Short, practical overhaul guide for the timing/drive gear set on a Toyota 4Y (beginner‑friendly). This covers what each component is, why you do the job, how the system works, step‑by‑step teardown and rebuild guidance, measurements to check, and common failures. Read the factory service manual for your exact model and VIN for torque specs, tolerances, and special tools — I give typical guidance and safety notes, not absolute spec replacements.

Why overhaul the gear set (theory and symptoms)
- Purpose: The gear set (crank gear, idler/intermediate gear(s), cam gear) times the cam to the crank so valves open/close in precise relation to piston position. It also transmits drive to oil pump/other ancillaries in some layouts.
- Why it fails: Wear (tooth profile wear/pitting), oil contamination, lack of lubrication, broken keys, excessive endplay/backlash, bearing or bushing wear, or impact damage. Worn gears cause timing drift, noise (grinding/whine), poor running, misfires, loss of power, and potentially catastrophic internal damage if timing changes.
- Analogy: Imagine two combs meshed together driving a third comb — if the combs’ teeth round off or the shafts wobble, the rhythm (timing) slips and the whole machine runs rough or collides.

Main components — what they are and what they do
- Crank gear (drive gear): Mounted on the crank snout, smallest gear. Transmits rotation to idler and cam gears and often drives oil pump or distributor drive. Usually steel, press‑fit or bolted on.
- Idler/intermediate gear (if present): Between crank and cam; changes gear direction or ratio and supports lubrication path. Typically rides on a journal/bushing or bearing in the front cover or block.
- Cam gear: Larger than crank gear (typically 2:1 ratio on 4‑cyl OHV) mounted on camshaft nose. Controls cam timing.
- Gear key / Woodruff key: Locates gear on shaft to prevent slippage.
- Camshaft: Runs in bearings; its nose accepts the cam gear.
- Front cover / timing cover: Houses gears, seals, and provides bushing/bearings for idler/cam. Holds oil and keeps contaminants out.
- Oil seal (front crank and sometimes cam): Prevents oil leakage at shaft exits.
- Bearings/bushings: Support axial and radial loads for idler/cam. Wear here increases backlash.
- Bolts/fasteners: Gear bolts, cover bolts — must be inspected and torque‑rated.
- Timing marks: Dots/lines on gears used to set timing.

Tools and parts you’ll need (summary)
- Factory service manual (specs and procedures)
- Basic hand tools + sockets, wrenches
- Torque wrench
- Gear puller or press (for cam/crank gears if pressed)
- Camshaft holding tool / method to prevent rotation
- Dial indicator with magnetic base for backlash and endplay measurement
- Feeler gauges or plastigage (for certain clearances)
- Micrometer/calipers (for gear tooth/shaft wear)
- Shop press (if you’ll press on/off gears or bushings)
- New replacement gears (OEM preferred), new gaskets, front cover seal(s), new bolt(s) if one‑time torque bolts are used
- New idler bushing/bearing(s) if worn
- Clean engine oil / assembly lube, gasket sealant
- Safety gear: gloves, eye protection

Safety first
- Disconnect battery. Drain engine oil and (if needed) coolant. Support the vehicle safely if you need to get under it. Label and bag small parts. Avoid working with crank rotated unless at TDC and secured.

High‑level procedure (read fully before starting)
1) Prepare and remove accessories
2) Set engine to TDC for cylinder #1 compression stroke
3) Remove timing cover and front accessories to expose gears
4) Mark timing positions before disassembly
5) Remove cam gear/bolts, idler gear, crank gear as needed
6) Inspect and measure components; replace worn parts
7) Install new/inspected parts with correct clearances and torque
8) Set timing marks and verify backlash/endplay
9) Reassemble, refill fluids, run and check for leaks/noises

Detailed step‑by‑step (expanded, for a beginner)
A. Preparation
- Disconnect battery negative. Drain oil (and coolant only if removing water pump/front cover which contacts coolant).
- Remove fan, fan shroud, belts, crank pulley/harmonic balancer. Many 4Y jobs require removal of crank pulley/harmonic balancer to get to crank gear.
- Remove valve cover and rocker assembly if needed to access cam bolt or to set TDC by observing rocker movement.
- Clean area to prevent contamination.

