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Discussion Starter #1
Well except for a few frayed spots I now have 2 unbroken belts that have imo stretched out.

I don't know but in my experience they'd work if I could tighten them up...

...is there a way I can tighten up the PTO belt?

Thanks.

Just some further skinny I'm throwing out to the forum.

While conducting routine mowing operations under almost perfect PM conditions the PTO belt came off. Put it back on it would cut for awhile then throw off again.

Observed belt while engaged by the PTO and noticed a very distinct wobble from the deck drive pulley. After a few minutes the deck pulley would throw off the belt again.

Took deck off and manhandled pulley to see if pulley needed new bearings. FYI I replaced both pulley sealed bearings about 60 hours ago.

Well the pulley seemed fine to me so I mounted up deck with a new belt & observed that the pulley wobble was gone and the machine cuts fine again.

2 things on my mind here that's driven by the cost of replacement belts.

1 If I could tighten up the belt like the previous mule drive pulleys things would be rosy.

2 If the deck pto drive pulley had more of a sidewall the belt would set deeper and would not kick out. Then again the wobble might still be there and that can't be good either.

In my mind I'm maybe thinking modding a stepped holding device for the otherwise static belt tensioned rod.

^So what do you guys think about that possible solution? Thanks again for all the good info I get here. The little lady has planed the day out for me so I'll be back later.

PS I use OEM belts

:praying::thanku:
 

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I wonder if loosening up on the front U-hook deck hanger would allow for the deck to move rearward, thus tightening the belt some? Dunno. Just tossing (no pun intended) something out there. I know you can do just the opposite on some ZTRs. Tighten the U-hook to tighten the PTO belt, given the engine is in the back.

Joel
 

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My guess is you've got some unwanted vibration somewhere that is at a frequency that is sympathetic with the natural frequency of one leg of the belt between 2 pulleys, and this is making it flutter out of control. If you fixed the vibration problem I bet you'd fix the throwing belt problem.

Tightening the belt (or a spring on a tensioner pulley, but it sounds like you don't have one of those) would help because it would change the natural frequency of that leg of the belt. But that just moves the problem to a higher RPM setting. I think a better solution is to reduce the vibration if possible.

Edit: I guess regardless of vibration it sounds like you definitely are seeing a belt stretching problem as you said. Could it be all those "deck washes" you do by parking the thing in a big puddle and acting like a hovercraft? I'd guess the belts must be getting a bit wet when that happens.
 

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i had a 94 cub come in not that long ago it was throwing the drive belt off ..I had to adjust the idler pulley bracket as it bends easy do to pi$$ poor design and install the belt guides as this mower didn't have any ...After doing this i haven't had any trouble since
 

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Hello Savageactor

I think you found the probable cause, the bad bearings that caused the pulley to wobble. I am not sold on the quality of the deck bearings that Cub uses and in addition I don’t believe that those bearings can be lubed. I take the belt off from time to time and check the non-serviceable bearings as I do not expect great life out of them.

Adjusting the tension rod stop (on top of the belt cover) to tighten up the belt may not be a bad idea, as yours may be a little out of place – it’s not exactly a high precision set up. You would need to make sure you do not over do it – too much could shorten bearing life. Also, watch for the spring binding up on the flat plate of the tension rod. Mine hits already with the stop in the original position.
 

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Discussion Starter #6
^hummm well that's some food for thought pfreiburger as I've already replaced a broken tensioning rod spring. I'll take a second look at that.

There maybe something happening with that spring application I haven't keyed in on. btw those pulley bearings were OK, they were my first suspects as well.


JMoe I considered that but reasoned it would also change the attack angle of the deck and decided against it.

Toolin you're right on the vibration cause when I press to tighten the tensioning rod while the deck is engaged the belt tightens and pulley wobble disappears.

As far as my deck washing goes the top of the deck and belt doesn't get wet. I agree there's some additional stress but I try to minimize it by 'carefully shaving an inch of water or less'. Truthfully I'd settle for just buying belts at any price if that was the case. The puddle wash is just too sweet to pass up...and I've been doing it since the Reagan Administration.

roughrider do you mean the idler pulley on the mule drive? Because I can't see how the idler pulley on the deck drive would effect this...not that I'm claiming that as a fact...just surmising. Anyway one of the first things I did was eyeball the running deck from the front end to check the geometry of the mule drive and that's OK.

