gear mesh problem
 

hey guys,

my gear mesh has been good for about 2 months, so i took my engine out to clean it the other day and when i put it back it i thought it was as close as it was before but i ran it and stripped the 1st gear spur gear, so i had another one and made it a tighter mesh and it ran for about half tank and then they started to tear up the gear ... whats causeing this?? and is there a gear mesh base line?