B. Set engine to TDC, #1 compression stroke
- Rotate engine by wrench on crank pulley bolt until #1 piston is at TDC on compression stroke (both intake and exhaust valves closed). Confirm by watching valves or using timing marks. This is the reference for reassembly.

C. Mark timing and take photos
- Before removing any gear, mark the relationship of the crank, idler, and cam gears with paint/marker, and take photos for reference. Also note any timing marks stamped on gears.

D. Remove timing cover and front components
- Unbolt and remove timing/front cover. Be prepared for oil spillage. Inspect inside for metal flakes or scoring — severe scoring indicates deeper engine damage.
- Remove idler gear retaining bolt/fastener and slide idler out. If idler rides on a bushing press, you may have to press it out of the cover or block.
- Remove cam gear bolt. On some engines the cam gear is pressed on; use a gear puller or press to remove it. Hold the cam from turning while loosening cam bolt (use method in manual).
- Remove crank gear if it’s removable. Some crank gears are pressed and require a puller. Keep the crank stationary with suitable tool.

E. Inspect components carefully
- Gears: Check teeth for wear, pitting, chatter marks, chipped teeth, or rounded profiles. Worn teeth change tooth form and timing.
- Keys: Inspect Woodruff key for deformation. Replace if damaged.
- Gear bores/shafts: Check bore for fretting and wear. Measure shaft journals with micrometer.
- Bushings/Bearings: Examine idler bushing for wear ovality. Replace bushings if excessive clearance or scoring.
- Backlash and pitchline wear: Use calipers or micrometer to compare old and new gears; check manufacturer wear limits.
- Timing cover: Inspect the bore where idler/bushing sits. Too much wear means cover must be replaced or reamed and fitted with oversized bushing.

F. Replace parts as necessary
- Always prefer new OEM or high‑quality aftermarket gears and bushings. If an idler bushing is worn, replace it and install in cover (press fit). If camshaft nose shows wear, camshaft replacement or repair may be necessary.
- Replace front crank/cam seals and any gaskets.

G. Reinstallation — the critical bits
- Clean everything. Lightly coat new gear bores and shafts with assembly lube.
- Install idler bushing into cover with press or driver, to correct depth per manual. Lubricate.
- With engine at TDC #1, reinstall cam gear aligning timing marks (use photos/marks you made). Slide cam gear onto cam nose, aligning timing marks exactly. Use that point as reference — if the cam gear is mounted with key, ensure key seats in both gear and shaft.
- Reinstall idler gear (align marks). Ensure it meshes cleanly; no forced engagement.
- Reinstall crank gear. If pressed, use a proper press or driver and avoid hammering directly on gear face; use a sleeve to press on gear bore to avoid damage.
- Tighten cam gear bolt to specified torque in manual. If bolt is stretch/torque‑to‑yield type, replace it with a new bolt if required. Use correct torque pattern and possibly threadlocker if specified.
- Confirm timing marks: rotate engine two full turns by hand and recheck marks at TDC. The marks should realign exactly. If not, disassemble and correct.
- Check gear backlash: with a dial indicator mounted on cam gear face, pry gear back and forth to measure rotational clearance between teeth; compare to manual. Typical small engine gear backlash may be a few thousandths of an inch (0.003–0.010 in) but get exact spec from manual.
- Check endplay/axial movement of camshaft and idler (use dial indicator). Replace shims or bushings to correct endplay if out of spec.
- Replace front cover gasket and seals; torque cover bolts to spec. Install new crank front seal.
- Reinstall crank pulley/harmonic balancer, belts, accessories.

