Honda Rancher 350 Top End Rebuild Part 3: Valve Lapping & Cylinder Head Prep

Welcome to the third part of our Honda TRX350 top end rebuild, in which we lap the valves and prep the cylinder head for reinstallation after the piston and cylinder installation

Watch the video above and follow the steps below to do a Rancher 350 Honda ATV valve lapping and cylinder head prep. Use our Honda TRX350 parts diagrams for additional reference.

Tools and Parts Needed - Honda Rancher 350 Cylinder Head Prep

Tools

Parts

Honda Rancher 350 top end rebuild

Removing the Valves From a Honda TRX350 Cylinder Head

Step 1. Clean the valve head, removing as much of the carbon on the inside of the head as possible with a wire brush drill attachment. 

Honda TRX350 top end rebuild valve head cleaning

NOTE: Keep the old valves in place to avoid scratching the valve seats in the head.

Step 2. Remove the intake valve. Use a valve spring compressor to tighten down the springs, then remove the valve keepers with a magnet. Release the valve spring compressor and slide the valve from the cylinder head.

Honda Rancher 350 engine rebuild valve spring compression

Step 3. Repeat Step 2 for the exhaust valve.

Step 4. Remove the valve seals by gently prying them out from the cylinder head, being careful not to damage the valve guides beneath them.

Honda Rancher 350 ATV engine rebuild

Step 5. Check the valve stem seats and thoroughly clean them with contact/brake cleaner. Put a smear of marking compound around each valve seat, then push the valves down into the seats and push them out again.

Hinda TRX350 Rancher top end rebuild

Step 6. Inspect the face of each valve. There should be a consistent film of marking compound around the valve, which indicates the valve is seating evenly. If the marking compound is only on parts of the valve faces, you’ll need to lap the valves.

Honda Rancher 350 engine valves

Lapping the Valves on a Honda TRX350

Step 7. Lap the valves. Put a smear of valve lapping compound on each valve face and lightly oil the valve stems. Push each valve down into its seat in the cylinder head and twist the valve back and forth a few times. Push the valve out slightly, rotate it a few degrees, then push it down into its seat and twist it again. Repeat this process four or five times.

Honda Rancher 350 engine rebuild valve lapping

Step 8. Clean off the valve lapping compound, making sure all traces of the compound are removed from the valve and cylinder head.

Honda Rancher 350 engine rebuild valve prep

Step 9. Check the valve seats again by repeating Step 6. The valve faces should seat evenly with the cylinder head now, but it they aren’t, repeat the valve lapping process.

Reinstalling the Valves into a Honda TRX350 Cylinder Head

Step 10. Install new valve stem seals. Press the new seals over the valve guides, being careful not to push so hard you pop the springs off the seals.

Honda TRX 350 ATV top end rebuild valve stems

Step 11. Lube the valve stems and the inside of the valve guides with engine oil, then install the valves into the cylinder head.

Honda Rancher TRX350 top end engine rebuild

Step 12. Reinstall the inner and outer valve springs, then tighten them down with the valve spring compressor and reinstall the valve keepers to hold the springs in place. Remove the compressor, and tap the springs a couple of times to make sure the keepers and the spring collar are properly seated.

Honda Rancher 350 top end rebuild cylinder head

PRO TIP: Put a bit of grease on the valve keepers to help them adhere to the valve stems as you’re putting them back into position.

After the valves are replaced and lapped and the cylinder head is prepped for reinstallation, the next step is to reinstall the cylinder and the ancillary components. Watch the video below to continue with the Honda Rancher TRX350 top end rebuild: head installation. 

 
INTAKE VALVE
Honda

INTAKE VALVE

Qty.
EXHAUST VALVE
Honda

EXHAUST VALVE

Qty.
VALVE STEM SEAL
Honda

VALVE STEM SEAL

Qty.

body

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