David414 289 #1 Posted January 27, 2023 I have a 1990, 312-h that keeps dropping the drive belt. The belt (wheel horse belt), idler pulley, spring, and arm were replaced with new parts, including the mounting hardware. After 30 seconds of run time, the belt falls off. At a loss for correction...misalignment problem perhaps? Any suggestions or fixes are greatly appreciated! Share this post Link to post Share on other sites
moe1965 738 #2 Posted January 27, 2023 I can't tell from the picture but is the smaller pulley (the idler pulley) groved or flat. It looks groved to me. If so it needs to be replaced with a flat one. Share this post Link to post Share on other sites
Ed Kennell 38,166 #3 Posted January 27, 2023 Is the idler pulley "jumping" while running? Look for an obstruction wedged in the engine and transmission pulleys. Share this post Link to post Share on other sites
David414 289 #4 Posted January 27, 2023 Flat pulley, new from toro Share this post Link to post Share on other sites
David414 289 #5 Posted January 27, 2023 Ed, not sure what I am looking for an obstruction? Belt comes off within seconds. Share this post Link to post Share on other sites
David414 289 #6 Posted January 27, 2023 20230127_142412.mp4 Share this post Link to post Share on other sites
Ed Kennell 38,166 #7 Posted January 27, 2023 Just now, David414 said: Ed, not sure what I am looking for an obstruction? Belt comes off within seconds. I have seen small stones and chunks of wood wedged deep in the bottom of the Vee pulleys. This will cause a 1/rev tightening of the belt. This rapid tightening and loosening of the belt may not permit the idler to maintain tension on the belt allowing it to jump off the pulley. It would be evident as the idler pulley will be moving or jumping as the obstruction contacts the belt. 2 Share this post Link to post Share on other sites
Ed Kennell 38,166 #8 Posted January 27, 2023 Just saw your video....wow, that's quick. Is the idler free to turn and in alignment with the tranny pulley? Share this post Link to post Share on other sites
Lee1977 6,658 #9 Posted January 27, 2023 Did you replace the spacer that goes in that lift arm? As bad as that arm is worn the bushing spacer is worn too. Share this post Link to post Share on other sites
David414 289 #10 Posted January 27, 2023 It seems that parts purchased from Parts Tree are very close to original, but not always exact. The idler pulley from PT was slightly different than stock, the offset was different. Put on original pulley and now seems to work. Yes, spacer was replaced with new. Same thing with belts. PT and Toro have same part number but can be slightly different. Years of superseding part numbers and parts that are close enough but not exact as originals can cause problems. Share this post Link to post Share on other sites
953 nut 55,216 #11 Posted January 28, 2023 Is your belt being properly supported by the guides? Share this post Link to post Share on other sites
David414 289 #12 Posted January 28, 2023 5 minutes ago, 953 nut said: Is your belt being properly supported by the guides? Yes Share this post Link to post Share on other sites
NA73 70 #13 Posted January 28, 2023 Can you look down the belt from the engine to transmission and see anything misaligned? does the pulley on the transmission run true (no wobble or out-of-round)? Share this post Link to post Share on other sites
kpinnc 12,017 #14 Posted January 29, 2023 Either the swingarm for the pulley is bent, or something under the beltguard is pushing the belt off the pulley. Share this post Link to post Share on other sites