H. Fluids, prime oil, and first start
- Refill engine oil and coolant. Prime oil system if possible (turning oil pump with priming tool or cranking without starting briefly) to avoid dry start on cam/bearing surfaces.
- Start engine and listen for unusual gear whine or knocking. Initially, a faint new gear whine may be normal and should quiet after warm up; loud clatter indicates a problem — shut down and recheck.
- Check for leaks around front seal and cover.

Measurements and tolerances to check (always get exact numbers from manual)
- Gear backlash (tooth clearance): Use dial indicator to measure lash between meshing gears.
- Camshaft endplay (axial): Dial indicator on cam flange.
- Idler bushing clearance: measure bore vs shaft.
- Shaft journals and gear bores: measure for wear and compare to new parts’ service limits.
- Torque specs: Cam bolt, crank pulley bolt, cover bolts. Use factory values.

Common things that can go wrong and how to avoid them
- Mis‑timing on reassembly (marks not aligned): Causes rough running, lost power, valves open at wrong time. Avoid by marking before disassembly and verifying alignment after two full rotations.
- Damaged teeth from using improper puller or hammering: Use proper gear pullers/presses; never hit gear faces.
- Using the old key or a damaged key: Replace the Woodruff key if worn; a sheared key can cause slip.
- Improper torque or reused stretch bolts: Use new bolts where specified; follow torque sequence.
- Incorrect bushing installation (depth or orientation): Press to correct depth; use manual’s instructions.
- Not checking for cover bore wear: Installing new bushing into worn cover will fail quickly. Replace or rebush cover if necessary.
- Dry start after rebuild: Can damage cam lobes and bearings. Prime the oil system; crank engine with fuel cut if you can to build oil pressure before starting.
- Contamination introduced during reassembly: Clean all parts, use lint‑free cloths, cap oil passages.

Symptoms that indicate gear problems before overhaul
- Whining or gear grinding noise from front of engine
- Metallic knocking or clicking
- Oil contamination with metal flakes
- Timing irregularities: misfire, poor idle, rough running
- Excessive oil consumption or leaks at front seal (often from wear)

Troubleshooting quick reference
- Noise + metal flakes in cover → inspect gears and bearings, replace gears and bushings, inspect cam/crank for scoring.
- Timing marks misalign after rotation → incorrect assembly or damaged key/gear wear.
- Excessive backlash → worn gear teeth or bushings; replace and recheck.
- Persistent clatter after rebuild → camshaft journal or lobes not lubricated/installed, bolt torque wrong, or wrong parts.

Final checks and break‑in
- After first 20–50 miles (or hours for industrial use), recheck bolt torques, re‑inspect for leaks, and listen for persistent noise. Re‑check timing mark alignment if symptoms persist.
- Change oil after initial run‑in to remove any break‑in debris.

Bottom line checklist before you start
- Have factory manual and correct replacement parts.
- Use proper pullers/press and torque wrench.
- Mark timing and take photos.
- Measure backlash and endplay; replace worn bushings/gears.
- Prime oil before first start and recheck after initial run.

That’s the complete, practical overview for a gear set overhaul on a Toyota 4Y. Follow factory manual values exactly for torques and tolerances; if you don’t have the manual, get one (Toyota service manual / Haynes/Chilton are options).
rteeqp73

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Blown Head Gasket

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Tools & consumables (minimum)
- Metric socket/ratchet set (8–22 mm), extensions, universal joint
- Torque wrench (0–150 ft·lb / 0–200 N·m)
- Breaker bar
- Harmonic balancer / crank pulley puller
- Cam sprocket holder or strap wrench / impact or pry method to hold cam while loosening bolt
- Timing chain tensioner compressor/retainer tool (or equivalent pin/compression tool)
- Chain hook / wire to hold chain out of the way
- Small drift/punch, pin (for crank pin/TDC lock if required)
- Seal driver or suitable socket for crank seal
- Gasket scraper, brake cleaner or solvent, shop rags
- Drain pan, funnel
- Jack and stands (or lift), wheel chocks; engine support if motor mounts removed
- Safety gear: gloves, eye protection

