2010 250 Sherco main Bearings
Not trying to rubbish any manufacturer the comment's about samy's main bearings were made by myself.
The crank seals do require replacing due to heat, fuel and lack of lube
Normaly the stator side seal fails first because it only gets lube on one side (fuel oil mix) and hot dry dust on the other, the gearbox side seal lasts longer because it gets lube on both sides ( fuel oil mix & gear box oil) the fuel/ oil helps cool as well as lubricating helping them seal.
I think they are using sealed bearings to reduce air volume in the crankcase and increase the air pressure from the bottom to the top end between strokes, but i also think it causes a lack of lube and cooling to the rear of the seal and increased wear, when the seal starts to fail the bearing will then fail from excess air and dirt induction
all fuels and 2 stroke oils are different some better than others and may cause a different service life of the seals , but we should change the more often than we do its a cheap way to stop big failures
The bearings and seals replaced in samy's bike are genuine sherco parts but I removed the dust seals from the bearings
Just my opnion.
