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Discussion Starter #1
I have a used gt3100 that was not kicking in the pto very well (very weak mower blade spinning). I decided to change pto belts as they were pretty loose. I replaced and it started great with strong mower blade rotation but 10 seconds later I saw smoke and shreds of belt flying out. Somehow the front belt came off the tensioner pulley and pinched. Before I put on another belt, any ideas? I'm fairly handy but not experienced in engines or tractors. I did notice the tensioner pulley did not freely spin too well. Thanks!
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Idlers not spinning easily can readily wreck belts. Also check that all the other things that the belt goes over can spin without making much noise or feeling rough.

And those belts appear to be paired (two belts going over all the same pulleys, so more power can be transmitted vs a single belt), and they should be replaced with a matched set (vs two single belts with length X, which will be slightly different lengths).

Replace the bits that don't spin easily (either by replacing the bearings or the whole idler/spindle/whatever), and only once they all do, then put on two new belts. And then perhaps just turn on the engine or enable the pto briefly, then turn it off and double check that the belts have stayed on all the pulleys and don't appear to be getting damaged.
 

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Discussion Starter #3
Idlers not spinning easily can readily wreck belts. Also check that all the other things that the belt goes over can spin without making much noise or feeling rough.

And those belts appear to be paired (two belts going over all the same pulleys, so more power can be transmitted vs a single belt), and they should be replaced with a matched set (vs two single belts with length X, which will be slightly different lengths).

Replace the bits that don't spin easily (either by replacing the bearings or the whole idler/spindle/whatever), and only once they all do, then put on two new belts. And then perhaps just turn on the engine or enable the pto briefly, then turn it off and double check that the belts have stayed on all the pulleys and don't appear to be getting
damaged.
Thanks, I'll try again on weekend and ensure everything is spinning well.
 

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Many members have reported short belt life using OTHER than OE Matched Set...OE is the keywords, after checking and repairing any pulley issues and finish by using OE Belts, your PTO issues will be in the past....
 

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I had issues with this on some of my 3000 Series Tractors and have a couple threads about it.


 

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Discussion Starter #6
I took the belts off and checked the tensioner pulley bearing and it seemed fine. I put it all back and disconnected the vacuum hook and used my hand to apply tension and activate the pto to be able to watch belts and stop if needed. The front belt still slipped off towards the front and caught between the pulley and the brake arm. Luckily I stopped before it chewed up the belt this time. I plan on replacing the tensioner pulley just in case, if It still fails I'll order cub cadet belts. I am using STENS at the moment. Not sure what else to do other then see if I can find some slop in. A bolt like mentioned that's causing tilt? It seemed to slip off when going from on. To off. There does appear to be tension in belt even in off position so it's not really flopping around.
 

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Discussion Starter #7
I took the belts off and checked the tensioner pulley bearing and it seemed fine. I put it all back and disconnected the vacuum hook and used my hand to apply tension and activate the pto to be able to watch belts and stop if needed. The front belt still slipped off towards the front and caught between the pulley and the brake arm. Luckily I stopped before it chewed up the belt this time. I plan on replacing the tensioner pulley just in case, if It still fails I'll order cub cadet belts. I am using STENS at the moment. Not sure what else to do other then see if I can find some slop in. A bolt like mentioned that's causing tilt? It seemed to slip off when going from on. To off. There does appear to be tension in belt even in off position so it's not really flopping around.
I took the belts off and checked the tensioner pulley bearing and it seemed fine. I put it all back and disconnected the vacuum hook and used my hand to apply tension and activate the pto to be able to watch belts and stop if needed. The front belt still slipped off towards the front and caught between the pulley and the brake arm. Luckily I stopped before it chewed up the belt this time. I plan on replacing the tensioner pulley just in case, if It still fails I'll order cub cadet belts. I am using STENS at the moment. Not sure what else to do other then see if I can find some slop in. A bolt like mentioned that's causing tilt? It seemed to slip off when going from on. To off. There does appear to be tension in belt even in off position so it's not really flopping around.
So got the new idle pulley, installed, but still no luck. It ran good and strong (belts are tight) but after about 1 min the belt slid off the idler then popped off and broke... I'm debating to buy official cub cadet belts to see if makes a difference but don't want to spend 50 bucks and break a belt again... thinking of just trying to find a cub cadet service shop....
 

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Ejl in Pa.
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Make sure that both pulleys on the lower pto shaft as well as the ones on the the crankshaft do not have a large and uneven gap in them that causes the pulley to wobble and cause the problem your having. I have seen on used tractors I bought shredded pieces of belt stuck in between the pulleys on the crankshaft and a bent pulley on the lower pto shaft causing an uneven gap between the two pulleys and causing the belt to jump just as you've stated.
Resized_20200419_130036.jpeg
 

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Not sure if you went to the links that I attached to my earlier post, #5 where I explained issue I have had with front pulley groove being spead wider than the rear groove, causing the front belt to run loose and come off. Since I posted that info, I have encounter the same issue on another tractor, so I think it is a somewhat widespread problem, but people don't have the access to easily inspect the pulleys like I did on a lift. This is the first thread I did about it on another site. If your not a forum member there, you may not be able to see the photos so I C&P a few.



