Thread: ***valves, heads, exhaust seats,...***

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It's a little different with a flathead, the valves are in the block. So, is you were to do hard seats, you'd probably want to go ahead and do the bottom end as well. I mean, the motor's out of the car, so why not. I also have run soft seats on unleaded and you can get away with it for a while. In the end though, the valves will recede into the block and you're done.

I never fully understood how the valve recession thing worked until I read the explanation by Mr. Bob Parmenter. As I recall it, it is as follows:

When welding, you must have both surfaces to be joined together completely clean and free of foreign materials so that you get a good joint. If the joint is dirty, you can't weld it very well. That is what tetraethyl lead did for the motor. I dirtied up the joint between the valve and seat so that no welding could take place, because that is exactly what is happening in a motor running on unleaded. There is no foreign material in the fuel like there was in the earlier fuels using lead, so every time the valve seats itself, a little spot of weld takes place. Then, when the valve opens, that small piece of weld is torn from the valve seat and recession of the seat begins.

The other thing tetraethyl lead did was to place foreign material into the fuel/air mixture. This foreign material resisted burning and so slowed down the "explosion" initiated by the spark plug. With a slower "booooooooooom" instead of a "BOOM", the fuel was more detonation resistant. The speed of the burn can be likened to a football team. If the ball runner (the initial flame kernel) can travel down the field without encountering members of the opposing team, he can reach the other end of the field in short order. But, if there are foreign materials in the fuel/air mix (people trying to tackle him), he must bob and weave and that slows him down in getting to the goal. This explanation is perhaps too elementary, but it should give you an idea of what is going on inside the motor with unleaded versus leaded fuels.

yup.... the lead additive would be the cheapest way to run for a while, problem is its getting harder and harder to find lead additives, i dont know about other states but in california its nearly impossible because of the EPA