When the powder is exposed to the flame, it seat melts and fuses to the sides of the crack cracked to fill the repair area.
It all depends on the market value of the head and the cost to replace it with a valve new or used casting.
Guy I know will machine out one cracked valve seat, IE the exhaust, Install an oversize seat with a flange, then machine the intake one overlapping the exhaust where they meet.
When unfused powder builds.020 or thicker, it acts like an insulator between the flame and base metal.It takes a lot of heat to do cracked this, about 5,000.When unfused powder stacks up to about.020 or thicker, it wont wet out properly.Most small cracks in cast iron as well as aluminum heads cracked can be repaired by pinning.Prognosis, cracks do not necessarily mean a cylinder head has to be replaced.Some shops will even pressure repair test the head a third time if it has pressed-in valve seats to make sure no cracks opened up after the seats were installed.Combustion gases entering the cooling system through the crack can also accelerate coolant breakdown and corrosion.The seat process is similar to brazing but results in a much stronger repair.Before begining the repair make sure to read and follow any and all saftey precautions neccessary for whichever product that you decide to go with.Cracks in thin areas of a casting (thinner than 1/8) can be difficult to repair because the metal isnt thick enough to support the threads on a standard pin.Don't cut 10 peices to fill a 1" hole.But even pushrod heads have their limit, and when pushed too far will also warp and crack.A TIG welder prevents the formation of the oxide layer by bathing the weld with a steady supply of inert gas (usually argon). So you have valve a figure 8 deal-e-o where one sits in another, but the valves are the same distance apart.
When overhead cam study heads get hot, they often swell and bow up in the middle.
The basic technique for flame spray welding cast iron has been around for 40 years but has only recently been adapted for automotive applications.
The delux kit sells full for about.00 and it's ordered in the exact color that repair you need.
One solution is to data use locks to hold the two sides of the crack together, and/or to use special pins that have a spiral hook or reverse pitch thread pattern.
An experienced welder can even recast a badly damaged area, saving a head that would otherwise be junk.
One of the causes of cracking in cast iron heads is stress created when the valve seats are induction hardened.Stop, scrape away manual the unfused powder, and start over.Color, use as cracked many coats as needed and again, take your time.If the leak is large canada enough, it may even hydrolock the cylinder.Sanding may be required between applications in order to ensure that it's a smooth finish.
Dry cracks which do not leak coolant may or may not cause problems depending on where valve seat cracked repair they form.
When the head preheat temperature has stabilized (it takes about an hour a neutral flame oxyacetylene torch with slightly more acetylene than oxygen is used to melt the cast iron (which melts at 2,400 to 2,600 F).
In fact, many cracked heads that were once thought to be unrepairable are now being fixed.