Ask the Mechanic
Wobble Box Mystery
READER: I have a 488 New Holland haybine that we use for cutting hybrid sudan hay. It does a great job of cutting and crimping this cane-type of hay, no matter how tall and rank it sometimes gets. Plus, the reel will pick the hay up if it gets down. Because it only cuts 9 feet 3 inches and can lay the hay flat by lowering the swath gate, the drydown time is short in the Texas heat.
However, the machine has developed a problem of knocking out the bushing in the sickle head. I have replaced the lower bearing, but the bushing still fails after about 50 acres of cutting. There is no play in the remainder of the wobble drive. Do you have any tips on how to fix this haybine bushing "failure opportunity"?
STEVE: I agree that the New Holland haybine really handles the cane-type crops such as hybrid sudan very well. We use two of these cutters in hybrid sudan on our own farm. The wobble box must have no areas of play, or it will knock out bushings and break the cutter drive cap screw. The bottom bearing that fits in the pivot plate must have no play in the sickle drive, and there must be no wear on the bottom plate stub where the bearing runs.
If all of this is in order, then you probably have wear in the bushing where the cap screw fits. This is a very hard, heat-treated bushing, but it will eventually be worn on older machines and cause your problem. It is very tight in the arm drive, and it has a lip on it to secure it in the correct place. Also, aftermarket bushings that fit in the sickle head have been known to fail more quickly than the CNH bushings. During reassembly, always use grade No. 8 bolts with fine thread and lock nuts in the bushing. One last point that is very important is to tighten the three cap screws that secure the bottom plate before you install the lock collar on the bottom bearing.
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-- Email Steve Thompson care of askthemechaniccolumn@gmail.com, and be sure to include your contact information and phone number.
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