Posted by Dennis Novotny (126.96.36.199) on 17:01:24 25/02/05
In Reply to:Comparison data of hardfacing used on valve internal parts posted by Tony Smart
The hardfacing alloy used on valves must be integrated with the material used for the seat - namely, they must be compatible.
One also has to integrate the coefficient of thermal expansion of the H/F material to that of the parent metal on the valve.
More improtantly, the alloy that one chooses must be verified for use in the engine. That is, Stellite 6 might work fine in engine A but not so well in engine B. Yet Colmonoy 5 might work perfectly in engine B but fail miserably in engine A.
One has to keep in mind that seats can move around a bit and valvese need to be able to conform. If they don't, they will burn. Thus, if you make the seat "unwearable", you could end up with valve problems because all the wear/conformability will be confined to the valve.
Conversely, if you over fortify the valve, you could end up with seat pound-out and/or acclerated wear problems, especially in an aluminum head where the seats are moving around a lot.
The application and use of Valve seat and/or valve face fortification is an art as well as a science. Moreover, it is a technology that is loaded with compromises.
I'd suggest a review of SAE spec J775 for valves. I seem to recall that there has also been an SAE spec released for valve seats but the spec number escapes me at this time.
The Eaton, Mahle and TRW engineering departments are excellent sources of information regarding valve facing and seat alloy compatibility.
Their experiences can prove quite beneficial as compared to "alloy specification comparisons" when it comes to selecting and using valve fortification, especially when the H/F'd vavles will be used with seat inserts.
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