EX100-2 Swing Motor Seal

[MikePhua]

Introduction
The Hitachi EX100-2 is a mid-class excavator from the EX100 family that has been widely used in earthmoving, trenching and utility work. These machines are valued for a compact footprint, decent digging reach and a reliable Isuzu/4BD1 series diesel powerplant in many configurations. Swing system reliability is critical: a leaking swing motor seal not only wastes hydraulic oil but can allow contamination into the motor and swing gear, degrade performance, and lead to expensive repairs if ignored.
Why swing motor seals matter

• Swing motor seals isolate high-pressure hydraulic oil inside the motor from the exterior and from adjacent cavities (swing bearing, house cavity).
  
• A failed seal permits external leakage and internal cross-contamination, reducing motor torque, increasing loading on the hydraulic pump and risking metal contamination that accelerates wear. Seal failure therefore often starts as a small oil drip and can escalate quickly into lost swing function or catastrophic motor damage.
  

Terminology (quick reference)

• Swing motor — hydraulic motor that turns the house on the swing bearing.
  
• Seal kit / oil seal — collection of O-rings, lip seals and backup rings designed to restore the motor’s sealing surfaces.
  
• Shaft seal / gland — the primary lip seal around the motor output shaft (typical leak location).
  
• Swing bearing — large slewing ring between undercarriage and house; contamination here accelerates wear.
  
• Drain/house cavity — the space beneath the cab; oil that leaks into this area can be recovered or cause other problems if left unchecked.
  

Common symptoms of a bad swing motor seal

• Visible oil leak at the base of the house or around the swing motor area.
  
• Loss of swing speed or reduced swing torque, especially under load.
  
• Hydraulic oil level dropping faster than normal without external leaks elsewhere.
  
• Metallic particles or gritty contamination detected in hydraulic oil or magnetic drain plugs.
  
• Abnormal noises during swing operation (chattering or grinding).
  

Typical root causes

• Normal wear and age of rubber seals (heat, ozone, and pressure cycles shorten life).
  
• Abrasion from dirt or grit entering a partially degraded seal area.
  
• Excessive system pressure spikes (relief valve set incorrectly or shock events).
  
• Incorrect installation of aftermarket seals or using the wrong seal material.
  
• Previous repairs that did not fully clean or replace contaminated components.
  

Parts, sources and approximate costs

• Aftermarket swing motor seal kits for EX100-2 are widely available; single-kit prices observed in the market range from roughly US$35–US$75 depending on brand and seller. Genuine or OEM parts cost more and may require dealer ordering.
  
• Typical kit contents: primary lip seals, backup rings, O-rings, thrust washers and small hardware.
  
• Where to look: excavator parts suppliers, online marketplaces and specialized seal houses; confirm fitment for EX100-2 before purchase.
  

Diagnostic checklist (what to inspect first)

• Check hydraulic oil reservoir level and look for contamination (colour, smell, metallic particulates).
  
• Clean the swing area and operate the swing slowly; note the exact leak location — motor flange, shaft gland or sensor ports.
  
• Inspect the swing motor external housing for wetness, oil trails, or oil pooling in the house cavity.
  
• Pull a hydraulic sample or check the magnetic drain plug for high metal content if available.
  
• Confirm system relief pressures and look for recent shock loads or hydraulic system faults recorded by the machine.
  

Tools and materials you’ll need

• Basic mechanic’s toolset (sockets, torque wrench, pry bars).
  
• Lifting/lowering gear for supporting the house if removal is required (overhead hoist, engine crane or large jack).
  
• Clean rags, solvent and lint-free wipes; seal pick and O-ring tools.
  
• New seal kit sized for EX100-2, hydraulic oil for top-up or change, and new fasteners if required.
  
• Hydraulic filter(s) and oil testing kit (recommended if contamination suspected).
  

Replacement approaches
There are two practical routes depending on leak severity and shop capability:

• External service (seal replacement without removing motor) — Many kits allow replacing the external lip seals and O-rings without removing the swing motor from the housing. This is faster and less disruptive: you drain the small cavity, remove covers and plates, swap seals, clean mating surfaces, then reassemble and top up oil. This is appropriate when the motor internals are clean and there is no sign of internal damage.
  
