Pre-load is light, meaning about a 1/4 turn. The holes are for more or less shifting options,I only use the center hole as I couldn't tell a difference when put in 1-2 or 3. If you buy the heavier spring then you'll feel a BIG difference. There isn't a brass bushing on the driven unit as the belt rides at the top of the puilley during idle and goes closer to the shaft as you speed up- there are rivets close to the shaft that will shred the belt if it ever goes that low.
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