A compilation of some serpentine belt tensioner failures and discussion.
Thanks goes to all contributors. Feel free to contribute.
A picture from a recent thread. Maybe help others as to what to look for.
Thanks goes to all contributors. Feel free to contribute.
Two weeks ago, a question about the INA tensioner reminded me to look at mine. I found the belt running on the edge of the idler pulley:
Some pictures of fractured castings.
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So I’m making a left hand turn and seconds later I hear a loud bang and even felt it on the floorboard. Pulled over right away and saw this [emoji15]. I replaced the tensioner about 4 years ago. It was supposed to be an original part. [emoji2371]
Revised pic per One Call. Note that there is an "A" in the One Call casting pic. The pics of INA units above have "INA Germany" in that location.
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The surface texture tells a story.
The failure appears to have started over on the right, where there are (coincidently?) bubbles visible in the metal. There is no surface dirt or oxidation, so the initial crack likely progressed relatively quickly. Once the crack reached the “corner” the arm let go. The fine texture on the left is characteristic of brittle fracture, perhaps from a sudden impact loading, so I would double check your other belt train components like the alternator clutch and harmonic balancer, though given the spring tension on the part the belt pulses would likely be enough to trigger final failure.
Sorry for your troubles... hopefully your fan and rad were okay?
-dave
Looks like that part is die cast. Improperly cleaned mold, and air leak in the injection machinery, even fine dust particles can get into the metal, causing high porosity, and ultimately failure. Of course a seized alternator pulley could have contributed.
For those curious here is a brief overview of porosity/inclusion causes in die cast parts.
https://www.starrapid.com/blog/porosity-in-pressure-die-casting-and-how-to-control-it/
It could also be investment cast as well, hard to tell from the mold witness marks.
Cont.I would want a closer look at the crack area, but it doesn't really show any fatigue indicators that I can see from the photo. I would agree that it was likely a short term shock load, maybe 3-4 cycles which exceeded the materials strength. The crack then rapidly propagated.
If the pivot or spring was partially seized, that could have removed some the energy absorption ability, this increasing the shock loading to the breakage area.
A picture from a recent thread. Maybe help others as to what to look for.
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