This is a Broken-in replacement piston/sleeve/rod replacement for Ultimate Racing M5S or the OS B2103 type R. This Piston/Sleeve/Rod is bench broken-in using the heat cycle method using our special break-in fuel. This Piston/Sleeve/Rod has then had 250cc of the 30/8 blend of fuel ran through it as well. This replacement Piston/Sleeve/Rod allows you to rebuild the Ultimate Racing M5S or the OS B2103 type R with a drop in broken-in Piston/Sleeve/Rod. We recommend running 2 rich setting tanks of fuel through your vehicle before you put that race tune on it.
