In answer to PaulF's question, I believe that this is stock iron parts used on the AVL bottom end. It is sold in India as a kit including, as mentioned, an iron cylinder, piston,head and carb, which then simply bolt on. Other Indians are replacing their AVLs with standard iron engines, either new or rebuilt. Iron engines are both traditional and apparently have a different "sound" which the Indians prefer. I think the iron cylinder would be quieter as well.
If one were to use the AVL lower end, there would still be greater reliability of the mechanical oil pump and the piston rod's needle bearing big end. The mindset of Indians would also be different since they are so used to the irons and most seem to prefer them.
When I mentioned the figure 40K kms, what I was told, by Lalli Singh, of New Delhi, was that they were getting
at least that on their AVLs. Lalli rents bikes for tours and also repairs them, so is in position to know.
Last evening I went into an Indian site that gives diagrams of parts for Irons and AVLS
http://jainenfield.com/index.html and found that in reality, though there are different parts in the two types, there is also much that is interchangeable. I take it from what has been told me about the CI kits, that this includes the hole pattern for the cylinder studs in the casing. The stroke is the same for both engines, but, of course, the pistons are different.
I have had to consider what might be needed in the way of spare parts because of the long time delay in getting them, so have already been stocking up. I don't think spares will ever be a problem though - there will always be after market sources in India as well. With the low speeds and small size of the island I live on, I doubt if I'll wear my engine out in any case. Maybe I'll drive a thousand miles a year, mostly for local errands.
One interesting thing is that export markets for Indian parts has grown and this is driving up, to some extent, the price of parts sold in India. Part of the globalization process which will eventually see a leveling out of the economics of all participating countries throughout the world.
My own opinion is that we have happened on an ideal older British type of bike for which parts will always be in ample supply. We should consider ourselves very fortunate - at least I do.
Regards,
LJ