Another option is to avoid the entire problem, discard the idler pulley assembly and adjust the belt tension by sliding the whole compressor in or out on the slotted holes provided in the mount. All that's necessary is to slack off the 4 mount bolts and maintain alignment of the pulleys when doing this; a yardstick laying across the AC pulley and crank pulley is sufficiently accurate. The ball bearing inside the idler pulley is not long-lived and is difficult to change when (not if) it fails. Note you may need a slightly shorter belt if the idler is discarded. Mine went away in 1990 after failing at a Laguna Seca open track event, and hasn't been missed.
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