Serpentine Belt Tensioner Failures

seans said:

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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One call a/c said:

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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Nautamaran said:

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

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Midwestdrifter said:

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.

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Psbuckley said:

I hadn’t noticed this area of color change. Definitely a failure of the casting - bubbles or a crack that might have developed during the cooling?



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Midwestdrifter said:

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.

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One call a/c said:

... Something like INA or gates [emoji2371].


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Aqua Puttana said:

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The serpentine belt was showing wear on the one back side edge. When I first moved the tensioner it was pretty stiff. It was good that I caught it and changed the parts out when I did. Note the angled gap between the two pieces.



Some things I remember.

Most of my work was from below. Some access was from above.

Pin the idler tensioner or getting clear access to the one fastener is difficult.

The fan shroud will flex. Use than feature. (Especially with a 3" ratchet extension.)

I removed the unit out the bottom (shroud flex helped).

I used an offset 17 mm box wrench to hold the new unit up into place to start the bolts. Even using that method didn't make it fun.

View attachment 96763

Don't over-tighten and strip the bolts. I don't know the torque spec.

6PK2257 belt removed. 6PK2260 installed (on hand).

I realize the cracked casting was not predictable. If you notice edge wear on the belt don't wait. Change the tensioner and other parts before you need to do it on the side of the road without all of your tools.

Opinion:
I prefer the textured back serpentine belt like I show in the picture. I believe the one pictured is Conti brand. The Bosch belt is similar. The texture is what alerted me to the odd edge wear. A smooth back belt like NAPA and some other manufacturers supply will not show the edge wear as clearly.

Another Write-up.

'05 Serpentine belt tensioner replacement
https://sprinter-source.com/forum/showthread.php?t=4088

I also changed the viscous clutch unit.
Remove the 8mm Allen bolt to remove the fan and viscous clutch. Righty tighty, lefty loosey works on this one. I unclipped, but didn't remove the fan shroud for the viscous clutch. 3 clips to re-install (I lost one).



vic

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Aqua Puttana said:

Aqua Puttana said:

My admiration goes out to anyone who changed the tensioner when other than being home with their tools. ...
vic

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I can't believe it gets done so easily by others.

I noticed that the 2006 belt wasn't riding evenly on the tensioner pulley.

For removal I used Seans suggestion and disconnected the turbo intake manifold hose. That did make access from above better. Removal went fairly well.

Install... not so much.

I again had trouble getting the bolts started. I got the inside one started and figured that I'd just snug it up and then start the other bolt while held in position. The bolt began to bind as I (ever so slowly) turned it in. Great. I probably cross threaded it.

I decided that better access would help to get things back right. I proceeded to disassemble the front end to get the fan shroud out of the way. It turned out the fan shroud didn't need to be removed. Wedging the radiator stack out a bit using a block of wood on the right (passenger) side provided the clearance/access I needed.

I started the outboard bolt and snugged it in to get the tensioner basically in place. After it was in I started the other bolt that I thought was cross threaded. Fortunately it threaded in fine. It wasn't cross threaded at all. It must have been binding against the housing.

The cross bar removal and extra disassembly was worth the extra effort. Otherwise the thought of the bolt possibly being cross threaded would have nagged at me.

Anyway.
Disassembly to allow tilting the radiator does take a bit of extra effort (grill off, headlights loose, top bar removed, etc.), but tilting the radiator moves the fan shroud back just a bit for more clearance and does provide much easier access for my ham hands. Next change I believe that I will just do the extra work to tilt the radiator. For me it will avoid aggravation.

The removed tensioner had an uneven gap similar to the 2004 tensioner that I show in post #5 above. If the belt isn't riding evenly on the tensioner, the tensioner is definitely on the way out and should be replaced.

vic

P.S. - A 8mm or 5/16" 12 point socket kinda fits, but the proper E10 socket makes things a bit easier.

This "Deepwell" E set will be my next coupon purchase.
E10, E11, E12, E14, E16, and E18

6 Pc 3/8 in. Drive E-Socket Set
https://www.harborfreight.com/6-Pc-38-in-Drive-E-Socket-Set-68016.html

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