If I do make a multi-stepped tensioning rod holding rack I will make one step shorter that OEM because imo the new belt is 'OVER TIGHT' when first installed and that would lend itself to a prematurely stretched belt.

Anyway thanks again for all your thoughts...they make me think of things in a different perspective.
 

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JMoe I considered that but reasoned it would also change the attack angle of the deck and decided against it.
Yep, you'd probably have to loosen the rear hangers to drop the rear of the deck. Sounds like your on to something with that main drive pulley. A tiny bit of wobble shouldn't do anything. You say that pulley rolls fine w/out the belt on. Does it have a lot of play?
 

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Discussion Starter #8
JMoe I pulled deck maintenance today to check out the leads I got here. The deck drive pulley rotates fine w/o the belt. Now if I man handle it harshly yeah it gives some but the movement also goes out to the base of the spring assembly that's attached to the tensioned rod. <---and that looked good to me too.

I'm willing to bet serious $ those sealed bearings in there are good to go. I was cutting today and with the new belt the pulley rotates fine.

I got 179 hrs and am on my 4th belt but like I said 2 of the belts except for some lite fraying are imo still good.

I dunno all my past 4 cutting decks experience tells me I shouldn't trust that spring to properly tension the belt. When you put that new belt on it's a tight as a bow string.
 

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Got to thinking. You cut with the deck real low, don't you? Maybe the position is causing strain on the components.
 

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Discussion Starter #10
^Yes I cut low but the belt eyeballs out OK.

Now my neighbor and very good friend cuts with it on the high setting. The lady of the house prefers the lush carpet look like you have diesel_nut.

...and that's when the problem of the belt coming off 1st came up.
 

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once a belt is thrown, it breaks cords inside the belt and most likely will throw itself right back off. doesn't matter if its on your lawn mower or driving the fan on your car, that's what happens.

also, if your belt was new and it was thrown, then you have a problem with a misaligned drive pulley. misaligned pulleys (axle or axle mount gets bent) are the cause of "initial" belt problems. well, that and worn out belts of course. you should probably replace your drive belt every 200 hours because once it breaks a cord, it will pop off. if it pops off, it could bend the drive pulley mount...

so, check pulley alignment and put a new belt on it. problem should go away.

btw, the wobble in your pulley was with the old belt. it had broken cords, which cause deformation of the belt, which will cause the pulley to wobble...
 

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once a belt is thrown, it breaks cords inside the belt and most likely will throw itself right back off. doesn't matter if its on your lawn mower or driving the fan on your car, that's what happens..
I guess it's possible, but i've never experienced that. It's always been an improper install or one of the rotating elements out of alignment or w/ bad bearings that caused the belt to pop off. The PTO belt on my 2005 model year 2544 is chewed to he11 and still working @ 150+ hrs/5yrs. It popped off and jammed hard atleast 3x in it's life from me not being careful enough installing/routing it.

Joel
 

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it doesn't always break the cords, but when it does, and if you have some misalignment, they will come back off in a hurry. i had the same problem on my 301 deck when i first got it. belt kept popping off, but the alignment all looked okay. replaced the belt and have had 110+ trouble free hours since.

same thing on some of the cars i've owned. always the alternator belt, once on a '72 SS other on V8 240Z. both times during a race upon rapid reduction of rpms (shifting), although the 240z pulled the alternator down into the bracket, bent the alt fan and shot one of the fins right thru the hood of the car :banghead3. tried to run both belts again, but they just popped right back off. replaced the belts, and good to go....
 

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Savage, the lowest I regularly cut on is 3. Most times on 4. If I cut lower I get too much weed invasion.
 

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Discussion Starter #15
Good info there bry593 and I agree in a static world that could and will happen.

However on our last 3 cubs belts were allowed to be tightened with the mule drive. A 4" adjusting thread and bolt...they would flop off once.

After proper tighting they were good for a very long long time.

What I'm trying to address here is that these belts can't be tightened. You put them on and that's that.

Now I'm starting to wonder if it's me or these belts.:lalala: If I'm the only one this is happening to :fing20: YIKES!
 

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Well on a side note my new dog is laying at my side...Jack is a border collie I got 2 hrs ago.

My 5 yo German Shepard who was always unleashed at my side died suddenly after a fun man/dog day of golf, swimming and fetch.

After dying in my arms I buried him at his favorite spot by the pond he loved to swim in.

Long live Jack!
 
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