2006 year CC RZT 50 blades speed

[staninlowerAL]

This question is about positioning the 3 blades on the 6 point star spindles of this mower. I have used this setup for about 7 years without any problem of the rotating blades making contact with each other using OEM and aftermarket standard blades which the OEM parts manual lists as 17.9 inches. I recently changed the blades with a new aftermarket set and positioned the blades such that they were not in position to contact each other as is my usual practice. After installation I manually rotated the blades with the belt in position to ensure that all was well and as it should be and after a few revolutions the center blade made contact with the blade next to the discharge opening. I removed the center blade and compared it with the one that was removed and discovered that the new blade was slightly longer than the one removed so I removed the excess length and resized the length to match the old blade, reinstalled it and all was well. Ran it about 3 hours without further incident and concluded that the new aftermarket blades are slightly over length. So here's the question: how is it that the new blades, positioned on the spindles such as they are not in position to touch, driven by the same belt/sheave and the spindle sheaves the same size so in theory they would run at the same speed and not reposition the blades yet in actual use the blades are not maintaining their installed position relative to each other? This is in a no-load configuration. My conclusion is that there has to be some belt slippage for the blades to reposition. Agree or disagree? Any other reasonable explanation? I'M STUMPED!!!!! Sorry for the long post but I cannot come up with a reasonable answer. Thanks for any and all input. Stan

 

[Jim Becker]

A little slippage can do it. In a low speed and no-load situation there should be so little slippage that it would take a lot of turning to accumulate 1/4 revolution difference. Another source of a difference in speed is in the pulleys themselves. A slight difference in the width of the V in a pulley will slightly change the effective diameter. Over time, the pulley groove will wear, making it wider and reducing the effective diameter. Twenty years can take a toll. Is it a single belt drive or does one belt drive the center spindle with another belt from the center to the outer spindles? If multi-belt, the center pulley is subject to twice the load and more wear than the outer pulleys. This is why cogged belts are used where absolute synchronization is needed.

 

[staninlowerAL]

Thank you, Jim. This is a single belt drive system and the routing is from the engine/pto clutch to the right (discharge side) of the deck/sheave then to the center sheave then to the outer (left side) then back to the engine. I'm not an engineer and had not considered the possible variance in the width of the sheaves would cause a slight difference in the speed so that's probably the answer. Never having experienced this situation before and now this happening has taught me to be more aware of the absolute overall length of the blades. Having temporarily resolved the initial problem, my plan now is to sharpen and reinstall the blades that were previously removed and in the process I'll be sure to check the other 2 new blades for correct length, I will not be surprised if they also will not need a slight length adjustment to get them to spec. Best, Stan