As rogue mentions, get him & his saw in front of you and watch him tension his 36"B/C. That should answer the best part of your question. If you get a warm 36" .404 chain/bar tension it on the tight side then let the saw cool...you'll have issues, maybe not today but it will eventually bite ya ass. He's lucky he's only breaking tensioners....there fairly cheap. Break 1, it could be bad luck....2 well you think about what your doing & how your doing it and maybe put it down to very bad luck. 3 tensioners if you haven't realised your the problem & are blaming the 0EM part & guy that installed it....well your probably a friggin idiot.