Just to provide some perspective, I followed the LP manual's instructions for slipping the PTO clutch (loosen all PTO bolts two turns, slipped clutch verified by marks and retighten all PTO bolts two turns). The PTO clutch was working before I slipped it (did not allow slippage under normal operation but provided slippage during hard contacts - I have had a couple reclaiming a field), and it is back to where it was.
The PTO clutch friction/compression is not some highly precise setting. It just needs to be enough to allow normal operation with the ability to slip under a high stress situation - that is a very large envelope of acceptable adjustment. To be on the safe side, you would want to always be adjusted towards the lower end of the envelope (regardless of PTO HP). If you notice slippage during normal operation, you could tighten it to resolve it.
Cutters that use shear pins typically use one type of pin regardless of the tractor PTO rating (so long as it is within the appropriate range for the cutter).
There is no right choice between slip clutch and shear pin; each have their own benefits and problems. I prefer a slip clutch on a rotary cutter (high probability of a hard strike), but I have shear pins on my finish mower and spreader (low probability of a hard strike/blockage). Shear pins do not always work as expected either (breaking too easily or not at all); they are not a high quality control precision made product.
I wonder how many shear pin protected PTOs have rust on the mating surfaces/flat ends of the shafts at the shear pin? Would that impact the amount of force required to break the bolt?
The point of the post was a reminder to service your PTO slip clutch, and you should also periodically inspect/disassemble your shear pin link too - unless you have replaced it within a year or so.
