Sportsmaster lower has hairline crack ?

[hdtwncam88]

was told its common for this to happen just above carrier housing, exhaust section ? Has been welded once previously and just noticed a new hairline crack. How often can it be welded ? New crack going right around edge of weld.

[150aintenuff]

the metal wasnt preped correctly after it was welded.....

welding creates a week point at the edge of the weld due to heat changing the chemical make up of the alloy being welded... if not properly preped before durring and after welding the metal may be stressed along the weld and it will break right along both sided of the weld and fail again... the way to remody that is a preheat and post heat to slowly cool the metal to retain the strength and tensel of the original alloy along the weld... aluminum and other cast metals are very known for falure of this kind as they do not have the heat resistance to structural changes durring welding that say plate steel does and should not be welded by just anybody... no that being said I personally would not reweld the crack as the metal around it has already sustained the stress and heat changes once it will likely fail again even if it were to be cut away and re paired properly it would not hold up as a new part would... It is more expensive but the only way to ensure a failure again doesnt happen in the near future is to replace the casting and start with a unmolested piece that has not been under the stresses of a welding torch.

[Superdave]

Try this...after the welding take a chipping hammer, or othe small pointed hammer and "peen" the weld. All you do is tap on the weld and make small dents in it while it's colling. This relieves the stress across the welded surface and prevents the crack from restarting. I had to do this to a 3 cyl block with a hole in the top jug. It kept cracking and I was told to try this. The block is still holding up after 12 years.
SD