Notice the square bites taken out of the belt.
One of the bolts installed from the factory in the main pulley was too long. I saw no evidence that this had been previously disassembled.
Amazing how resilient some of these parts are.
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| Interesting find while replacing my timing belt http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=75365 |
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| Author: | etravlr [ Sun May 26, 2013 3:19 pm ] |
| Post subject: | Interesting find while replacing my timing belt |
Notice the square bites taken out of the belt. One of the bolts installed from the factory in the main pulley was too long. I saw no evidence that this had been previously disassembled. Amazing how resilient some of these parts are. |
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| Author: | geordi [ Sun May 26, 2013 4:28 pm ] |
| Post subject: | Re: Interesting find while replacing my timing belt |
Obviously there has to be something rotating on one of the pulleys that damaged the belt like that. Have you found it, and what was it? |
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| Author: | papaindigo [ Sun May 26, 2013 4:39 pm ] |
| Post subject: | Re: Interesting find while replacing my timing belt |
That's weird. Offhand I cannot imagine what would reach out and take a notch out of the belt every 4th tooth as the belt is passing by given that the damage is perpendicular to the direction of belt travel. Only thought I have is defect(s) in the teeth of one of the pulleys. |
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| Author: | geordi [ Sun May 26, 2013 5:34 pm ] |
| Post subject: | Re: Interesting find while replacing my timing belt |
Thinking about the speeds that each of the pulleys rotate at, rules out the water pump and the idlers - they aren't anywhere near an even multiple of engine RPM. The injection pump is something like a 3:2 ratio, so that is out too. Any of those, and over time the belt's tooth count would "walk" the damaged tooth away from the damage-giver... And every single tooth would end up getting notched. Because this is precisely every 4th tooth as Papaindigo noted (I hadn't even thought to count the teeth - good catch) the only thing I can point at is the crankshaft pulley. IIRC, 4 teeth would be just about 1/2 the circumference, so every time it came back around it would take another bite... And would match each previous notch so the damage didn't walk. Maybe a previous mechanic dropped a wrench and dinged the end of the pulley? Some careful work with a file could clean that up so it didn't happen to the next belt. Was this the factory belt installation? |
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| Author: | Hexus [ Sun May 26, 2013 7:01 pm ] |
| Post subject: | Re: Interesting find while replacing my timing belt |
Well at least you were lucky enough that it never caused your timing belt to fail. Although I believe these pictures lend credence to my thoughts that it's typically a rocker failure rather than a belt failure or a belt "SKIPPING A TOOTH" so to speak. This makes me appreciate how well constructed our Timing Belts are for sure. Whatever did this damage is something that moves in time, so the crank is where I would look first, then the cam sprockets. |
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| Author: | Glend [ Sun May 26, 2013 8:27 pm ] |
| Post subject: | Re: Interesting find while replacing my timing belt |
Really unlikely to be a factory installed bolt being too long, I'd suggest that the belt has stretched so much, or the tensioner had backed off so much, that a slack bulge was jumping into something. I agreee your very lucky to catch it before it did some serious damage. |
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| Author: | LMWatBullRun [ Mon May 27, 2013 9:13 am ] |
| Post subject: | Re: Interesting find while replacing my timing belt |
Hexus wrote: Well at least you were lucky enough that it never caused your timing belt to fail. Although I believe these pictures lend credence to my thoughts that it's typically a rocker failure rather than a belt failure or a belt "SKIPPING A TOOTH" so to speak. This makes me appreciate how well constructed our Timing Belts are for sure. Whatever did this damage is something that moves in time, so the crank is where I would look first, then the cam sprockets. X2 on all that, especially the rocker issues. |
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| Author: | DOC4444 [ Mon May 27, 2013 10:52 am ] |
| Post subject: | Re: Interesting find while replacing my timing belt |
See how the tip of that extra long crank pulley bolt is polished? I think you found the culprit. If it were me, I would buy four new crank pulley bolts from the same place to make sure that they all weigh the same. DOC |
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| Author: | CATCRD [ Mon May 27, 2013 10:52 pm ] |
| Post subject: | Re: Interesting find while replacing my timing belts |
All it takes is that the number of belt teeth and the number of crank pulley teeth are both a multiple of 4. I bet the factory bolt was too long. Seen it happen at our factory when a bin of 1000 bolts gets stocked to the assembly line. 1 wrong bolt mixed in is all it takes. I bet that bolt ate the belt in the first few revolutions of the motor and it's been that way ever since, after the bolt "made room" for itself. |
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| Author: | etravlr [ Sat Jun 01, 2013 9:27 pm ] |
| Post subject: | Re: Interesting find while replacing my timing belt |
It was the bolt pictured, one of the 4 was longer. New bolts were ordered. I wasn't alearted that there were responses or I would have replied earlier. I willl have to check my settings. geordi wrote: Obviously there has to be something rotating on one of the pulleys that damaged the belt like that. Have you found it, and what was it?
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| Author: | etravlr [ Sat Jun 01, 2013 9:30 pm ] |
| Post subject: | Re: Interesting find while replacing my timing belt |
I pondered over it for a while as well, seemed but then found the longer bolt. Amazing that a belt can hold with all those bites out of it. All evenly spaced. papaindigo wrote: That's weird. Offhand I cannot imagine what would reach out and take a notch out of the belt every 4th tooth as the belt is passing by given that the damage is perpendicular to the direction of belt travel. Only thought I have is defect(s) in the teeth of one of the pulleys.
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| Author: | etravlr [ Sat Jun 01, 2013 9:33 pm ] |
| Post subject: | Re: Interesting find while replacing my timing belt |
Glend wrote: Really unlikely to be a factory installed bolt being too long, I'd suggest that the belt has stretched so much, or the tensioner had backed off so much, that a slack bulge was jumping into something. I agreee your very lucky to catch it before it did some serious damage. Updated above |
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