How to Rebuild a Swing Drive

How to Rebuild a Swing Drive

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If you’ve spun around in an excavator cab, you know that an important part making that happen is the swing drive and, if you’ve worked in an excavator long enough, you know that the swing drive is a part that often comes with an expiration date. A good swing drive will have a long life, but due to the nature of its work, it just won’t last forever.

Not every swing drive that passes through our salvage shop is able to be saved, but often heavy worn parts can be replaced and combined with original OEM parts to create a perfect rebuilt part. In this case, our Part Technician Matt puts his skills to work on a Komatsu PC490LC-11 swing drive. Watch the video to see our process or read the detailed steps below.

 Want to see how a swing drive is disassembled? Watch that process in our How to Dismantle a Swing Gearbox post.



Rebuilding a Swing Drive Step-by-Step Process

  1. Every rebuild in the H&R Recon and Rebuild shops starts with a mix of salvaged and new parts.
    • In the video the tech starts with a new lower bearing, new retainer plate, and new oil seal.
  2. The oil seal is pressed into the retainer plate. 
    • Using an extra plate on top of the seal helps the seal move evenly into the retainer plate without damaging the seal.
  3. The seal surface of the pinion shaft is oiled. Then the retainer plate is oiled and slid onto the pinion shaft. The lower bearing is also guided onto the pinion shaft.
  4. Using a hydraulic press, the lower bearing and retainer plate are pressed fit onto the pinion shaft. A sleeve is placed over the pinion shaft for extra safety. 
    • In the video, notice the tech uses extra spacers on top of the pinion shaft to account for the top height of the press.
    • Throughout the process, lifting eye bolts are used for moving parts. In this case, a lifting eye bolt attaches to a forklift and later an overhead crane to help the tech return the freshly-pressed parts to his working area, the same way it was brought to the press.
  5. The lower bearing is oiled by adding oil and gently spinning the bearing to evenly spread the oil throughout the bearing.
  6. Now, the technician turns his attention to the housing. The housing will need to be heated using H&R’s industrial parts oven. 
    • To prevent the inside of the housing from rusting while it is heated in the oven the tech oils the inside of the housing.
    • The tech transports the swing drive to the oven for heating. The process will expand the steel just enough to fit the bearing, and when the parts cool, the fit of the two parts will be sealed.
A diagram show the location and interaction of a swing drive in an excavator.
The internals of the swing drive contain a planetary gear system designed to create high torque output to power the swinging the excavator's house.
  1. While the housing bakes for 20 minutes, the tech starts with the planetary. Before installing the pins, a taper punch is used to open the holes. 
    • Previously they had been closed to prevent the pins from backing out.
  2. The planetary carrier is oiled, and the planetary gears and thrust washers are oiled and assembled.
  3. The retainer plate is installed inside the carrier.
  4. The planetary gear and the pins are installed and the steps are repeated for each of the 4 gears.
  5. The thrust washers, thrust plate, and planetary gears are oiled and installed and the snap rings are fastened to each of the planetary gears.
  6. The upper bearing is placed inside of the housing while the housing is still in the oven.
    • Expanding the upper bearing with heat will help the parts properly fit together.
  7. Bolts are washed to remove rust and for polishing using a stone washer.
  8. After the parts have finished heating in the industrial parts oven, the housing and and the parts are brought back to the workbench so that the pinion can quickly be installed inside the upper bearing before the parts start cooling.
  9. Silicone is added to the pinion and the housing is placed over the pinion. Once the parts cool, they will contract and the parts will be pressed into a tight and sealed fit. 
    • In the video, notice how small the tolerance of the parts is.
  10. The pinion is then bolted to the housing.
  11. The tech sprays WD40 inside of the housing and the lower planetary carrier is installed.
  12. The lower sun gear is installed, followed by the upper planetary, and finally the upper sun gear.
  13. A new o-ring is greased and fit around the top of the housing.
  14. The ring gear is installed.
  15. Locktite is applied to the bolts and the ring gear is securely bolted to the housing.
  16. The plug is inserted into the housing.
  17. Finally, the tech will create a temporary cardboard cover to avoid contamination inside the drive when it is painted or moved through the warehouse. Afterwards, the drive will be heading to our shipping department to get painted, secured to a pallet, and shipped out to a customer.

If you’re planning your own swing drive rebuild we hoped a look at our process was helpful, if you’re just inquisitive about parts we hoped you found our process interesting, and if you’re in search of a replacement swing drive we’re, of course, always here as a resource for you.