Heat exchanger repair

[MagicalArmchair]

I had an idea the exhaust elbow was blowing from the bottom a little, and after hearing some horror stories, I wanted to swap the elbow out for a SS one with a composite gasket. I took the elbow off last week and had a chance to inspect the face of the heat exchanger today. On removing the old steel gasket, and cleaning the surface up, I was left with this mess.

What would you suggest to fill and fix this? At least I caught it before it ate right the way through!!

 

[oldgit]

I had an idea the exhaust elbow was blowing from the bottom a little, and after hearing some horror stories, I wanted to swap the elbow out for a SS one with a composite gasket. I took the elbow off last week and had a chance to inspect the face of the heat exchanger today. On removing the old steel gasket, and cleaning the surface up, I was left with this mess.

What would you suggest to fill and fix this? At least I caught it before it ate right the way through!!

Looks the studs are still secure and will bolt up tight.
One of the good quality twin pack chemical metals might well do the job.

A cast iron exhaust riser on my boat started to hint at problems within, Rust streaks.eventually the clamp securing the riser onto the exhaust failed and the job could not be put off .
The riser had been repaired at some point in its life with chemical metal, had the boat for five years and the repair had obviously been done before that, so it probably lasted for 5 + years.
Other than thats its manifold off .

 

[jwfrary]

If your after a long lasting repair, take it to an old fashioned radiator shop the time that still brazes and repairs rads. They should be able to build it back up.

You could have a go yourself all you need is a propane torch. And Ali brazing sticks.

don’t try welding it will crack the castin

if I was in the middle ofknow where I would be breaking out the chemical metal for a temporary repair.

best to take the core out and inspect the rest as it looks to me like there been some electrolysis....possibly this is of course the disadvantage of stainless elbows going forward!

Good luck.

What engine is it hrs and age just for historical record!

 

[MagicalArmchair]

The engine D2-55 A. I guess to take the heat exchanger off I will need to drain down both the fresh and raw water systems? Any tips for removing it?

I’ll take it off and see what engineering shops locally can do.

 

[superheat6k]

I had a similar looking lousy surface on my turbo charger outlet face. I removed the studs and milled the surface back to clean metal right around the face.

An hours work for a well equipped machine shop.

 

[jwfrary]

The engine D2-55 A. I guess to take the heat exchanger off I will need to drain down both the fresh and raw water systems? Any tips for removing it?

I’ll take it off and see what engineering shops locally can do.

bit of penetrating fluid on the studs before you remove the nuts, go a 1/2 turn everywhere first before you remove completely to keep things even.
Have a cup ready to receive the studs/nuts

wet vac can be handy as there’s always a bit of residual to make a mess

 

[MagicalArmchair]

I had a similar looking lousy surface on my turbo charger outlet face. I removed the studs and milled the surface back to clean metal right around the face.

An hours work for a well equipped machine shop.

At the bottom, there isn't enough metal left I'm afraid.

How about this (from my good friends in the Bavaria forums), in situ.

• Get hold of some of this jollop (HighHeatEP | JB-Weld), good to 230 degrees C.
• Grid the areas back with a dremel to bright metal.
• Build the eaten away areas back up.
• Use a blind flange with release film on it to make the mating surface nice and flat and squish the goo in. Bolt that guy down, allow to set.
• Remove blind flange.
• Tidy up and grind down any overage.
• Keep a weather eye on it, remove next season and check thoroughly.

Go sailing?

 

[PaulRainbow]

At the bottom, there isn't enough metal left I'm afraid.

How about this (from my good friends in the Bavaria forums), in situ.

• Get hold of some of this jollop (HighHeatEP | JB-Weld), good to 230 degrees C.
• Grid the areas back with a dremel to bright metal.
• Build the eaten away areas back up.
• Use a blind flange with release film on it to make the mating surface nice and flat and squish the goo in. Bolt that guy down, allow to set.
• Remove blind flange.
• Tidy up and grind down any overage.
• Keep a weather eye on it, remove next season and check thoroughly.

Go sailing?

This sounds like it might work, but, it would be better if, instead of a temporary flange, you made a permanent one. Make it 3 or 4 mm bigger than the flange, all around the outside, coursely key the side that will bolt up against the heat exchanger and Dremel the heat exchanger back to clean metal a few mm back from the mating surface. Put plenty of JB weld on the mating surface, bolt it up tight, put some JB weld around the outer edge to bring the heat exchanger surface up to the edges of the new flange. Let it all fully cure, tidy it up with a file and and paint over the repair, then fit the elbow with a new gasket, lightly greased on both sides.

 

[MagicalArmchair]

This sounds like it might work, but, it would be better if, instead of a temporary flange, you made a permanent one. Make it 3 or 4 mm bigger than the flange, all around the outside, coursely key the side that will bolt up against the heat exchanger and Dremel the heat exchanger back to clean metal a few mm back from the mating surface. Put plenty of JB weld on the mating surface, bolt it up tight, put some JB weld around the outer edge to bring the heat exchanger surface up to the edges of the new flange. Let it all fully cure, tidy it up with a file and and paint over the repair, then fit the elbow with a new gasket, lightly greased on both sides.

