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Old 06-13-2012, 01:34 PM   post #1 of 10
bobinyelm
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Default Belt Adjustment/Replacement on Troy Bilt PONY

I started a thread a while back about too-frequent belt replacement on my lightly used 7 year old Pony mower.

The first set of belts lasted 3 years, and each successive set has lasted less and less, until the last started slipping after only TWO mowings.

It was suggested that the Variator Pulley was likely hanging up, and sticking, not allowing the center sheave to move freely and apply pressure to the belts.

I ordered an new Variator (about $50) and just installed it, and had questions.

First, the old one upon removal appeared PERFECT. The center sheave slides freely on the center shaft (barely tilting the shaft from horizontal allows the sheave to slide from one end to the other and back). The bushing is not worn, and so there is no wobble to the center sheave (0.008" on a dial indicator) vs. 0.010" on the new one, in fact. Both allow the sheave to slide exactly the same when tilted, or moved with a finger.

There is an adjustment shown by the Red Arrow #1 that is ALL the way out right now, and I am wondering if that is correct.

When the clutch pedal is completely released, there is a "free throw" of only about 1/8" before the pedal starts moving against the spring, eventually opening slack in the main belt (deck belt?), but moving the adjustment would not seem to change that. With the clutch released, there's what appears to be plenty of tension on both belts to me.

Obviously if the belt were kept from being under proper tension, it would slip, but when operating the mower, the clutch "catches" quite a while before it is fully released, so I don't think that's the problem.

Before I replaced the deck, I wanted to ask for opinions.

I did NOT change the belts this time since the new ones have only about 3 hours use, and "look" just fine. They are NOT MTD belts, however, and some have said that ONLY MTD belts can be used with the variator drive system.

If it still slips, I guess I will go pay $65 for a set of MTD belts, but having just spent a LOT on belts and pulleys, I am reluctant to throw more at the mower "this week" at least.

I frankly cannot see WHY it's slipping. It usually is MUCH better when cold, and after 10 minutes, the slipping starts, and by the time I finish my sloped lawn, I almost have to get-out-and-push to get it back to the barn.

Pushing the clutch in and releasing it will sometimes help a tad for a few seconds before the almost total slipping recurs. If on perfectly level ground, the tractor WILL always move OK. It takes at least a slight slope (or the steering wheel turned on level ground) to feel the slippage.

I posted a couple of photos below to show the old vs. new, and the new pulley installed. I have one photo before removal of the old pulley, but it's absolutely identical, so didn't bother posting it here.

The ONE "good thing" (I guess) is that I now have enough practice so I can remove the deck in mere minutes. The first time I did it, it took me a while to find all of the fasteners under the decals to get it off.

BTW, when replacing belts, if they both look and feel good (not hard glazed), is one of them usually the first to "need" replacement. In other words, does one of the belts tend to "last" longer than the other, so replacing one belt will restore performance? It would be a way to save $30 if one typically lasted twice as long as the other. Only ONCE did I actually see or felt any visual damage (the edge of the shorter drive belt was torn up a bit on one edge) of any belt I removed. I assumed they were slipping because the edges of the "V" portion had lost their "grippiness", but it's gotten ridiculous with belts slipping badly in days or weeks after replacement. SOMETHING has to be going on here!

The mower guy at Lowes (where I bought it) said the Pony is a "trow-away" after 5 years, and that they just wear out so completely that they cannot be fixed, but dog-gone it, I see NOTHING in my unit that indicates any wear, sloppiness, or other flaw in the drive system (unless I don't know where to look, which is why I am asking here).

I've owned several automotive shops over the years, and have been a licensed aircraft mechanic for almost 40 years-I ought to be able to keep a darned mower going! This is FRUSTRATING!!

More suggestions?





Last edited by bobinyelm; 06-13-2012 at 01:48 PM.
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Old 06-15-2012, 09:56 AM   post #2 of 10
tomw0
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Default Re: Belt Adjustment on Troy Bilt PONY

I make no claim to 'knowledge' or anything close, but after looking at the upper picture, it occurs to me that you have a drive system with two springs in 'opposition' to each other.
The lower spring, in the bottom right of the picture,(de-tensioned by the clutch/brake pedal) engages the PTO pulley(on the crankshaft) with the variable pulley(lower). Take your foot off the clutch pedal, and the spring pulls the variable towards the rear of the mower. The second, or upper spring tries to pull the variable towards the far side of the picture.
Spring tension is the 'force' that keeps the belts tight, no matter what 'gear' you are in.

