Hi can any of you clever bods tell me how to change my 18speed marin quake 7.2 to a 9 speed with slalom chain device such as BLACKSPIRE NSX C4 CHAIN DEVICE 4 BOLT WHITE 32-36t or MRP System 3 Slalom chain device. As i just do not use the lower gears and wish to reduce chain slap more. I am currently running a shimano hollow tech B/B and truvativ drive.??

I have already removed the front derailleur but it keeps dropping to the lower Cog over the lumpy stuff.