Outboard motor repair

Date 09-16-2009 12:36

One of my regular customers runs a campground/boat rental service and I often do repair work on their pontoon boats. A couple of boats have had debris sucked into the prop and cracked the anti-cavitation plate(the horizontal plate right above the prop). I repaired it once, and they broke it again, so I just fixed it again, but I had a devil of a time cleaning the aluminum. So here is my request. If any of you have pictures of a cast aluminum repair that has the bead ground down to flush, I would love to see them. I just can't seem to get rid of porosity at the toes of the weld. To look at the weld when it is finished, it looks great, but when I grind/sand it down I still see porosity. I know the three C's of aluminum welding, and on the hulls of these pontoon boats cleaning is easy, but this cast s*** drives me bonkers. My cleaning procedure is as follows. 1. I use a dynabrade baby belt sander to get most of the powdercoating off of the lower unit/cav plate. 2. With a vigorous unidirectional stroke, I spend about one minute per inch of crack brushing with a SS brush soaked in acetone, with generous acetone irrigation in between. I try for a two inch buffer between the crack and the last visible traces of coating. 3. Using a carbide burr and a slow speed pneumatic die grinder, I grind out the crack most of the way down. By the way, running the die grinder at about 40 psi allows me to get good removal rates without clogging the burr. 4. Weld the topside. 5. Grind out crack to good metal and weld the other side. To make things even more fun, I do this on the motor in situ, and the underside of the cav plate has a recess for the zinc, and I end up using a curved round die sinkers file to clean the corner of the recess. This is done with Tig .125" tungsten 45%EN. I have found that a backhand technique(tungsten pointed toward the finished weld) seems to work better to get the junk to come to the surface. I told the customer that since the lower unit casting was brand new and still failed in service, any repair, no matter how well it's done, won't bring it back to factory strength, but I would love to hear from any of you who have experience with this type of repair. Would chemical cleaning be worth a try? My camera is working again, so I'll try and post some pics of my repair.

By tazmannusa (**)

Date 09-16-2009 15:18

I am no expert on alum but learnen, Could it be the air die grinder contaminating the surface from the air discharge? everytime I try to use any air tools preping or cleaning alum I get little contamination from the oil-moisture.
Just a thought
Tom

By aevald

Date 09-16-2009 17:15 Edited 09-17-2009 00:40

Hello devo, first and foremost the words "cast aluminum" can sometimes be the kiss of death when related to welding and welding repair. You have no way of verifying the grade or quality of these castings, thus it is often a crap shoot to make successful repairs on these sorts of items. Your technique sounds very reasonable and likely will give you reasonable results for the scenarios of repair you have described. A few items could be considered to possibly increase the quality of the finished repair: you mentioned using a dynabrade belt sander, if you are using belts with a "carbide" component in the belt description this could possibly include some undesirable additions to the weld repair area. I believe the aluminum oxide belts are the preferred ones. One of the other posters mentioned pneumatic tools and the oil mist associated with their use. If the exhaust of these tools is directed towards the part then there is a possibility of some contamination because of this, so it is certainly something to consider as well, yet cleaning with a good grade of acetone should negate any undesirable issues. You will possibly find some information describing different types of acetone, some contain oils others do not, so try to select the type that doesn't include oils.
I have run into many cast aluminum repairs where there will be porosity along the toes of the welds or directly adjacent to the welds. I don't believe you can do anything about these due to their origins being in the castings themselves. A bit more for you to consider. Best regards, Allan

By chris2698 (****)

Date 09-16-2009 23:48

It may very possibly be like aevald has said there are different grades of cast and some repairs can be made with lots of success while others aren't.

I'm a aluminum welder and I work for a company that builds 47ft marine life boats like the US coast guard has and this company built the Navys hovercraft and I have experienced lately when I weld the doors that go to each room of the boat well there cast and they don't weld worth a crap. I am useing a wire for cast but they still don't weld very good. I had to weld something else oneday that was cast on the boat it is like where you would tie the boat up from the boat to the dock (forget what they call it) and that was cast and it welded extremly well so I guess it depends on what grade of cast it is.

Sorry I can't be of much help

By F-17

Date 09-17-2009 03:06

The gizmo your thinking of is a "cleat".

By chris2698 (****)

Date 09-17-2009 09:04

thanks

By F-17

Date 09-17-2009 03:27

I've welded all kinds of cast aluminum crap,from outboard motors to Ford diesel bellhousings,transmissions,lawnmower parts,Motorcycle engine blocks everybit of it living in the nastiest unfriendly weld repair enviornment.

What we started out with,.......Simple green and smoking hot water and a stainless wire brush,Step2 was large fluted die grinder bit,3 laquer thinner,4 preheat to boil the junk out of the crack,5 more cleaning with a clean brush,6 more laquer thinner,7 put a pass in it,8 grind that pass out,9 put another pass in it,if porosity shows up,die grinder it out(used an electric grinder),10 fill er up with as many passes as it takes.

I did the skeg on my buddies outdrive when he forgot to lift it up at the launch(cause he was drunk),It took some doing but ended up good as new,like it never happend.

Steer clear of using anything with "Sand" such as polifans,bead blasters,the grinding belt your using,The grit breaks of and get's in there(because it smears rather than cuts) and creates the "porosity" look when it floats free and the weld metal solidifies around it,Same goes for welding on something that has been "Sand Cast" you'll grind and grind and while it get's less and less basically your displacing the sand with the fillermetal.Your fillermetal "patch" will be pure fillermetal but right next to where your welding will have all the original defects from the sand cast process.

