I'm thinking of giving up on the JD 420

BTS

BTS

Tractorologist
Member
Still having nothing but trouble with the JD 420 mower deck, I can not keep a belt on it for the life of me. Nothing is bent, nothing is out of alignment, all the bearings are good in the spindles and in the gear box. Everything is greased, I put a new belt on about 15 mowing hours ago (bought the belt from JD). All was mowing fine until the belt jumped off, now whenever I start up the blades at a idle, the belt is very shaky and when the engine is throttled up it pops right off. I also looked over every square inch of the belt and I can't find anything wrong with it. The tension spring still feels tight and it's quite the pull to get it hooked up so I'm guessing it's tight enough?.

I've thought about buying a new belt, but to be honest money is running short and I don't have a spare $50+ to spend on one.

I'm thinking about just selling the garden tractor cheap without the deck, any ideas?
 
There has to be something that is causing that situation. First off is the the belt from the tractor to the deck or the actual deck belt. It soulds like your talking about the deck belt. Can you see where it is jumping off at? Center spindle or one of the outside blade spindles.? Can you watch the belt and have a helper throttle up the engine? Are you sure the belt is routed the dorrect way.
 
Make sure the belts you buy are Kevlar belts. Just because they are from JD don't mean they are Kevlar. The FHP belts do not last long and once they jump or get stretched out they usually won't work very well. I had a JD F525 and it would go through at least one JD deck belt a season. Bought a belt from another source that I know was kevlar as it was printed right on the belt. It lasted 3 years and was still on the machine when I sold it.

Hard to really say what the problem is without being there but my first bet is the pulleys are not lined up with each other. Deck sprung and one pulley is tilted up or down enough to throw the belt.
 
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Try turning the belt over next time you put it on. If it has been jumping off the top, flipping it may cause it to jump off the bottom. If it does, it is probably the belt. If it jumps off the top, more than likely an alignment problem. Lay a straight edge across the top of one of the side pulleys with the end at the drive pulley. Should line up with the top. Try in 3 different places on the side pulley. If it lines up different on the drive pulley you may have a bent pulley. Somebody stepped on the edge of the pulley getting on and off the tractor is one possibility. Good luck.
 
Did your problems start with the new belt? Maybe the old belt had one or more of the pulleys worn enough that the old belt will not ride in the same spot. I had a JD 110 deck that I put a new belt on and couldn't keep the belt on ended up putting a washer under the idler pulley and it fixed it. Old belt had worn the edge enough that it caused the new belt ride up and over the lip. Ordered a new pulley and still have that belt and pulley on the deck. Right now the same tractor will not keep a brand new rototiller belt on...it's frustrating don't give up.
 
Thanks for everyone's help I'm uploading a slow motion video now, I'll post it once it's done
The pulleys all seem to be inline, I checked it all with a straight edge and it all looks dead on. I also checked over the tensioner and it all seems to be inline and straight. The idler pulleys all spin freely with no noise or slop. The 420 mowed just fine when I got it all put together. I mowed with it for a week or so and the belt came off, but I knew the old belt was junk (the layers were separating) so I replaced it with a belt from JD (was the belt they recommended) and it mowed great, like I said earlier, I put around 10 to 15 hours on the new belt, I had issues after I mowed for over 3 solid hours mowing over 4 acres. Then I brought the mower home and started mowing again. I mowed maybe 30 minutes when the belt kicked off.

I'm really wondering if it's not my belt that's causing the issues???, it seems like the belt just has a lot of slack in it, there isn't any slack at all when the mower is off, but as soon as it's turned on the belt starts doing the wave. I can't find if the JD belt I bought is kevlar? Since it doesn't say it is I'm guessing it's not???. Leave it to JD to sell me a belt that doesn't last...... Either way, I get paid in a couple days and I might try buying a new kevlar belt, there is some on eBay for $50 free shipping so I guess I can give one of those a shot.

Thanks again for the help
 
I wouldn't think that spring would be moving like that. Got to be something in that tensioner causing it to do that or possibly a pulley that is squeezed together in a small area.
After posting the above, I went back and watched the video full screen. Check that pulley the belt came off of. After the belt came off, I could see a difference in the inside area that the paint is wore off of. Looked bent or something as the paint was warbling as it slowed to a stop. Also, the belt on that pulley moved in & out of the groove!
 
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I agree with the above - tensioner arm is not functioning right. Also that belt pulley the belt jumped on is not right. I would guess on side is bent. Just happened to miss that area when you checked with straight edge. No belt will stay on when it is bouncing around that much. Mechanical issues, not a belt problem.
 
Change the spring to more tension, or add another spring and see if it changes any thing, original spring may have lost its tension over time, make sure every thing is free, keep at it, you'll get it fixed.

Noel
 
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