Just curious what others are doing to adjust v-belt tension. I have a Universal M-25, but this issue should be similar to many engines. M-25 service manual says to tension belt so it deflects.25-.35” deflection (7-9mm) @ 20lbs deflection force. I tried my best to do so (using a fisherman's scale) when I installed a new belt last year (a Gates XL 7390 belt, after completing the alternator bracket upgrade). Judging by the visual "slop" in the belt (belt oscillates about +/-1.0 belts heights up/down with engine running), I always felt tension was a little loose. Still, I never heard any squeaks or saw any signs of slippage.
Going back to the factory specs of .25-.35"deflection, I thought: "Well, that's for an old 1985 belt." Wouldn't a new, modern belt be likely to stretch less (meaning, too loose with the stated amount of deflection). But then, wouldn't a new, modern belt with better rubber compounds and grooves have more grip even with less tension (so maybe the .25-.35" at 20 lb is okay).
There are various tension meters available, but without a chart showing the recommended tension for a particular belt, the meters don't help much. Gates' website shows no tension charts for XL belts specifically. A second belt that came with the alternator bracket kit was a Gates 3VX400. Gates' website does show tension settings for 3VX belts. The biggest visual difference I see between the XL and the 3VX is that the former has different/alternating rib sizes, while the latter has uniform ribs.
Going back to the factory specs of .25-.35"deflection, I thought: "Well, that's for an old 1985 belt." Wouldn't a new, modern belt be likely to stretch less (meaning, too loose with the stated amount of deflection). But then, wouldn't a new, modern belt with better rubber compounds and grooves have more grip even with less tension (so maybe the .25-.35" at 20 lb is okay).
There are various tension meters available, but without a chart showing the recommended tension for a particular belt, the meters don't help much. Gates' website shows no tension charts for XL belts specifically. A second belt that came with the alternator bracket kit was a Gates 3VX400. Gates' website does show tension settings for 3VX belts. The biggest visual difference I see between the XL and the 3VX is that the former has different/alternating rib sizes, while the latter has uniform ribs.
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