7130 Magnum serpentine belt issues

[1967806]

Got a belt that wont track right. Rubs the first two ribs off closest to the engine. Put a new crank pulley on it a couple falls ago because the rubber was coming apart. Have replaced the idler tensioner, fan hub bearings and the alternator was replaced a while back because bearings were starting to make noise. Parts man said he thought there was a service bulletin on that subject several years ago. Any ideas? 

[756puller]

I think I've had a few plates that the belt tensioner attached to be bent a bit thru the years.

[snoshoe]

Parts man is right. Had something to do with tensioner mount. All I remember. 

[Dan Robinson]

Our 8920 always had a belt squeak. Had put belts on it and couple different tensioners and idlers.

Never found it.

Until one day I got to looking at it, the idler was running at a slight angle to the belt. 

The tensioner bolts to the thermostat housing. 

Last person to bolt the housing to did not get it square. To me its something that should have been doweled. 

I didnt want to pull the thermostat at the time, so I folded a piece of emery paper and put behind the one side of tensioner and bolted it back tight. Back square again and no squeak anymore. 

[Kevin in ky]

Put a new belt on my 7120 right after I got it in 2005 and it cut 2 ribs off after cranking it.the belt is still working fine.That’s my experience.

[HydroTek]

Only takes a slight misalignment on that type of belt to give squeaks and tracking problems

the T-stat housing had a dowel added that helped align the idler -- but still could tilt if one was careless with the install

always seemed a stupid place to mount the belt idler to me 

Alternator mounting also has some wiggle in it
and seen the fan bearing walk out of the housing 

All these need to be checked if you are having belt problems 

@Kevin in ky there is a guide knob on the timing cover lower bolt -- if you get the belt on the top of that knob , will cut the belt like you describe

[bwop2017]

Your front crank pulley isn't old is it?. If the rubber ring gets weathered, then the outer ring could run crooked and drift the belt

[1967806]

1 hour ago, bwop2017 said:

Your front crank pulley isn't old is it?. If the rubber ring gets weathered, then the outer ring could run crooked and drift the belt

Replaced it a couple years ago after the rubber started coming apart. Seems like that's when the problem started. 

[1967806]

7 hours ago, Kevin in ky said:

Put a new belt on my 7120 right after I got it in 2005 and it cut 2 ribs off after cranking it.the belt is still working fine.That’s my experience.

It still runs fine. Just short two ribs. 

[cedar farm]

Check your dampener. When they start to fail, they walk forward.

[1967806]

On 12/20/2025 at 2:14 PM, cedar farm said:

Check your dampener. When they start to fail, they walk forward.

It was new a couple years ago. Started having problems after that. Kept the old one and measured it compared to the one we recently replaced and didn't see any difference. 

[SDman]

This is probably the bulletin you were asking about. The second part might help you more than the first part, which announces the new t-stat housing with the alignment dowels.

[1967806]

6 hours ago, SDman said:

This is probably the bulletin you were asking about. The second part might help you more than the first part, which announces the new t-stat housing with the alignment dowels.

Thanks for the info. I'll print that off and take it to the shop tomorrow. 

[cumminstinkerer]

21 hours ago, SDman said:

This is probably the bulletin you were asking about. The second part might help you more than the first part, which announces the new t-stat housing with the alignment dowels.

I remember that bulletin well, I only ever had one that had that issue, was in an 821C wheel loader, but that thing had a lot of issues and things got janked by others before I found the real issue, the belt was customer induced issue, the main issue was the water pump was missing the impeller, the head had been gone through 2 times before I got stuck on it so fairly easy to mess things up with the tensioner mount. I actually never did find any of the impeller, it appeared to have just vanished, the center hub and back big flange were there but no vanes or small flange!

[1967806]

On 12/23/2025 at 10:05 AM, cumminstinkerer said:

I remember that bulletin well, I only ever had one that had that issue, was in an 821C wheel loader, but that thing had a lot of issues and things got janked by others before I found the real issue, the belt was customer induced issue, the main issue was the water pump was missing the impeller, the head had been gone through 2 times before I got stuck on it so fairly easy to mess things up with the tensioner mount. I actually never did find any of the impeller, it appeared to have just vanished, the center hub and back big flange were there but no vanes or small flange!

Interesting. Suppose they just went in the radiator and fell to a low spot and didn't cause any more problems? 

[cumminstinkerer]

On 12/25/2025 at 9:11 PM, 1967806 said:

Interesting. Suppose they just went in the radiator and fell to a low spot and didn't cause any more problems? 

I honestly can't answer where it went, the radiator got boiled at Holmes/American before I ever got my hands on the machine, I looked in the block with a bore scope as best I could and never found one piece, I wish I had pictures, it was unreal, and the really weird part was the pump didn't leak and felt great, just didn't have the fins of the impeller at all

[1967806]

1 hour ago, cumminstinkerer said:

I honestly can't answer where it went, the radiator got boiled at Holmes/American before I ever got my hands on the machine, I looked in the block with a bore scope as best I could and never found one piece, I wish I had pictures, it was unreal, and the really weird part was the pump didn't leak and felt great, just didn't have the fins of the impeller at all

I bet it ran a little warm with the fins gone. 

[cumminstinkerer]

1 hour ago, 1967806 said:

I bet it ran a little warm with the fins gone. 

It sure did and really didn't take long at all to get there, assume that is why they did the radiator and head gasket. It was strange and took a bit to figure out, everything seemed fine from the outside, had basically condemned the head gasket again, but when I pulled the belt I thought man that water pump spins pretty easy, so I pulled it and found the issue. Boss couldn't believe it nor could the field tech that had been out on it like 3 times!

[1967806]

4 hours ago, cumminstinkerer said:

It sure did and really didn't take long at all to get there, assume that is why they did the radiator and head gasket. It was strange and took a bit to figure out, everything seemed fine from the outside, had basically condemned the head gasket again, but when I pulled the belt I thought man that water pump spins pretty easy, so I pulled it and found the issue. Boss couldn't believe it nor could the field tech that had been out on it like 3 times!

Sad thing is the water pump on an 8.3 is way easier to pull than a radiator.