Skip to main content

What to Know When Choosing a Fork Oil

Fork Oil – Which do I use?

We sell a good amount of fork oil in Sioux Falls thanks to some great motorcycle shops who know how to maintain the various units out there. But if you have a shop manual, the right tools and some patience give it a try!  Some units are very simple, quick and easy.

A fork oil’s number-one task is to deliver consistency. Consistent dampening despite temperature changes. Consistent rebounds despite different terrain. Consistent performance so you can ride or drive confidently.

Consistency.

What fluid would provide the best shock consistency?

Water.

Yes, water. But you don’t want to use it in your shocks for reasons you can probably guess, but we’ll get to that in a bit.

What shocks do

The shocks on your dirt bike, race car, ATV or other vehicle absorb abnormalities in the terrain and help stabilize the ride. They also absorb impact when landing a jump, taking some of the beating off the vehicle and your body. And they “load up” with energy when approaching a jump, helping you fly over whatever’s in your way.

The shock uses fluid to control dampening and rebound.

Say you’re riding your dirt bike and land a jump. The force depresses a piston inside the shock that pushes fork oil through calibrated valves. The fluid’s rate of flow through the valves influences the amount of dampening and rebound.

A thin fluid flows faster and results in quicker, springier shock feel. In contrast, a thick fluid flows more slowly and results in slower rebound and stiffer shock feel.

Fork oil viscosity matters

The fluid’s viscosity (often thought of as its thickness) influences how fast or slow the oil flows through the shock valves. If you prefer quick rebounds, use a lighter fluid. If you like slower rebounds, use a heavier fluid.

Buy AMSOIL Shock Oil

Easy, right?

Sure, if the viscosity of the shock oil never changes.

However, cold ambient temperatures increase the oil’s viscosity, resulting in slower rebounds. Then, after you’ve made a few laps and the vehicle’s heated up, the fork oil thins as it warms. That’s because fluids become thinner when they warm up. Think of molasses or honey. The warmer oil flows faster through the shock valves, leading to inconsistent shock feel.

H2O, no

That’s why water theoretically would provide the most consistent shock feel. Its viscosity doesn’t change between 33ºF (0ºC) and 211ºF (100ºC).

On a cold morning, after a long ride or on a blazing-hot day, water maintains the same viscosity provided it doesn’t freeze or boil. When was the last time you had a thin or thick glass of water? Hence, it would flow at the same rate through the shock valves, resulting in consistent feel.

Much more than flow, though

But the fork oil must do more than influence rebound and ride feel. It also must protect against wear and corrosion, two tasks at which water is notoriously bad.

The shock oil has to protect the shock tubes, seals and valves from wear as they constantly rub together. Minus good wear protection, the shock would tear itself apart in short order. Plus, the oil must form a layer on parts to prevent formation of corrosion. If corrosion starts, it won’t stop, spreading and depositing flakes of contaminant in the oil that act like sandpaper and scour metal parts until they’re worn out.

Look for a high-VI fork oil

Instead, look for a fork oil with a high viscosity index (VI). A higher VI indicates better resistance to viscosity changes throughout broad temperature swings. That translates into consistent shock performance and feel despite the ambient and operating conditions. And a consistent ride equals a more effective rider.

Points to consider when looking for fork oil

1) No standard viscosity

Your engine manufacturer recommends a specific viscosity of motor oil for best protection and performance. In the world of shocks, there are no universal viscosity requirements or recommendations. Each shock oil manufacturer is free to formulate its oils to whatever viscosity it deems appropriate. That means one brand’s “light” fluid could behave like another brand’s “medium” fluid, and so on.

2) Once you find a shock oil you like, stick with it

For the reasons listed above, avoid switching between fluids if you can. Once you have the proper suspension set-up for your body weight and riding style, stick with it. The shock oil is one of the biggest variables in your suspension tune, and messing with it can throw off suspension feel and your riding confidence.

3) Look at viscosity at 40ºC

If you decide to switch shock oil, compare the viscosity of the fluid you’re currently using at 40ºC to the same data for the new fluid. The closer the results, the more similar the oils will perform. Reputable manufacturers publish product data bulletins for their shock oils and post them online. If you can’t find a data sheet for the oil you’re considering, think twice before using it.

