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LarryC

48" Mower Drive Belt Problem

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LarryC
I have an odd problem with the 48” mower on my 7100 Series Sovereign (7117H). The PTO mower drive belt is “jumping” around when the PTO is engaged. The section of the belt from the mower pulley to the idler pulleys is moving quite a bit, which causes the front idler pulley, tension spring, tension rod and bracket to “chatter” as the tension spring adapts to the belt movement. It only started doing this recently after I changed the belt.
First off, the P/N I have referenced for the drive belt is #108508, The Simp dealer tells me this has been replaced by #1713515. This is what I am using. Is this the correct belt?

Other information that may be helpful:
- Drive belt has been adjusted “by the book”, currently re-adjusted to 7/8” space, front idler pulley bracket to belt stop.
- PTO Clutch adjustment, “by the book”, 3/32” engagement.
- Front idler pulley is in top mounting hole and is new, last season.
- Mower drive pulley and PTO drive pulley do not appear bent or damaged. Both spin free and true.
- The rear idler pulley has a little damage (slight bend), as it was before the belt was replaced.
- Mower blade height is 2 ¾”; blades are not bent or damaged. Nothing seems wrong under the deck. Cleaned and scrapped all the debris from the deck.
- I grabbed hold of each of the three arbor shafts to check for play and wear; the right arbor had a little play, the other two are tight. The mower spins free, but I did feel one area where it and made a little noise and had a little bit more resistance.
- The mower does not appear to have any strange vibrations (other than the belt and idler pulley chatter), but I may not recognize it if it did, since I have only mowed with this machine about a dozen times.
- Before I got the new belt, I was using a belt from a 42” deck that was longer and wider. It worked when the rear idler was adjusted all the way back, although I only had about ½” between the front idler pulley bracket and belt stop. I did not have the chatter problem when I used the wrong belt.


Sorry this is so long. I figured the more I could tell you, the easier it would be to figure it out. Any comments would be appreciated.

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DoubleT
If the belt is still new yet it may take a little time to break in and take a "set" to the pulley configuration. You should also be running at full speed for this to happen - otherwise partial speed will cause a vibration in the belt slack. Doesn't your sys have a red-green-red decal behind the idler for measuring the proper PTO belt tension adjustment? If so set it at least in the middle or towards the rear of the green zone.

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tej
Thanx Jeff.
The front idler pulley arm is in the middle of the green zone.
I'll loosen it and drop it towards the back a bit.
I run the throttle at 3/4 to full for mowing. I have been reluctant
to run at full with the belt chatter for fear of throwing the belt completely.
At $30 a pop, I would like to try and keep it in one piece.
I plan on pulling off the belt cover on the mowing deck to see if there is anything
out of the ordinary. Otherwise, I'll just keep running it.


Sincerely,
Jeff H.

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tej
Check to make sure the mower belt is in the proper PTO pulley - it should be the inside one. Take the belt off and feel all around and look for a burned spot in the "V" area - if the blades jammed even temporarily it could have "smoked" the belt - it only takes a worn small section to cause a bad vibration. Did it run OK for a while or did it start vibrating from the first? If from the first check for a "lump" in the belt construction that would cause it not to run smooth in the pullies. Also check pulleys for wear - you will see the belt "sunk" in too far. Also check for the unusual - like a small piece of wood or chip lodged in one of the pulley sheaves.

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tej
In case anyone is interested.......
I removed the mower belt covers and noticed the the source of the noise/ and belt problem was the arbor drive belt.
It had a bad wear spot (thinned out) causing it to drop into the pullies to deeply. This caused the arbor belt idler to jump around, causing the noise, and ultimately, the drive belt movement.
Thanx
Jeff H.

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