Like all of us that have the XT660`s , the cush drive rubbers wear is a pain.
I found an article some time ago on the XT660.com thread.
The chain drive sprocket takes a tremendous load from the power of the engine , which causes the rear wheel bearing to wear excessively , even wearing the Chain Drive Hub Housing ,
The bearing will become loose in the housing at a later stage,
I fitted a double row bearing as apposed th the std single *row bearing.
And with Polyurethane rubbers .I got 56 000km without changing the rubbers again.
You only have to machine the rear hub bearing housing 5mm deeper /
The Bearing I used is still the same dia. as the original.
And machine the inner spacer also 5mm shorter.
It still uses the Standard Yamaha Seal
[size=10pt][size=10pt]Bearing no, 62364.EE From Bearing Man
Polly Rubbers R950 posted , South African Rands or $95 Aus Dollars / R800 in SA