intAct YTZ5 S Gel Motorcycle Bike Power Battery Lighting_Bulbs & Accessories Early engines were also fitted Vespa GTS Early engines were also fitted with a shorter cylinder (Only 3 cooling fins under the exhaust port rather than 4 for the later cylinders) recommended chain length: 112 links (58T) Model Year 491 RR 50 2001 2002 491 RR LC 50 2001 2002 2003 2004 2005 2006 491 Racing LC 50 2001 491 Replica LC 50 2002 2003 2004 2005 2006 491 ST 50 2001 2002 491 ST AC 50 2001 2002 2003 2004 2005 2006 Naked 50 2001 2002 Naked 50 2T AC 2002 2003 2004 2005 2006 Pepe LX 50 2T 2003 2004 2005 2006 Derbi one of the toughest series in motorcycle racing