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  1. #1
    Join Date
    Oct 2009
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    306

    Default 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. #2
    Join Date
    Jan 2007
    Location
    South Carolina, Dixie
    Posts
    515

    Smile

    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.
    Mustangs Forever!

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  3. #3
    Join Date
    Oct 2009
    Posts
    306

    Default

    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. #4
    Join Date
    Jan 2007
    Location
    South Carolina, Dixie
    Posts
    515

    Smile 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. #5
    Join Date
    Oct 2009
    Posts
    306

    Default

    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. #6
    Join Date
    Jan 2007
    Location
    South Carolina, Dixie
    Posts
    515

    Smile 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.
    Mustangs Forever!

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  7. #7
    Join Date
    Oct 2009
    Posts
    306

    Default

    great thanks for the advice. I'll give it a go and snap some pics sometime this week.
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    and wp2025 weldcraft torch
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  8. #8
    Join Date
    Dec 2005
    Location
    wisconsin
    Posts
    836

    Default 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. #9
    Join Date
    Oct 2009
    Posts
    306

    Default

    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. #10
    Join Date
    Apr 2009
    Posts
    362

    Default

    Quote 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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