The gear selector lever positions the variable pulley in an arc(I asume...) to one of several 'fixed' positions. If the variable moves towards the far side, the effective diameter of the 'upper' pulley will get larger, and at the same time, the effective diameter of the 'lower' half will get smaller. The result is a 'lower' gear. PTO spins faster on 'small' lower pulley, driving upper 'large' pulley at slower rpm.
If the variable moves towards the close side, the opposite occurs. The upper diameter gets small, the lower gets larger, resulting in a 'higher' gear. The PTO belt can drive the transaxle (upper) belt faster.
The problem occurs when the motion of the variable pulley, moving from hi to low, or vice versa, leaves one of the two belts loose, allowing slippage. The solution lies in adjusting the two springs so that there is enough 'contact' friction, i.e., the belt is tight, across the travel of the variable pulley.
I have not seen one of these in 'real life', think I have one on a Yard Machines, but don't want to remove a buncha stuff to see.
I think if I had your slippage problem, I would get the TB manual

http://www.mymowerparts.com/pdf/Troy...RVICE-BOOK.pdf

or

http://www.mymowerparts.com/pdf/Troy...ir-manual..pdf

depending on which applies. I *think* there is a procedure in there explaining how to adjust the belts.
Off the top of my head, I'd expect the adjustment to suggest putting the selector in a middle gear, then adjusting the PTO which you mentioned is at its full adjustment, to get good tension on both belts. My guess is that the far spring is not getting an opportunity to tighten because all the 'slop' is being taken up by the PTO belt adjustment. In the picture, it appears the spring is totally compressed. It should be applying tension at all times. As a matter of fact, both belts should be in tension at all times unless the clutch pedal is depressed.
If this makes sense, so much the better. If not, comment...
tom

... Added ...
Just went and re-read the whole thing. One thing I didn't mention is that the 'effective' length of BOTH belts matters. If the PTO belt is tight across the variable pulley's travel, and the transaxle belt is tight ditto, then it should work. What I think is happening is that one or the other belts, or perhaps some of the linkage further away from the variable pulley, has worn, and allowed the belt {one or the other} to be loose when it shouldn't.
In that sense, I'd look at the far upper pulley mount, as it is spring loaded to keep the transaxle belt tight across the variable's travel, yet looking, there is no tension on the spring. It MUST be tensioned or the belt will slip. Ditto the PTO belt.
tom

Last edited by tomw0; 06-15-2012 at 10:10 AM.
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Old 06-15-2012, 12:21 PM   post #3 of 10
bobinyelm
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Default Re: Belt Adjustment on Troy Bilt PONY

There is no "slop" anywhere, and the springs put quite a decent amount of tension on the pulleys, and belts themselves.

Because no one responded right away, and I wanted the mower OUT of my garage (so I could put my car back given the hail we get here near Dallas), I re-assembled the mower.

It works perfectly w/ the new pulley, and the old belts that slipped hopelessly, and I can climb 50% grades (that's 22 degrees!) easily w/ not a hint of slippage.

The old pulley had belt friction surfaces so polished from use that they were slick like a chromed bumper, or more. The new pulley is smooth, but not shiny or slick. You can see some reflections in the sheaves of the old pulley in the pictures above. You could shave in the reflection they are so mirror-like, in fact.

I'm thinking the slickness allows a marginal system to slip, and slippery surfaces encourage that slippage.

The center sheave is absolutely free on the old one, so I don't think that was the problem.

I kept the old pulley, and my plan is to protect the centers with cord or tape, and try to sand-blast the friction surfaces to give them some "tooth" but not so much they will tear up belts.

Next time I notice slipping (if I do) I will re-install the old pulley to "prove" (or dis-prove) my theory.

But for now, the mower is performing like new.

