I notice that the new Yamaha YZ motors have covered crank wheels with just a slot for the rod to pass through. The European ICC kart motors also have this. What is the "on track" benefit to this?Has anyone tried to retrofit this setup to a CR125? How would this effect the life of the big end bearing?
Covering the crank journals increases the compression of the piston down stroke-less crank case volume.
This increases the velocity of the fuel mixture up through the transfer ports.
I would not expect any change in crank bearing life.