Hi. I have Sherco st 300 2014 and i just ordered new crankshaft bearings to it. Now when they finally arrived i noticed that they are rubber sealed. Is that normal? Have anyone used such crankshaft bearings with seals on?

 

4 hours ago, Markus-R said:

Hi. I have Sherco st 300 2014 and i just ordered new crankshaft bearings to it. Now when they finally arrived i noticed that they are rubber sealed. Is that normal? Have anyone used such crankshaft bearings with seals on?

 

Yes that is standard on Shercos. Initially (in 1999) Shercos came with open main bearings and they didn't have a long service life. It was found that sealed bearings lasted longer.

Main bearing ventilation/lubrication ports that existed on many two strokes previously, was lost in pursuit of a narrower engine when the Sherco trials motor was designed.

This cleared it up. Thank you! 🙂

2016 Beta 125 also has sealed main bearings.

Yes, it is normal for crankshaft bearings to be rubber sealed. The rubber seal helps to prevent dirt and contaminants from entering the bearing and causing premature wear.

Rubber sealed crankshaft bearings are a relatively new development, and they are not yet as common as traditional non-sealed bearings. However, they are becoming increasingly popular, as they offer a number of advantages over non-sealed bearings.

It's a little simpler then that;  All 2-stroke engines need main bearing seals to function.  Crankcase on a 2-stroke engine is used to force air and gas mixture through the engine via vacuum or positive pressure differentials, if the 2-stroke crankcase was not sealed on at least one side of a main bearing the engine would not function because air pressure differentials caused by the movement of the piston would leak past the crankshaft bearing.  A crankshaft roller main bearing will be open to whatever side it receives lubrication from, be that via lubrication in an adjacent transmission case or via oil pre-mixed in the air/fuel mixture.

The seals in the crank bearings aren't for sealing the cases, both Beta & Sherco who use the same bearings still run normal crankseals outside of the bearings

1 hour ago, tony27 said:

The seals in the crank bearings aren't for sealing the cases,,,,

It's a 2-stroke engine, if the crank case is not sealed from atmospheric pressure your engine would not operate.

Edited August 26, 20233 yr by lemur

11 hours ago, lemur said:

It's a 2-stroke engine, if the crank case is not sealed from atmospheric pressure your engine would not operate.

No argument about why two strokes need crankcase seals but we are not talking about crankcase seals, we are talking about seals for the internal parts of the crankshaft main bearings. Rubber - sealed bearings are used to help the bearings last longer in motors that have poor ventilation/lubrication of the crankshaft main bearings.