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Discussion Starter · #1 ·
My 8 rib belt jumps one rib (towards the engine) but it doesn't do it regularly......just very, very random.

I haven't checked actual crank endplay with a dial indicator, but just eyeballing it, it is about .010"-.012". Yeah, that's a lot, but is it enough to cause the random rib jump?

Also, the belt tensioner jumps around a LOT at idle. It isn't nice and stationary at all. Is that a concern?
 

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have you had a look at it with a straight edge across the pulleys ? no worn water pump or tensioner bearings ? my tensioner jumps around a bit at idle. it smooths out when you rev it up a bit though. also, have a good look at the end float in the crank. my suspicion is if you can feel it when pushing the crank pulley in and out, it's time. my engine had a leaky rear main which replacing the spacer cured. it has a heap of slop when the thrust is gone, which may be contributing.
 

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On our 6bs in the Trackmobiles I have seen several sets of worn out pulleys do this, we have changed the complete pulley set, crank, alt, wa pump and the idler, just beause. What happens is the groves ware down to the point it doesn't hold the belt in place anymore. I have also seen a brand new engine do this but that was a missalignment of the fan hub on the shaft. Covered under cummins warrantee.
 

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Discussion Starter · #5 ·
I saw one that did the same thing. Turned out the idler pulley tension arm was bent. swapped tension arm and it worked great.

Hmmm.....wondering what part number I need.
 

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If the motor sits without running for a long time the belt can take a "set" and not run smooth. Get a new belt first.

I had a 6bt on a well and it was jumping all over after sitting all winter. The belt shredded and then the new one ran very smooth.

Some folks take the belt off for storage.
 

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Discussion Starter · #7 ·
If the motor sits without running for a long time the belt can take a "set" and not run smooth. Get a new belt first.
I drive the truck everyday. The belt is about 2 mos old.
 

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Hey there neighbor! Ive had this happen several times on my 6bt, everytime it was the tensioner. Mine was jumping one toward the engine and the alternator was chewing it up. It looks as though it could be a combo of the two, that crazy jumping around the tensioner does is it hitting a weak spot in the belt. Change both and that should have it.
 

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Discussion Starter · #9 ·
This is the one I have.
Can I get it from Napa or Rockauto.com or do I HAVE TO buy it from Cummins?
 

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Although its in a different spot, it looks very close to the one I have on my 4bt and my 6bt. I bought both the belt and the tensioner at the CarQuest on Loop 340 in North Waco. The new tensioner takes a 1/2" drive instead of the 3/8, that helps a ton having the extra length when prying on it to get the belt on. Just for funnies, call "diesel power" off of University Parks Dr. Give them your CPL and they will be able to tell you the exact part you need and might have it in stock.
 

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I had the same problem too.

I had the same problem. I got to checking closer and the altornator bracket was off a little. After adjusting the bracket and bringing the pully into line it hasn't happen since. May not help you but it worked for me.
 

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Discussion Starter · #12 ·
OK guys.....I am on the road for the holidays. I am thinking this tensioner pulley is about to seize up on me, it squeals pretty bad now. It might fail on the return trip.

I need a number, application..... anything to help me find one "commonly".
I doubt I'll have much luck at Cummins, it sounds like the part guys hate playing Sherlock Holmes when it comes to finding the right part.
 

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Hey Linctex,

Looking at the thumbnail pic you posted, the part # for the tensioner should be on the arm between the hole for the pulley and the square hole . At least that is where it is on mine. The Dayco # that fits mine is 89409 $70 at Autozone had to order. The Gates brand would not work on mine because it hit the belt for the vac pump. Since you don't have a belt on the aux. pulley the Gates will fit. The Gates seemed to not bounce as much compared to the Dayco. Also the # that was stamped on my original was a Cummins #, any of the parts stores can cross ref. it.
 

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OK guys.....I am on the road for the holidays. I am thinking this tensioner pulley is about to seize up on me, it squeals pretty bad now. It might fail on the return trip.

I need a number, application..... anything to help me find one "commonly".
I doubt I'll have much luck at Cummins, it sounds like the part guys hate playing Sherlock Holmes when it comes to finding the right part.
If that's the stock 4BT tensioner, then NAPA part number is 38504 from here:
http://4btswaps.com/forum/showthread.php?t=1418&page=2

That's for the entire tensioner, though.

I'm assuming that, even though the tensioner is different (clockwise vs counterclockwise tension) on the Dodge, the pulley it has is the same, so I looked up the tensioner pulley alone (if it's still giving good tension, but just the bearing going out..) for a 91 Dodge w/ Cummins and that lists as 36094 in the NBH line at NAPA. Specs for that pulley are:

Glass Reinforced Polymer

O.D.:78mm
Width:32.5mm
Material:Thermoplastic
Contact Surface Type:Smooth/Backside
Additional Contents:Thermoplastic Smooth/Backside (78mm x 17mm x 32.5mm)

Considering the pulley alone is only $29 and the whole shooting match is $119.. Guess which one I'd buy.

That number is a Gates number, so it's the same at Advance Auto Parts, Dayco number (Autozone) appears to be 231105.

Dunno if that's any help, but might give the countermonkey a place to start..
 
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