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svcattales · 12-26-2021, 07:04 AM

I have a Ford 2006 E450 Super Duty Chassis on my '08 Coach House RV. I started the engine two days ago and within seconds I heard a loud bang. The engine was still running, but I shut it off to investigate. To my surprise, the serpentine belt was hanging down below the radiator. I removed the belt and it was still wrapped around the tensioner pulley and half of it's support bracket lying free near the bottom of radiator. I need some help trouble- shooting this failure. Here are some details:

I changed the serpentine belt, the tensioner, and idler pulley about 2 years ago with NAPA parts and have put about 8,000 miles on it since then. I didn't have any belt chirping, alignment issues or pulley bearing issues, but I changed everything to prepare for a long trip out west. Now that belt is off, I checked each of the pulleys on AC compressor, power steering, water pump, alternator, and idler pulley and all spin freely with no wobbles. I looked at the serpentine belt carefully and there were no distortions or worn areas and it looked like it was still in excellent condition. I would think that a major pulley seize-up would be needed to snap the tensioner in half, but that doesn't appear to be the case. Perhaps the belt tensioner was defective, but that doesn't seem likely either. Any ideas?

99dart · 12-26-2021, 08:02 AM

Well, you did your due diligence when replacing components a couple years ago. Myself, I would chalk it up to a faulty casting in the tensioner arm. Who knows where that NAPA part really came from. If by chance you hung onto the original arm, I would install a new bearing on it and be good to go. Good luck and happy trails.

HarryStone · 12-26-2021, 09:26 AM

Stress or fatigue failure. If everything else is fine, replace it and move on. Don't over stress the item when you put the belt back on.

avfordguy · 12-26-2021, 10:14 AM

Have had a couple of tensioner fail, looks to be the same bad China casting, one failed on a 2009 focus, the other was on a 2006 4.6 econoline. Lesson learned,if at all possible oem only aftermarket is getting hit and miss with all the discount auto parts places/websites.

CRV2 · 12-26-2021, 10:40 AM

When you changed the belt and tensioner in the past, was the tensioner positioned in the center of its spring loaded travel, or was it all the way against the stop (as if the belt was too short)? ~CA

gatorb8 · 12-26-2021, 10:46 AM

I have read about confusion on belt sizes, to small could be a problem. Looks like cheap pot metal may have let go even of right belt was used. I would double check belt size and just replace belt tensioner. And, knowing me, would probably have spares if it happened once….

CRV2 · 12-26-2021, 10:54 AM

Quote:

Originally Posted by gatorb8

I have read about confusion on belt sizes, to small could be a problem. Looks like cheap pot metal may have let go even of right belt was used. I would double check belt size and just replace belt tensioner. And, knowing me, would probably have spares if it happened once….

Too small of a belt is certainly a possibility that I was thinking as well. Many people (even mechanics) believe that belts stretch with age as was commonly seen on the "V" belt style of belts. However the reason they got loose (v-belts) is not that they stretched (maybe many many years back they did), the reason is that the "V" sides of the belt wears and falls further into the groove of the pulley making the belt looser which would make one think the belt stretched. What actually happens though on most belts is that as they age they slightly shrink as they dry out (there is a name for this that I don't remember) instead of stretching as many may believe. If the serpentine belt was already tight against the tensioner's stop, and then with age and with the belt's small shrinkage, there certainly could be enough shrinkage to break the tensioner pulley's arm... or it could have simply been manufactured with a defect if the tensioner was not up against its stop. ~CA

twinboat · 12-26-2021, 02:23 PM

Check the air conditioner pulley with the key and AC switch on.

Could have a seized AC compressor but without power, the clutch is not engaged so it freewheels.

edge68474 · 12-26-2021, 02:31 PM

Watching this one.

F4Gary · 12-26-2021, 02:38 PM

Made out of chinesium...

svcattales · 12-27-2021, 04:34 AM

Thanks for all the great inputs.

I'm leaning towards a defective tensioner based on your inputs. It was not made in China, but was made in Mexico... much better right? Also, it does look like pot metal. Twinboat may also have identified a problem with a seized AC compressor. I checked my switch positions since the incident and I think the AC was off when the incident happened, but I'm not sure. I'll find an OEM tensioner and hold my breath when I turn on the AC.

I learned another trick from my son. A mechanic told him that if you tap all the pulleys with a box wrench when the serpentine belt is off, the pulleys should "ring like a bell." If they don't ring, the bearings are bad. I tried that and most of them did ring except the alternator pulley sounded like a "thud." Perhaps the alternator spins fine when there is no load on it, but after start-up it could have seized up or got very stiff? Should I take the alternator to one of those "auto electric" shops that repair them and get it checked out? The alternator is on top, so it should be easy to remove.

svcattales · 12-27-2021, 08:50 AM

Quote:

Originally Posted by twinboat

Check the air conditioner pulley with the key and AC switch on.

Could have a seized AC compressor but without power, the clutch is not engaged so it freewheels.

I turned on ignition and put the AC switch on. The electric clutch didn't activate (maybe too cold ambient temp). I grabbed the clutch with the pulley and rotated both together. The resistance seemed minimal. Is that an effective test? Thanks! Greg

twinboat · 12-27-2021, 09:27 AM

Yes, if you can turn the compressor by hand, it's not locked up.

baraff · 12-27-2021, 09:43 AM

Too small a belt may have contributed to this also. I would not trust an auto parts store to find the right belt. There have been multiple reports where people were sold either too large or too small a belt because the store's cross reference database was wrong. Personally, I would call a Ford truck dealer, give them your VIN and let them give you the proper belt. Will cost more, but...