Cometic Yamaha YFZ450 Top End Gasket Kit 96mm Bore (C3066-EST) by Cometic

Oil on the garage floor, lost compression or an exhaust tick all point to one fix: a quality gasket installed correctly. The Cometic Yamaha Top End EST Gasket Kit 96 mm (part number C3066-EST) is a complete top end gasket kit with the head gasket, base gasket and the O-rings and seals needed to pull and reinstall the top end, built in the USA by Cometic, the gasket specialist trusted by racers and engine builders.

Witchdoctors stocks genuine Cometic gaskets by their Cometic part numbers. Match your part number, check the fitment below and order with confidence.

Why Choose the Cometic Yamaha Top End EST Gasket Kit 96 mm

A top end rebuild is only as good as the gaskets that seal it. Reusing an old head or base gasket, or mixing parts from different sources, is one of the most common causes of compression loss, coolant or oil seepage and blown head gaskets after a rebuild. A Cometic top end kit puts every gasket and seal for the job in one box, made to the correct specification for your engine and bore size.

Key Features and Benefits

• Sized for a 96mm bore
• .027" MLS cylinder head gasket
• EST (Extreme Sealing Technology) rubber-coated stainless gaskets
• Includes the head gasket, base gasket, cylinder O-rings and the top end O-rings and seals needed to remove and reinstall the top end
• MLS head gaskets promote even torque load and better ring seal
• Precise fit to the engine’s sealing surfaces
• Made in the USA

Specifications

• Brand: Cometic Gasket
• Part number: C3066-EST
• Product type: top end gasket kit
• Bore: 96mm
• Gasket material/thickness: .027" MLS
• Made in: USA
• Quantity: 1 kit

Cometic Gasket Technology

Multi-layer steel (MLS) head gasket

Cometic’s MLS head gaskets use several layers of embossed stainless steel. The outer layers are coated with Viton® rubber. The design spreads clamping load evenly across the sealing surface, which means less bore distortion, a better ring seal and more usable power. Cometic builds these gaskets for today’s highest-output four-strokes, both naturally aspirated and boosted.

EST: Extreme Sealing Technology

The EST kit uses embossed stainless steel head, base and rocker gaskets covered with a proprietary rubber material. The head gasket material draws heat away from the combustion ring and spreads it evenly across the gasket surface, eliminating the hot spots that lead to gasket failure.

Every Cometic gasket is engineered and manufactured in the USA, and the company supplies professional engine builders in powersports, motorsport and performance automotive.

Fitment and Compatibility

Cometic lists part C3066-EST for: Yamaha 2004-2013 YFZ450 (carbureted).

Witchdoctors catalog fitment (models and years): Yamaha YFZ450 4X2 2004–2008.

Fitment is listed by part number. Always compare the Cometic part number with your current gasket, your service manual or your parts supplier’s lookup, especially on engines that have been modified.

Choosing the Right Bore and Thickness

Head gasket kits are sold by bore size, so match the bore to the piston you are installing. Kits larger than your engine’s stock bore are made for oversize pistons and big-bore cylinders. Head gasket thickness affects compression ratio and piston-to-head clearance: a thinner gasket raises compression, and a thicker one lowers it. If you have machined the head or cylinder, or are building for race fuel or boost, confirm clearances before final assembly.

Why Gaskets and Seals Fail

Every gasket lives a hard life. Heat cycles expand and contract the metal around it thousands of times. Vibration works at the joint, oil and coolant chemistry slowly attack the materials, and over-tightened or unevenly torqued fasteners crush one side while leaving the other loose. Off-road machines add water crossings, mud and long idle periods in the heat. Eventually even a good gasket loses its ability to rebound and seal. Replacing gaskets during any service that disturbs a joint, and choosing a premium material like Cometic’s, is the most reliable way to keep an engine dry and making full power.

