I always use OEM belts and never use substitutes.

Aftermarket belts have failed to do the job too many times and they are so much fun to change that I learned my lesson.

When shopping one has to make sure they are getting the OEM belt even if you have to call. Many online sellers only supply aftermarket parts and it's too expensive to ship a belt back for credit or refund.

One question that comes to mind is that if these generic light duty industrial belts are suitable, why do the mower manufacturers use different belts? Bending causes belts to heat and flexing both ways around pulleys and idlers causes much more heat. Heat ruins the belt.

I go both ways on the issue of OEM vs. generic belts. In some applications an OEM belt works best and in others you can successfully substitute a generic FHP belt.

Generally the biggest problem is that OEM design for and specify odd length belts. The trade supplies 1/2" (4L or A) in 1 inch increments and 5/8" (5L or B) also in 1" increments. Some shorter 1/2" belts can be had in half lengths (34.5, 42.5, etc.) but harder to find. OEM belts are often Kevlar reinforced, while the less expensive FHP belts are nylon or cotton corded. Lastly, some OEM belts (especially MTD drive belts) are deliberately designed with less grip (ordinarily more grip is better), to ease clutch engagement and prevent "wheelies".

As I said, I go both ways, depending upon what works. I'm willing to go under the machine two or three times and will start generic to save money and only then go OEM.

As an example I have an older Deere R72 rider. I use in the fall because it vacuums leaves better than anything else I have. I have successfully used generic 4L53 for ground drive and pay $4 vs $20 for the OEM. On the other hand, the deck belt is actually 63.5" and if I use a 4L64, I keep jumping off the motor pulley. Tears me up because the generic would be $4.50 and the OEM is almost $25. However, in this case I use the OEM.

Similar situation with MTD. I have successfully substituted generic belts on the deck drive, and the front belt of the Transmatic. My experience is that you have to go OEM for the rear belt on the Transmatic to work properly and get acceptable life. On the front belt, which also functions as the clutch, I lightly rub the side walls with hard milled bar soap to get a little less grip and get smoother engagement. Start light and add more later, becuase you can't go back.

As for comment about "heat ruins the belt", I agree with concept but not cause. While flexing and back-side idlers contribute, majority of heating comes from belt slipping against pulley groove. In the 90's I worked with both Goodyear and Gates on high speed drives and their engineers consistently preferred back side idlers to increase the "wrap" of the belt, particularly on the smaller pulley. Although belt flexing (and heating) from idler remains constant from no-load to full-load, at full-load total heating was 90% from slip.

Thanks for the informative post. I have no formal studies, only experience about flexing and heat. I did an alternator conversion on an old farm tractor (actually have done several) and the belt drove the alternator only, no other load. To improve alternator exciting at low engine speed, I used a small pulley on the alternator. For determining belt length, I bought low cost belts and left the best size in place. The belt got so hot- stinking- that it failed in less than 2 hours. I bought an equivalent size automotive belt and it is still in service after 12 years. I attribute the heating to the pulley size, belt design, materials and the attendant flexing plus no opportunity to cool between flexings due to the short belt length of 22".

Following up on this issue, I bought a genuine OEM belt and returned the 4L870. It was black rubber, quite odorous, no cloth covering. I did measure both on one of the V-belt gauges and the lengths are identical. The OEM was costly. Since then I found at Tractor Supply Huskee belts that are blue, cloth covered, labeled as Kevlar, and in sizes such as 4L870. Better price than the Murray belt. I suspect that the Huskee would work well. By the time I need another belt, something will have changed or I will personally be beyond doing any mowing.

I had the same expereince as you on a Scotts (by Murray) from HD in the mid 90's.

Tried three different aftermarket, substitution, and power equipment belts that were hi tech with kevlar and such. They all failed quickly. Bought the Murray belt for too much money and as you noted, it looked unremarkable. When I sold the Scotts 5 years later... that Murray belt was still on it.

No more wasted time for me... as rarely as I need a belt I just buy OEM.

For OPE application the belt must be cloth covered and kevlar reinforced.

Such belts will generally perform well, though the comments about size (above) are a factor as well.

"Fractional horsepower belts" from a hardware store are not suitable, nor automotive belts.