In my experiance ...............unless it's one off,or a REALLY expensive part with minimal damage your better off to just get a replacement part.I spent a half day screwing around with the outdrive skeg,I spent a half day fiddling with a sidecase for a 4 wheeler, the new part was 300 bucks and the old one was HAMMERED.I got it fixed with no leaks per the dye pen but it was 5 hours in the making.If it wasn't a buddy project on my own time I'd never have taken either of them on because I'd feel guilty charging the time spent to some guy off the street.Plus those kind of "jimmy" repairs can last weeks or years depending on various factors.

By Tommyjoking (****)

Date 09-17-2009 08:42 Edited 09-17-2009 08:45

devo,

I have welded entire lower units back together that where shattered into TOO many pieces. The cast is simply dodgy to work with because you never know how clean the casting procedure much less the metal itself was. Acid etch I have found helps more then anything because it seems to be able to break down and separate the contaminants. I agree with the above comments by Alan on abrasives, make sure your using an aluminum oxide abrasive (like scotchbrite) OR better yet grind only with carbide rotary or flat files. No matter what on cast AL you WILL pull contaminants up in your weld pool. The best you can do is pull them all up above the parent metal surface in a repair weld. Use a little xtra gas flow and a larger then normal cup and it will help you stay in place a little longer to work those impurities out. Will it ever be good as new, probably not no matter what you do, especially if you have to buff off your weld buildup and flush them out. Now if you butt weld that together and can run a stringer up either side of your original weld and leave it....well the reinforcement of the xtra material would make difference....but since your working on what you are I understand the need to grind it down.

By the way you are doing good cleaning procedures right now...its not you man...its the dang metal.

Tommy

By devo

Date 09-17-2009 11:26

Thanks for all the replies. I'm no expert aluminum welder, but I am getting there, and this type of repair has certainly been the most challenging yet. Of the seven pontoon boats my customer has, three of them now have cav plates that have been repaired. One is still holding 24 months later ( probably because no one has hit a log with it yet) and two have been repaired twice. I have since done a little research into the function of the anti-cavitation plate, and it is just there to keep the prop fully engaged in water, and not suck any air into the prop, so it isn't exactly structural. Another friend of mine has a mercury I/O with two half moon shape chunks taken completely out of the cav plate(drunken boating=$$$) and he called me up recently with a "real easy repair"(that's what they all say). After consulting my alcotec filler selection chart, it looks like 3003 is compatible with some cast grades, so I may be able to splice in a piece, but compared to the cost of a replacement, I'm not so sure....

By Leefy Date 09-17-2009 12:40

Devo

I'm new to the tig world but I had to repair a skeg for a guy and had the same problem when I hit the casting I got pours. I posted looking for help on the Miller site and FusionKing helped me out with the pointer about lowering the Frequency down to about 40 and make passes without using filler against the casting until you get clean aluminum. When you don't see any junk floating then it is time to use the filler. It worked on a 1968 Johnson motor. Hope that helps.

Leefy

By weldwade (***)

Date 09-17-2009 22:51

Devo, I have been repairing Aluminum tanker trailers for the past 18 years and every other thing made of aluminum also. Most of the valving on these tanks are cast alum. Many times I have to do repairs where it is not possible to access the dirty garbage on the other side of the crack or on crappy castings. As Leefy said make passes without filler burning the junk to the surface. You can then grind this junk off using a wheel designed for "non ferris" grinding a file or burr. The burrs I use are very aggressive and only have 5or6 flutes depending on the size, the steel carbide bits will pack with alum very fast overheat and chip or dull. Acetone is good but I don’t use it most of the time because I am inside the tank. Brush, brush and more brushing with SS brush. I do use a SS wheel in a drill that turns fairly slow to clean with. I would 3 pass to add reinforcement and then contour the weld not completely grind it flat. I doubt that these boats are High Performance and leaving some reinforcement on the bottom of the cav plate will not cause cavitation. I have never had any success with "backhand" technique in alum. As stated in an earlier post a larger cup and a little more gas flow will help. A little bit of pre heat can sometimes help. I never know what the casting is made of??? I have had best luck with 5356 filler on cast alum. Hope this helps.

By devo

Date 09-18-2009 11:28

Thanks for all the replies and good advice. Regarding weldwade's reply on filler metal, the manufacturer recommended 4145 filler or 4043. The 4145 has a 12% silicon content, apparently for better wetting of the puddle. Would using 5356 create a cracking risk due to the formation of magnesium silicide? I can't quite remember the conditions, but I do remember reading Tony Anderson's column regarding cracking from poor filler choice. As far as using the arc to clean the junk off. this plate is tapered in thickness from about .185" to .105" and to try and keep any kind of puddle going without filler metal was beyond my abilities. the puddle just fell through, or the arc would jump from one side of the crack to the other. If I didn't have to grind off the weld reinforcement, it would look great, with no visible porosity, but there is a little zinc fin that attaches to the plate in a little recess(.095") so I have to grind that bit close to flush. And regarding the preheat, the manufacturer warns against excessive heating of the lower unit, something about seals melting, so my method is to weld a bit and let it cool a bit. I would like to try using a stainless backer so I could grind the crack out a bit more and support the puddle, but what does the code book say about "intimate contact"? With the gradual and variable taper of the cav plate, it would take forever to try and fit a backer plate to the thing and have it actually work. But I can sleep a little better thanks to all the info you all have provided, and the bottom line is, this 6000$ Honda outboard was less than a year old when the log got sucked into the prop and cracked the plate, so if the original factory condition was not strong enough to withstand that kind of abuse, no repair, no matter how well done, will be enough to withstand another hit. At least it's a rental....

By Leefy Date 09-18-2009 21:02

Devo

Why don't you go to the miller welding forum and write a message to FusionKing or a private message to him. He is super helpful and works all the time on aluminum boats and motors. I'm sure he could answer any and all of your questions and sure has saved my bacon a few times already. Leefy