Buy AMSOIL Shock Oil

New ATV/UTV Oil Change Kits Offer Maximum Convenience

New ATV/UTV Oil Change Kits Offer Maximum Convenience

AMSOIL ATV/UTV Oil Change Kits combine everything needed to perform an oil change on the most popular models of Polaris* ATVs and UTVs in one convenient package, including…

To find the correct ATV/UTV Oil Change Kit for your machine, consult the appropriate Product Guide.

Look up My ATV

Look up My UTV

WHY YOU SHOULD UPGRADE YOUR ATV/UTV PROTECTION

Accessories equal weight. It’s common to burden your UTV or ATV with accessories designed to increase power or productivity, especially for UTV owners. Enthusiasts often add roof and door panels, a winch, a plow, skid plates and other accessories. Plus, how often do you haul a load of gravel or pull a trailer or other implement?

This all adds weight, and a good rule of thumb is that extra weight equals extra heat. Heat, in turn, causes lubricants to break down sooner, which places your engine and differentials at risk of wear.

Heat invites engine wear. The oil’s primary job is to form a protective layer on metal parts to keep them separated so they don’t rub together and wear out. High heat from the stress you place on your machine, however, can cause oils formulated for standard service to become thinner (lose viscosity). Oil that has lost viscosity can fail to develop an oil film of adequate thickness or strength to protect against wear.

Plus, high heat invites sludge and performance-robbing deposits inside the engine. Sludge can clog oil passages and starve the engine of oil, while deposits can cause the piston rings to stick or interfere with proper valve operation, leading to reduced engine compression.

Since compression equals power, over time your engine can make less power, limiting your ability to ride or work as effectively as possible. Eventually, deposits and sludge can wreck the engine completely.

Shift to better performance. The story is similar inside the transmission, differential and front drive. All the extra weight and stress of hard work and performance riding concentrates intense pressure on gears. The lubricant coats the gear teeth during operation, guarding against metal-to-metal contact and wear. The added stress, combined with high heat, can break the fluid film and literally squeeze the lubricant from between the gears, leading to wear. As with the motor oil, high heat causes the lubricant to thin, which negatively affects wear protection.

Upgrade to synthetic lubricants. So what’s the solution? Ride more conservatively? Haul lighter loads and work less?

Never. Upgrade to high-quality AMSOIL synthetic motor oil, differential and transmission fluid, front drive fluid and other lubricants, especially if you’ve modified your ATV or UTV for greater power or productivity. AMSOIL synthetic ATV/UTV lubricants don’t contain the impurities inherent to conventional lubricants, meaning they deliver better performance and last longer. Their naturally tough base oils resist extreme heat and maintain a strong protective film better than conventional products.

Think of synthetics as just another performance upgrade. You don’t think twice about dropping a few hundred dollars on a snowplow or work trailer. Over the course of your machine’s life, the few extra dollars you spend per oil change or transmission/differential service is a drop in the bucket by comparison.

*All trademarked names and images are the property of their respective owners and may be registered marks in some countries. No affiliation or endorsement claim, express or implied, is made by their use. All products advertised here are developed by AMSOIL for use in the applications shown.

Why You Should Be Wary About Using Break In Oil in Powersports Equipment

Why You Should Be Wary About Using Break In Oil in Powersports Equipment

Marco Navarro asks on our Facebook page about break in oil, with attention paid to powersports engines.  (Break in oil importance, drain interval on it, and applications. To include motorcycles and ATVs since life of engine is shorter and rebuilding occurs more often.)
Thanks for the question, Marco.

Let’s get to it.

Maintaining an engine is a constant fight against wear. Over time, wear not only results in expensive damage, it reduces compression, robbing your engine of power.

That’s why it can be tough to accept that “controlled wear” during a new or rebuilt engine’s break in period is critical to maximizing its power and longevity.

Take a seat

One of the primary reasons to break in an engine is to seat the piston rings, and that means allowing the rings and piston skirt to carefully wear down the peaks (called asperities) on the cylinder wall.

The images show what we mean.

Although a new or freshly honed cylinder appears smooth to the naked eye, it contains microscopic peaks and valleys. If the valleys are too deep, they collect excess oil, which burns during combustion and leads to oil consumption.

The sharp peaks, meanwhile, provide insufficient area to allow the rings to seat tightly. That means highly pressurized combustion gases can blow past the rings and into the crankcase, contaminating the oil and taking potential horsepower with it.

