AMSOIL 10W-40 100% Synthetic Metric Motorcycle Oil

Superior Protection for Engines and Transmissions

AMSOIL 10W-40 Synthetic Metric Motorcycle Oil is specially formulated for four-stroke sport bikes, cruisers, touring, and adventure motorcycles.
It delivers maximum performance in both engines and transmissions.
Wet-clutch compatible for smooth, reliable shifting and confident ride control.

Outstanding Heat Resistance and Wear Reduction

High-Temperature Film Strength

This oil surpasses industry standards for heat resistance, maintaining strong film strength to protect engine parts.

Advanced Anti-Wear Formula

Loaded with anti-wear additives, it reduces engine wear under all conditions.
Prevents sludge and carbon deposits, ensuring superior engine cleanliness and longevity.

Enhanced Clutch and Shift Performance

Friction Modifier Free

Free of friction modifiers, this oil promotes smooth, positive clutch engagement.
Designed to reduce heat and prevent clutch slippage or glazing.

Long Clutch Life

Protects the clutch system for extended life, even under aggressive riding conditions.

Reliable Foam Control

Advanced anti-foam agents prevent oil foaming during high-RPM riding.
This ensures consistent lubrication and protects critical components under extreme conditions.
Allows riders to push performance confidently and safely.

Learn More

For detailed specifications, refer to the product data sheet.

AMSOIL 10W-40 100% Synthetic Metric Motorcycle Oil – Deep Dive For Real-World Riders

AMSOIL 10W-40 100% Synthetic Metric Motorcycle Oil is built specifically for four-stroke metric motorcycles – sport bikes, standards, cruisers, touring machines and adventure bikes that see serious miles and real-world abuse.

It’s not a repackaged car oil. It’s a motorcycle-first formula designed for engines, gearboxes and wet clutches that all share the same sump. It delivers:

• Strong protection in high-heat, high-RPM conditions
• Smooth, predictable clutch feel and shift quality
• Long-term engine cleanliness and wear protection

If your owner’s manual calls for 10W-40 and a JASO MA/MA2 motorcycle oil, this is the “do-it-all” metric choice for riders who want maximum performance and long engine life.

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Why 10W-40 Is The Sweet Spot For Many Metric Motorcycles

Understanding The Grade

10W-40 is a classic motorcycle viscosity for good reason:

• The “10W” side gives you easy cranking and fast oil flow at cold start.
• The “40” side provides a strong, stable film at full operating temperature.

For many four-stroke metric bikes, that balance is ideal because they:

• Rev higher than big twins
• Run hotter under fairings
• Spend a lot of time at mid-to-high RPM

With 10W-40, you get cold-start protection and hot-running strength in one grade.

Built For Shared-Sump Engine + Transmission + Clutch

Most metric motorcycles use a shared sump, where one oil must:

• Lubricate the engine (crank, rods, pistons, cams, bearings)
• Cushion and protect the transmission gears
• Provide the right friction for the wet clutch pack

That’s a harder job than anything in most cars. AMSOIL 10W-40 Metric Motorcycle Oil is tuned specifically for this environment, so the same fluid can:

• Handle shear forces from gears without thinning out too fast
• Support strong, predictable clutch engagement
• Keep the engine clean even in high-heat, stop-and-go riding

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High-Temperature Strength And Wear Protection

Staying Strong When The Oil Is Hot

Sport and touring motorcycles often run:

• In dense traffic
• Behind bodywork that traps heat
• At high RPM on the highway

Under those conditions, weaker oils thin out and lose film strength, which allows more metal-to-metal contact. This 10W-40 is formulated for outstanding high-temperature film strength, meaning it continues to:

• Maintain a protective layer between moving surfaces
• Support bearings, journals and gear teeth under load
• Resist burning off or oxidizing quickly

That’s a big part of why riders can push their bikes hard without feeling like they’re abusing the engine.

Advanced Anti-Wear Additive System

On top of the synthetic base oil, AMSOIL loads this formula with dedicated anti-wear additives. Under high pressure, those additives chemically react to create a microscopic sacrificial layer on metal surfaces.

They help protect:

• Cam lobes and followers
• Main and rod bearings
• Gear teeth in the transmission
• Piston rings and cylinder walls

So whether you’re rolling gently through town or repeatedly revving near the redline, the oil is actively working to minimize long-term wear.

Fighting Sludge, Varnish And Carbon

Heat, fuel dilution and moisture can make oil oxidize and leave behind:

• Sticky varnish on pistons and rings
• Heavy sludge in low-flow areas
• Carbon deposits on hot surfaces

The synthetic base oils plus detergent and dispersant additives in this 10W-40 are designed to:

• Resist oxidation
• Keep contaminants suspended
• Limit the formation of sludge and carbon

Cleaner internals mean better compression, smoother running and easier maintenance over the life of the bike.

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Clutch Feel And Shift Quality

No Friction Modifiers – Built For Wet Clutches

Automotive “energy-saving” oils often contain friction modifiers that are great for fuel economy, but terrible for motorcycle clutches. They can cause:

• Clutch slip under heavy throttle
• Plate glazing
• An inconsistent engagement point

AMSOIL 10W-40 Metric Motorcycle Oil is friction-modifier free on purpose. Its friction profile is dialed in for JASO MA/MA2-type wet clutches, which helps:

• Promote smooth, positive engagement
• Reduce slippage during hard acceleration or two-up riding
• Prevent glazing that can shorten clutch life

You get a clutch that feels the same when it’s hot, cold, loaded or unloaded – and that consistency builds rider confidence.

