Pulley & Belts falling off: coincidence, or mechanic?

#1

I have a tan '94 Mazda Protege with 200,000 miles. The car passed inspection in November, no concerns expressed about belts/pulleys. In December the timing belt was replaced after having an oil leak in that area repaired.



On Jan. 4, I was driving the car normally and noticed that the battery idiot light came on. I stoppped and looked under the hood. Here is what I saw: the alternator and power steering belts were gone, and a pulley was lodged in the engine compartment, out of place. A bolt head for the pulley shaft was sheared off, and the pulley itself looked concave with hairline fractures.



Now, can it be coincidence that all this happened a few weeks after work was done that involved the belts and pulley? The garage says the car is old, things happen. Or is it more likely that the mechanic doing the work in December nipped off the bolt’s head or torqued the bolt wrong, leading to the eventual failure?



I realize one can never know for sure, but what are the odds either way?

#2

Which pulley was out of place?

The only pulley that would have been removed from its shaft during the timing belt replacement is the crankshaft pulley. If this is the pulley that came off, then, yes, it is probably related to the timing belt job.

If the alternator pulley, power steering pump pulley, AC compressor pulley, or idler pulley (if there is one) came off its shaft it is probably just a coincidence.

#3

Agree on all points with mcparadise.

#4

I know of shops that would endlessly explain to the customer how “things just happen” but fire the mechanic.

#5

If the tensioner has never been replaced, that could be the cause of the problem and it could just be a coincidence.

If a mechanic is going to sabotage the car, he’d have a hard time making a belt fall off after a few weeks, and there isn’t an easy way to make a pulley look artificially fatigued.

#6

The issue here is that it is not only the shop’s responsibility, but their DUTY, to inspect everything on the way in to that timing belt and on the way out.

This means inspection of external belts, tensioners, idlers, and even the fit of the Woodruff key on the crank pulley if it has a key in place.
No way should they install a worn idler, pulley with fractures, etc. without a strict warning to the car owner and preferably a signed disclaimer absolving the shop of any blame if something goes wrong.

One would think that with a broken bolt head this problem would be caused by either a seized tensioner (easy to determine) or an overtightend crank pulley bolt.

There’s 2 ways of tightening that crank bolt; a torque wrench or an air wrench.
Locking the engine down to prevent rotation while using a torque wrench is more difficult than hammering the crank bolt down with air pressure which requires no effort to lock the engine…

#7

My knowledge of parts is limited; I think it was the camshaft pulley. It was the pulley closest to the timing belt cover, the one that had to be removed in order to replace the timing belt.

The middle part of the pulley is still bolted onto the engine block. The metal of the pulley where the break occurred is shiny. I see stress fractures also, and the metal is concave.

The garage did not advise me as the job was being done that there were any metal deformities or missing bolt heads in the area being worked on.

#8

The garage has told me that the pulley suffered from metal fatigue due to being taken off and being put back on again so many times. Since the timing belt has been changed 4 times, and this was the pulley involved in a timing belt switch, the explanation sounds a little shaky to me. But the mechanic made it sound like I wouldn’t be charged for labor, so that’s the best I can do. Hopefully they will remove the bolt stuck in the pulley shaft.

#9

It was the pulley attached to the crankshaft. The mechanic says the failure of the pulley was due to metal fatigue, because the pulley had been taken off and put back on again so many times (I think it’s been taken off and put back on again a total of six times, tops).

#10

Is this pulley up top or near the bottom of the engine?
The camshaft sprocket (up top) does not have to be taken off for a timing belt change.
There is a sprocket on the crankshaft (bottom) and it does not have to be removed either, BUT the outer pulley must be removed access that sprocket.

Sorry, but repeatedly taking the pulley off (top or bottom, makes no difference) does not cause metal fatigue unless someone has been getting ham-fisted when tightening it.