• Full motor removal and overhaul — Required if seals are ruined by contamination, if internal bearings are damaged, or if the leak source is internal. Removing the swing motor (or motor and swing bearing assembly) allows inspection of pistons, vanes, shafts and internal seals, and ensures a full clean rebuild. Expect higher labour and rigging needs. Parts such as bearings or pistons may be needed.
  

Step-by-step (typical external seal replacement workflow)

• Park machine on level ground, lower attachments, isolate hydraulic system and disconnect battery. Lock out/tag out.
  
• Drain swing circuit/house cavity to a clean container; retain fluid for inspection.
  
• Remove inspection covers, guard plates and any auxiliary plumbing that blocks access to the motor flange.
  
• Carefully clean around the seal area to avoid pushing dirt into the motor during work.
  
• Remove the old seals and backup rings with pick tools, noting orientation and placement.
  
• Clean mating surfaces thoroughly; inspect retaining grooves for nicks or corrosion — dress or replace if necessary.
  
• Install new seals per kit instructions (light film of hydraulic oil on lips), ensuring correct orientation and seating.
  
• Reassemble plates and fasteners to recommended torques where available; if torque specs are not at hand, tighten evenly and consult OEM manual for values.
  
• Refill swing circuit with clean hydraulic oil to the correct level and bleed any trapped air per machine procedure.
  
• Run functional tests: no-load swing, loaded swing, check for leaks and verify normal operating pressures and temperatures.
  

Post-repair testing and acceptance criteria

• No visible leaks after 1–2 hours of continuous testing under varied swing speeds.
  
• Hydraulic oil level stable (no unusual drop) after 24 hours of operation.
  
• Smooth swing motion with full rated swing speed and torque restored.
  
• Oil sample shows no excessive metal contamination after short trial period; if present, perform further filtration or system flush.
  

Troubleshooting tips and common pitfalls

• Don’t just replace seals and re-use contaminated oil — metal particulates and abrasive sludge will quickly ruin new seals. If contamination is evident, plan an oil and filter change and consider flushing the swing circuit.
  
• Avoid over-tightening cover bolts — distorted housings or uneven seal seating causes leaks. Use a torque pattern and nominal torque values from the manual where possible.
  
• If the leak returns quickly, suspect an incorrect seal material (temperature/pressure rating) or a worn shaft surface/groove that must be repaired.
  
• If swing performance is still weak after leak repair, check for internal motor wear (piston cups, swash plate, drive shaft) and valve block condition.
  

Preventive maintenance to extend seal life

• Keep the swing area and bulldozer house cavity clean of mud and debris; daily brushing on dusty sites helps.
  
• Maintain proper hydraulic oil cleanliness (ISO codes), use recommended oil spec and change hydraulic filters at regular intervals.
  
• Monitor for pressure spikes (transient overpressure) and ensure relief valves are set and functioning.
  
• Inspect external seals and hose fittings at intervals; early detection keeps repairs small and inexpensive.
  

Case story
A municipal contractor found progressive oil dripping into the EX100-2 house cavity after months of working in a sandy riverbed. The initial quick-fix (external seal swap) stopped the visible drip but the machine soon lost swing power. A full motor removal revealed sand-etched piston chambers and scoring on the motor shaft; the internal rebuild required piston seals, shaft polishing and a bearing replace — a job that cost several times the original seal kit price. The takeaway: in abrasive environments, inspect and service more often; when seals fail, check for internal contamination rather than assuming a cheap fix will last.
Practical guidance and cost expectations

• A simple external seal kit and DIY labour can be a low-cost repair (kits commonly US$35–US$75). Professional labour and rigging for motor removal and rebuild will be substantially higher — plan for parts + several hours of shop time or a day or two in a field service scenario.
  
• If the machine is old and the swing motor shows signs of repeated failure, weigh repair cost against machine remaining life and replacement value — sometimes a motor exchange or used replacement motor is the most economical route.
  

Final recommendations

• Confirm the exact model (EX100-2 vs other EX100 variants) before ordering parts — part numbers differ among sub-models.
  
• If you lack a service manual, get one or consult a dealer for torque specs and hydraulic procedures. Precise torques and bleed sequences are model-specific and prevent rework.
  
• Document the repair (photos, oil samples, parts used) — good records help if the leak recurs or if you need warranty/parts returns.