Hi All
Have got a 318 and am about to fit new exhaust valves. Is it a good idea to recut valve seats on unleaded heads 1975 onwards? I don’t know whether they have got hardened inserts or the ‘spray on’ hardening coating. My concern is that if it is the hardened coating, getting the valve seats recut will remove all the hardening.
Any thoughts very much appreciated.
Terry
Factory heads have induction hardened seats, not that I know what that is. I have cut the seats on later big block heads for bigger valves and they were rock hard all the way so it's not just on the surface. Re cutting your seats won't go through the hardening IMO.
yeah induction hardening goes right through on small parts
they use a magnetic coil to induce currents through it which heats it up mighty fast then they quench it
as such becasue the magnetism heats reasonably evenly all the way through, if the part is small enough the quenching results in a work hardened thing
its just another way to basically work harden something, tangle up the crystalline structure of the metal alloy so it doesn't flow or move easily under force i.e increase hardness toughness but with that comes some brittleness
convert one to the other by hitting it or heating it, and then based on material fixing the tangle you cause, by quenching at the point of maximum tangleness. (if you let it cool naturally, you let it untangle)
or you make an alloy from a soft and ductile metal and stick a load of stuff in it to cause irregularities in the structure to stop easy movement
think aluminium with silicon in it rock hard and brittle
lead with antimony in it not so good in ya pencil
or iron with the right amount of carbon cast basically
same principal for a seasoned engine block well worked... its been vibrated and heat cycled to the extent that it has work hardened to a final position. a brand new block will slightly change shape many times throughout its first few years of use until every molecular tangle in its structure gets well knotted and stops the movement .
Dave
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