Cracking welds on crankshaft

I know, everybody who reads this is probably saying to themseves that welding on to a crankshaft is stupid. I tend to agree. But the customer wanted me to weld a disc from a harrow to the end of a crankshaft in order to make a bird bath. The disc has a short axle running through it and there is a big bolt threaded into this axle. The bolt is rusted into the axle. To the head of this bolt I welded the harmonic balancer end of the crankshaft. After a tig pass all around with 70S2 rod I noticed cracking down the center of the weld. So I just used some 308 tig rod to weld right over the first bead. The SS weld didn't crack. So I'm wondering what crankshafts are made from and why the cracking. I know, I should have used SS rod to begin with but the customer wanted the weld to rust so it would match the rusty crank and disc. I also know I should have ground out the cracking weld before running a stainless bead over the top. But it is just a bird bath and the woman I welded it for is a cheapskate who didn't even want me to spend the time to grind off the rust before I started to weld. She thought I was just trying to pad the bill. Anyway, back to the original question, why did the weld crack? The woman is bringing me another crank to weld on, this time she wants several discs to be welded to the cheeks on the throws so that she can have a cascading bird bath/fountain. Eric

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It was likely cast iron.

From the American Foundry Society (AFS) web site

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"Cast ductile iron, GM casts 99% of its crankshafts in ductile iron (which has a higher modulus than gray iron). The main reason for this is cost. The finished, cast ductile iron crankshaft for a 4-cylinder engine costs $25 less than a forged steel one "

Reply to
John B.

Because the crank worked as a heat sink and thermal differences cracked the metal. Thats a mighty big piece of metal and it should have been preheated with a rosebud before welding.

Maybe. Couldabeen. Mighta.


Reply to
Gunner Asch

Knowing what engine the crankshaft came from would help a lot in determining what material it is. If a petrol engine then a good chance it is cast iron, diesel then likely forged steel.

Reply to
David Billington

I believe Cranks are made from medium carbon steel. Something close to 5160 or 8260. They are heat treated to increase strength and reduce wear.

Next time splurge on some 309L SS filler wire. It is a dissimilar alloys filler rod designed to stick weird stuff together. Keep your heat low so you don't melt too much of the base metals. Treat it more like brazing, where you apply it to the surface of the base metals. The technical term for this is "limited dissolution into parent metal".

Then allow it to cool slowly.

Reply to
Ernie Leimkuhler

Thanks for the info Ernie. I don't think the crank was cast iron because I have welded on cast iron many times and it did not act like cast iron. Since I need to order more welding wire I'll add the 309L to the order. And I'll watch out for "limited dissolution into parent metal" when I weld on the next crank shaft for the next bird bath. Eric

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