Replacement parts (recommended)
- Timing chain kit: new chain, chain guides, chain tensioner (replace all)
- Cam & crank sprockets (only if worn/damaged)
- Front crankshaft oil seal
- Timing cover gasket and/or RTV sealant
- Valve cover gasket (if disturbed)
- Engine oil and filter (change recommended after work)
- Coolant (only if timing cover/water pump removed)

Safety & preparatory precautions
- Work on a level surface; chock wheels, set parking brake.
- Disconnect negative battery terminal.
- Drain engine oil and coolant if you remove timing cover/water pump. Collect fluids properly.
- Support the vehicle on jack stands or lift; never rely on a jack alone.
- If motor mounts are loosened, support the engine with a trans jack or engine support bar.
- Keep hands and clothing away from rotating parts.
- Follow torque and tightening sequences from the factory service manual for final tightening.

Overview of the procedure (sequence)
1) Prepare & access engine
2) Set engine to TDC #1 compression stroke and lock
3) Remove front accessories, belts, crank pulley/harmonic balancer
4) Remove timing cover; expose chain, guides, tensioner
5) Remove old chain, guides, tensioner, inspect sprockets
6) Install new chain, guides, tensioner with correct alignment/preload
7) Reassemble, torque to spec, rotate engine, final checks

Step-by-step procedure

1 — Prep & gain access
- Disconnect battery. Drain engine oil (recommended) and coolant if cover/water pump removal will open cooling passages.
- Remove radiator fan shroud, fan (if needed), accessory belts, alternator bracket or other obstructing components to get clear access to crank pulley and timing cover.
- Remove any engine covers and the valve cover only if needed to verify cam position/marks.

2 — Set engine to TDC (No.1 cylinder, compression stroke)
- Rotate engine by turning the crankshaft bolt clockwise with breaker bar until the timing mark on the crank pulley (or timing mark on flywheel/flexplate if visible) aligns with TDC. Confirm #1 cylinder is on the compression stroke by checking that both intake and exhaust valves are closed (feel cam lobe positions or observe rocker arms if valve cover removed).
- If the engine has a crank pin/TDC lock provision, insert the pin to lock the crank. If not, note exact position of marks. DO NOT rely solely on mark approximation — lock if possible.

3 — Remove crank pulley/harmonic balancer & timing cover
- Use breaker bar to loosen crank pulley bolt (hold cam sprocket so crank does not turn; use cam holder strap or apply parking pawl technique if manual trans).
- Remove bolt, then use harmonic balancer puller to remove pulley. The puller threads into the pulley and pulls it straight off the crank snout — follow puller tool instructions, turn center bolt to pull pulley evenly.
- Remove all bolts securing the timing cover; carefully pry cover loose (be prepared for residual oil) and remove cover, exposing chain, sprockets, guides, and tensioner.

4 — Document and mark alignment
- Photograph or mark the relative positions of the crank sprocket, cam sprocket(s), and chain with paint pen/marker. Confirm timing marks on sprockets align to the block/head marks at TDC. These marks are critical for reassembly.

5 — Remove tensioner and guides
- Retract tensioner: for mechanical tensioners, there is usually a lock pin or bolt. Compress the tensioner plunger with the tensioner compressor tool or vise carefully and remove retaining bolt/pin; then remove tensioner assembly. For ratcheting or hydraulic types, follow manual method — typically loosen and remove.
- Remove guide bolts and remove worn guides. Keep parts in order so you know which goes where.

How the tensioner compressor tool is used:
- The tool engages the tensioner body and uses a screw or clamping action to push the plunger back into its bore so you can remove/install the tensioner without damaging it. Compress the plunger fully, insert the retaining pin/bolt (or install the tensioner while compressed) and then remove tool. On installation, release the retainer so the tensioner can apply tension to the chain.

6 — Remove chain and sprockets (if replacing sprockets)
- Support chain so it doesn’t drop into the oil pan. Unbolt cam sprocket(s) while holding the cam so they don’t turn — use cam sprocket holder or strap around cam and hold with pry/vice to prevent rotation. Remove sprocket(s).
- Remove crank sprocket: it may slide off; if tight, a small two-jaw puller or mild heat on crank snout can help (be careful).

