1999 Toyota Corolla 1999 tensioner pulley bolt

1999 TOYOTA COROLLA
160,000 MILES • 4 CYL • FWD • AUTOMATIC
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AIRFRAMER08
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In the last 4 months the bolt holding the tensioner pulley onto the engine block has broken 3 times right where the threads start. I have drilled out the remaining piece each time and had a new bolt installed. I have even replaced the pulley assembly and a few weeks later the bolt broke again.

What might be the root cause of the bolt failure?

Not sure if it would help but just prior to each failure of the bolt I can hear the belt squeal slightly a few hours before it breaks.
Nov 4, 2010 at 3:55 AM
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KHLOW2008
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Hi airframer08,

Thank you for the donation.

Possible causes for bolt breaking are :

1. Quality of bolt used. Ensure bolt used is OEM or equivalent.

2. Over torquing. When bolt is over torqued, it would be weakened and being subjected to high torsional stress, it would break in time.

3. Under torqued. When the bolt is under torqued, it would result in vibrations and break off.

From what you have described, item # 2 is the more likely cause. Tightening torque is 51 ft lbs ( 69 n.m)
Nov 4, 2010 at 7:11 AM