in a pan of water on the cooker and closes when cool, so yes, it survived. Even the rubber seal was undamaged.

I am the ultimate recycler. I pulled the pistons, did the valves and seats, freed off and removed the stuck piston rings, cleaned the piston grooves and rings and re-used them. Put the old big end shells back too. I honed the cylinder liners in situ.

Fortunate the install on our Kiwi boat allows the sump to be removed with the engine in place.

Forewarned about the cost of Bukh parts in NZ I took a head gasket with me, half the price here.

Water ingress had caused the ring trouble, also knackered the injector nozzles.

Touch wood- going really well now.

 

[joyfull]

Quick update.

Still filing away the engine anode, try and fit then grind some more (scraping around with screwdriver inside had little effect - would be more effective if I undid the gear/throttle quadrant to get straight access). Not much anode left now - shorter and thinner.

Soaking the thermostat housing insitu with the rubber dam. Not expecting it to work, but did have a feel of the manifold nuts which are as expected very solid so not looking forward to that exercise.

Rivalredwing: yes suggest you reseat your thermostat housing on your DV24 before too long, though I think mine hasn't been moved for many many years.

Just thinking about the fuel system as well. Original steel tank looks sound and holds diesel. There is a glass Fram filter in the fuel line that I can clean. I think probably best to leave the final filter on the engine as access is difficult and don't really want to disturb.

Considering the lack of regular use over the last 44 years I was also thinking about residue in the fuel tank. It looks like there is some sort of drain under the tank away from the tap ( see pic below). Can't feel much like a head on the bolt. Looks a bit mauled. I wonder if I should have a go at it. Though the tank is half full with 20 litres so not sure what might come out and whether I could get the bolt back in place. Any advice very much appreciated as always.

 

[Malish]

Drain the tank before undoing the bolt, you'll likely regret it for some time if you don't.

One job at a time if I were you too.

 

[Catalina36]

Rig a hose from your galley pump into the seawater feed to the engine via a 1/2" stopcock and a T piece, then finish each run of the engine with a 1 minute burst of fresh water with the seacock closed. Your exhaust elbow will live longer than you will and so will the anode in the heat exchanger.

 

[sgr143]

this thread is making me want to ease and then copper grease in turn all my DV24 thermostat bolts next time I am on the boat doing some maintenance. I had them off 3-4 years ago without issue but I am starting to feel paranoid about the next occasion ;-) Yes I know to take care on retightening with grease on the threads but I suspect Bukh have built in a wide torque tolerance.

This all makes me very grateful that I take the thermostat out of my DV20 at the end of every season, so that I can more easily thoroughly flush the engine with antifreeze /corrosion inhibitor for the winter lay-up. It means those long bolts get taken out, greased and put back in twice a year. I think the previous owner may have had some trouble with them because several of the threads are helicoiled.

 

[LittleSister]

this thread is making me want to ease and then copper grease in turn all my DV24 thermostat bolts next time I am on the boat doing some maintenance. . . Yes I know to take care on retightening with grease on the threads but I suspect Bukh have built in a wide torque tolerance.

I thought that torque specifications assumed greased threads - i.e. related to tension, not friction. Am I mistaken?

 

[vic008]

Torque specs assume dry threads.

 

[joyfull]

Drain the tank before undoing the bolt, you'll likely regret it for some time if you don't.

One job at a time if I were you too.

Anode and new exhaust elbow fitted and engine running fine. That's a relief.

There is enough water coming through the exhaust (not very much - but the same as before) so I can now get back to fitting the diesel heater and contemplate another sailing season.

I have decided to leave the thermostat housing and fuel tank purge for another year. Thanks to your advice I now understand what is needed and the enormity of the job of liberating those four long bolts.

Marine engineering with a 44 year old engine that has not been regularly maintained in recent years is not my favourite hobby. Hopefully they will be opening the golf course next week.

Thank you all for your support and advice and living through this with me.

 

[Malish]

If you wish to make a quick check for crud in the bottom of the tank the a Pela type oil extraction pump can often be employed.

 

[ScillyPuffin]

Having now had a chance to get started on this elbow replacement job, there were indeed spring washers on the manifold flange bolts. I've been very lucky and the fittings were all very easy to remove, bar taking the elbow itself out of the flexible exhaust hose. That was hard work!

 

[joyfull]

Having now had a chance to get started on this elbow replacement job, there were indeed spring washers on the manifold flange bolts. I've been very lucky and the fittings were all very easy to remove, bar taking the elbow itself out of the flexible exhaust hose. That was hard work!

Excellent. Mine is running ok. I have given up on the thermostat for this year.

Not much water passing through, though I have only had the boat since last year so I do not know what to expect. It spits away and occasionally throws out a bit more. If yours in the water and back running maybe you could confirm how much to expect. I am not sure if the forum takes videos as it always asks me to compress my still pixs. I guess a link to vimeo or YouTube upload would work. I will try from my end.

 

[seumask]

This all makes me very grateful that I take the thermostat out of my DV20 at the end of every season, so that I can more easily thoroughly flush the engine with antifreeze /corrosion inhibitor for the winter lay-up. It means those long bolts get taken out, greased and put back in twice a year. I think the previous owner may have had some trouble with them because several of the threads are helicoiled.

Ditto Annual job to empty the raw water after running on fresh for 5 mins and then filling with antifreeze via the thermostat housing on our DV24. Emptying done via the drain plug on the port side of the engine as its mounted in the boat. I keep the 2 thermostat housing bolts nicely greased, although this does not sound like the same set up described by others.
This year Ryde-Lyme'd the engine on lay up which I'm hoping got rid of the residue of pencil anodes, a few over the last years had not re-emerged on removal!