Originally Posted by retrodog
Belts are hard to give expected lifespans to. There are a whole lot of different variables. I have seen belts fail at 1 hour and at over 1000 hours. If a belt fails twice the same way is the usually when someone figures out there is an issue. Anytime a belt fails i recommend inspecting each pulley for play, bearings out, rough spots on the pulley where the belt rides by spinning pulley with your finger sitting where the belt rides to notice imperfections. Also i like to look at the entire belt when its on to make sure there is nothing loose or out of place that can hit it. I would rather spend the extra 10 minutes than shelling out another $50 to realise something is wrong...
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You're right of course, however, if we assume that all these other factors did not lead to a failure, and we are only talking about the belt, then the lifespan of the belt should be something greater than 70 hrs that I first experienced. Also, when I replaced the belt (by the dealer), the second belt lasted roughly the exact same number of hours. Leads one to believe that something in the belt (materials, manufacturing process, handling, etc.) caused the failure and that it was consistent between the two belts purchased from JD. I was informed by the dealer when I bought the third belt that the belt had been redesigned. I expect that is true since the failures stopped every 70 hrs or so and now I've gotten around 400+ hrs on this belt. Like you said, one never really knows when a belt will fail, or for what reason, so I now carry a spare in my truck. Extreme useage is another factor that can shorten the life of a belt, as I can attest from a Gravely 36" walkbehind I once had. Started cutting some knee-high grass with it, and the heat generated at the belt from the high load & resulting friction caused a premature failure of the belt. As you pointed out, when a belt fails, it should indicate to us to start checking these other factors to ensure we don't have additional failures that could have been prevented if we had just done due diligence and done some checking of the pulleys, bearings, etc. I believe the JD belt was about $75!