HONDA Retainer Upgrade Kit. The Honda AP1 S2000 F20C is an excellent engine but had some underlying issues. The F20C has been known for dropping valves as a result of the valve retainers cracking after being over revved. What is the best fix . Upgrading your valve retainers to the improved and much stronger AP2 retainer. This kit contains the required quantity for the intake valves, which are more prone to cracking. If you want to upgrade both intake and exhaust valves, you will need to select 2 units.. Maintain your engine just as Honda intended. Suitable only for S2000 F20C engines. You will receive 8x 14765-PRB-A01 & 16x 14781-PCX-004.