3rd strengthens gear box for engine YX 140/149/150/160/170

This set of reinforced gears is updated with the new drum reference 4121
 
Specially suggested for YX 1P60FMJ et 1P60FMK
engine shaft 18mm (after 2009)
a 3rd gear modified from left side
a 2nd gear standard (because the tooth wear at the same time as those of the gear 3rd
an additional washer to place on the right side of the 3rd gear
 
should control the fork, when the gear disconnect too much it need to replace simultanely