They work a lot better with the casings done,supposed to cool the cylinder better. As already said they are tight as new and will even seize at 30 mph . I have done a few 166's , one made 15 hp with a Simonini and 28 mm carb ,another with a Scorpion and 24 mm carb wasn't dyno'd but blew the other one away with similar weight riders. The kit benefits having the compression lowered to prevent pinking.
they do need a good hone out, very tight from new. but good vfm. one of the local lads runs one just bolted on , sito plus, 24mm carb, 21 tooth clutch, goes well and a few oversizes when it needs it.