Berts, To clarify for newbie home mechanics. The water dribbling clears the "swarf" (metal grains) from the abrasive paper so that it can continue to cut. Need your opinion on warped heads...are they typically softened and therefore likely unlikely to hold valve seats and guides tight? motoman
Haven't seen any warped heads and if I did it would be a no brainer replacement .
They erode &/or distort at the bridge.
If you want a ten page thesis on why this happens pm me & I will ( eventually ) get back to you.
Basically it is bad design allowing the alloy to flow upwards between the two bolts on the push rod tunnel which could have been fixed easily but wasn't for some pig headed reason probably made at board room level.
The fact that some do & some don't is most likely due to subtle differences in the chemical composition of the alloy which will vary a little from batch to batch and within an actual pour as silicon in particular burns out of the metal.
This has led to all sorts of myths like inteks on Toros are better than Inteks on AYP's but it is most likely a random selection as to which engines got what heads from which pours & at what time in the pour and even what alloy had been in the furnace immediatly prior to the heads.
Aluminium silicon alloys used in cast heads on air cooled engines actually harden with age.
In order to softem the head would need to be solution heat treated which means getting up to around the 300-400 deg C mark and staying there for a long time.
The Aluminum - Silicon- Copper - Manganese -Iron alloys used in die cast water cooled car heads is a different matter.
While some spots on the head can ge quite hot momentarily the heat is conducted away very quickly so very rarely gets above a critical level.
People who do not understand heat flow through metals see combusion temperatures and tables of heat treatment temperatures and jump to totally wrong conclusions.
I liken it to welding.
The temperature of an oxyflame is around the 2000 deg C mark.
Aluminium melts at around 700 deg.
So why does the entire head not melt when you weld ?
Because heat gets conducted away which is why you need to preheat aluminium to oxy weld it properly.
For the exact opposite reason you also have to preheat cast iron before you weld it or it will crack.
