Polaris Sportsman 90 Crank Seal Replacement

Notice a pesky oil drip under your kid’s Polaris Sportsman 90? Maybe you’re seeing oily gunk building up around the CVT cover or the stator housing. That small leak is more than just an annoyance—it’s a sign your engine’s crankshaft seals are calling it quits.

You’ve come to the right place. Ignoring a bad crank seal can lead to bigger, more expensive problems down the road. But don’t start dialing the repair shop just yet. We promise this is a job you can handle right in your own garage.

This guide will walk you through everything you need to know for a successful polaris sportsman 90 crank seal replacement. We’ll cover the symptoms of a failed seal, the exact tools and parts you’ll need, and a detailed, step-by-step process to get your youth ATV running leak-free and reliably once again.

Why Bother Replacing Your Crank Seal? The Telltale Signs

Before we tear into the engine, let’s confirm the problem. The crankshaft seals on your Sportsman 90 have two critical jobs: keep the engine oil in and keep dirt, dust, and air out. When they fail, things get messy and performance suffers.

Understanding the benefits of polaris sportsman 90 crank seal replacement starts with recognizing the symptoms of failure. A new seal restores engine integrity, prevents catastrophic oil loss, and ensures your machine runs as it should.

Look out for these classic signs of a worn-out crank seal:

Visible Oil Leaks: This is the most obvious sign. You’ll see engine oil dripping from either the CVT side (right side) or the stator/flywheel side (left side) of the engine case.
Oily Mess in the CVT: If the right-side seal fails, it will sling oil all over the inside of your CVT cover, potentially contaminating your drive belt and causing it to slip.
Erratic Engine Performance: A failed seal can create a vacuum leak, allowing unmetered air into the crankcase. This leans out the air/fuel mixture, which can cause a high or unstable idle, bogging, and even engine damage over time.
Difficulty Starting: A significant air leak from a bad seal can disrupt the delicate balance needed for the engine to fire up easily.

Gearing Up: Tools and Parts You’ll Absolutely Need

Having the right tools makes all the difference between a frustrating afternoon and a successful repair. This isn’t a job you can do with just a basic screwdriver and a crescent wrench. Gather these items before you start.

This list covers what you’ll need for a complete polaris sportsman 90 crank seal replacement guide, addressing both sides of the engine.

Essential Tools List

Metric Socket Set & Ratchet
Torque Wrench
Impact Driver (highly recommended for clutch and flywheel nuts)
Flywheel Puller: This is non-negotiable for the stator side. Make sure you have the correct thread pitch for your Sportsman 90.
Clutch Puller: Necessary to safely remove the primary drive clutch on the CVT side.
Seal Puller or a set of small picks
Rubber Mallet
Screwdrivers (Phillips and Flathead)
Brake Cleaner & Shop Rags
Drain Pan

Required Parts List

New Crankshaft Seals: Order both the stator-side (left) and CVT-side (right) seals. They are often different part numbers. We recommend OEM or a reputable aftermarket brand like All Balls Racing.
New Gaskets: Get a new stator cover gasket and a new CVT cover gasket. Reusing old ones is asking for a leak.
High-Temp Grease or Assembly Lube
Blue Threadlocker
Fresh 2-stroke Engine/Transmission Oil

The Complete Polaris Sportsman 90 Crank Seal Replacement Guide

Alright, let’s get our hands dirty. We’re going to break this down by which side of the engine you’re working on. The process is similar, but the components you need to remove are different. Always refer to a service manual for your specific year if you’re unsure about torque specs.

H3: Safety First: Prepping Your Workspace

Before you turn a single bolt, set yourself up for success. A little prep work prevents major headaches.

Clean the Machine: Pressure wash or clean the engine area thoroughly. You don’t want dirt falling into your engine cases.
Find a Good Spot: Work in a clean, well-lit area with a flat surface.
Disconnect the Battery: Disconnect the negative battery terminal to prevent any accidental shorts.

Tackling the CVT (Drive) Side Seal

This is often the side that fails first due to heat from the exhaust and CVT. The telltale sign is oil coating the inside of your CVT cover.

Gain Access: Remove any plastics or footwells that are in the way of the CVT cover.
Remove CVT Cover: Undo the bolts around the perimeter of the black plastic CVT cover and gently pull it off. Inspect the inside for oil residue.
Remove the Clutches: Use your impact driver to remove the nut on the front (drive) clutch and the rear (driven) clutch. You may need a clutch holding tool if you don’t have an impact.
Pull the Drive Clutch: The front clutch is pressed onto the tapered crankshaft. Thread your clutch puller tool into the clutch and tighten it until the clutch pops off the shaft. Do not pry it off!
Expose the Seal: With the clutch removed, you will see the crank seal pressed into the engine case. Take a picture so you know how deep the new one needs to be seated.
Remove the Old Seal: Carefully use a seal puller or a small pick to hook the edge of the old seal and pry it out. Be extremely careful not to scratch the crankshaft or the aluminum engine case where the seal sits.
Clean the Seal Bore: Spray some brake cleaner on a clean rag and meticulously wipe out the pocket where the seal was. Any debris left behind will cause your new seal to leak.
Install the New Seal: Lightly coat the outer edge of the new seal with grease. Apply a thin film of oil to the inner lip. Find a socket that matches the outer diameter of the seal. Place the seal squarely in the bore and use the socket and a rubber mallet to gently and evenly tap it into place until it’s seated at the same depth as the original.
Reassemble: Reinstall the clutch, apply blue threadlocker to the nut, and torque it to the manufacturer’s specification. Reinstall the CVT cover with its new gasket.

