An improperly tightened bolt leading to pulled threads is one and this can take 10 miles to manifest itself or it may be 10k miles. Who knows.
Failure to replace an idler or tensioner bearing because “it feels fine and turns smooth as silk”. The fact that it appears to be fine one day does not mean that it will be fine 2 weeks later. The hard coating on the bearing races may be on the verge of disentegrating. Once it starts disentegrating things can go downhill in a hurry. This is why the tensioners or idlers should always be changed at the same time.
The above also applies to a water pump, which can go south very quickly.
There’s 3 examples.
You’re also incorrect that a belt being off a tooth will be noticeable immediately. Not necessarily. It’s quite possible to be off a tooth, or even two, and the driver may be blissfully unaware this is the case. A tooth or two off does not guarantee that the engine will run poorly or even slam valves into pistons. It may go totally unnoticed unless a vacuum gauge was put on the motor to verify it.
If a bolt takes 10k miles to come out after replacing it, even if it wasn’t tightened correctly, there’s no way that you’re going to be able to prove that it was solely because the mechanic failed to tighten the bolt properly.
As for the tensioner and idler, many repair manuals do not say that these items need to be replaced at the same time as the timing belt. While I always replace these items when I do a timing belt, the mechanic can’t necessarily be faulted completely, if the customer just asked for the belt to be replaced, and the other components checked out per the workshop manual.
As for the water pump, these can definitely go bad quickly, but it usually has little to do with the competence of the mechanic, and more to do with the bad luck of getting a faulty part.
And I am not flat out incorrect on the timing belt being off by one tooth. I have read dozens of accounts on numerous forums about people doing a timing belt job, and as soon as the car is started up or driven home, it idles like crap, or stalls out. They then find out that the new belt was off by only a tooth or two. Based on this, I submit that a car whose belt is off by a few teeth will run poorly more often than it will run silky smooth.
I guess I should amend my post to say that “most” issues dealing with mechanic’s incompetence would rear themselves shortly after a timing belt change, not 2500 miles later (especially considering this mechanic is a trusted individual).
One thing that happens with a cam that is off by a tooth is the distributor will also be off (meaning the timing), this happens when the distributor is a third item that must be aligned (more common on older cars).
We are at a point that we need a picture of the chamber side of the cylinder head,OP can you provide this?
That’s too much dude. I just blew a piston on my 2013 HyundaI Accent. Used motor on ebay with 43,000 is $500 plus $200 shipping from California to Massachusetts. My mechanic wanted $1000 to install but found a guy to do it at another shop for $700.
All I can add is that I agree.
But proving it is probably not possible. You may have to simply look at your current options and choose the one that feels best to you. If it truly did throw a rod, there’ll be cylinder damage and the engine is history. Your options will be a boneyard motor, a rebuilt motor, or a new motor (if available).