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Old 28-04-2018, 07:22   #1
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Heat exchanger repair Braze/Solder?

Hi,

After a long winters rest I am back at it. Got the engine fired up today and ran perfectly. In checking around running engine with flashlight I noticed a couple drips, one rather serious from raw water hose, pump-> heat exchanger inlet.

I tried tightening up on the hose clamp but I could tell the leak wasn't going to be fixed like that. Used camera phone and saw that the leak was slow but persistent, almost looked like it was coming from hose.

Removed HX and put on bench. I can see where a previous owner cranked down on hose clamps and it almost looks like a snake bit. I can feel same thing on inside. Fairly confident this is source of leak. So I wire brush to get it clean and wiped back side of copper braze. There was a "wet spot". I waited 5 minutes and I could see moisture wicking back up to surface.


In the interest of time I'd like to attempt a repair. I have an oxy acetylene rig, although mainly for rosebud work. The inlet is either brazed or soldered to the outer shell. Wondering what you think would be appropriate material for this? I have 50/50 lead tin Kester, silicone bronze rod, silver solder.

My most immediate concern is repairing the "snake bite" but I suspect the inlet to shell joint is also not great and since I'll be applying a fair amount of heat to it, might as well be prepared to fix that too. A new HX is around $500 and I am unsure about delivery times. Boat goes in water in 2 weeks.
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Old 28-04-2018, 07:26   #2
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Re: Heat exchanger repair Braze/Solder?

Had very good luck having a professional radiator shop do this and even more complex repairs.
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Old 28-04-2018, 12:22   #3
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Re: Heat exchanger repair Braze/Solder?

Spot soldering has less chance of disrupting nearby joints. You could use an old damage control trick: Use a small drill bit to round out the holes, then put a stainless or compatible self-tapping screw into the, as short as possible, and bed it in JBWeld or a similar high-temperature epoxy. Obviously you want to protrude as little as possible into the tube. And for insurance, apply a 3/4" or so spot of the same epoxy inside the tube, so it is pressure sealed from the inside, as well as structurally sealed through. Belt and suspenders, no heat, no worries about alloy matching needed.
I have a tool that I repaired around 1964 with a thick epoxy called PC7 (used to come in a pair of matching 35mm film cans) that's still rock hard and stable. Marinetex is similar.
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Old 28-04-2018, 13:26   #4
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Re: Heat exchanger repair Braze/Solder?

You’ll want to use “silver solder”
Most heat exchangers are made of “copper nickel”
Heat can be an issue if your not experienced in this.
If you get it too hot you risk compromising the other joints.
If only concerned about the “snake Bight” use regular solder as it melts at a much lower temp. That should fill in the voids and with a good (undamaged) hose, and the proper clamp, should be fine
Hope this helps.
PS: had too re silver solder the exchanger on my generator a few years ago due to a bad factory joint. It’s been fine for 3 yrs now.
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Old 28-04-2018, 14:50   #5
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Re: Heat exchanger repair Braze/Solder?

Thanks, Was thinking silver solder. Want to avoid 15% due to the galvanic separation. Seems Stay Silv 5% would be ideal. I have a TIG welder and I've TIG brazed before but cast iron with silicone bronze. The snake bites seem pretty simple, just heat and fill.

Maybe wash over the bad joint with low amps on TIG to control heat and the use silver solder to help flow in that joint. I'd feel more in control with low amp TIG than flooding with heat with oxy torch.

I'm a pretty good hobby TIG welder and done a lot of aluminum so I'm used to heat control. I was just unfamiliar with what type of filler would be ideal.

I read that no flux is required for copper to copper as the copper phos silver rods self flux. Any experience with that?

Then cap and run low air pressure with soapy water to check for leaks?
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Old 28-04-2018, 20:25   #6
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Re: Heat exchanger repair Braze/Solder?

My yanmar’s hx is out at the shop for the same problem. This type of repair is usually affordable and they do well. Best left to those experienced in this.
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Old 29-04-2018, 03:58   #7
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Re: Heat exchanger repair Braze/Solder?

Thanks Stu. I'm stubborn when it comes to working on my boat. It's certainly a repair that is affordable, but knowledge is expensive. I take every opportunity to learn a new skill, I find that they come in handy down the road.

I have the tools to repair just like a shop would. Only difference is that they've done it before.

When I pressure test it, and it leaks, then I'll admit that it's time for a pro. I have just the guy too, a complete welding, brazing, machining ace that specializes in marine repairs. No doubt he could fix it.

Just ordered the flux and stay silv 15 rods, I'll post up the results next week when I start repairs.
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Old 29-04-2018, 15:13   #8
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Re: Heat exchanger repair Braze/Solder?

OK so I think I was wrong. I asked a marine fabricator/machinist who does these repairs all the time. He said all copper nickel heat exchangers he's worked on were done with soft or silver solder. He said def don't braze it or you'll make a mess. His advice was to clean really well, flux and flow in some silver solder. Which I did with MAPP gas torch and being super careful to not overheat. I think it came out great. The pin holes were super easy, the joint I took a few passes, cleaning with alcohol every time to remove any junk in the solder.

Flowed and wet out just perfect. Taped off and gave a fresh coat of paint.

Thanks for all the advice, appreciated. I ordered some Stay Silv 15 and some flux for the next repair job. Will keep a close watch to see if any leaks reappear.
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