My thought . because of the molded single piece, flanges & toothed pulley design, the chain oil dirt combined solids, packed in, have no place to go..
Wondering if a few holes thru the flanges .. a part of some of the CNC after market pulleys . gives some of that inevitable accumulation a way to sluff off and out..
3 speed , its no issue , backing disc gets a bit grimy , but it does not rotate in unison with the lower pulley ..
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