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Narrowboating Quickies – Webasto Heater Exhaust Rehash

Since rebuilding the burner for the Webasto water heater on board nb Tanya Louise, I figured it was about time I sorted the exhaust out as well. The standard Eberspacher / Webasto type exhaust system components are shit. Nothing is properly gas tight, no matter how you build the system, due to how the pipe is constructed – it’s spiral ribbed stainless flexi tube, and even proper clamps don’t exert enough force to create a gas seal on the fittings, leaving gaps in the spiral for exhaust to leak out. Unfortunately I don’t have a photo of the old exhaust setup – it was however awful.

So to fix the problem of the messy setup, and to fix the issue of leaking exhaust gases, I got to work creating a custom system from 22mm copper pipe, brazing all the joints together.

Completed Exhaust
Completed Exhaust

Here’s the completed system, matched to the location of the heater unit in the engine bay, and the exhaust skin fitting. The ends of the pipe are expanded with a hydraulic tool to allow them to fit onto the heater & skin fitting, these being too large for 22mm pipe normally.

Brazed Muffler
Brazed Muffler

The muffler is also fully brazed to keep exhaust gases inside the exhaust. These are supplied just crimped together as they’re intended for use under vehicles. A sealed marine grade exhaust silencer is available, but very expensive. Again the copper pipe ends are expanded with the hydraulic tool to allow them to fit into place on the stainless tails. Brazing was done with 55% silver brazing rod.

Fibreglass Wrap
Fibreglass Wrap

To keep the heat away from sensitive parts in the engine bay, the entire assembly has been wrapped in fibreglass insulation tape, and secured with stainless steel ties. It’s important to use only stainless in these applications – the fibreglass wrap will hold any moisture in contact with all the parts, and mild steel will rapidly convert back into Iron Oxide 😉

Heater End
Heater End

The heater itself is on the other side of the plywood board in the photo, the cooling water pipework can be seen on the lower left, along with the diesel dosing pump. The main fuel tank is just visible in the bottom right corner.

Skin Fitting Connection
Skin Fitting Connection

The other end is sized for a snug fit onto the exhaust skin fitting, just astern of the old oil cooler. This is set to be removed at some stage, and be replaced with an engine bay blower for ventilation.

Silencer
Silencer

In the corner, next to the bulkhead sits the silencer.

In all, this setup also made the heater quieter, probably due to the longer length of exhaust pipework, which is now about 1.5 metres from the heater outlet to the skin fitting. This is a bonus – the exhaust of these heaters without any silencing sounds like a jet engine!

 

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Webasto Thermo Top C Burner Mesh Replacement

It recently became rather obvious there was something amiss with the water heater on board nb Tanya Louise – lots of smoke from the exhaust, failed starts, and finally a total refusal to start altogether.

Combustion Chamber
Combustion Chamber

On disassembly, it was clear the burner was the issue – above. The mesh at the back where the fuel inlet enters the burner is completely knackered. The burner in these heaters, like the Eberspachers, is evaporative. Diesel fuel is led into a high-surface area mesh tube, or pad in this case, where it is vaporized to be burned with air from the combustion blower. Initially, this heat is provided by the glow plug, but after the unit has fired, the heat of combustion keeps the process going.

Burner Deposits 1
Burner Deposits 1

As can be seen at left, there’s quite the build-up of solid carbon around the burner, blocking most of the mesh & the air mixing holes in the tube. This was also after I’d removed most of the fouling!

Burner Deposits 2
Burner Deposits 2

 

More deposits are seen on the other side, along with some of the air mixing holes.

 

Inlet Plate
Inlet Plate

Now, the problem is that these burner units are not meant to be refurbished. These units are considered by the manufacturer to be disposable, and are welded together as a result. There’s another issue – I don’t believe that a component costing around £295 in a service kit as DISPOSABLE. There’s nothing wrong with the structure of the burner at all – it’s Stainless Steel, and is in good shape with no heat damage. The only fault is with the mesh being burned out from long use. Luckily, replacement burner meshes are available on eBay from Chinese suppliers, so on with the repair!
One of the welds that needs to be removed can be seen here next to the glow plug well, and there are 3 spots around the rim that are welded in this way. Delicate use of a grinding wheel on the welds allows this to be removed intact.

Burner Tube
Burner Tube

Once the welds have been ground off, the fuel inlet plate with the mesh can be pulled from the back of the burner. It’s a good idea to add some registration marks to both pieces before they’re separated, so they can be put back together in the same orientation – required for both the glow plug wiring, and the fuel inlet tube to line up with the hole in the heater housing. The ring of slots visible around the edge of the tube are the combustion air inlets, and the air is directed through a ring of holes in the combustion chamber, quite similar to a turbine engine combustor.

Old Burner Mesh
Old Burner Mesh

Now I’ve got the back of the burner removed, the clogging is much easier to see. The mesh itself has clearly been subject to very high heat, and is partially burned away, along with most of the surface being clogged up with coal from incomplete combustion. It’s difficult to see here, but the mesh pad is held in place with a large circlip around the edge, all will become clear after cleaning. All the hard carbon needs to be scraped out of the cup, clearing the way for the clip to be pried out of it’s groove.

Cleaned Cup
Cleaned Cup

After a lot of scraping with the sharp end of a small screwdriver, the cup has been relieved of enough carbon to be recognisable again! The fuel inlet tube is in the centre of the backplate, with the circlip groove around the edge. Crimp marks are visible on the top edge of the groove – I think Webasto actually crimps the ring in place after fitting, which does make removal a bit more tricky, but I did manage to get it out intact, even if heat has removed most of the heat treat from the steel – making it soft. Be careful here!

New Mesh Fitted
New Mesh Fitted

Fitting the new mesh is pretty simple. These have a sharp pressed side & a convex side, the convex side must face outwards from the cup. The circlip is visible around the edge of the mesh, with the ends next to the glow plug well. Make sure that the clip is equally spaced around the glow plug  to make sure it doesn’t foul the plug when that’s replaced.

Now comes the issue of reattaching the cup to the back of the burner tube. I didn’t want to re-weld, since the assembly is Stainless Steel & I don’t have a TIG setup at present. I do have some stainless wire for the MIG, but this would also leave me with the issue of future disassembly if the mesh needs replacement again. Brazing is also not possible for the same reason – once brazed, it’s a permanent assembly.

Burner Reassembled
Burner Reassembled

Since there are some tabs that were never welded, I decided to drill & tap M2.5 through these & use 304 stainless screws to hold the components together. This should allow removal in the future if required.

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nb Tanya Louise – Hydraulic Hose Failure

Well it was only a matter of time until we had a major failure of the onboard hydraulic system on board the boat, and this weekend proved to be that point in time.

Hose End
Hose End

This is what remains of one of the main hoses to the propulsion motor, the fitting has been blown off the end of the hose! This occurred when I moved into reverse to stop the boat for oncoming traffic, and suddenly I lost all drive. The end result is a bilge filled with hydraulic oil, and zero power for manoeuvring.
The hose outer cover has been cut through by the fitting, like it had been sliced through with a knife, what remains of the inner liner & outer sheath is still in the fitting:

Fitting
Fitting

Here’s the end of the offending fitting, with the remains of the hose. I suspect this termination wasn’t done correctly in the first place – either the swage was done too tight, cutting into the hose, or the fitting was never pushed all the way onto the hose before swaging, resulting in reduced strength.

Now comes the effort of cleaning out the roughly 40L of oil now in the bilges, refilling the oil tank & getting new hoses made up.