Positive, Predictable Shifting

Because the transmission shares the same oil:

• Shear stability matters for gear protection
• Friction characteristics matter for shift quality

This 10W-40’s stay-in-grade viscosity and strong film help:

• Cushion gear tooth impact under load
• Support smooth, precise gear engagement
• Reduce notchiness as the oil ages

You feel that as crisper shifts, less grinding and more “snick-snick” precision, even toward the end of the oil change interval.

Extended Clutch Life Under Aggressive Use

Aggressive riding, track days, heavy two-up touring and frequent stop-and-go will stress any clutch. By controlling heat and friction at the clutch interface, this oil helps:

• Limit hot spots and glazing
• Reduce chronic slip that leads to premature wear
• Maintain consistent engagement characteristics over time

In short, it supports a clutch you can trust, even when you ride the bike like it was meant to be ridden.

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Foam Control For High-RPM Riding

Why Foam Is Bad News

At very high RPM, spinning parts and meshing gears can whip oil into foam. Foam is basically air bubbles in oil, and air:

• Doesn’t carry heat well
• Doesn’t lubricate well
• Can cause wild swings in oil pressure

That’s not something you want when you’ve got the tach needle buried.

Advanced Anti-Foam Agents

AMSOIL 10W-40 Metric Motorcycle Oil uses advanced anti-foam additives to keep bubbles under control, even when the engine is screaming at high RPM.

That means:

• More consistent oil pressure
• A stable oil film on bearings, cams and gears
• Reliable lubrication when you’re pushing the bike hard

You get to focus on your line and throttle, not on wondering whether the oil is still doing its job inside the crankcase.

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Engine Cleanliness And Long-Term Health

Detergents And Dispersants Doing Quiet Work

Inside the engine, the detergent/dispersant system:

• Keeps microscopic contaminants suspended
• Helps prevent them from clumping into sludge
• Cleans hot surfaces where deposits would otherwise bake on

That helps maintain:

• Clean piston ring grooves for better sealing
• Clean oil control rings for proper oil usage
• Unrestricted oil flow through galleries and spray jets

Over time, that adds up to better overall health and longevity for your engine.

Corrosion Protection Between Rides

Motorcycles often sit:

• For several days between commutes
• For weeks during bad weather
• For months over winter storage

During that time, condensation and combustion acids can attack unprotected metal surfaces. This oil’s additive system helps:

• Resist rust on internal steel and iron parts
• Neutralize acids that can form in the oil
• Keep critical surfaces protected until the next ride

If you change to fresh oil before a long storage period, your engine spends the off-season soaking in clean protection instead of dirty, acidic leftovers.

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Who This 10W-40 Metric Motorcycle Oil Is Ideal For

Sport And Naked Bike Riders

If you ride a four-cylinder or twin sport bike / naked that specifies 10W-40, this oil is a natural fit. It supports:

• High-RPM runs
• Quick changes in load and speed
• Hot fairing and city traffic conditions

You get strong film strength at temperature, tuned clutch friction and clean internal operation.

Cruiser, Touring And Adventure Riders

For riders who:

• Tour with luggage and passengers
• Ride long highway stretches at steady RPM
• Mix pavement with gravel or dirt

…this oil’s high-temperature stability and shear resistance help it stay in grade over long days. It also helps the engine stay smooth and quiet as miles accumulate.

Daily Commuters And Mixed-Use Riders

If your bike:

• Goes to work during the week
• Sees weekend fun runs or group rides
• Occasionally does long trips

…you need oil that works in all three modes. AMSOIL 10W-40 Metric Motorcycle Oil provides:

• Reliable cold-start protection
• Heat resistance for traffic and hot days
• Consistent clutch and shift feel in all conditions

It’s a strong “set it and go ride” choice for riders who want to keep things simple without sacrificing protection.

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How It Fits Into The AMSOIL Metric Oil Lineup

AMSOIL’s Metric Motorcycle line includes multiple viscosities (10W-30, 10W-40, 5W-40, 15W-50).

10W-40 is the middle-weight, all-around workhorse:

• Lighter than 15W-50 for easier cold flow and less drag
• Heavier than 10W-30 for extra film strength in hotter, heavier use
• A common OEM recommendation for many metric bikes

The entire line shares core benefits:

• 100% synthetic base oils
• Strong anti-wear and deposit-control chemistry
• Wet-clutch-friendly friction behavior
• Anti-foam and corrosion protection

Choosing between them comes down to what your manual allows and how/where you ride. If 10W-40 is listed, this formula is engineered to make the most of that specification.

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Basic Use And Maintenance Approach

Check Your Manual First

Before you pour any oil in:

• Confirm that 10W-40 is an approved viscosity
• Verify the required JASO rating (typically MA or MA2)
• Note any special OEM recommendations for high or low temperature ranges

If 10W-40 is specified or strongly recommended, this oil is squarely in its wheelhouse.

Oil Change Rhythm That Works

A practical pattern for most riders:

• Start the main riding season with fresh oil and filter
• Change again mid-season or before winter storage if you rack up a lot of miles
• Shorten intervals for track use, heavy city traffic or very dusty conditions

Because this is a strong synthetic, it handles stress better than basic oils, but matching change intervals to your actual usage is still smart.

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Bottom Line: A True “Do-Everything” Metric Motorcycle Oil

AMSOIL 10W-40 100% Synthetic Metric Motorcycle Oil is built for riders who expect a lot from their bikes and don’t want to compromise on protection. It delivers:

• High-temperature film strength for hot, hard running
• Advanced anti-wear protection for long engine and gearbox life
• Deposit control to keep internals clean
• Wet-clutch compatibility with no friction modifiers
• Smooth shifting and stable clutch feel across the interval
• Foam control and corrosion resistance for reliability in all conditions

If you ride a four-stroke metric motorcycle that calls for 10W-40 and you want one oil that can handle commuting, touring and aggressive weekend riding, this formulation is designed to be that single, trusted choice in your metric toolbox.