MEOclassIIexamnotes

1) Cast iron is that the metal is filled with impurities. When you melt the metal the embedded dirt and sand contaminated the weld and tend to not mix well with the cast iron filler rod.What you end up with is not a fused intermixed metal bead but a porosity filled weld that can be easy to chip away with a chisel because it has not bonded to the base metal.  2) Pre heat & Post Heat required.And different as per its composition.Pre heat to stress relieve & post heat to control rate of cooling.  3) The large amount of carbon in the base metal tends to segregate itself along grain boundaries as the weld puddle solidifies and cools. What this does is lower the tensile strength even lower so that in the weld fusion boundary the shrinkage force pulls the metal apart as it cools, ie it tends to crack along the weld when cools.  4) Cracking. If it cools down too quickly you will get cracks along the weld.  5) Proper selection of filler rod & flux required as per the grade and compo

The cam for the air distributer serves its purpose only while starting the engine . Actually if you see there is no other requirement of this particular cam while the engine is continue in operation.  Therefore if a cam ( normal possitive ) is used then wear of this particular cam will be abviated and will be expensive to repair / replace this cam. So when the engine has started and the vessel is enroute a voyage , then this particular cam turns without any running gear touching it. It comes into play only starting