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Deck belt pops off idler pulley

The mower is a Troy-Bilt Pony, model no. 13AN77TG766, made in 2006, with a 17.5 HP B&S engine and 42 inch deck.  The manual is available at .

When mowing today, I found the deck belt kept coming out from around the right-hand Idler Pulley (near where the "PTO" cable is (incorrectly) shown attaching to the Deck Idler Bracket in Figure 17 on page 19; also in Figure 21 on page 23).  There seems to be a vertical misalignment between the Engine Pulley and the Idler Pulley, so that the belt, coming off the Engine Pulley horizontally, runs into the top edge of the Idler Pulley (which isn't _meant_ to be horizontal, is it?  'Cos it isn't).

So you see that tab on the Deck Idler Bracket in Figure 17 next to the right-hand Idler Pulley?  The belt squeezes between the rim of the Idler Pulley and the tab, getting a big groove worn into it, a puff of smoke (can't see it, but I can smell it), and no more power to the blades.
I probably put that belt back around the Idler Pulley about ten times today before I gave up and changed the belt.  The other belt gave exactly the same thing.

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  • dah31 Jul 19, 2009

    Short: Grab a 3/4-inch deep-well socket and tighten the nuts on the front lift rod nearly all the way down.

    Well, since then, I've replaced the Belt Covers (parts 47 on page 40 of [URL]) and the nut that holds on the left-hand Idler Pulley (incorrectly labelled as part 19 on page 40; perhaps part 18 (the description looks right)). When I lost the nut, the deck belt got shredded (shrod?), so I replaced that, too.

    That worked quite well up to about 96% of the lawn done, when I found a shredded (shrodden?) Belt (the rear drive belt, part 31 on page 34). Page 22 says, "Several components must be removed and special tools (i.e. air/impact wrench) in order to change the tractor's drive belts. See an authorized Troybilt Service Dealer to have your drive belts replaced." Not having those tools nor any instructions, I asked a neighbour to take me and the mower up to the local dealer.

    But a couple of days later, I had a look at the diagrams and decided to order the belt and try and install it myself. Turned out it was pretty straightforward, and I only needed hand tools. It took me a while to work it out, but I reckon I could easily change that belt in well under half an hour now. (And it was only US$16 on eBay (for the official MTD part), too.)

    Once I had everything back together, I tried it out. It threw the belt off the idler again.

    The next day, I tightened the nuts (parts 21 and 22 on page 40) on the Deck Rod, Front Adjustable (part 41), almost all the way down. This left the front of the deck (page 16) probably higher than the rear (I haven't checked), but it also loosened the deck belt. It would appear that the part of the deck belt between the Engine Pulley and the right-hand Idler Pulley needs to be loose (-ish) (and it /will/ be the loosest part of the deck belt, since it's ahead of the driving pulley): the slack allows the belt to approach the Idler Pulley approximately horizontally, so there's no way it can get pinched and thrown.

    At least, that's my interpretation. I'm now up to 200% mown at height setting no. 3 with no problems. Hooray! Next time, I might try no. 2.



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SOURCE: engine bogs big puffs of white smoke from front

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If your going through belts that often you better order some spindle bearings and have them rebuilt,excess play in your deck spindles can cause you a lot of money repacing belts.

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SOURCE: troy-bilt model 13AN77TG766 wont go

The manual probably won't be of much help with this problem. Your transaxle may have seized up or failed due to the introduction of water into it. A lot of riders have had this problem, especially the ones with the DANA manufactured transaxle. I hope this is not your problem, and that the problem is in your shifter linkage between the lever and the transmission.

I am continuing to look for the manual. In the meanwhile, here is your complete machine with All parts, diagrams, breakdowns and part costs included. Hope this helps. It is sometimes tough to locate manuals as you have found.

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