I found a solution. There is a cable that runs from the lever that engages the blades down to the tensioner pulley on the deck. The cable runs through a black cable guide that is secured on the deck with a bracket. Loosen the bolts on the bracket and slide it back (away from the pulley). This will tighten up the cable and keep more tension on the belt. I think that the cable stretches over time and usage.

I think something is awry if you had a failure in such a short time. If the blades were loose enough to strike - off goes your timing right there. The tensioning part really isn't difficult in itself. After I set tension, I roll the spindles around a few times and loosen the tensioner pulley a turn and make sure the tension is correct - then resecure the nut. The barrel like guide should be in place and facing the correct way. If you watch the rotation of the deck- are the blades on the proper sides? Is there reason to suspect wear on the slide area or the cone? It sounds like you are saying that someone else did the work prior. Loosen the idler as far as you have to to roll a spindle inside the belt to get it back in time and then follow your bulletin and all should be fine if the rest looks as it should. Use the JD parts look up as a guide.

Good grief, Charlie Brown!! How fast were you going when ya hit that tree?? Or, did the curvy neighbor lady walk by as you were mowing? (not that it would affect the outcome, but it sounded funny.) I think, the only way that hitting the tree could or would affect the belt tightness, would be if ya bent the frame, while speeding around the yard, trying to get 'er done before the game! Those frames aren't known for being beefy, and a hard jolt against a tree might very well have bent the frame/floor pan, say buckled it, just enough to loosen the belt. And, does the clutch/brake pedal seem too loose, or not in the correct position? Does it return to its correct position? Or stay down some? A kink in the frame could damage the clutch setting position.

FWIW - Just changed the tensioner on my 1991 2.2L Cavalier. Step 1: Disconnect Battery. Step 2: Remove Belt (15mm wrench clockwise to remove tension) Step 3: Remove Power steering pump. Remove small bolt on back side of power steering pump (next to hose with clamp)Use a box-end wrench or one of those ratchet box-end wrenches. Next, there are 3 bolts in the front behind the pulley(13mm). There are holes in the pulley specifically for the purpose of removing these bolts. I used a magnet to pull the bolts out after loostened. You should now be able to rock the top of the pump toward the firewall. Be careful to not break the plastic top. If you have to pry it, do it on the metal part. Step 4: Remove alternator. Remove all bolts holding the alternator in place. It should just be laying there (Upper bracket removed). Step 5: Remove belt tensioner assembly plate. Remove four 15mm bolts that hold the plate on the engine block. Mine were on pretty tight so I had to use a breaker bar to get em off. Re-assembly: Step 6: Compare new tensioner assembly with old one. They should match. Attach plate to engine block with four 15mm bolts. Make sure they're tight. You don't want this to come loose. Step 7: Re-align power steering pump to 3 holes in tensioner plate and screw in the 3 bolts (don't tighten yet). Now here's the hard part - carefully take the small bolt that goes in the back of the pump assembly and get it started with your fingers (the 2 holes should be aligned). Tighten all 4 bolts. Step 8: Alternator - Re-install the long bolt and nut that goes in the bottom of the alternator but don't tighten. You may have to loosen the lower alternator bracket so the two holes align. Let the alternator swing towards the engine. This will make it easier to get the belt on. Step 9: Serpentine belt install. If new belt, make sure it's the same length as the old one. Route the belt like the diagram sticker. The alternator is the last pulley it will go over. If you can get someone to help you here, it's a lot easier. Turn the 15mm bolt on the tensioner pulley clockwise until there's enough slack to slip the belt over the alternator pulley. While keeping the tension off the pulley, replace the other 2 bolts/upper alternator bracket. Slowly let the the tensioner spring back. Replace and tighten the rest of the alternator/bracket bolts.