Good points. I will measure the sheaves and box with calipers to be sure. If it is possible to increase the diameter of the sheave I will definitely do that. I doubt that I can increase the width.
These sheaves carry loads for outhaul and reef lines. The outhaul has been modified adding purchase and loads are not high, but the reef lines get big shock loads. I'm guess that the reason for using aluminum vs. delrin is the high loads. Can delrin handle high shock loads?
Do you think that the fiber bushing is important?
These sheaves lasted 30 years, what finally did them in was corrosion. Unless I get the wrong sheave I won't be replacing them again in my lifetime.
And, thanks for the help!
The outhaul is typically 30% of the clew load, and as a guess to what kind of boat you have (34'), I thinking the max outhaul load is in the 750lbs range, but because you are turning the line 180 degrees the sheave is seeing twice that load.
Rough calculations for Delrin at 9000psi tensile gives you a sheave strength of roughly 3800lbs = plenty strong. The best part about Delrin is that it is a natural bushing material, so you dont need to bush it for low friction or wear strength.
Aluminum, on the other hand, MUST have a bushing. My only suggestion, if you go with oillite, would be to make sure that the wall thickness is at least .125", A typical oillite bronze bushing is sintered where you take a bunch of bronze powder and force it into a mold with a little heat and out pops a bushing - good for cheap manufacturing options, not so good for long term durability - I've seen bronze bushings egged out and squeezing out of the hole they were pressed into. I dont see phenolic used much anymore - it works well, but is a mess to machine, and Delrin works just as well.