Tearing into the disc cutterbar

The mower is one of the most overlooked pieces of equipment when it comes to yearly maintenance. It’s not that most hay cutters are abused, but few people can say that they have taken apart their disc cutterbar on a regular basis. Many disc mowers have a cutterbar that is “lubed for life,” according to the manufacturer. This means that the oil or grease in the cutterbar never has to be changed for its entire useful life.

Manufacturers of these maintenance-free cutterbars have found effective ways to clean and seal this important component. I’m not saying that they are incorrect or suggesting that after six years of use you will have problems if you don’t change the oil or grease, but I feel the smart play is to at some point think about doing some serious cutterbar maintenance.

If the oil in your car was supposed to last 100,000 miles, wouldn’t you still change it before it reached threshold? I know that I would not go that long.

The cutterbar, whether it is gear or shaft driven, has many fast-moving parts that are the backbone of your mower. The cutterbar is an intimidating machine component, as timing is everything. One tooth off when reassembled can be detrimental to the disc mower’s operation.

I recommend my customers tear their cutterbar down if they don’t bring the mower into our shop for a winter inspection. Maybe not all the way down by removing the internal gears or shaft, but to at least remove all of the discs. After all, it’s probably time to rotate them anyway, which means rotating the clockwise discs with the counter-clockwise discs. This is also a great time to inspect the hub that drives these discs. I’m almost certain most of you will find either net wrap or twine wrapped around the drive hub. Finally, check the drive hubs for wear and any “slop” in the bearings. Replacing the bearings and seals in the drive hubs is much less expensive than replacing the gears in the cutterbar.

Speaking from experience

If you’re competent in shop skills, I think it’s a good idea to tear the cutterbar down even further and remove the hubs to inspect the “guts” of the cutterbar. Before you get to this point, however, you should read your operator’s manual to find out what the specifications are for the oil or grease needed to refill the cutterbar.

I say this because my dad and I were tearing down a shaft-driven mower one winter and we looked up the type of grease needed in each pod. We went to every parts store in town and none of them could get that particular type of grease. So, we went to our dealer at the time and they also did not have this grease in stock, which tells me that they never had problems or not many people perform yearly maintenance on their cutterbar.

We ordered the grease, and the dealer actually asked me why we were tearing into our cutterbar and said that there was no need to. We opened up the first disc and the grease looked almost new, as did the grease under the second disc. When we go to the third disc and pulled up the hub, the grease in this pod was jet black. So, we started to investigate why this hub got hot. We could not find much wrong but went ahead and rebuilt that hub. The next winter, when we tore down the cutterbar again, that hub’s grease looked clean. Essentially we stopped a problem before it even showed signs of starting.

Maybe it would have never been a problem, but I know I did not want to take the chance on tearing up that mower to save the $100 for a bearing and a little inspection time. The same can be done on gear-driven mowers, although it’s harder to isolate a single hub. If you use a paint stick to mark the timing on the hubs once removed, you can inspect the teeth on the gears. Maybe you’ll find a tooth missing, and maybe you don’t replace it this time, but you will know where it is and can reevaluate in the future. Flushing out the cutterbar is one way to get rid of the broken tooth. After the flush, refill the cutterbar and replace the seals or O-rings as needed, then start to reassemble your “like-new” mower.

This big job doesn’t need to happen every year if you are only mowing 500 acres annually, but removing the discs to check for twine and net wrap around the hub is essential for extending the life of your mower. Check with your local dealer; I’m sure they would be glad to offer you some suggestions when tackling this project.

I look at cutterbar maintenance like changing the oil in your car. Sure, you can run it a long time without changing the oil, but is that really the way you want to treat the second most expensive piece of equipment in your hay arsenal?

Be safe turning wrenches this winter.

This article appeared in the February 2019 issue of Hay & Forage Grower on page 14.

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