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JWLSC · 05-16-2016, 04:16 PM

I was having belt tensioner chatter on my Cummings C8.3. I was thinking the belt tensioner was going bad as it is the original with 154K miles. I got a new OEM belt tensioner # 3976832. I also replaced the serpentine belt with a NAPA 25 080635 which is 64 ¼ in OD. Well even after replacing those parts I’m still getting the chatter. I read somewhere that to stop this I need a specific length belt, which is different then what they call for. Any ideas on how to fix this issue with the belt tensioner chatter.

dennis45 · 05-16-2016, 04:46 PM

Quote:

Originally Posted by JWLSC

I was having belt tensioner chatter on my Cummings C8.3. I was thinking the belt tensioner was going bad as it is the original with 154K miles. I got a new OEM belt tensioner # 3976832. I also replaced the serpentine belt with a NAPA 25 080635 which is 64 ¼ in OD. Well even after replacing those parts I’m still getting the chatter. I read somewhere that to stop this I need a specific length belt, which is different then what they call for. Any ideas on how to fix this issue with the belt tensioner chatter.

When you had the Surpentine belt off, did you check the Idler and Water Pump Bearings?

JWLSC · 05-16-2016, 05:11 PM

They seem fine. What I'm seeing is the belt tensioner wheel moving left to right. As if the belt is the wrong size. What length it needs to be is a what I need to know.

mackwrench · 05-16-2016, 06:30 PM

John,
Not sure if we've the same set up.....
I just recently replaced mine, Cummins belt # 3911581, I looked my number up in Cummins quickserve...perhaps your napa man can cross it.

Btw, mines a 1999 isc8.3

dennis45 · 05-16-2016, 06:57 PM

Quote:

Originally Posted by JWLSC

They seem fine. What I'm seeing is the belt tensioner wheel moving left to right. As if the belt is the wrong size. What length it needs to be is a what I need to know.

I just installed a new one recently. I used a Dayco 5080695. No chatter.

Old Scout · 05-16-2016, 07:02 PM

If driven by your serpentine belt--might check your alternator output to see if your voltage is loping.

JWLSC · 05-16-2016, 07:17 PM

Cummins Quick serve calls for belt # 3926866. Anyone have a way to cross reference that.

dennis45 · 05-16-2016, 07:21 PM

Quote:

Originally Posted by JWLSC

Cummins Quick serve calls for belt # 3926866. Anyone have a way to cross reference that.

http://www.daycoproducts.com/parts?oe_number=3926866

JWLSC · 05-16-2016, 09:16 PM

could the issue be the true belt size. Look at the differences of belts that fit the C8.3

DAYCO -5080640: 64 in
NAPA 25-080635: 64.25 on packing 64.305 online
NAPA NBH 25080638HD: 64.375
Gates K080638HD: 64.375
Gates K080635: 64.305

I'm using the NAPA 25-08063 right now. So what is the correct size of belt. I have a Cummins shop in town. I might just go and get the OEM belt and see if it resolves the issue.

Wdebarmore · 05-16-2016, 09:24 PM

Mine chattered. I found the noise was coming from the large washer in front. Tightened the bolt, chattered less, but still chatters a bit. Belt tension is correct, I had it checked using a sonic tensiometer, which I'm told is very accurate.

JWLSC · 05-20-2016, 07:50 AM

Update:* I replaced the Belt Tensioner with an OEM #3976832 and the serpentine belt with an OEM # 3289012.* I still have the tensioner chatter at idle, not sure about when running at higher RPM as I did not have anyone around.* I have checked the alternator and it seems fine. Anything else I can check.* Is this normal when at idle?* Is the belt to short and is near the max of the belt tensioner. Maybe a belt that is about .25 to .50 in longer would solve this. Any help would be greatly appreciated.

https://www.dropbox.com/s/u6q3mzid9z...0belt.jpg?dl=0

https://www.dropbox.com/s/64yim4c51v...0belt.jpg?dl=0

JWLSC · 06-10-2016, 06:53 AM

So any ideas what could be the issue. Is my alternator going bad, or the pully.

Dutch Star Don · 06-11-2016, 07:52 PM

My guess would be that you have an alternator or pulley that is not turning in a perfect circle. Often, the belt tensioners have a 1/2" square hole where you can insert a breaker bar to relieve the tension while changing the belt. If you can get to that safely while the engine is running, you might want to take a little pressure off of the tensioner and see if it quits chattering. This might tell you the alternator is the issue.

79cvx20 · 06-22-2016, 07:06 PM

Quote:

Originally Posted by JWLSC

I was having belt tensioner chatter on my Cummings C8.3. I was thinking the belt tensioner was going bad as it is the original with 154K miles. I got a new OEM belt tensioner # 3976832. I also replaced the serpentine belt with a NAPA 25 080635 which is 64 ¼ in OD. Well even after replacing those parts I’m still getting the chatter. I read somewhere that to stop this I need a specific length belt, which is different then what they call for. Any ideas on how to fix this issue with the belt tensioner chatter.

If you have $150 you can waste it on a belt from Fleetwood. But it won't help anyway. Either Gates or Napa are fine belts. Dayco is lower quality. I doubt the belt quality or length has anything to do with that chatter. More likely, the condition of your batteries are overloading the alternator. About a 15-30 minutes after start with nothing else in the coach turned on your alternator should be putting out low amps at about 13.8 V to 14.5 V if your batteries are able to take their proper charge. If it keeps charging 45A or 50A or more constantly and doesn't go over 14.5 V you have a bad battery someplace or are a large current draw. Go buy a little $3 tester at the auto supply and test the electrolyte in every one of your batteries. Make sure they all read the same. If you let them cool off several hours they would probably read about 75 to 90%. If one cell reads lower than the rest you need to get rid of that battery. Weak batteries are notorious for tearing up belts and alternators (BTW, also almost anything in your 12 V electrical system). I've been a mechanic for 55 years and an ASE master technician since 1976. Now, I service Honda/Acura cars only and my poor old 92 American Eagle.
Semper Fi