How is the Small End Bearing Lubricated

[Chris0381]

Its been about 2k miles since I re-did my top end after either a wrist-pin or a small end bearing failed after 6k hard miles. So now that I am working on my scooter again while working reduced hours I am wondering what caused the initial failure.

Some questions come to mind: Would upjetting for more lubrication help with the prevention of a circlip or small end bearing failure ? Could a lean condition have caused the failures. when there was no signage of seizing soft or hard?

I don't know exactly what part actually failed as the small end bearing  disintegrated along with one of the circlips.

The scooter is running well now after 9k total miles and wonder if a little extra lubrication from an upjet would add a factor of safety to prevent a wristpin(circlip) or small end bearing failure.

Then the question is: how is the small end bearing lubricated in a 2 stroke motor since its at the bottom of the piston ?

[dan v.]

Like any two-stroke the lubrication is from the fuel/oil mix drawn into the crankcase - so the wrist pin bearings are lubricated the same way the piston and crank bearings are.

Lack of proper lubrication usually causes a seize first.

Poor quality small end bearings or improper installation of the circlips will cause small end failure.  Extreme care must be used in ensuring that the circlips are seated and clocked properly.

Increasing the jet size will not increase lubrication per say.

Kymco has an adjustable oil pump - is it within spec?   Are you adding additional oil to the fuel?

Did you dis-assemble the engine and rebuild it after the failure?  You don't want metal bits remaining in the crankcase.

[Chris0381]

Kymco has an adjustable oil pump - is it within spec?   Are you adding additional oil to the fuel?

Did you dis-assemble the engine and rebuild it after the failure?  You don't want metal bits remaining in the crankcase.

Yep oil pump cam is withing marks. Replaced with a HOCA piston kit. Working nice after 2k miles so far but wondering if I should maybe some how add a factor of safety in there.

[Ruffus]

Just to show you what can happen to a four stroke motor too:
This was / is a piston of a Like 125 ( we don't know exactely what caused it, because the scooter came without cylinder and cylinderhead) but a friend of mine who built and rebuilt motors for decades, said after seeing it, most probably wrong or old or no oil at all in the motor. Piston bolt was tight but easy removeable and its lubrication openings are free. Odometer says around 24000 km. Mainbearings are pretty good and free of friction or play. Like I said we do not know for sure what this demage caused.
Happy and safe scootering, Ruffus