It is an important result, Paul: it proves that the combination of that height of decompressor lift, and valve train compliance, can't make the decompressor work. Since the valve train isn't worn out or broken, the only way we can fix the problem is to increase the lift of the decompressor, at the camshaft.
The ideal way to wrap that point up would be if someone has access to a new Tecumseh camshaft and can measure the decompressor lift. Failing that, a measurement from a camshaft that has a working decompressor, would at least complete the record for us - but what is really needed is the correct dimension for a brand new camshaft.
It seems to me there are now two feasible ways to go. The first is to make a longer decompressor pin. The second is to replace the camshaft. Can you post some detail on how the decompressor mechanism comes to pieces, so we can talk about the first option?
The decompressor pin height does not need to be doubled, it just needs to be increased enough so that it will take a while to wear down to the point where the decompressor stops working. We know that your decompressor just barely works if the tappet clearance is reduced to zero. The correct tappet clearance is 0.004", so if you added 0.004" to the decompressor pin, it would just barely work with the correct clearance. It therefore seems the pin needs to be at least 0.008" longer if it is going to work for a few years. Making it longer than necessary is likely to impose some ugly side-loads on the pin, and might score the surface of the tappet. By far the best solution would be to get a measurement from a new camshaft, if anyone knows how we can obtain that information. If we can't find out, in the end a new pin will need to be made with a guessed length.
So:
Question 1: what pin height do we need?
Question 2: can the old pin be removed and replaced without damaging anything?
Question 3: can we get exact dimensions of the old pin, so a new one can be made (access to a lathe required, followed by flame-hardening).
