Polaris Sportsman 850 Engine Rebuild: Cylinder Head & Valve Removal

Welcome to part two of our Sportsman 850XP top end rebuild project. After removing the engine from the Polaris ATV, it’s time to disassemble the top end. 

Watch the video above and follow the steps below to tear down the top end of a Polaris Sportsman engine. Use our Polaris Sportsman 850 parts diagrams for additional reference. 

Tools Needed - Polaris Sportsman Cylinder Head Removal 

  • Ratchets and extensions
  • Sockets set
  • 14mm 12-point socket
  • 8mm, 10mm, 12mm wrenches
  • Allen set
  • Screwdriver
  • Pick tool
  • Hammer
  • Magnet

PRO TIP: Collect the nuts, bolts, screws, washers, etc. from each component as you remove them, put them in a zip-lock bag and label the bag to make it easier to put the motor back together.

Polaris Sportsman 850 top end teardown

Tearing Down a Polaris Sportsman 850XP Top End

Step 1. Remove the valve cover from the top of the engine.

Step 2. Bring the engine to top dead center (TDC) by rotating the camshaft clockwise until the small protrusion on the camshaft is 60 degrees past the vertical, and the mark on the cam sprocket is level with the cylinder head.

Polaris Sportsman top end teardown TDC

PRO TIP: Setting the engine to TDC removes the tension on the rocker box.

Watch the clip below to see the TDC segment of our Polaris Sportsman 850 engine rebuild video.

Step 3. Remove the cam chain tensioner from the side of the crankcase.

Polaris Sportsman ATV top end teardown

Step 4. Remove the eight rocker box bolts and the rocker box itself.

Step 5. Remove the camshaft bolt, then lift the cam chain off the sprocket, and remove the sprocket and the camshaft.

Watch the clip below to see the rocker box and camshaft removal segment of our Polaris Sportsman 850 engine rebuild video.

Step 6. Remove the two 8mm bolts from the outside of the cylinder head, then remove the six main cylinder head bolts in the sequence shown in the image below. Loosen the main bolts a quarter turn at a time to release the tension on the cylinder head evenly and prevent it from warping.

Polaris Sportsman 850 cylinder head removal

Step 7. Remove the cylinder head from the crankcase.

Watch the clip below to see the cylinder head removal segment of our Polaris Sportsman 850 engine rebuild video.

If the cylinder head and the valves are in good condition, you can keep the assembly in one piece, ready to be reinstalled when you rebuild the engine. However, if you want to lap the valves or replace them, follow these steps:

Removing the Valves From a Polaris Sportsman 850XP

Step 1. Clean and number the valves and valve ports to ensure each valve is reinstalled in the same port it came out of.

Polaris Sportsman 850 valve removal

Step 2. Use a valve spring compressor to remove the valve keepers and springs, then remove the valves themselves.

Polaris Sportsman ATV valve spring compression

Watch the clip below to see the valve removal segment of our Polaris Sportsman 850 engine rebuild video.

After tearing down the top end of our Polaris Sportsman 850XP, it’s time to tear down and rebuild the bottom end next. Watch the third part of our Polaris Sportsman 850XP engine rebuild video below to continue.

 

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