Sealing the Chaincase on Bobcat Skid Steers with Silicone vs Gasket

[MikePhua]

Bobcat Skid Steer Chaincase Design and Maintenance
Bobcat Company, founded in 1947 and now a global leader in compact equipment, has produced millions of skid steer loaders. Among its most popular models is the 863, introduced in the late 1990s. This machine features a chaincase system that houses the drive chains connecting the hydraulic motors to the wheels. The chaincase is partially submerged in hydraulic oil, which lubricates the chains and helps dissipate heat.
Routine chaincase maintenance is essential, especially as machines age. While Bobcat originally used foam-style gaskets to seal the chaincase access cover, many operators now face the question of whether to replace the gasket or use silicone sealant instead.
Terminology Annotation

• Chaincase: A sealed compartment in a skid steer loader that contains the drive chains and lubricating oil.
  
• Foam Gasket: A compressible sealing material originally used by Bobcat to seal the chaincase cover.
  
• RTV Silicone: Room-temperature vulcanizing silicone, a flexible sealant used in automotive and machinery applications.
  
• Permatex Ultra Black: A high-performance RTV silicone known for oil resistance and durability.
  

Why Silicone Is Replacing Foam Gaskets
Foam gaskets were once standard in Bobcat chaincases, but they have proven prone to leakage over time. Exposure to oil, heat, and vibration causes the foam to degrade, leading to seepage around the cover edges. Newer Bobcat models have moved away from foam gaskets entirely, favoring silicone sealants for their superior sealing properties and longevity.
Operators report that foam gaskets often appear greasy and compressed, indicating oil bypass. In contrast, silicone forms a flexible, oil-resistant barrier that conforms to uneven surfaces, including welded seams and casting imperfections.
Best Practices for Chaincase Oil Change and Seal Replacement
When changing chaincase oil, especially on machines with over 1,000 hours of use, it's advisable to remove the access cover and clean out accumulated sludge. This allows for inspection of the chains, sprockets, and bearings.
Recommended steps:

• Drain the chaincase using the rear plug beneath the machine, located under a rectangular plate with a rubber grommet and steel plug.
  
• If the plug is damaged or difficult to access, use a wet-vac or drum pump to extract oil from the top.
  
• Clean the interior with rags and inspect for wear or debris.
  
• Remove the old gasket and clean mating surfaces thoroughly.
  
• Apply a continuous bead of RTV silicone (e.g., Permatex Ultra Black) around the perimeter, with extra sealant at welded seams.
  
• Allow the silicone to cure per manufacturer instructions before refilling with AW 46 hydraulic oil.
  

Field Anecdotes and Operator Insights
In Australia, a Bobcat 753 owner switched to silicone after discovering that the foam gasket had failed. He used a drum pump to clean out the chaincase and reported improved sealing and no leaks after 12 months of operation.
In Missouri, a technician recommended “The Right Stuff,” an aerosol-based sealant known for rapid curing and oil resistance. He found it easier to apply and more durable than traditional silicone tubes.
In New York, an operator used Permatex Ultra Black RTV and the “suck bucket” method—a wet-vac adapted to extract oil from the chaincase. He noted that the machine had never had its oil changed in over 1,300 hours, and the foam gasket was visibly leaking.
Recommendations for Sealant Selection

• Use high-temperature, oil-resistant RTV silicone such as Ultra Black or Ultra Grey
  
• Avoid low-grade sealants that may degrade in hydraulic environments
  
• Apply a uniform bead and avoid over-tightening bolts, which can distort the seal
  
• Consider aerosol-based sealants for faster setup and cleaner application
  

Preventive Maintenance and Long-Term Reliability
To maintain chaincase integrity:

• Change chaincase oil every 500–1,000 hours depending on operating conditions
  
• Inspect the seal annually for signs of leakage or degradation
  
• Keep the machine indoors or protected from water intrusion
  
• Avoid pressure washing near the chaincase cover
  
• Document sealant type and application date for future reference
  

Conclusion
Replacing the foam gasket on Bobcat skid steer chaincases with RTV silicone is a proven upgrade that enhances sealing performance and simplifies maintenance. With proper cleaning, inspection, and sealant application, operators can extend the life of their machines and prevent costly oil leaks. Whether using a wet-vac or drain plug, the key is to do the job thoroughly and seal it right the first time. As Bobcat continues to evolve its designs, silicone remains the preferred choice for chaincase sealing in both legacy and modern models.