Honda TRX420 FourTrax service schedule

1. Stop the engine, take the key out and remove the seat.
2. Unclip the air cleaner housing cover, slacken the screw and lift out the air cleaner assembly.
3. Remove the clamp and slide the foam off its frame.
4. Wash it gently in non-flammable solvent such as paraffin, never petrol. Squeeze it out; do not twist or wring it, or the foam tears.
5. Check for tears or split seams and replace it if damaged.
6. Let it dry fully, then work foam filter oil evenly through it inside a plastic bag and squeeze out the excess.
7. Refit it to the frame, put a thin coat of grease on the sealing face, refit the clamp and put the assembly back in the housing. Tighten the screw and refit the cover so its cut-out fits the tab.
8. Check the breather dust cover at the same time and clean it if dirty.

Tools: Bowl of non-flammable high-flash-point solvent (such as paraffin), Plastic bag, Gloves, Grease, Screwdriver

1. With the engine off, find the clear drain tube under the air cleaner housing.
2. If you can see water or dirt in it, release the clip and pull the tube off.
3. Drain the deposits, refit the tube and secure it with the clip.
4. If there was a lot of water, check the air cleaner too.

Tools: Pliers for the clip, Rag

1. Let the engine cool, take the key out and remove the seat and tank cover.
2. Clean dirt from around the plug, pull off the cap by the cap (not the lead) and unscrew the plug.
3. Look at the electrodes. Replace the plug if it is heavily fouled, worn or the insulator is cracked.
4. Check the gap with a wire feeler gauge: 1.00–1.10 mm. Bend only the side electrode to adjust.
5. Screw the plug in by hand to avoid cross-threading. A used plug: 1/8 turn after it seats. A new plug: NGK 3/4 turn or Denso 1/2 turn after it seats, loosen, then 1/8 turn after it seats again.
6. Refit the cap, tank cover and seat.

Tools: Plug spanner (in the tool kit), Wire-type feeler gauge, Wire brush

1. Only check with the engine cold. Take the key out.
2. Follow the Honda service manual to remove the covers and set the piston at top dead centre on the compression stroke.
3. Check the gaps with feeler gauges: inlet 0.15 mm, exhaust 0.23 mm.
4. Adjust if needed as the service manual describes, then recheck.
5. If you do not have the service manual and tools, have your dealer do it.

Tools: Feeler gauges, Spanners and adjusting tool, Socket set, Service manual

1. Park on level ground, engine off, parking brake on.
2. Check the front brake fluid is between the marks in the reservoir window. A falling level usually means worn pads or a leak.
3. Look at the pad wear indicators on both front calipers. Replace both pads on both sides if the indicator reaches the edge of the reference mark.
4. Rear drum: apply the brake fully and check the arrow on the brake arm. If it lines up with the reference mark on the brake panel, the shoes need replacing.
5. After wet work, remove the drain bolt under the rear brake panel. If water comes out, the brake seals need replacing by your dealer. Refit the bolt with a new washer at 12 N·m.
6. Check hoses for cracks and leaks. Brake fluid damages paint and plastics, so wipe up spills at once.
7. Every 2 years have the brake fluid replaced.

Tools: Torch, Rag, Torque wrench (12 N·m), Small spanner

1. Park on level ground, engine off, key out, parking brake on.
2. Check the propeller shaft boots and the yoke joint boot for cuts, damage or leaking grease.
3. On 4x4 models, check the front driveshaft boots at both ends of each shaft, turning the steering to see all round them.
4. Have any split boot replaced by your dealer before the joint is damaged.

Tools: Torch, Rag

1. Park on firm level ground, select neutral, set the parking brake, stop the engine and take the key out.
2. Ride or idle the quad briefly so the oil is warm, then stop it. Hot oil and exhaust burn, so wear gloves.
3. Take out the oil filler cap/dipstick, put the tray under the engine and remove the drain bolt and its sealing washer.
4. Take off the seat and tank cover, put towels under the filter cover on the right of the engine, undo the cover bolts and take off the cover. Let the last oil drain and throw the old filter away.
5. Oil the new O-rings and fit them. Put the spring back on the crankcase and fit the new filter with its rubber seal facing out, towards the cover. The filter is marked OUTSIDE (TOWARDS FILTER COVER). Fitted the wrong way round it can wreck the engine.
6. Refit the cover and tighten the bolts to 10 N·m. Refit the drain bolt with a new washer at 25 N·m.
7. Fill with about 2.7 L of 10W-30 JASO MA oil and refit the dipstick.
8. Start the engine and idle for 3–5 minutes, stop it, wait 2–3 minutes and check the level is between the marks with the dipstick resting in, not screwed in. Check for leaks and refit the tank cover and seat.
9. Take the old oil to a proper disposal point.

Tools: Drain tray (5 L), Socket set, Torque wrench (10–25 N·m), Funnel, Shop towels, Gloves

1. Ride the quad first so the gear oil is warm, then park on firm level ground, set the parking brake and take the key out.
2. Rear: put the tray under the case, remove the fill cap and the drain bolt, and let it drain. Refit the drain bolt with a new washer at 12 N·m.
3. Rear: remove the level check bolt, then fill slowly until oil starts to run out of the check hole (about 85 ml). Wait 2–3 minutes. Refit the check bolt with a new washer and the fill cap with a greased new O-ring, both at 12 N·m.
4. Front (4x4): remove the fill cap and drain bolt, drain, refit the drain bolt with a new washer at 12 N·m.
5. Front: fill with about 210 ml to the lower edge of the fill inspection hole, then refit the fill cap with a greased new O-ring at 12 N·m.
6. Look at the old oil. Milky oil means water has got in; have the seals checked.

Tools: Small drain tray, Socket set, Torque wrench (12 N·m), Oil syringe or squeeze bottle, Grease

1. Work only on a cold engine. Never take the radiator cap off hot: coolant can spray out and scald you.
2. Honda says coolant replacement needs the service manual; if you do not have it, have your dealer do the drain and bleed.
3. Mix antifreeze 50/50 with distilled water only (not tap water). Do not go below 40% or above 60% antifreeze.
4. For top-ups, always add to the reserve tank up to the UPPER mark, not through the radiator cap.
5. Clean mud from the radiator core with low-pressure water only. Pressure washing damages the fins. Have it checked if more than 20% of the core is blocked.
6. Coolant is poisonous to animals: catch it all and dispose of it properly.

Tools: Drain tray, Funnel, Antifreeze tester, Soft brush and low-pressure hose for the radiator