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Sorry I haven't been keeping up with this thread, but I have been having to work non-stop since my last post. I've hardly had a chance to ride either; I think it has been one wash and about 150 miles in almost 2 months.
Anyway, increasing the bore isn't quite so easy because Triumph uses an open block configuration; meaning the upper half (approximately) of the liners are not supported. The liner has to be thick enough to withstand combustion pressure and piston thrust without excessive deformation wile only being supported at the top and bottom. And the liner geometry is more complex than one that is intended to fit a conventional block. There is a flange in the middle of the liner that registers it against the upper case and provides the water-tight seal (along with some sealer) as well as a flange at the top that registers against the head.
To increase the cylinder bore, you first need to overbore the upper case to accept a larger liner (assuming there is sufficient case material to allow that). Then you need to enlarge the flange clearance in the head in a similar manner, again assuming there is enough material in the head to allow that. Then you need to have new liners made that are sufficiently thick to provide the proper support for the larger pistons and fit the new, larger openings.
To minimize the amount of additional space you need, you want to use the strongest possible material that has thermal expansion properties matching those of the piston, otherwise you need to run excessive clearance. That means either using high silicon content aluminum alloy (Alusil, Nikasil, etc.) liners like are used in the Daytona engines or MMC (metal-matrix composite) if you really want maximum strength, minimum thickness and to spend lots of money.
As for sources, U.S. Chrome is as good as it get for the actual coating as far as I'm concerned, but I'm not aware that they actually custom machine sleeves for anything but conventional blocks. In fact, I don't know of any firm here in the U.S., with a track record, that is, (no pun intended) that does. I certainly don't know nearly all the firms in the business, so I'm open to suggestions. As far as I know, Perfect Bore in England is the most likely source of custom sleeves of that type.
I have a spare upper case that I purchased on eBay for the purpose of determining if there was sufficient material in the case to make this practical. I need to either have it sonic tested to determiine just how much material there is to play with. Then I need to find someone to loan me a head to do the same thing. Unless there happens to be nayone on the board with connections to the factory. That would be the easy way to get the job done.
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