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Old 08-10-2015, 17:35   #16
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Re: Aluminum brazing

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Originally Posted by Charlie View Post
Saw a video where it was done wanted to see if anyone had real life experience with it.
In case you doubt, I actually do have real life experience with the aluminum braze (actually, a solder). I was a sales rep to maintenance shops and handled the product for several years. You could make a few repairs at low temperature, but not your kind of repair. An alternative would be to use an aluminum welding rod with a torch, assuming you didn't want to use it as a DC rod as intended. The flux would throw up a passable oxygen shield, but as a previous poster said, you had to know exactly when you are at the right temperature, as the whole part will collapse and dribble on your feet. The oxide coating melting at about 1000 degrees higher than the base metal doesn't make the job any easier. If the part is absolutely irreplaceable, you do have a chance of success by using coil inserts, or by having a good machinist cut it down and build it back up with a heliarc deposit. The cheapest and best solution will probably be to simply replace the part. Sorry the forum software won't recognize paragraph breaks, not my fault!
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Old 10-10-2015, 10:58   #17
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Re: Aluminum brazing

I too have tried the Al brazing rods with generally poor result. ONLY success I ever had was with a part that I had excellent access to all the surfaces both before and after the repair. Zero luck with any repair that had poor access, both to pre-clean the surfaces and to properly heat and apply the braze material.
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Old 11-10-2015, 13:31   #18
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Re: Aluminum brazing

I use to race sprint cars with aluminum blocks and heads. While aluminum is easy to repair, welding high stress aluminum engine parts seems to lead to other failures. To be competitive, once welded and repaired, the part either was sold or used as a spare.
On the other hand, I have replaced threads in aluminum many times with a couple different brands of threads and never had a failure.
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Old 12-10-2015, 06:06   #19
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Re: Aluminum brazing

Quote:
Originally Posted by ryon View Post
In case you doubt, I actually do have real life experience with the aluminum braze (actually, a solder). I was a sales rep to maintenance shops and handled the product for several years. You could make a few repairs at low temperature, but not your kind of repair.

An alternative would be to use an aluminum welding rod with a torch, assuming you didn't want to use it as a DC rod as intended. The flux would throw up a passable oxygen shield, but as a previous poster said, you had to know exactly when you are at the right temperature, as the whole part will collapse and dribble on your feet. The oxide coating melting at about 1000 degrees higher than the base metal doesn't make the job any easier.

If the part is absolutely irreplaceable, you do have a chance of success by using coil inserts, or by having a good machinist cut it down and build it back up with a heliarc deposit. The cheapest and best solution will probably be to simply replace the part.

Sorry the forum software won't recognize paragraph breaks, not my fault!
Huh??
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Old 12-10-2015, 06:17   #20
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Re: Aluminum brazing

Helicoil or tig in a bolt and tap it out.

I had an XR250 where the previous owner put in a helicoil for the head bolts. It came loose and as it was already oversized the only option was to weld in a bolt and tap that out.

End result was stronger than factory, but a hassle to do.
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Old 12-10-2015, 08:15   #21
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Re: Aluminum brazing

@ Reef Magnet. Used a helicoil and then tried a dry run and a bolt in a different area pulled its threads.

@Ryon Thanks was wondering about the practical use. I tried it on some scrap Alum and got it to work. Be nice if I could just fill the hole with molten rod and drop a bolt in as shown on the video

@ Jamhass I tried using some flux and got a little better result.

@ Lepke This bike won't be stressed as a race vehicle would. Will that make a difference?

@ Moonos If this doesn't hold I will try what you suggest.
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Old 12-10-2015, 13:00   #22
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Re: Aluminum brazing

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@ Reef Magnet. Used a helicoil and then tried a dry run and a bolt in a different area pulled its threads.

...
A correctly done helicoil shouldn't do that. The helicoil thread into the original hole is a bigger diameter than the bolt thread itself which is akin to using a larger bolt. The thread may have been damaged inserting the helicoil. I use red or blue loctite on the insert when screwing it in to act as both a lubricant and to assist with retention once in place.

If you stay with the brazing route, here's some tips:

A 4000 series aluminium filler rod melts slightly lower than the parent material (or should). The temperature different between melting of the rod and the part is the range that needs to be adhered to in order to successfully braze. The part will require preheating to approximately 400 deg C prior to commencing the braze. A tip for preheating the part prior to brazing (assuming you are using oxy-acetylene) is to turn the oxygen off and quickly "blow" the flame over the part. This will leave a sooty deposit. Now turn the oxy back on and set the flame to slightly carburising and evenly heat the part. At the point the soot vanishes is the point where the part has sufficient preheat.

Needless to say, the area to be brazed needs to be exceptionally cleaned within 20 minutes of brazing. Aluminium oxide forms quickly and has a melting point of around 2000+ deg C whereas aluminium itself melts at around 700 deg C. Mechanically clean and then wipe with acetone. Now I haven't aluminium brazed for around 30 years, but I recall that the flux could be mixed with water or alcohol and painted onto the part and the rod to ensure adequate flux coverage. It's also essential to allow the flame to protect the molten braze as much as possible during the operation as well.

Personally, If not wanting to helicoil I'd prepare the hole for TIG welding by drilling out slightly and countersinking both sides and then take it to someone to weld. Wouldn't cost much at all for such a small job.
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Old 12-10-2015, 14:05   #23
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Re: Aluminum brazing

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...If not wanting to helicoil I'd prepare the hole for TIG welding by drilling out slightly and countersinking both sides and then take it to someone to weld. Wouldn't cost much at all for such a small job.
Welding so close to a precision bore might require re-boring. The cylinder head mounting surface might warp also.

"Wouldn't cost much" is relative. A Heli-Coil seems the right fix for this.
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Old 12-10-2015, 15:02   #24
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Re: Aluminum brazing

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Originally Posted by Terra Nova View Post
Welding so close to a precision bore might require re-boring. The cylinder head mounting surface might warp also.

"Wouldn't cost much" is relative. A Heli-Coil seems the right fix for this.
True, but no less a risk than oxy-fuel. Having said that corroded water jackets in alloy heads are regularly repaired by TIG welding with only the occasional issue of warping being too great to machine out. I've assumed the job was a removable part. In place I'd say forgeddaboutit.

I'd prefer to use a helicoil as well but the OP has his reasons for not wanting to go this path I guess.

Edit: Just had a thought if not already mentioned. Perhaps re-tapping to, say 7/16" imperial could work?
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Old 12-10-2015, 15:35   #25
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Re: Aluminum brazing

@ Reefmagnet thanks for th tips on brazing. I ended up using a helicoil. A friend had the proper diameter tool so all I had to do was replace the inserts. I'm just trying to cut down on the tools I buy. It is an expensive habbit/addiction and when I do go crusing it will be less that I have to give away. A second bolt ripped its threadds out on the valve cover. I ended up using a MAPP gas torch Alumi weld rods and flux to clean the valve cover. Next thing I need to do is drill and tap the hole. I am not sure that the aluminum rod that I filled the hole with is solid but will test it prior to assembling the engine. The torque spec on the engine is pretty low.
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Old 12-10-2015, 15:58   #26
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Re: Aluminum brazing

Don't give a helicoil kit away! Very common for aluminium threads to be damaged after removing a stainless fastener that's been there for a while. Guess what the best repair is? My mast and alloy anchor winch are full of helicoil inserts lol.

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