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Implement Alley Discussion Forum

NH 489 Haybine gearbox issue

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07-09-2012 17:14:02

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I was cutting a 20 acres piece today, I had many troubles with the main gear box that runs the sickle. First thing that happened was the top bolt sheared right off. I drilled it out and put a new grade 8 bolt in there. Machine ran fine. 1 round later I see the gearbox shaking again, now the bottom bolt was loose. I tightened it along with the top one again. I sheared the top one 2 more times and stopped to tighten the bottom one several times. When all was said and done, I came home with both bolts sheared off and a loose gearbox. What could be causing this? The hay was a bit tall, but I was going very slow, especially after a few bolt replacements. The shaft that drives the gear box has 2 u-joints in it, they have some slop but not bad, 1 was cool all day, the other was a bit warm, but not hot. The sickle seems to move freely, and it was cool to the touch as well. I just can't figure this one out, but it is binding quite badly if its shearing a grade 8 bolt.

Not sure if its related, but the bolt that holds the sickle to the gearbox came loose today too. But had problems before that, and after, but it never loosened again once I replaced it, but gearbox problems did go on. I hope you can help.


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07-10-2012 11:15:42

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 Re: NH 489 Haybine gearbox issue in reply to picassomcp, 07-09-2012 17:14:02  
I have a NH489 and had to replace the wobble gear box. I had the gear box come loose, bolts broke, and I replaced the bolts also. Then I started having the sickle bolt break and sickle heads break in thicker head. Turned out that there was too much play in the arm that drives the sickle bar. Only fix was to replace entire gear box. I have had no problems since, not even needed to change sickle bars in a few years. If I remember right, the torque value for the gearbox bolts are pretty high. The allowable play for the sickle arm is very small.

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07-10-2012 00:43:16

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 Re: NH 489 Haybine gearbox issue in reply to picassomcp, 07-09-2012 17:14:02  
What kind of shape is the sickle and guards in??? If they are worn out then they will not cut and bind the sickle every stroke.

If the sickle and guards are in good shape then check to see if there is a lot of back lash in the gearbox. When they get worn out and have too much of a dead spot at the end of each stroke they jerk harder rather than run smooth. This will break the mountings bolts/brackets.

Just turn the gear box over by hand and see how it feels. Just about bet that there is a bad bearing in the gear box.

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07-09-2012 21:50:07

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 Re: NH 489 Haybine gearbox issue in reply to picassomcp, 07-09-2012 17:14:02  
Things must be badly out of alignment for that to happen.

You should be able to turn a bine by hand,..if not,..then something is binding.

Find the cause!!

A knife should slide back and forth in the guards by hand without effort and with little play.

i've seen to many times that people need a truck to pull them out cause the guards are so badly out of alignment or the whole cutter bar has a 6' bow in it.

Knife drives and wobble arm bushings should be bolted down in the center of the knife stroke.

If things don't line up, you got to adjust til it does.

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