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Start ShoppingCometic C9110-020 MLS Cylinder Base Gasket Set for Harley-Davidson Evolution Big Twin/Twin Cam (3.500 in Bore)
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Description
Ensure optimal engine performance and reliability with Cometic's premium MLS cylinder base gaskets. Designed for Harley-Davidson Evolution Big Twin/Twin Cam engines, these gaskets deliver superior sealing and durability for both stock and high-performance applications.
Key Features
- MLS Multi-Layer Stainless Steel: Constructed from high-quality MLS material for exceptional heat resistance and long-lasting performance.
- Proprietary Coating: Specialized coating enhances sealing surface compatibility and reduces the risk of leaks or compression loss.
- 3.500 in Bore Compatibility: Precision-engineered for 3.500 in bore cylinders to ensure perfect fit and function.
- 0.020 in Thickness: Optimal thickness for balanced sealing pressure and engine efficiency.
- Pair Packaging: Includes two gaskets (one per cylinder) for complete engine rebuilds or replacements.
Why Choose This Product
Cometic's C9110-020 gaskets are engineered to withstand extreme temperatures and pressures, making them ideal for high-performance riders and mechanics. The proprietary coating ensures superior sealing integrity, while the USA-made construction guarantees quality and reliability. Whether you're maintaining a stock engine or upgrading to a performance build, these gaskets provide peace of mind with their leak-proof design and durable construction.
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Ensure optimal engine performance and reliability with Cometic's premium MLS cylinder base gaskets. Designed for Harley-Davidson Evolution Big Twin/Twin Cam engines, these gaskets deliver superior sealing and durability for both stock and high-performance applications.
Key Features
- MLS Multi-Layer Stainless Steel: Constructed from high-quality MLS material for exceptional heat resistance and long-lasting performance.
- Proprietary Coating: Specialized coating enhances sealing surface compatibility and reduces the risk of leaks or compression loss.
- 3.500 in Bore Compatibility: Precision-engineered for 3.500 in bore cylinders to ensure perfect fit and function.
- 0.020 in Thickness: Optimal thickness for balanced sealing pressure and engine efficiency.
- Pair Packaging: Includes two gaskets (one per cylinder) for complete engine rebuilds or replacements.
Why Choose This Product
Cometic's C9110-020 gaskets are engineered to withstand extreme temperatures and pressures, making them ideal for high-performance riders and mechanics. The proprietary coating ensures superior sealing integrity, while the USA-made construction guarantees quality and reliability. Whether you're maintaining a stock engine or upgrading to a performance build, these gaskets provide peace of mind with their leak-proof design and durable construction.| SKU | GME74BE848 |
|---|---|
| MPN | C9110-020 |
| Brand | Cometic |
| Category | Gaskets/Seals |
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Featured Review
| Make | Model | Years |
|---|---|---|
| Harley-Davidson | Twin Cam 88 (select engines) | 1999-2006 |
| Harley-Davidson | Evolution Big Twin (select performance builds) | 1984-1999 |
Frequently Asked Questions
It is designed for a 3.500 in bore cylinder. You must confirm your engine’s bore size before ordering.
C9110-020 is a 0.020 in thick multi‑layer steel (MLS) cylinder base gasket.
It fits 3.500 in bore Evo Big Twin and Twin Cam applications, commonly in performance builds. For a stock engine, verify your factory bore and existing base gasket thickness or check with your engine builder before purchase.
Cometic MLS base gaskets are typically installed dry on clean, flat surfaces unless your engine builder or Cometic specifies otherwise. Avoid RTV at the sealing surface unless directed.
Yes, it is generally sold as a pair of base gaskets—one for each cylinder on a Harley-Davidson V‑twin.
Installation Guide
Difficulty
Hard
Est. Time
4 hr 0 min
Tools Required
- Factory service manual for your Harley-Davidson model
- Complete SAE socket and wrench set
- Torque wrench (inch‑lb and ft‑lb)
- Allen/hex key set
- Feeler gauges
- Scraper or plastic razor for old gasket removal
- Brake cleaner or similar solvent
- Lint‑free rags
- Engine support / jack (for in‑frame service)
- Ring compressor and piston pin tools (if cylinders are fully removed)
Pro Tips
- Confirm your bore diameter and target compression ratio with your engine builder; base gasket thickness affects deck height and compression.
- Clean mating surfaces with a plastic or brass scraper to avoid gouging aluminum cases.
- Dry‑fit cylinders and pistons to confirm ring end gaps and clearance before final assembly.
- Follow Harley‑Davidson factory tightening sequence and do final torque in multiple even steps.
- After first heat cycle, inspect for weeping around the base and re‑check external fasteners you’re allowed to retorque.
Common Mistakes to Avoid
- Not verifying bore size (3.500 in) and base gasket thickness (0.020 in) against the engine build
- Reusing old base bolts or not following the correct torque sequence and specs
- Leaving old gasket material on the crankcase or cylinder base surfaces, causing leaks
- Using RTV or sealant on MLS base gaskets when not specified (can actually cause sealing issues)
- Not checking deck surfaces for warpage before reassembly
Comparison vs Stock/OEM
Compared to typical OEM composite base gaskets, the Cometic C9110-020 uses multi-layer stainless steel construction for improved sealing and stability in high‑performance or high‑heat applications.
Improvements
- Multi‑layer steel resists blow‑out and fretting better than many OEM paper/composite gaskets
- More consistent compressed thickness for predictable deck height and compression
- Better long‑term oil and combustion sealing in high cylinder pressure builds
Considerations
- Deck surfaces must be very clean and flat; MLS is less forgiving of surface imperfections than soft composite gaskets
- Base gasket thickness (0.020 in) may differ from OEM and can alter compression; verify with your build specs
Durability & Warranty
Expected Lifespan
Designed to last the life of a properly assembled top end under normal use; commonly used in high‑performance Harley builds with many thousands of miles of service.
Warranty
Coverage is typically limited to manufacturing defects only and handled through the retailer or Cometic; not a wear item warranty.
Maintenance
No periodic service required. Inspect for oil seepage at cylinder bases during routine oil changes; any leak indicates a top‑end teardown is required.
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