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TexasKnucklehead
Jedi Knight
Offline
Alternator failure up-date
As you may recall, my 35amp Kubota/Denso alternator had a front bearing seize and sort of stranded me in Ohio. After replacing the bearing (which is the exact same bearing as is used in the front of the original generator) and looking more closely at the failure, I am convinced the pulley spun on the shaft. The pulley nut tightens with the same rotation as the belt is driving it, and will automatically re-tighten itself. The pulley material is softer than the nut, shaft, bearing or washer and ground material away until the back side of the pulley dug into the housing, finally causing enough heat to seize the front bearing. The rear bearing was fine. The attached picture shows how much the nut receded into the face of the pulley. It took over 5,000 miles before the pulley dug into the alternator case and I really didn't see it coming. I am amazed I was able to make it back to Houston with a pulley (on a new alternator) that fit poorly -loose on the shaft and held from spinning by the tension on the nut and a lot of blue lock-tight.
To keep this from happening again, I used my Dremel and small cut-off wheel to grind a crescent into the shaft much like the one on the generator and water pump. With the key installed, there is no way for the pulley to spin on the shaft. I also drilled and tapped a set screw into the center of the pulley, but I'm sure that's just me being overly cautious. Since I had to disassemble the case to remove the bearing, I painted the case black so it looks less like an alternator. And since it was apart anyway, I opted to rotate the field so when reassembled, the voltage regulator would not be as close to the exhaust manifold and the wire connections are on the outboard side, instead of inboard.
During this whole ordeal, I discovered the alternator really needs a different belt. The relative location of the tension bolt of the alternator is different from the generator. The alternator is at 12oclock, while the generator is at 10oclock compared to the pivot bolt. Apparently when I first installed the alternator, the belt was stretched enough to work. When I tried to install a new belt (because the old one broke upon bearing seizure) it was too short. The interim 'fix' (in Ohio) was to drill a hole in the tension arm. That probably would have been OK, but I should have realized that in this position the belt could vibrate enough to rub against the pivot bolt -since I installed it with the exposed threads forward, instead of rearward... So by the time I got to Houston, the belt had a groove dug away and the tension arm had broken at the bolt by the water pump. -Now the pivot bolt is installed with the exposed threads rearward, the nut no longer interferes with the regulator cover, and I'm using a narrower belt so a stock non-drilled arm can be used.
Original Generator Belt Gates Truck green stripe TR28386 7/8"x39-1/8". New Alternator Belt Gates Truck green stripe TR24379 21/32"x38-1/2". Note how odd it seems to have a shorter belt that yields more 'length' due to thickness. The new belt does not bottom out on the pulleys. It no longer rides higher than the top edge of the pulleys.
If you are running an alternator with the original wide pulley, and without a key installed, I suggest you install a key. I am hoping for more than 5,000 worry free miles from my latest repairs.
As you may recall, my 35amp Kubota/Denso alternator had a front bearing seize and sort of stranded me in Ohio. After replacing the bearing (which is the exact same bearing as is used in the front of the original generator) and looking more closely at the failure, I am convinced the pulley spun on the shaft. The pulley nut tightens with the same rotation as the belt is driving it, and will automatically re-tighten itself. The pulley material is softer than the nut, shaft, bearing or washer and ground material away until the back side of the pulley dug into the housing, finally causing enough heat to seize the front bearing. The rear bearing was fine. The attached picture shows how much the nut receded into the face of the pulley. It took over 5,000 miles before the pulley dug into the alternator case and I really didn't see it coming. I am amazed I was able to make it back to Houston with a pulley (on a new alternator) that fit poorly -loose on the shaft and held from spinning by the tension on the nut and a lot of blue lock-tight.
To keep this from happening again, I used my Dremel and small cut-off wheel to grind a crescent into the shaft much like the one on the generator and water pump. With the key installed, there is no way for the pulley to spin on the shaft. I also drilled and tapped a set screw into the center of the pulley, but I'm sure that's just me being overly cautious. Since I had to disassemble the case to remove the bearing, I painted the case black so it looks less like an alternator. And since it was apart anyway, I opted to rotate the field so when reassembled, the voltage regulator would not be as close to the exhaust manifold and the wire connections are on the outboard side, instead of inboard.
During this whole ordeal, I discovered the alternator really needs a different belt. The relative location of the tension bolt of the alternator is different from the generator. The alternator is at 12oclock, while the generator is at 10oclock compared to the pivot bolt. Apparently when I first installed the alternator, the belt was stretched enough to work. When I tried to install a new belt (because the old one broke upon bearing seizure) it was too short. The interim 'fix' (in Ohio) was to drill a hole in the tension arm. That probably would have been OK, but I should have realized that in this position the belt could vibrate enough to rub against the pivot bolt -since I installed it with the exposed threads forward, instead of rearward... So by the time I got to Houston, the belt had a groove dug away and the tension arm had broken at the bolt by the water pump. -Now the pivot bolt is installed with the exposed threads rearward, the nut no longer interferes with the regulator cover, and I'm using a narrower belt so a stock non-drilled arm can be used.
Original Generator Belt Gates Truck green stripe TR28386 7/8"x39-1/8". New Alternator Belt Gates Truck green stripe TR24379 21/32"x38-1/2". Note how odd it seems to have a shorter belt that yields more 'length' due to thickness. The new belt does not bottom out on the pulleys. It no longer rides higher than the top edge of the pulleys.
If you are running an alternator with the original wide pulley, and without a key installed, I suggest you install a key. I am hoping for more than 5,000 worry free miles from my latest repairs.
