And of course i experienced every possible complication.
The repair was to the lower unit of an outboard motor. So it had 20 years of gear lube soaked into it.
Apparently the lower unit had cracked and the original owner attempted to JB weld it. Not only did the crack continue traveling down the casting it also came thru the jb weld. So it was leaking oil out and water in.
It was for a friend of mine who has a bass tournament on Sunday. So no time to order a new lower unit. And not time to take the seals and gears and bearings out of this one.
So i attempted to do a hack job repair to the best of my ability given the circumstances.
I needed to perform this repair without putting much heat into the part so i didn't melt the seals. Luckily the crack was in the middle of the case far away from any seals.
I laid damp cloths over any areas of the case where there were seals to slow the heat
Of course this is obviously not what you want for AL because its going to pull the heat out of the weld faster causing increased risk of hot short cracking. But i had to do what i had to do.
Perhaps i could have went about this in a better way but i'm new to this so bare with me and constructive criticism is welcomed as i am trying to learn.
The case at the point of the crack was approx 1/4" thick. Thicker in other areas close to weld area. So it was a large heat sink.
I used a 17 series torch with 3/32" tungsten, #6 cup, standard collet body. Machine was set to 150 amps because that is all the torch is rated at. I set the freq 50-60Hz to maximize my ability to puddle at the low amperage. Cleaning was set as low as possible but higher than i would use for sheet aluminum, approx 40% cleaning. Argon flow was set at 20cfh which is probably more than necessary but again i wanted to maximize cleaning. I would have added some helium if i had it to puddle faster and reduce heat input. I used 3/32" 4043 filler. I chose 4043 for its ductile attributes to reduce the risk of cracking. And the lower unit doesn't see high usage temperatures.
Summary:
- 17 Series Torch
- 3/32" Tungsten
- #6 Cup
- 20cfh 100% Argon
- 150 Amps
- 55Hz
- 40% Cleaning
- 3/32" 4043 Filler
After removing the JB weld it exposed a very rough Aluminum surface. Deep groves some 1/16" deep.
I used a die grinder and a paint removing wheel to take down the AL ridges and smooth the surface so i could see the crack.
I did not have any die or developer, i wish i had...
I then used a carbide bur to groove out the crack about half way thru the material and a little past the crack on each end.
I knew i wouldn't get full penetration but i was trying to minimize the amount of gear lube that would pull thru from the other side. I did not drill the ends of the crack or groove thru 100% because i didnt want to get AL shavings into the gearcase. I then poured acetone into the groove and brushed it out really good with a Stainless brush.
Added some more acetone and wiped it out with a rag. Then took a propane torch and lightly heated for about 30sec to 1min to remove the shock of welding a 40degF casting. This removed allot of condensation and boiled some oil out. I then acetoned it again and heated again. This time i didnt see anything weeping out.
I lit up on the crack at a very low amperage and let the cleaning action work all the way down the crack which brought all of oils out of the metal surface. I wire brushed it again and acetoned it again. I then lit up on the top side about 1/8" above crack and let it clean for a while then increased amperage until it puddled but no more amperage than necessary to puddle. I didnt want to pull any more impurities up from the casting than necessary. I welded down the full length of the crack. Let it cool. Then welded down each side of the first weld. And let it cool. It the surface was very porous and allot of crud was in the puddle the whole time. So I cleaned it off really good and then went back in and blended the three welds together which cleaned up the surface allot. However after it cooled the crack had already worked its way back to the surface. Which i had a good feeling was going to happen for multiple reasons.
So i started grinding out the weld. Even though the surface looked good the weld was filled with voids. I ground all the way down to the root of the crack this time. The AL was paper thin at the bottom. I then cleaned it all up with a Stainless brush and acetone again.
As i welded this time the weld puddle was much cleaner and it was like doing an open root weld. As i moved the torch along the crack would open up to almost 3/32" and i would add rod to close up the gap. After i got the root pass in i added two fill passes on each side to build up just above the surface. The main problem this go round was the aluminum casting would get little pit holes in it where the cleaning action was cleaning. You can see them in this photo. I'm very interested in learning the best way to keep this from happening.
I increased the freq to 250Hz for a tighter arc and reduced cleaning to about 35% and welded lightly with low amperage over the porous areas. I then ground down the weld surface to make it more hydrodynamic and to look a little better. I left about 3/32" build up above the surface just for extra reinforcement.
How long do you think this weld will hold before it cracks? If it will make it thru this season til winter i will be very pleased. If it makes it thru this weekend i will still be satisfied.
Ideally if i were doing this repair i would have gutted the casting. Heated the part, die tested the crack, drilled out the ends of the crack, and ground out all of the base of the crack until i was at fresh base metal on both sides. Then welded it up and kept a heat gun on it to slowly cool the part. But given i wasn't able to do that on this how was the process that i performed?