Thanks,
Bob
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Old 06-15-2012, 10:55 PM   post #4 of 10
tomw0
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Default Re: Belt Adjustment on Troy Bilt PONY

Well, I gave it a shot... Your proposal to de-polish the surfaces makes sense. I did notice that there appeared to be some grooving of the older pulley surface in the picture but was not sure if that was an artifact of the camera or reflection.
I have noted that if I depress the clutch pedal just a smidge when shifting to another gear, moving the selector is easier. I can upshift relatively easy, but downshifting while in motion seems to put a load on the mechanism that makes it more difficult.
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Old 06-16-2012, 06:27 AM   post #5 of 10
bobinyelm
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Default Re: Belt Adjustment on Troy Bilt PONY

Yes, there are "grooves" in the reflection, but they are so slight that if you run a finger over them, you can't feel them. You only notice them in the photo because the surface is mirror smooth and it shows up everything magnified. No way would they appear prevent the belt from sliding in/out on the pulley to effectively change the drive ratio. The pulley surfaces are so smooth I doubt a fly could stand up in them without sliding off. I can see it would be easier for a belt to slip on a pulley which is that slippery, especially after the surfaces of the belt get glazed a bit and are not as "grippy" as when new. Kind of like rubber tires on ice vs. dry concrete. The new pulley provides "concrete" pavement for the rubber belt.


On my Pony, I could NEVER shift "On the fly" unless I depressed my clutch a tad. I think I COULD force it "up" a gear, but never down because of the ratchet teeth on the little bell crank the shift lever controls (under your left foot inside the chassis rail).

Last edited by bobinyelm; 06-16-2012 at 06:32 AM.
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Old 08-09-2012, 05:48 PM   post #6 of 10
daklander
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Default Re: Belt Adjustment on Troy Bilt PONY

Quote:
Originally Posted by bobinyelm View Post
.......

I kept the old pulley, and my plan is to protect the centers with cord or tape, and try to sand-blast the friction surfaces to give them some "tooth" but not so much they will tear up belts.
Bob, something else that works well for breaking that glaze is either a Scotch-Brite pad (Roloc or Hook and Loop) or a glaze breaking pad (Roloc™ Brake Rotor Surface Conditioning Discs). 3M makes a selection of them that work great for not only home repairs but also for professional equipement and automotive repair shops.
For cleaning up something like the pulley surfaces I would use the Scoth-Brite pad over the Rotor Surfacer and I'm partial to the Hook and Loop system rather than the Roloc though the abrasive used seem to be the same. Those also have several different grits available for different uses and different metals. They also work great on cleaning up gasket residue on some surfaces.
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Old 08-09-2012, 09:46 PM   post #7 of 10
bobinyelm
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Default Re: Belt Adjustment on Troy Bilt PONY

Actually it's not so much a glaze as an incredibly polished surface.

It will take something PRETTY abrasive to give the pulley some "tooth."

After installing the new variator pulley it worked like a CHAMP about 3 times, and now the NEW pulley is slipping like mad again.

I let it slip for maybe 15 seconds and you could SMELL the belt burning.

I do NOT get it. The mower worked GREAT for the first 3 years or so, then I can't get it to grip enough to go up my gentle property.

I haven't taken it apart again yet, but it's fine on the level, but sharp turns or up hill it slips like mad.

The speeds are just right, so the linkages and springs are apparently FINE.

This think is driving me NUTS.
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Old 08-09-2012, 11:40 PM   post #8 of 10
daklander
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Default Re: Belt Adjustment on Troy Bilt PONY

Quote:
Originally Posted by bobinyelm View Post
Actually it's not so much a glaze as an incredibly polished surface.

It will take something PRETTY abrasive to give the pulley some "tooth."

After installing the new variator pulley it worked like a CHAMP about 3 times, and now the NEW pulley is slipping like mad again.

I let it slip for maybe 15 seconds and you could SMELL the belt burning.

I do NOT get it. The mower worked GREAT for the first 3 years or so, then I can't get it to grip enough to go up my gentle property.

I haven't taken it apart again yet, but it's fine on the level, but sharp turns or up hill it slips like mad.

The speeds are just right, so the linkages and springs are apparently FINE.