Front groove, see how deep the belt sets in the groove?

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Hard to see in photo, but front groove is significantly wider.
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Belt sets a lot higher in the rear groove. Same belt in all photos
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Belts sets a lot deeper in front groove.
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After I installed a new lower pulley I have run cheap belts off of Ebay (< $15 a pair) and have not had issues with belt coming off.
 

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Discussion Starter #10
Thanks, I ordered another lower pulley to try. Trying to do on my own as not many cub cadet service near here and I don't own a truck. Just trying not to blow through too many belts....
 

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Ejl in Pa.
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Not sure if you went to the links that I attached to my earlier post, #5 where I explained issue I have had with front pulley groove being spead wider than the rear groove, causing the front belt to run loose and come off. Since I posted that info, I have encounter the same issue on another tractor, so I think it is a somewhat widespread problem, but people don't have the access to easily inspect the pulleys like I did on a lift. This is the first thread I did about it on another site. If your not a forum member there, you may not be able to see the photos so I C&P a few.



Front groove, see how deep the belt sets in the groove?

View attachment 2453354


Hard to see in photo, but front groove is significantly wider.
View attachment 2453355



Belt sets a lot higher in the rear groove. Same belt in all photos View attachment 2453356


Belts sets a lot deeper in front groove.
View attachment 2453357


After I installed a new lower pulley I have run cheap belts off of Ebay (< $15 a pair) and have not had issues with belt coming off.
Joelk I felt it was necessary to post my reply because the OP is still having issues and doesn't appear to have taken your advice.
 

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Joe, that sure is a beautiful 1968 Firebird in some of your photos!
It belongs to a friend of mine and it is a very nice car. He knows cars, but I know Pontiacs, and he asked me to do some work on it for him.

My first car, at 17, was a 68 GTO and I have had several other Pontiacs since then. I currently have a 68 LeMans Convertible (GTO clone, that I have had for about 30 years) My car is a lot faster than his, but mine is cosmetically rough, at the moment.
 

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I run cheap Ebay belts with no issues. I had the same issue on my 3165. Watch the idler pulley when the pto pulls in. Mine was not pulling in straight and throwing the belts off because of the worn nylon flange bearing (part #741-0491). I replaced all 4 and the issue went away. Good luck and let us know what you find.
 

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Discussion Starter #15
I run cheap Ebay belts with no issues. I had the same issue on my 3165. Watch the idler pulley when the pto pulls in. Mine was not pulling in straight and throwing the belts off because of the worn nylon flange bearing (part #741-0491). I replaced all 4 and the issue went away. Good luck and let us know what you find.
Thanks, I'm going to replace the bottom pulley and might as well replace those bearings as well. Just have to wait on the long shipping times....
 

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Ejl in Pa.
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Did you look at the gap between the two pulleys and did it appear that one was bent with the gap being uneven? Did you rotate it and did it wobble?
 

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Discussion Starter #17
Did you look at the gap between the two pulleys and did it appear that one was bent with the gap being uneven? Did you rotate it and did it wobble?
I didn't notice any wobble. When you mean gap do you mean a difference in the grooves on the bottom pulley? I haven't checked that yet, but with how old and rusted the bottom pulley is I just ordered another. I plan on replacing the 4 plastic bearings, replacing the bottom pulley, (already replaced the idle pulley). Then see how it goes.
 

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Ejl in Pa.
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I mean the gap between the two pulleys.If you look at the picture I posted of the bottom pulley you will see there is about a 1/16" gap between the two pulleys. If one pulley is bent the gap will be larger and uneven. Usually the front one gets bent by hitting something.
 

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Discussion Starter #19
Its Alive! So I pulled the muffler off to get to the plastic bearings to replace them. With the muffler off and looking straight down I could tell the idle pulley was not centered and as the idle pulley was engaged it got worse and worse. Replacing the plastic bearings did not help and I tried seeing how much play was in screws for both the idle pulley and the screw it pivoted on. None of it made enough difference. I then bent the bar the idle pulley attaches to. It was better but not perfect. Finally I found there was a lot of play by loosening the screws (part 7) in the attached image. At first the replacement belt behaved odd, it was fairly tight without the idler engaged and started melting onto the engine spindle without the pro engaged... I then bought MTD belts and they were noticeably looser even though the measurements said the same size. They also were more fiber than rubber. Finally it all worked, at least I mowed the front yard with no belt slipping off and no burnt rubber smell....
So I think in my case it was a mixture of...
1. Part 1 in image was slightly bent
2. Play in part 3 holes, loosening part 7 screws gave me play to line up the idle pulley.
3. The official MTD belts seemed to fit much better.

Thanks all! Fingers crossed it keeps working...
 

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