TF100 issues

[speedpro]

That porting, except for the inlet, looks very much like my old TS motor. The exhaust port shape is quite distinct. i see on the piston below the ring on the exhaust side that it has picked up a little bit. I can't see it but I bet there is a little bit of smeared alloy above the ring on the exhaust side. The smear will be up making a little lip on the edge of the piston crown. The little bit of staining above the ring is similar to what I used to get.
RG pistons in TF motors crack regularly once you open the ports up enough to make some power and rev them. I think the KT conversion is a good idea. The TS combustion chamber shape is not flash but can be machined to correct without the need for welding.
In my experience kart shops have some "distinct" ideas about the finish required on the bores which is at odds with regular motorcycle theory. I had my MB/KT bored and honed to 1.5-2 thou and then ran a whole tank of gas through it to run it in. My piston & ring has done lots of hours. I'm gonna run it up on the dyno and get some numbers and then fit a new ring. I'm not convinced about the need for new rings every few hours.

[F5 Dave]

. . . I'm not convinced about the need for new rings every few hours.

Yes but your ports will have been chamfered properly. Sharp port edges will accelerate wear. Some ring materials wear quickly but lots of revs & minimal oil are not good. Thinner rings are good for revs but I would venture wear the circumference quicker in extreme conditions. Measurement of the gap will answer the question pretty quickly. Good point about the ring land smear.