Building a 393 for my 69 Fastback and while taking apart the 351w that is in there, I was pretty surprised how badly recessed the exhaust valves in three cylinders had become. One of the valves is the thickness of a 50 cent piece into the head. Hopefully you will be able to tell from the picture. Remember, if you are using old heads, put hardened seats on the exhaust side.
That's what happens with no lead in the fuel any more. The additives I tried a few year back never worked and lost the valves in less than 8k miles. Now there are hard seats in place. Later on toward 1980, the iron was hardened in that area to help this problem.
I think I may have worn through the seats and into the head! Nothing a new set of aluminums won't cure!!!
Wow, now that got me worried about mine! When I had my iron heads done, they are 71's I wanted the guy to put in stainles steal ex. valves and asked about hardened seats. He said that was a myth and said brass valve guides where all I needed. He said the brass dissipated the heat and the valves would not be damaged. I have 900 miles on them so time will tell. Joe H.
Ray & Max, I couldn't get a hold of my machinist today but work with a very close friend of his. This guy also stands by the myth theory also. He runs Chevy 350 built up very well and run hard for 5 yrs. now, same builder. Said the problem with no lead is when the exh. valve gets hot it magnetizes and the carbon deposits get stuck up around the seat area and this causes the valve wear. The brass guides help prevent this and also help with a better lube of the valve stem, they slide better. I work at a powder metal plant and a possible future product line in the works is a high alloy copper valve seat for an auto maker in Europe. They are looking at heat dispersion for the alum. heads. The guy that built my engine has a good following in my area, thats why I went with him. I have also heard other comments from guys at car shows that said for a classic that is driven few miles yearly there does't seem to be any problems. I guess time will tell and if my valves wipe out then I'm the idiot for listening to the wrong one. Joe
Well, even the proponents of hardened seats and all the studies suggest that most the wear occurs at higher rpms over longer duration trips, so if your just puttin around town, there is no need to worry too much. Not sure if the bronze valve guide theory really has any merit. I'm not an engineer, but I did stay at a Holiday Inn Express last night!
