i have been boring out the stock tc cylinders for the 107 kits for 10 years or more. never had a bad set and most of them were ridden on the hard side with no issues. the only problem i see is it is a one time bore. there are no rebuilds using this kit, however the S&S kit has .010 smaller pistons so they have one more bore job left when a rebuild comes. if the 107 kits were having issues the info would be all over the net. dvr