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Discussion Starter #1
A little background: 2001 MDX with 250k miles. It runs great. I rebuilt the transmission at 200k miles and replaced the timing belt, water pump, and both pulleys at the same time. I did not replace the hydraulic tensioner because it looked fine and was not leaking.

The other day, the wife was driving it and it shut off. It turned over but didn't start. Further investigation showed the timing belt had shredded and wrapped itself around the crankshaft, locking the engine.

All of the exhaust valves have contacted the pistons but none of the intake valves appeared to have hit. Two cylinders have exhaust valves that are bent enough to fail a leakdown test. I'm going to replace all of the exhaust valves.

I'm replacing the pulleys, water pump, and the tensioner this time. The old tensioner appears to be fine.

Here's the mystery. The parts of the belt that were not totally shredded appear to be ok (no melted back side, no frayed edges, no missing teeth). All of the pulleys spin freely and none of them are damaged. The last thing i want to do is to put it all back together and have this happen next week.

Anyone heard of this happening?

Thanks!
 

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Check the auto tensioner bearing and idler wheel bearing. A siezed bearing would cause the belt to overheat and fail. For sure replace these parts during rebuild.

Sometimes a belt can wear prematurely (why? oil leak, coolant leak) and fail by losing lugs of the traction side of the belt.

Changing at correct interval is no absolute garuntee that a belt won't break. Small manufacturing defects might be at play in your case.

good luck
 

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That's the weird thing. Everything appears to be ok. The pulleys all spin freely and the tensioner appears ok. The belt isn't melted anywhere and shows no signs of contamination or heat damage. Unfortunately, it became wrapped around the crank timing gear and became more shredded, destroying evidence of the failure point.
 

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I'd bet money it was either a defect in the belt itself, or that it got nicked or otherwise damaged during the install. Once an nick develops in the edge of the belt, it's going to work on enlarging the rip every revolution (and there are a LOT of revolutions). That would certainly match the evidence (no signs of slippage or melting on the remaining "good bits" of the belt).
 
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