Conquering the Stator (Flywheel) Side Seal

This side holds the engine’s electrical charging and ignition components. The process is similar but requires that all-important flywheel puller.

Drain the Oil: This side of the case contains transmission oil. Place your drain pan under the drain plug and drain the oil completely.
Remove Covers: Take off the plastic pull-start cover, then unbolt and remove the metal stator cover. Be prepared for some residual oil to drip out.
Remove the Flywheel Nut: Use an impact driver or a flywheel holding tool to remove the large nut in the center of the flywheel.
Pull the Flywheel: This is the crucial step. Find the correct threads on your flywheel puller and thread the main body into the flywheel. Then, tighten the center bolt of the puller. It will press against the crankshaft and pop the flywheel off its taper. Never hit a flywheel with a hammer or try to pry it off.
Remove the Stator: Unplug the stator wiring harness. Remove the screws holding the stator plate to the engine case and carefully lift it away.
Access and Replace the Seal: You now have clear access to the left-side crank seal. The replacement procedure is the exact same as the CVT side: carefully pry out the old one, clean the bore, and gently tap the new, lubricated seal into place.
Reassemble: Reinstall the stator plate, ensuring any timing marks are aligned correctly (if applicable). Reinstall the flywheel, apply threadlocker to the nut, and torque to spec. Install the stator cover with a new gasket and refill the engine with the correct type and amount of oil.

Pro Tips and Common Problems with Polaris Sportsman 90 Crank Seal Replacement

Knowing how to polaris sportsman 90 crank seal replacement is one thing; doing it without creating new problems is another. Here are some pro tips and best practices to ensure a smooth, leak-free job.

Avoiding Common Mistakes

Scratched Surfaces: The biggest mistake is gouging the soft aluminum case or the hardened steel crankshaft when removing the old seal. Use a proper puller and be patient. A deep scratch will create a new leak path.
Backwards Installation: Most seals have a “spring side” on the inner lip. This side should always face inward, toward the oil and pressure you’re trying to contain.
Dry Installation: Never install a seal dry. The friction can damage the delicate rubber lip. Always use a little grease on the outside and oil on the inside.
Forgetting to Clean: A tiny piece of grit or old sealant left in the seal bore is all it takes to ruin your hard work. Cleanliness is key.

Best Practices for a Leak-Free Job

Follow these polaris sportsman 90 crank seal replacement best practices for lasting results. Take your time, and do it right the first time.

Always use new gaskets. They are cheap insurance against oil leaks and vacuum leaks. Also, take photos as you disassemble components. They can be a lifesaver when you’re trying to remember how everything goes back together.

Post-Replacement Care and Sustainable Practices

You’ve done the hard work, and your Sportsman 90 is back together. The job isn’t quite finished yet. Your polaris sportsman 90 crank seal replacement care guide starts now.

After the repair, start the engine and let it run for a few minutes. Carefully inspect both sides of the engine for any signs of oil leaks around your new seals and gaskets. Take it for a short, gentle ride and check again.

When it comes to eco-friendly polaris sportsman 90 crank seal replacement, the most important step is responsible disposal. Take your used engine oil to an auto parts store or local recycling center. Don’t just throw oily rags in the trash; place them in a sealed metal container to prevent fire hazards and dispose of them according to local regulations.

Frequently Asked Questions About Polaris Sportsman 90 Crank Seal Replacement

How long does it take to replace a crank seal on a Sportsman 90?

For a first-timer with the right tools, budget about 3-4 hours for the entire job (both sides). An experienced mechanic could likely do it in under 2 hours. The key is not to rush the delicate steps of removing and installing the seals.

Can I reuse the stator or CVT cover gaskets?

We strongly advise against it. Gaskets compress and deform when tightened. Reusing them is one of the most common causes of oil leaks after a repair. New gaskets are inexpensive and critical for a proper seal.

What happens if I don’t replace a leaking crank seal?

Ignoring it can lead to serious engine damage. On the CVT side, it can saturate your belt, causing it to slip and fail. On either side, it can cause significant oil loss leading to engine seizure. It can also create an air leak, causing the engine to run lean and hot, which can damage the piston.

Do I really need a flywheel puller and a clutch puller?

Yes, absolutely. Both the flywheel and the primary clutch are press-fit onto the tapered ends of the crankshaft. Attempting to remove them by prying or hammering will almost certainly damage the components, the crankshaft, or the engine cases, turning a small repair into a very expensive one.

Congratulations! You’ve just completed a critical piece of engine maintenance that will keep your Polaris Sportsman 90 running strong for years to come. Taking on jobs like this not only saves you money but also deepens your understanding of your machine.

Now, double-check your work, top off the fluids, and get that ATV back on the trail where it belongs. Ride safe, and stay dirty!

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Thomas Corle

Founder & Automobile expert at FatBoysOffroad

Automobile expert and off-road enthusiast, sharing in-depth knowledge of vehicles, gear, and adventures. Helping readers make smart decisions and enjoy the thrill of off-roading safely and confidently.