Head button?

Just exactly what is a "head button"? A disk with a hole in it for the glow plug thst sits on top of the cylinder sleave and is held in place by the head? Why are the used?

Some engines are manufactured with a 2 piece head assy. The
"button" is just as you described, a cap for the cylinder that contains the machined combustion chamber w/ glow plug. This is secured to the cylinder liner / case assy by the head or "Clamp".

Some reasons for its use may be ease of manufacturing, parts commonality, i.e. use different head buttons on different models with the same clamp / case assy. Also good for prototype work or modifications, the head button is a smaller easier to machine peice that can be experimented on without the need to machine all the cooling fins, bolt holes, etc.

Heads can be made with a casting process, but still need machining in the combustion chamber. Using a finned "clamp" with a head button lets the button be made entirely by simple machining processes, faster and easier than machining on the casting. You have a two piece head, NOT a "button plus a head". Casting is a comparatively less expensive way to produce model engine parts. Machining type processes are expensive in comparison.
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Kiwi

>Just exactly what is a "head button"? A disk with a hole in
>it for the glow plug thst sits on top of the cylinder sleave
>and is held in place by the head? Why are the used?

The Fox 40 (and others) used a head button with the cast head "clamp". The Fox "hemi" head does the same. I suspect that Marvin, when "playing" with these, first machined a stock head to accept the "button" so he could develop the best head shape. In fact, the process allows him to continue experimentation along these lines if he so desires. When Art Adamisin developed the wedge head for the FP 40, he machined a stock head to accept a "button" and then made the button into a wedge. This also allowed him to turn it to match the direction of fuel flow from inlet to exhaust which is at an angle on the FP (and similar) designs. Lew Woolard takes advantage of this with his Fox 40 conversion. He machined a number of different head buttons to come up with the best compustion chamber shape for his engines. We did the same thing for the FP for a while. In fact, we have a special head that takes a Fox button so we could use it to experiment with different chamber sizes. Trouble was, in our case we never came up with one that was better than the stock FP for the way we modified them. So we work with deck height only and don't mess with the chamber. But it would have been a long process if we would have had to machine a new head for each contemplated change. Oh, and some manufacturers may do this during the development stage and then cast a one-piece head for production models. Usually the only part that needs to be machined then is the glow plug seat on one side and the gasket or head shim on the other.