Signs You Need This Gasket

• Loss of compression or hard starting
• Oil or coolant weeping at the head or base
• White smoke or coolant loss (liquid-cooled engines)
• Ticking or puffing sounds at the head joint
• A planned piston, ring, cylinder or big-bore job

Installation Tips

1. Clean every mating surface down to bare metal. Use a plastic scraper or gasket remover, never a power wire wheel, on aluminum.
2. Check the head and cylinder for flatness with a straightedge and feeler gauge.
3. Install the gaskets dry unless the instructions say otherwise. Cometic MLS and EST gaskets are designed to seal without sealer.
4. Torque the head fasteners in the factory sequence and steps listed in your service manual.
5. Recheck valve clearance, refill fluids and follow a proper break-in if you installed new rings or a piston.

Always follow the torque values and tightening sequence in your factory service manual. Replace any stretched or damaged fasteners, and never reuse crush washers or O-rings.

Who This Gasket Is For

• Trail, mud and dune machines that see hard use
• Racing and big-bore performance builds
• Rebuilding high-hour work and utility machines
• Restoring older ATVs to like-new condition

Complete the Job

Doing the job right? These parts share an application with this gasket. Check them against your model:

• Yamaha Bottom End Gasket Kit (C3338)
• Yamaha Exhaust Gasket (EX641)
• Yamaha Clutch Gasket (EC763032AFM)
• Yamaha Top End EST Gasket Kit 98 mm (C3068-EST)
• Stator Cover Gasket (EC899032AFM)

Browse every Cometic part in our Cometic Gasket collection. For bolts that need it, see our Loctite thread lockers.

Helpful Guides From the Witchdoctors Blog

• Low ATV/UTV Compression? How to Check Engine Cylinders & Power Loss
• Expert Installation Guide: Stop UTV Gasket Leaks- Install them Correctly
• ATV or UTV Ticking Noise? How to Spot a Bad Camshaft & Valves

Frequently Asked Questions

Does this kit fit a stock bore?

Check the bore listed in the specifications against your piston. Cometic makes kits in several bore sizes, so a bore larger than your engine’s stock size is meant for an oversize piston or a big-bore kit.

What does EST mean?

EST stands for Cometic’s Extreme Sealing Technology: embossed stainless steel head, base and rocker gaskets covered with a proprietary rubber coating.

Do I need gasket sealer?

In most cases, no. Cometic gaskets are designed to install dry. Use sealer only where your service manual specifies it, such as at case parting lines.

Can I reuse my old gasket?

No. Gaskets compress and take a set when they are torqued. A new gasket is cheap insurance against leaks and a second teardown.

Is Cometic better than OEM?

Cometic engineers its gaskets to meet or exceed OEM sealing performance and offers performance options, such as MLS head gaskets and multiple bore and thickness choices, that the OEM does not.

Where are Cometic gaskets made?

Cometic gaskets are manufactured in the USA.

Where to Ride

Once your engine is sealed up and broken in, take it somewhere worth the effort:

• Burning Rock Offroad Park (Tams, West Virginia): 100 miles of trails (UTVs up to 64 in. wide)
• Mine Made Paradise Adventure Park (Leburn, Kentucky): 100+ miles of ATV and UTV trails (UTVs up to 70 in. wide)

Order Your Cometic Yamaha Top End EST Gasket Kit 96 mm Today

Seal it right the first time. Add the Cometic Yamaha Top End EST Gasket Kit 96 mm (C3066-EST) to your cart, and Witchdoctors will ship genuine Cometic gaskets fast. Questions about fitment? Contact our team with your year, make and model, and we’ll help you get the right part.

Shipping

Qualifying Retail orders $159.99 or more will receive free ground shipping. Free Shipping Terms and conditions.

All orders over $500 will require a signature.

Please see International Shipping page for orders shipping outside the US.

See our full Shipping Policy page for further details.

Product Availability

We show real time product availability. These products normally ship the same business day but may ship from one of our warehouses across the country. If an item requires additional processing time you will be notified.

Returns

If your order arrives and it is not right, we will we'll fix it. We promise!

Doesn't fit or just not happy with it? You can return any new, unopened, unused or unaltered item within 30 business days of delivery receipt of your item. We will issue a refund to your original payment method.

See our full Return Policy for all of the pertinent details.