Radial shaft oil seals should be installed firmly into the crankcase for a tight and secure fit. The inner circumference of the ring is the contact point to the rotating shaft and is mostly held in place with a circular spring to keep it sealed tight around the shaft. These items wear out regularly and should be replaced during every service of your motor. If the motor has not been run for a while the seals could be damaged. If the revs of your motor increase while it should be ticking over, the oil seal on the flywheel side of the crankshaft is probably defective or damaged. If you discover fuel mixed with your gearbox oil, the oil seal that sits on the clutch side of the crankshaft is the likely suspect.
We have oil seals produced by several manufacturers available, constructed using a variety of materials. The blue and black versions are made of a synthetic rubber, the blue type mostly produced by CORTECO are a little tougher than the black type which can be found in most engines as an OE PIAGGIO component. The brown seals are produced using a fluoro polymer material (FPM) are especially heat resistant (up to 160°) are harder wearing with more resistance against oil. Both types see wide spread use in all two -stroke motors.
Here at SIP there is no consensus amongst us as to which type is best, so we have solved this problem as PIAGGIO has done and stock all colours and types to keep everybody happy.
Helpful hint: As a rule of thumb, to ensure correct positioning of your fresh oil seals, the 'open' side of the seal always faces towards the one of the chambers that it separates, with the higher pressure. This higher pressure also helps the inner circumference maintain the seal to the shaft by pushing the inner edge against it.
SIP-TIP: Loctite oil seal adhesive keeps oil seals in place effectively, even in worn crankcases.