Goal: remove, inspect, and replace the camshaft(s) on a 1997 Nissan Navara (D21). This guide is written for a beginner mechanic — thorough but practical. Confirm your engine type first (look at engine code sticker: KA24E, KA24DE, Z24, etc.). Procedure and some parts differ between SOHC and DOHC engines; wherever a step differs I’ll note it.

SHORT THEORY / ANALOGY
- The camshaft is the mechanical “piano player” that tells each valve when to open and close. Its lobes push followers/rockers which open intake and exhaust valves at precise times so the engine breathes and fires correctly.
- It’s driven by the timing belt or chain tied to the crankshaft; if cam timing is off, valves and pistons aren’t synchronized — engine runs poorly, or valves hit pistons and get bent (like a badly-timed orchestra).
- Cam lobes and journals need clean oil and correct clearance. Excessive wear, broken bearings, or a snapped timing belt/chain are common reasons to service or replace the camshaft.

MAIN PARTS (what every component is and why it matters)
- Camshaft: a shaft with lobes (raised areas) that push valve train parts to open valves. Inspect lobes (wear = flat spots = lost lift).
- Cam journals: smooth bearing surfaces the cam rotates in. Scored journals cause oil pressure loss and binding.
- Cam followers (tappets/buckets/rocker arms): parts that sit between cam lobes and valves. They transfer motion. In SOHC the rocker arm is often present; DOHC uses bucket tappets.
- Valve stems & valve springs: return valves closed; weak springs cause float and poor sealing.
- Valve stem seals: prevent oil from running down the valve stems into the combustion chamber.
- Cam bearings (if separate): babbitt or pressed-in bearings that support cam journals in the block/head.
- Cam caps (bearing caps): bolt the camshaft into the head in the correct orientation and torque sequence.
- Sprocket/gears: attach to camshaft and connect to timing belt/chain.
- Timing belt/chain: ties cam to crank; belt/chain failure = major damage (if interference engine).
- Tensioner and guides (belt systems) or guides/tensioner for chain: keep belt/chain at correct tension and routing.
- Cam oil galleries and passages: internal lubrication passages that supply oil to lobes and journals.
- Valve cover (a.k.a. rocker cover): covers cam/valvetrain; gasket seals it to prevent oil leaks.
- Crankshaft and piston (not removed here but vitally linked): timing reference for cam; pistons can be hit if timing is wrong on an interference engine.

WHY YOU MIGHT NEED TO SERVICE THE CAMSHAFT
- Noisy valvetrain (ticking, knocking) from worn lobes, followers, or incorrect valve clearance.
- Low compression or misfire from worn cam lobes or damaged valves.
- Metal filings or sludge in oil or filter — cam/journal wear.
- Oil leaks from camshaft seals or valve cover gasket.
- Timing belt/chain failure, or worn tensioner/guides.
- Camshaft bearing failure (seizing, scoring).
- Over-advanced/retarded cam timing after previous work.

SAFETY & PREPARATION (don’t skip)
- Work on a flat surface; use jack stands — never rely on a jack alone.
- Disconnect negative battery terminal.
- Wear gloves and eye protection.
- Drain engine oil and (if needed) coolant if you'll remove the timing cover and disturbance to water passages may occur.
- Have a factory service manual (FSM) or reliable repair manual for your specific engine — it contains exact torque specs, timing marks, and sequences. I strongly recommend using it for torque numbers and any engine-specific steps.

TOOLS & PARTS NEEDED (basics)
- Complete metric socket set, extensions, wrenches, breaker bar.
- Torque wrench (essential).
- Screwdrivers, pliers, hammer, pry bar.
- Feeler gauges (for valve lash on adjustable systems).
- Camshaft locking/holding tool or equivalent (if available for your engine).
- Timing belt/chain kit (new belt/chain, tensioner, guides, sprockets if worn).
- New camshaft seals (front and rear), valve cover gasket, valve stem seals if removing buckets.
- Assembly lube for cam lobes/journals.
- Clean rags, solvent for cleaning parts.
- New engine oil and oil filter (change oil if metal debris detected).
- Service manual for torque specs and timing marks.

GENERAL STEP-BY-STEP (SOHC/DOHC notes included)
This is the standard flow. Do NOT skip marking timing positions and recording the order of disassembly.

1) Verify engine & set engine to top dead center (TDC)
- Remove spark plugs for easier rotation.
- Rotate engine by hand (socket on crank pulley) to TDC for cylinder 1 on compression stroke. Confirm using timing mark on crank pulley aligning with head/timing cover mark. Also check camshaft timing marks and document their positions (take photos).

2) Remove obstructing components
- Disconnect battery negative.
- Remove air intake, intake tubing, any accessories in the way (alternator belt can often remain but remove if obstructing).
- Remove valve cover(s) (six to eight bolts typically). Note and label any hoses or vacuum lines removed.
- Drain oil if you’ll be opening oil passages or plan to replace seals (recommended to refill after).
- Remove timing cover(s) (upper/lower) to expose timing belt/chain and sprocket(s). For chain systems you may need to remove additional front covers.

3) Secure TDC & mark timing components
- With engine at TDC, mark the relative positions of crank sprocket and cam sprocket(s) with paint/marker. Take clear photos. This is critical — if you reassemble wrong, pistons and valves will collide on an interference engine.