This think is driving me NUTS.
A glaze in this type of application is a very polished surface. Some have hot spots, some do not.
If the thing still has belt slippage issues look at the other belt/s in that routing. Any other pulley with a slick surface will also allow the belt to slip so have a very close look at them.
The products I mentioned will take care of the slickness of the pulley/pulleys. I use them for not only cleaning up metal but also for putting a non-directional surface on disk brake rotors and flywheels. The flywheels are the toughest to deglaze when you take into consideration the hot spots that sometimes would cause a lathe to chatter if the cut was just a bit too deep. I've had such great success with using the 3M abrasives that I have not used a machine shop to resurface a brake rotor or flywheel in a couple of decades unless there's such a warp on the rotor that it would still cause issues. Then it's often cheaper to just purchase a new rotor. I have yet to run into a flywheel that I could not resurface a flywheel to acceptable usage capabilities using them. Also, while not mower sheaves/pulleys, I have dressed others with no problems. It will certainly be worth it to give the 3M abrasive disks a shot.

Other than that, I'd be looking for the issue if everything else in adjusted as it's supposed to be.
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Old 08-11-2012, 11:06 AM   post #9 of 10
tomw0
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Default Re: Belt Adjustment on Troy Bilt PONY

I think there are four things left to check. 1)PTO pulley surface. 2)transaxle pulley surface, 3)drive belt spring tension, 4)transaxle belt spring tension.
From your reports, a polished pulley will slip more readily than a 'satin' finish new pulley. Makes sense. However, a polished pulley will have great traction when it is seated well with a 'rubber' faced drive belt. The rubber should grip to the surface even when polished, I think. Maybe there is a 'tension vs length' chart for the involved springs in the service manual. If either spring were weak, and I don't know how to judge what would be considered 'weak', you'd get slippage, and more 'polishing' effect.
tom
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Old 08-19-2012, 11:16 AM   post #10 of 10
bobinyelm
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Default Re: Belt Adjustment on Troy Bilt PONY

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I think there are four things left to check. 1)PTO pulley surface. 2)transaxle pulley surface, 3)drive belt spring tension, 4)transaxle belt spring tension.
From your reports, a polished pulley will slip more readily than a 'satin' finish new pulley. Makes sense. However, a polished pulley will have great traction when it is seated well with a 'rubber' faced drive belt. The rubber should grip to the surface even when polished, I think. Maybe there is a 'tension vs length' chart for the involved springs in the service manual. If either spring were weak, and I don't know how to judge what would be considered 'weak', you'd get slippage, and more 'polishing' effect.
tom
I agree with ALL.

The springs in the variator system "balance each other" with the drive speed determined by adding or subtracting tension on one of the springs against the other fixed one, as I understand it. In order to increase overall spring tension w/o unbalancing the gear selection, one would have to replace BOTH springs with proportionally stronger springs. That would imply that if ONE spring has gotten weak, the speed range would be "off" now, which it isn't. The OTHER conclusion could be that BOTH springs have gotten weaker over time at the same rate, which seems unlikely at best, since none of the springs is that highly tensioned, or subject to heat.

The "other" pulleys (other than the variator) have far larger diameters and contact surfaces (more of the pulleys contact the belt along more of their circumferences,), providing much greater friction even if polished. The variator is the exception for the final drive belt that drives the transaxle belt.

I took the deck off again last night, and replaced the "NEW" variator (one use only an hour before slipping started AGAIN. It was not yet highly polished, but very smooth satin) with the OLD one which I'd "roughed up" with an angle grinder run over the belt-contact surfaces to give them a little "tooth."
I retained the old belts (they were only maybe 10 hours old, that I replaced earlier in the summer), I re-assembled the mower (I can now easily R&R the deck and Variator in well under an hour-the only "good" think about this hassle), and the mower performed flawlessly for the hour I used it afterwards.

This tells me that the slippage IS at the variator pulley, though it doesn't tell me which belt was slipping (If I remove the battery and the battery tray, with someone operating the mower I COULD observe this, however-a thought for next time).

The drive belt from the engine has contact w/ the variator pulley of at least 180deg, while the transaxle drive belt only contacts it about 120 degrees, making me thing THAT's the one that is probably slipping.

We'll see how long THIS non-slippage lasts. I am NOT running OEM belts as of the last belt change 10 hours ago, so possibly that is PART of the problem, though the belts still look and feel good.

The previous slipping belts WERE OEM MTD belts, however. I just got tired of spending $60 so often on OEM vs $30 for other manufacturer's belts. Maybe MTD are superior, or maybe they just charge more to buy and re-brand them. I don't really know.
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