Not a metallurgist by any means, but given the orientation of pulled thread, I'm assuming body wasn't held to engine tight enough and was being pulled down on every time the BAS would kick in. However, there does not look to be any rubbing marks on tensioner contact point or bolt shank that would indicate movement as in it was being flexed back and fourth until it snapped. In the interest of full disclosure. I never used torque wrench on first install given no extension( nor knowing I need one at the time) and never having raised engine to remove tensioner assembly. Pulled from bottom with AC comp. dropped away. I tend to go by feel when installing fasteners based on the force to remove them( except critical applications of course, gaskets, bearing caps, etc.) and nothing about this initial install caught my attention as far as excess force to remove. I believe I threw a torque wrench on the top bolt to make sure it was at least 16lb.ft., but I'm sure the lower was tightened past 16lb.ft. with an extended length wrench due to limited access, but probably not the SI of 43 lb.ft. as sited in the following years info.

Apologizes for late response as I work alone and was hustling to get other stuff out while pondering situation and waiting for other consensus to come in to help limit a repeat failure on this. I appreciate everyone's input and try to reply to all . In the end, I believe a note should have been included with the updated tensioner specifying if a new bolt was required and/or revised specs for torque tightness. Even the TSB mentioning if/ then/ or about updated tensioner/bolt directs you to follow the same miss information in SI. I've done plenty of tensioners with notes on discarding/reusing certain parts including a new bolt supplied. [bolt in engine] [tensioner with bolt] [bolt with tensioner part number] [broken bolt] [tensioner bolt]

Paul Sanders
Owner/Technician
Parkway Auto Rebuilders
Harvey, Illinois, USA

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