John Deere 420 deck belt

[BTS]

I hope this all post ok, I'm down to using my phone since my internet has been out all day.

Anyway, the old John Deere 420 has been running and mowing great. I mowed 4.5 acres with it and it didn't miss a lick. HOWEVER, when I was finishing up the belt on the deck came off. I drove the mower over to the shope to take a look at it.The belt just fell off of one pulley. I put the belt back on and then I turned the deck on at a idle. The belt waved back and forth and then fell off the same pulley. I called it quits since it was already late evening. The next day I looked over everything. All the spindles are tight, no loose or bad bearings. Nothing wobbles or has unusual play. I put the belt back on and turned the blades on when running at a idle, the belt did not come off, but the belt sure jumps around a lot. I throttled up a little and the belt seems to have a lot of movement and it flaps around a lot. My brother stopped by and he took a look at it and he also has no idea?. I pulled the mower deck and I noticed when I turn the PTO shaft by hand, the tensioner pulley almost works like a cam. When the pto is turned the tensioner arm slowly moves (about a inch overal) then as I turn the pto the tensioner works it's way back and the it starts over the process. I checked and no pulleys are bent and there is nothing stuck in a pulley. The spindles also do not look bent. I have no idea what the problem is? Anyone have any thoughts?

 

[Cat385B]

How tight is the spring holding the arm of the tensioner pulley?

 

[Cat385B]

Also, which 60" deck does it have? Is there one tensioner pulley or two?

 

[Shorty]

Would a weak spring cause that? A year ago I had a belt with a bad spot on it cause the tensioner to act like that.

 

[BTS]

FINALLY my internet it back.

This has the 1 tensioner pulley, I don't think it would be the spring, when I turn the PTO shaft by hand, the spring pulls the same way every time it make one rotation. The belt is new (has around 10 hours on it) and I looked over the belt and I don't see anything wrong with it.

I did remove the gear box mounting plate and I found that the linkage that the spring hooks to going to the pulley bracket was all shined up and it had a grove worn in it. There was a bun of grass clippings, dirt and junk under the linkage holding it up high enough I believe it was rubbing the pulley. If that linkage was rubbing against the pulley, I think it could have been pulling on the linkage causing the movement on the tensioner???.
I haven't got it put back together yet, to test it out yet. I don't know what else it would be, all the spindles are tight, bearings are all good, pulleys are all straight and the spindles don't appear to be bent.

Thanks for the help

 

[olcowhand]

On the 60" 430 deck, there is a rubber block that you slide up behind the tensioner pulley arm to prevent it from kicking back. Maybe yours doesn't come factory with one, but if it did and it's missing, that would likely be your problem.

 

[BTS]

I'm still messing with the deck, I believe it might (maybe) be a bent spindle I think it's just very lightly off to give the belt a little movement each time it circles around, the problem is when that creates are LOT of movement when the PTO shaft is turning at whatever RPM at full throttle.

Although I don't know if it matters, I have someone that is real interested in the garden tractor and cultivator along with NOTHING else. It seems sad to separate it from it's mower deck but he is willing to pay a decent price for it so I don't know what to do.

 

[Rustysteele]

I would check the belt over closely. If it has a chunk missing out of it, it will behave as you are describing.

 

[BTS]

I believe I have the mower deck sorted, I'm waiting on parts now. I found that the center spindle is ever so slightly bent. I remove the spindle and checked it with a straight edge and it is bent. I checked on a new spindle and JD is wanting $150 for it. I ended up buying a used spindle in a hub on eBay for $60.