Breaking in the engine wears the cylinder-wall asperities, providing increased surface area for the rings to seat tightly. The result is maximum compression (i.e. power) and minimum oil consumption.

Getting the shaft

That brings us to the other primary reason to break-in an engine: to season, or harden, the flat-tappet cam. Flat-tappet cams can wear out faster than their roller-cam cousins, especially in engines modified with high-tension valve springs.

And cam wear is bad. Really bad. Worn lobes or tappets affect valve lift and duration, which reduces engine power and efficiency. In extreme cases, increased pressure can remove material from the lobes and deposit it in the oil, where it circulates through the engine and causes damage. Break-in helps harden the metal so it’s more resilient to wear.

That raises a critical question: How do we simultaneously allow controlled wear to the cylinder wall/piston rings while protecting the cam against wear? Those two tasks seem mutually exclusive.

In a word, oil

The solution is to use a properly formulated break in oil that allows controlled wear at the cylinder wall/piston interface, but that also protects the cam lobes and tappets from wear.

How do we accomplish this black magic?

Most break in oils, including AMSOIL Break-In Oil, use conventional base oils. Compared to their higher-quality synthetic counterparts, conventional base oils result in a thinner, less durable protective oil film on engine parts. The thinner fluid film allows controlled wear at the cylinder wall/ring interface.

But what about the cam? Won’t it wear, too?

ZDDP

That’s where anti-wear additives come into play. ZDDP anti-wear additives are heat-activated, meaning they provide wear protection in areas of increased friction. In this case, it’s at the cam lobe/tappet interface. The additives form a sacrificial layer on the surface of parts, which absorbs contact and helps prevent cam and tappet wear.

As a rule of thumb, a good break in oil should be formulated with at least 1,000 ppm ZDDP. At AMSOIL, we take it a few steps further; our Break-In Oil contains 2,200 ppm zinc and 2,000 ppm phosphorus.

How long does break in require?

Another rule of thumb states you should season a flat-tappet cam by running the engine above 2,500 rpm for 15 minutes.

As for seating the rings, our testing has shown it can take as little as seven dyno passes. That time varies depending on the engine, ring tension, cylinder hone and other factors.

If you don’t have access to a dyno, follow the engine builder’s or manufacturer’s recommendations. If none are provided, consult the recommendations on the break in oil label. In general, run the engine under light-to-moderate loads for about 500 miles. Again, that duration is a rule of thumb, but break in shouldn’t exceed 1,000 miles. Then, drain the break-in oil, install the synthetic oil of your choice and commence driving.

An engine dyno provides the best method of determining exactly when the rings are seated. You’ll notice a boost in horsepower as the rings seat. Eventually, horsepower will stabilize once the rings are seated.

Check out 5 Ways to Boost Horsepower for Under $500

You can also perform a leak-down test. Another, albeit more time-consuming, method is to remove the exhaust headers and check for oil residue in the exhaust ports. Presence of oil shows the engine burning oil, meaning the rings aren’t completely seated. Once the oil residue is gone, the rings are seated.

What about powersports engines?

Ask yourself a few questions about your motorcycle, ATV or other powersports application before using a break in oil:

  1. Does it have a wet clutch? If so, the break in oil may not be formulated for wet-clutch compatibility, leading to reduced performance.
  2. Does it use a shared sump with the transmission? Many motorcycles use one oil to lubricate the engine, transmission and primary chaincase. The churning action of transmission gears, especially in high-rpm applications, can tear apart – or shear – the oil if it’s not formulated to handle the stress. Using a break in oil not designed to handle high-shear applications can lead to damage.
  3. Does it have a dry sump? Some motorcycles store motor oil in a tank separate from the engine. Residual break in oil can collect in the system following the break in period and contaminate the service-fill oil. In this case, run the engine long enough to circulate the oil throughout the system and change it a second time to ensure the break in oil is completely removed.

Given the above challenges, we recommend breaking in a rebuilt powersports engine using the motor oil you’ve always used. Run it according to the original equipment manufacturer’s (OEM) new-engine recommendation, then change the oil. In short, treat it like a new engine from the factory.

For new engines, just follow the OEM guidelines. Typically they recommend a shorter interval for the first oil change to remove wear particles and contaminants from the factory. Then, change to the AMSOIL synthetic motor oil that’s recommended for your application and commence riding.