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I think that the reason you don't see anything beyond 3rd bore is at that point you would be affecting more than just the pistons required. You would need to look at re-jetting, maybe even re-carbing, possibly cam profiles, valve sizes, etc to handle the increases.

If it wasn't that I had heard about the hourglass shape, oh and that refers to the outside diameter of the cylinder liner, not the bore as it gets worn, I would have no problems punching it out to 82mm. I know that at that point I will have to re-carb, and maybe even go bigger on the valves, check valve clearances, etc. Plus the 600 cam is ground for torque down low.

I was hoping I would not have to go it alone on this. That there had to be some sage wisdom out there.

Cheers,

RD

Kurt in S.A. wrote:RE: the cylinders and sleeves... I just measured the liners on my R100/7 cylinders...I did my best to measure right at the top where the edge of the sleeve is exposed. Not a very accurate number but it's about 6mm.

I always thought that the iron liners had a flange at the top (to "rest" the liner against the cast cylinder, and prevent it from slipping and sliding in towards the crankshaft), but now I cannot say from where I got that impression. Perhaps since the spigot diameter of the R100 cylinders is smaller than the visible diameter at the top.

Anyhow, I just went and measured the diameter of the iron liner at the bottom of a couple of R100 barrels I plan to install in the spring; and the liner is about as thick "outside" the machined 99 mm diameter spigot as the thickness of the spigot itself, so then presumably 6 mm thick (where it is in contact with the alu cylinder) all the way.

My view on the max 3 rebore over-sizes is that a rebore shall not modify the capacity significantly, from a taxation / insurance etc. point of view. And not that it isn't neccessarily technically possible to bore out R60 barrels to R75, or R80 capacity. Obviously, if one could bore out e.g. 73.5 mm cylinders to 84.5 mm, there would be much more material to remove. Which may translate to higher cost, and perhaps also the risk of ending up with a mis-aligned bores if the job isn't done properly. But even if the rebore job would cost a bit more, that could be balanced against obtaining used standard size R75 (or R80) pistons, instead of perhaps hard to find, and expensive new R60 +1, or +2, sized ones?

I also see the point that the barrels have _cast_ 10, 80 or whatever capacity markings. If they indeed were intended for only one displacement, this would perhaps be shown by the outer diameter of the iron liners of R60, R75, R80, R90 and R100 cylinders?