Honda TRX 400 Top End Rebuild Part 2: Cylinder Head Inspection
After we disassembled the top end of our Honda TRX 400EX quad, the next step was to inspect the cylinder and piston before reassembling the engine.
Honda TRX 400EX Cylinder Head Inspection
Step 1. Remove the valves from the cylinder head using a valve spring compressor.
PRO TIP: Number each valve and the port it’s in so you can reinstall each valve in the correct port when reassembling the top end.
Step 2. Inspect the valves for wear, and check the valve seats in the cylinder head for anything that might prevent the valves from seating properly.
Step 3. Check the valve stem seals in the cylinder head for signs of leaks.
PRO TIP: Replace the valve stem seals. They’re inexpensive and should be replaced while the engine is dismantled, regardless of their condition.
Step 4. Inspect the cylinder for scratches or wear, and feel for any imperfections on the inside wall of the cylinder.
Step 5. Inspect the piston rings for wear, and feel around their outside edges for uneven surfaces.
If you find the piston rings or the cylinder is worn, you don’t need to throw them away. You can move up a +1 piston size and piston ring size, take the cylinder to a reputable machine shop and get it bored out to match.
After the piston and cylinder inspection, it’s time to reassemble the top end. Watch the video below to see the third part our Honda TRX 400EX top end rebuild.