7 — Inspect components
- Inspect camshaft and crankshaft sprocket teeth for wear, chain stretch, guides for scoring, tensioner for proper operation. Replace any sprockets if tooth wear or damage is present. Replace all guides and the tensioner as a set for best longevity.

8 — Install new chain and components (alignment critical)
- Transfer new chain onto sprockets following kit marks: many kits have colored links that align to crank and cam timing marks. Match these links to the timing marks on the sprockets exactly — manufacturer instructions vary.
- Fit chain over crank sprocket first, then cam sprocket(s). Ensure arrows/marks on chain/sprockets are correctly oriented; chain slack should be on the non-tension side.
- Reinstall cam sprocket(s) and torque bolt(s) to factory spec. Use the cam holder to prevent turning while torquing.
- Install new guides and torque to spec.
- Install the tensioner: if required, compress the tensioner with the compressor tool and install the retaining pin/bolt. Then release the compression tool or remove the pin per the service procedure to allow the tensioner to apply preload to the chain.

9 — Verify timing & tension
- With tensioner installed and applied, rotate engine by hand (using a socket on the crank bolt) two full revolutions clockwise. This lets the tensioner settle.
- Re-align marks to confirm the crank and cam timing marks return to their original TDC positions. If not aligned, stop and re-evaluate.
- Check chain slack and guide contact; ensure tensioner is applying pressure correctly.

10 — Reassemble
- Replace timing cover gasket and install timing cover using new gasket or RTV per spec. Torque cover bolts to spec.
- Install new crankshaft front oil seal using a seal driver or appropriate socket — seat flush and evenly.
- Install harmonic balancer/crank pulley; torque crank bolt to factory specification. (If crank bolt is torque-to-yield, use new bolt per manual.)
- Reinstall belts, fan, alternator bracket, any other removed accessories. Refill engine oil (and replace oil filter if drained) and coolant (if drained). Reconnect battery.

11 — Start-up and final checks
- Start engine and listen for abnormal noises (rattles, knocks). A new chain/tensioner may make light noise briefly while seating — but no loud rattle.
- Check for oil or coolant leaks around timing cover, seals, and the valve cover.
- After warm-up, re-torque accessible bolts if required by manual. Reinspect timing marks after some runs or after 100–200 miles.

Common pitfalls & how to avoid them
- Failing to lock or correctly set TDC: always lock the crank or double-check marks; incorrect timing can cause poor running or damage.
- Reusing tensioner/guides/chain: these wear as a set — reuse increases risk of premature failure. Replace the full kit.
- Improper compression of tensioner or incorrect release order: use the proper compressor/retainer procedure — releasing too early or over-compressing can damage the tensioner.
- Not holding cam while loosening/tightening sprocket bolts: cam will rotate and timing will be lost; use proper holding tool or strap.
- Damaging crank seal during removal/installation of pulley: use a puller; install seal straight with the correct driver.
- Using incorrect torque values or sequences: always use factory torque specs — over- or under-torquing causes failures.
- Not rotating engine by hand to verify: always turn two full revolutions and recheck alignment before final assembly.

Notes about specs and service manual
- Torque specs and the exact method of tensioner lock/compression vary by engine revision. Use the Toyota 4Y service manual for exact torque numbers, bolt sequences, and tensioner pin procedures. If you don’t have the manual, get one or a reputable repair database before starting.

Done checklist before starting engine
- New chain/tensioner/guides fitted and tensioned correctly.
- Timing marks align after two full revolutions.
- All bolts torqued to spec.
- New seals/gaskets installed and fluids refilled.
- No loose tools or rags left in engine bay.

Follow this procedure methodically, use the tensioner compressor tool to compress/lock the tensioner during install, and replace all wear items (chain, guides, tensioner, seals). That approach minimizes risk and gives long service life for the timing system.
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