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  • welding cast aluminum engine block

    Anyone welded on a cast aluminum engine block before? The one I need to fix is from a 08 BMWx5 it was hit and the engine mount tapped bungs on the block snapped off in a few spots. Sorry I don't have pics. I'm wondering what would be the ideal filler rod to use, and also will I ruin the block welding on it if the cylinder sleeves are nikasil? Here is a link to the engine used in this model BMWx5 it's the 4.8l

    http://en.wikipedia.org/wiki/BMW_N62#N62B48
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  • #2
    The Nikasil cylinder coating is a nickel and silicon carbide matrix coating about 0.07mm (.0025-.003") thick. The Nikasil treatment coats a layer of nickel-silicon carbide, usually by electrolytic deposition, to the inner surface of aluminum cylinders. The nickel matrix is very hard, yet it is relatively ductile. Dispersed through the nickel are particles of silicon carbide less than 4 microns in size. These extremely hard particles make up 4% of the coating and form a multitude of adhesion spots where oil can collect. Beside providing a long wearing surface for the piston and rings, the silicon carbide particles contribute to longer engine life by ensuring good cylinder lubrication.

    Check your engine. Only the M60 and the European M52 engines are affected.

    Engine Casting Number
    M60B30
    1 725 970 or 1 741 212

    M60B40
    1 725 963 or 1 742 998

    Welding the cast aluminum isn't a problem. Cast will weld with 4043 and 5356 filler wires. I usuually use 4043. But I know some welders who swear by 5356. How close to the cyliders are these engine mounting tabs you're trying to repair?

    Perhaps a call or email to BMW would help. Their USA plant for the East Coast is located in the Greenville-Spartenburg metro area in upstate South Carolina.
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    • #3
      thanks for the fast reply. After a little more digging I've found the block to be made of alusil which has 30% silicon and 70% aluminum after boring the cylinders they etch the cylinder to expose the silicon in the cylinder which basically creates a surface like the nikasil with the ability to retain oil and high wearability.

      I'm welding on the sides of the block where the engine mounts bolt on, it is directly beside the cylinders but there should be the water jacket between the outside of the block and the actual cylinder. I'm just hoping that the heat doesn't distort the cylinder bore and cause failure. I've gotta try to weld it first since the replacement block is 9K
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      • #4
        Alusil

        Alusil as a hypereutectic aluminium-silicon alloy (AlSi17Cu4Mg) contains approximately 70% aluminium and 30% silicon.[1][2] This alloy was created in 1927 by Schweizer & Fehrenbach[3] of Baden-Baden Germany and further developed by Kolbenschmidt.[2]

        The Alusil aluminium alloy is commonly used to make linerless aluminium alloy engine blocks.[4] Alusil, when etched, will expose a very hard silicon precipitate. The silicon surface is porous enough to hold oil, and is an excellent bearing surface. BMW switched from Nikasil-coated cylinder walls to Alusil in 1996 to eliminate the corrosion problems caused through the use of petrol/gasoline containing sulfur.

        Engines using Alusil include:

        Audi 2.4 V6[1][5]
        Audi 3.2 FSI V6[5]
        Audi 4.2 FSI V8[1][3]
        Audi 5.2 FSI V10
        Audi/Volkswagen 6.0 W12
        BMW N52 I6
        BMW M62 V8
        BMW N62 V8
        BMW V12[6]
        Porsche 928 V8
        Porsche 924S I4
        Porsche 944 I4
        Porsche 968 I4
        Porsche Cayenne V8[3]
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        • #5
          Think I'll have distortion problems in the cylinder bores from welding on the outside of the block? Like I said there should be a thermal break with the space that has the water jacket in it. However now I'm stuck on what type of filler material to use to properly weld this.
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          • #6
            Caution

            And a reminder that heated crankcase vapors can be highly explosive.
            A flash can blow the pan and covers off of an engine.

            Both 4043 and 5356 can be used. 4043 is usually specified. 5356 is not recommended for service at elevated temperature.
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            • #7
              great thanks for the advice. I'll give it a go and snap some pics sometime this week.
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              • #8
                Do not use 4043 or 5356

                Do NOT use 4043 or 5356 filler. Anyone that tells you its fine for use on a 30% silicon aluminum casting is obviously not familiar with that material. You will end up with an outer edge of the puddle that has a high silicon concentration, and therefore crack prone. 4047 is about the best choice of fillers that are easily obtainable as it has about 12% silicon vs 5% for 4043. The idea is to use a filler with as close of a silicon content as you can get to the base alloy. Good luck!
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                • #9
                  Thank you for the input on the filler rod I was going to call my supplier to see what was the highest silicon content filler they had available because I was thinking about the difference in the composition of the 2 different materials. I was worried about the area where the 2 materials fused together having different properties and possibly causing a brittle area.
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                  • #10
                    Originally posted by jrscgsr View Post
                    Think I'll have distortion problems in the cylinder bores from welding on the outside of the block? Like I said there should be a thermal break with the space that has the water jacket in it. However now I'm stuck on what type of filler material to use to properly weld this.
                    I wouldn't be worried about it. Has the block been drained of coolant?

                    If it was my car though, I would want a new block, rather than have it welded on. After all, what's insurance for?

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                    • #11
                      The vehicle was bought from an auction as is and therefore could not go through insurance. I welded the block in place still installed in the SUV. It was a surprisingly clean cast aluminum welded up well. I had to leave off one of the broken mounts because it just started cracking when getting welded. I think it was cracking because of the force applied to it when it was snapped off causing stress cracks in the piece. I didn't have a camera on me but it was not fun trying to get under it on the hoist and jam my head into the space to fix it. I LPI'd the areas after welding them and found an additional crack in the water jacket that I had to weld. Thanks for the input from everyone, the job worked out and I saved my brother in-law 9k on having to buy a new block.
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