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I usually service my Mitsubishi L200 Sportero 4x4 5FWD Diesel at Mechanic A, but I had not for several months. Needing a service, I tried another mechanic, Mechanic B, who did the usual 'tune-up'. Two weeks after that, while driving, the power-steering stopped working. Upon investigation, I realized that all of the belts (alternator, power steering, A/C) were either destroyed or twisted and that the crankshaft bolt (the bolt that holds all of the pulleys at the front of the engine) was missing.

  1. What could cause this bolt to come loose?
  2. Is Mechanic A at fault, or Mechanic B? Mechanic A says they use 'lock-tight' and air tools to tighten bolts, and if it were only slightly loose, it would come off completely in a week or two, not last for the several months it did since their last service. Mechanic A also surmised that Mechanic B, while trying to do other stuff in the engine, might move the engine around in the engine bay somehow and loosen the bolt.

I don't know who to believe. What do you guys think?

UPDATE 01: The bolt is not missing - the head of the bolt broke off, leaving the rest of it inside.

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I'm not sure it would be either mechanics fault, mainly because a crankshaft bolt is not something which is attended to during normal maintenance, either in checking or removal. It sounds to me like the bolt may have come lose on it's own (which does NOT happen very often), backed out, and allowed the main hub pulley to become displaced somewhat destroying the belts. Diesel engines do have a lot of vibration which could allow the bolt to become lose. This type of bolt should have some thread locker on it. Since the bolt is now missing, it would be hard to tell if there was any on it in the first place.

Like I said, this is not something which should or would be messed with in the first place. It sounds to me like it's just one of those "things" which can neither be explained or blamed.

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    My money would be on a factory defect. Robots are only human. – Captain Kenpachi Dec 1 '14 at 15:27
  • Is it perhaps more likely that it was done on purpose? – Ryan Shripat Dec 2 '14 at 16:21
  • @RyanShripat Realistically I'd say it is not ... just one of those things. Anything is possible, but like I said, there would be no reason for them to be messing with this in the first place. Also, if it could ever be proven they were messing with it, they would leave themselves open for a huge lawsuit. – Pᴀᴜʟsᴛᴇʀ2♦ Dec 2 '14 at 19:21
  • As @JuannStrauss stated, this is a factory defect. The bolt broke, pure and simple, which caused the rest to occur. Also, since you put the update in your question, you don't really need to update mine as well ... Please point out that you updated your question though as a comment here. Your update didn't make sense in my answer. – Pᴀᴜʟsᴛᴇʀ2♦ Dec 3 '14 at 12:08
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    @paulster2, I updated your answer in error, but could find no way to undo it, besides editing it again :| – Ryan Shripat Dec 3 '14 at 20:36

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