4) Release tensioner and remove timing belt/chain and cam sprockets
- On belt systems: release tensioner to slacken belt, slide belt off cam sprocket(s). Do not rotate crank or cam after belt is off — keep marks aligned.
- On chain systems: remove chain tensioner and guides as per manual, then lift chain off cam sprockets. Keep chain alignment marks.

5) Remove cam caps/cam retaining bolts in sequence
- Loosen cam cap bolts gradually in the correct sequence (usually from ends toward center or follow FSM). Caps are machined and must remain in their original orientation and positions. Number and bag each cap and bolt in order. Do NOT pry camshaft out by force.
- Lift camshaft(s) straight up once caps are removed. Keep cams level to avoid damage.

6) Inspect removed components
- Cam lobes: smooth and rounded with correct profile. Faults: flat spots, pitting, scoring, discoloration (overheating).
- Journals: smooth; scoring or galling is bad.
- Followers/rockers: wear at contact surfaces, cracks or broken tips are bad.
- Cam bearings/caps: look for uneven wear or embedded debris.
- Timing sprockets: worn teeth, elongated bolt holes.
- Oil passages: clear of metal slurry; sludge indicates poor maintenance.

7) Replace parts as needed
- If cam lobes/journals are worn beyond spec, replace camshaft.
- Replace camshaft seals, belt/chain, tensioner, guides, valve cover gasket, and ring seals as preventive measures.
- If cam bearings or caps are damaged, address per FSM (may require machining or replacement).

8) Install new (or inspected) camshaft
- Clean bearing surfaces and apply assembly lube to journals and lobes.
- Place camshaft in correct orientation. Make sure dowel pins/locator fits match.
- Fit cam caps in original order and orientation. Tighten bolts in multiple stages following manufacturer torque sequence. If you don’t have exact values, tighten progressively and check manual for final torque. DO NOT over-tighten; under- or over-torque causes bearing damage.
- If cam gear/sprocket was removed, install with timing marks aligned.

9) Reinstall timing belt/chain with correct tension and timing
- Put belt/chain on cam sprocket(s) and crank sprocket, keeping marks aligned. Apply correct tension per manual. On belt systems, commonly tighten tensioner then rotate crank twice and recheck marks and tension.
- On chain systems, ensure tensioner preload is correct and that guides are fitted.

10) Re-check and adjust valve clearances (if applicable)
- For adjustable lash systems (screw-and-nut, shims over bucket types vary): set clearances per FSM when engine at correct position. For hydraulic lifters (self-adjusting) they typically don’t require lash adjustment but must be inspected.

11) Final reassembly
- Reinstall timing cover(s), valve cover with new gasket, intake parts, accessories.
- Refill oil (change filter if metal noted) and coolant if disturbed.
- Reconnect battery.

12) Initial start & checks
- Crank engine and verify it starts and idles. Listen for unusual knocks/ticks.
- Check for oil leaks at cam seals, valve cover, and timing cover.
- Let engine reach operating temperature; recheck timing marks/valve clearance if necessary.
- After 50–100 miles, re-torque accessible fasteners as per FSM and recheck belt tension.

INSPECTION CRITERIA & MEASURING
- Cam lobe lift: measure with micrometer or compare lobes against spec or between lobes; flats or reduced lift = replace cam.
- Journal diameter & roundness: measure vs spec; out-of-spec means regrind or replace.
- Valve spring free length and pressure: springs lose tension with age — replace if weak.
- Oil passages: flush if clogged; metal debris means full oil system flush and filter replacement.

COMMON THINGS THAT GO WRONG (and how to avoid them)
- Incorrect timing reassembly → bent valves or catastrophic engine damage. Avoid: mark parts, take photos, don’t rotate crank/cam after marks removed.
- Mixing up cam cap order/orientation → rapid bearing failure. Avoid: label caps and bolts; reinstall in same position and order.
- Improper torque sequence/values → warped caps, seized cam, or oil leakage. Avoid: use torque wrench, follow FSM torque sequence and values.
- Not replacing tensioner/guides with belt/chain → premature failure. Avoid: replace when you have access.
- Not using assembly lube on new cam → initial dry wear. Avoid: coat lobes and journals with assembly lube.
- Forgetting to replace cam seals → oil leak after assembly. Avoid: always replace seals when cam removed.
- Not checking valve clearance after reassembly → noisy valvetrain and poor performance. Avoid: adjust lash as specified after timing set.
- Metal shards in oil after removal → indicates internal wear. Avoid restarting engine without thorough cleaning and replacing oil/filter.

TROUBLESHOOTING SYMPTOMS
- Ticking noise and loss of power: check valve clearances, worn lobes, weak springs.
- Oil pressure drop: scored journals or blocked oil passages.
- Engine will not start after reassembly: timing marks off; verify TDC and alignment.
- Rough idle/misfire: valve timing off, bad cam sensor (if equipped), damaged valves.

FINAL TIPS
- Get the factory service manual for your exact engine code before starting. It contains critical specs.
- Replace the timing belt/chain and tensioner when you have the cam out — it’s good preventative maintenance.
- Keep everything extremely clean. Dirt plus soft bearing surfaces = quick failure.
- Take many photos during disassembly so you can reassemble exactly.
- If you find severe cam/journal damage or metal in oil, consult a machinist or engine rebuilder — often better to replace the head or engine.

This covers the why, how, every major component, and what commonly goes wrong. Follow the FSM for torque numbers and engine-specific timing procedures. Good luck; work methodically and don’t rush.
rteeqp73

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