Interesting find while replacing my timing belt

etravlr · **Posted:** Sun May 26, 2013 3:19 pm

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.

geordi · **Posted:** Sun May 26, 2013 4:28 pm

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?

papaindigo · **Posted:** Sun May 26, 2013 4:39 pm

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.

geordi · **Posted:** Sun May 26, 2013 5:34 pm

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?

Hexus · **Posted:** Sun May 26, 2013 7:01 pm

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.

Glend · **Posted:** Sun May 26, 2013 8:27 pm

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.

LMWatBullRun · **Posted:** Mon May 27, 2013 9:13 am

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.

DOC4444 · **Posted:** Mon May 27, 2013 10:52 am

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

CATCRD · **Posted:** Mon May 27, 2013 10:52 pm

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.

etravlr · **Posted:** Sat Jun 01, 2013 9:27 pm

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?

etravlr · **Posted:** Sat Jun 01, 2013 9:30 pm

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.

etravlr · **Posted:** Sat Jun 01, 2013 9:33 pm

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

Interesting find while replacing my timing belt

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