Joined: Jan 2010
Posts: 9,797
Likes: 1,762
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
If any of the shims/washers that come with derailer pulleys are made of plastic, beware.
I've seen carnage (including my own visits to a doctor) resulting from a loosened pulley bolt, which can result from any crud that might be sandwiched between the mating surfaces that are clamped together by the bolt. When the dirt/crud (or plastic washer!!!) later takes a set from the compressive forces, the bolt may lose significant tension and allow either pulley to wander about.
The moral of this story is to use Loctite on pulley bolts, or to at least have only wiped-clean, metal surfaces being clamped by the bolts.