Thanks Paul, this stuff has a working time of an hour as well - so plenty enough to mix it fully, squidge it into place and bolt it up. It could be a convincing long term repair. Being epoxy, will it create a barrier against galvanic corrosion also I wonder? I have a composite gasket anyway mind you, to try and prevent this happening again.

 

[superheat6k]

At the bottom, there isn't enough metal left I'm afraid.

How about this (from my good friends in the Bavaria forums), in situ.

• Get hold of some of this jollop (HighHeatEP | JB-Weld), good to 230 degrees C.
• Grid the areas back with a dremel to bright metal.
• Build the eaten away areas back up.
• Use a blind flange with release film on it to make the mating surface nice and flat and squish the goo in. Bolt that guy down, allow to set.
• Remove blind flange.
• Tidy up and grind down any overage.
• Keep a weather eye on it, remove next season and check thoroughly.

Go sailing?

With a working maximum of 230oC I would be worried the JB Weld would fail at higher engine power - a domestic oven gets to 250oC, your exhaust will be way way hotter than that.

How about a cast weld build up, then mill back to restore the gasket face ?

 

[MagicalArmchair]

The exhaust elbow itself would not exceed 100 degrees C I suppose, however that is after water injection, what temperature would the exchanger reach at that point?

They also produce this stuff:JB Weld 37901 ExtremeHeat High Temperature Resistant Metallic Paste-3 oz JB Weld 37901 ExtremeHeat High Temperature Resistant Metallic Paste-3 oz: Amazon.co.uk: Car & Motorbike

I was concerned it may sag due to it being runny in viscosity.

 

[PaulRainbow]

With a working maximum of 230oC I would be worried the JB Weld would fail at higher engine power - a domestic oven gets to 250oC, your exhaust will be way way hotter than that.

How about a cast weld build up, then mill back to restore the gasket face ?

Yet, the green paint will only withstand 170 deg C. How do you suppose that survives "way, way hotter" than 250 deg C ?

Exhaust hose is typically rated up to 100c, i find it hard to believe that one side of the elbow can only be 100c max, yet the other side is way, way above 250c

I would respectfully suggest that you may be mistaken here.

 

[AndrewB]

In the past I've repaired a crack in the engine head with epoxy - an emergency measure, but it seemed to cope with the heat and pressure, and lasted until I could get another head.

However, looking at your photo, I do wonder about the internal condition of your head exchanger. Does it have a stack, and if so, have you checked it?

 

[MagicalArmchair]

No, I haven’t had it apart, and I would suggest now is probably a good time to bite the bullet and get it off.

Additionally, the below (found here http://www.darthaven.co.uk/userfiles/products/files/Technical data D2-55.pdf ) would suggest gas at that point (not sure where the turbo charger comes in!) can reach 570 degrees C at 3000rpm, leaving that epoxy technically under spec at the inside of the flange unless I am missing something?

https://imgur.com/qXRjudr

 

[jwfrary]

Quoted exhaust gas temps are generally for when the engine is operating at the propeller curve. That means that once you have a little fouling built up they can rise considerably.

Big MTU’s operate stout 650-700 deg at WOT and start de rating at 800deg

expoxy might get you home but isn’t really a solution!

 

[MagicalArmchair]

Quoted exhaust gas temps are generally for when the engine is operating at the propeller curve. That means that once you have a little fouling built up they can rise considerably.

Big MTU’s operate stout 650-700 deg at WOT and start de rating at 800deg

expoxy might get you home but isn’t really a solution!

Which puts me square back on your first idea @jwfrary of trying to get someone to braze it to build it up. The alternative is getting it machined down flat by removing the studs and getting the surface lapped (if there is enough flange left to facilitate that!). See below, the bottom is the most eaten away.

 

[rogerthebodger]

It is possible to weld cast iron but it does need care and skill.

welding cast iron - Google Search


We have a famous (Vasco da gama clock that was cast iron and was being vandalised.

Some of the guys at RNYC moved it and repaired it buy rewelding a lot of the broken bits.

The historic Vasco da Gama Clock - Durban Local History Museums

 

[MagicalArmchair]

It is possible to weld cast iron but it does need care and skill.

welding cast iron - Google Search

Its aluminum I'm afraid - and @jwfrary has counseled if I try and get it welded, its likely to crack the casting.

 

[rogerthebodger]

Its aluminum I'm afraid - and @jwfrary has counseled if I try and get it welded, its likely to crack the casting.

If its aluminium its it can be welded.

My cast aluminium heat exchanger corroded away when the O ring seals the end caps and internal tube stack.

One of my local welders built it up and I filed it back to the required profile.

A specialist welder /casting repair shop should be able to reweld and then file back flat

 

[jwfrary]

Its aluminium I'm afraid - and @jwfrary has counselled if I try and get it welded, its likely to crack the casting.

Its possible to weld aluminium castings, but requires additional skill above that of welding aluminium sheet or sections and so the result can be a little The other problem is the porosity of the casting tends to lead to poor weld characteristics. Best solution is to braze it especially for a DIY repair and its a little kinder to the casting as a whole.

It doesn't look like there's enough left to skim the flange without rebuilding the material at least in part. If you do skim it off then you might find your left with something that's much more difficult to repair.