Cometic Yamaha YFZ450 4X2 Exhaust Gasket (EX641) by Cometic

A gasket is the smallest part of an engine rebuild and the one most likely to cause a do-over. The Cometic Yamaha Exhaust Gasket (EX641) is an exhaust gasket that seals the joint between the head and the header pipe, made to Cometic’s exacting specifications so the job is done right the first time.

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 Exhaust Gasket

An exhaust leak at the head robs power, causes popping on deceleration, can skew the fuel mixture readings from O2 sensors, and lets hot gases cook nearby wiring and plastic. A fresh Cometic exhaust gasket restores a tight, quiet seal.

Key Features and Benefits

• Seals the head-to-header joint
• Built to withstand extreme exhaust heat
• Made in the USA

Specifications

• Brand: Cometic Gasket
• Part number: EX641
• Product type: exhaust gasket
• Made in: USA
• Quantity: 1 gasket, unless noted otherwise

Cometic Gasket Technology

Application-specific construction

Cometic varies the material and construction of its exhaust gaskets by application. Four-stroke gaskets use heat-resistant cores with a double-sided Viton® rubber coating for a leak-free seal under all conditions.

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

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.

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

• Ticking or puffing at the exhaust port
• Popping on deceleration
• Soot around the exhaust flange
• A new header or pipe install

Installation Tips

1. Let the engine cool completely.
2. Remove the header and the old gasket, and clean the port face.
3. Install the new gasket and header, then tighten the flange nuts evenly.
4. Run the engine and recheck tightness after a heat cycle.

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

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

• What is the difference between OEM Exhaust Gaskets vs Permatex Gasket Sealer?
• Do I Need to Tune My UTV/ATV After an Exhaust Upgrade?
• Expert Installation Guide: Stop UTV Gasket Leaks- Install them Correctly

Frequently Asked Questions

Can I reuse an exhaust gasket?

It isn’t recommended. Exhaust gaskets crush to seal and rarely seal properly a second time.

Do I need sealer?

No. Cometic exhaust gaskets are designed to seal without sealer.

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:

• Georgia Offroad Adventures (Union Point, Georgia): about 150 miles of signed trails
• Mine Made Paradise Adventure Park (Leburn, Kentucky): 100+ miles of ATV and UTV trails (UTVs up to 70 in. wide)

Order Your Cometic Yamaha Exhaust Gasket Today

Seal it right the first time. Add the Cometic Yamaha Exhaust Gasket (EX641) 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

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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.