Goal: remove, inspect, repair or replace, and reinstall the crankshaft on a Toyota 2H / 12H-T engine — explained step‑by‑step for a beginner mechanic with the theory, the parts you’ll touch, what tools and measurements matter, and common failure modes. Follow the factory service manual for exact torque values, clearances and part numbers.

Key theory (why the crankshaft matters and why you’d repair it)
- The crankshaft converts the pistons’ back‑and‑forth motion into rotation to drive the transmission and accessories. Think of the crank as the engine’s spine and the pistons as people pushing on seesaws (connecting rods). The crank converts those pushes into a smooth spin.
- The crank rides in bearings (main bearings) and each connecting rod attaches to a rod journal with its own bearing. Oil keeps the bearings separated from the crank surface. If bearings wear, fail, or oil supply is interrupted, the crank journals can be scored, worn, or even cracked.
- Symptoms that indicate crank/ bearing work is needed: loud knocking from the bottom end, low oil pressure, metal filings in the oil filter or pan, excessive crankshaft endplay (axial movement), sudden loss of power, engine vibration, or seized rod journals/pistons.

Major components you will see/handle (detailed)
- Crankshaft: main journals (ride in main bearings), rod journals (offset surfaces for connecting rods), counterweights (balance rotating assembly), fillets (stress relief at journal transitions), oil holes and passages (deliver oil to rod journals).
- Main bearing shells: split half‑shells that sit between crank journals and main bearing bores in the block. Typically steel backing with soft metal (Pb/Sn) layer.
- Thrust bearings/washers: control axial (back‑and‑forth) movement of the crank (endplay).
- Main bearing caps: heavy cast pieces bolted to the block that clamp the main shells around the crank.
- Main cap bolts/studs and dowel pins: clamp the caps and align them. Some bolts are torque‑to‑yield (replace).
- Connecting rods and rod bearings: connect pistons to rod journals.
- Pistons and wrist pins: come off with rods if you remove them.
- Flywheel / flexplate: bolted to rear crank flange; contains starter ring gear.
- Rear main seal (and front oil seal / harmonic balancer seal): seal oil at crank ends.
- Harmonic balancer (vibration damper): rubber/metal assembly bolted to the nose of the crank; often drives the timing gear or accessory drive.
- Timing gear/drive: on 2H/12H‑T (diesel OHV) the timing is gear driven; crank gear mates with cam and injection pump gears. Oil pump or oil pump drive may be gear‑driven from the crank.
- Oil pump: often driven by crank or intermediate shaft — must be removed/inspected.
- Bearing oil galleries and plugs: passages in crank and block for oil flow.
- Fasteners and alignment dowels: keep orientation and alignment.

Essential tools and consumables
- Factory service manual for procedures, torque specs and clearances.
- Basic tools: sockets, wrenches, breaker bar, torque wrench, extensions.
- Engine stand and hoist (recommended): work safer and get access.
- Harmonic balancer/gear pullers, press or arbor press, seal installer, flywheel holder.
- Plastigage, micrometer (0.01 mm or 0.0001 in), dial bore gauge or inside micrometer, dial indicator (for endplay), feeler gauges.
- Engine assembly lube, clean engine oil, solvents, lint‑free rags, compressed air for passages.
- New bearings, seals, gaskets, bolts (especially torque‑to‑yield), and possibly a new crankshaft or regrind service if journals are worn.
- Inspection tools: magnaflux (for cracks), straightedge, runout indicator if checking crank runout.

High‑level disassembly sequence (assumes engine on stand; in‑car is possible but harder)
1) Preparation
- Drain oil and coolant. Remove intake, exhaust, turbo (12H‑T), accessories, and wiring to access top and sides.
- Remove timing chest/front cover and note timing gear orientation and marks. Photograph everything; label fasteners and brackets.
- Remove valve cover(s) and rocker assembly if they prevent cylinder head removal.
- Remove cylinder head(s) if pistons/rods will be removed or if you need rod access. On an inline engine you may be able to remove lower parts without removing head, but it’s usually clearer to follow manual.
2) Remove ancillaries that bolt to crank
- Remove harmonic balancer / vibration damper from nose (use puller).
- Remove timing gears/chain and front timing cover. Mark gear timing before removal.
- Remove oil pump and any drive gears attached to crank nose.
- Remove flywheel/flexplate (support it and remove bolts).
3) Lower end teardown
- Remove oil pan (keep track of any magnets with debris).
- Remove oil pickup tube if it blocks main cap removal.
- Mark each main cap with its corresponding position and orientation (use numbers and arrows facing front). NEVER mix caps or flip them.
- Loosen main cap bolts evenly and remove caps one at a time. Keep caps in order.
- Lift crankshaft out carefully (heavy). Avoid dropping or nicking journals. Keep clean surfaces.
- If keeping rods attached to pistons, remove rod caps in numbered order and push pistons up and out of cylinders (support them on a clean surface).
4) Clean and initial inspection
- Inspect bearing shells for scoring, embedded metal, heat discoloration (blueing).
- Check oil pan and pickup for metal shavings.
- Inspect main bores in block for ovality or scoring with dial bore gauge.
- Inspect rod bores and pistons for damage.
- Thoroughly clean oil passages and block; blow out galleries with compressed air.

Measurements and inspection (how to decide repair vs replace)
- Journal diameters: use micrometer to measure each main and rod journal. Compare to factory specs and consecutive measurements to find taper or out‑of‑round. If beyond limit, crank needs grinding/regrinding or replacement.
- Main bore diameters: use dial bore gauge to measure each main bore for wear, taper, or oval. If mains are worn past service limit, block line‑boring or replacement is needed.
- Bearing clearances: use plastigage or calculation from measurements. Plastigage gives quick check: place a strip across journal, torque cap to spec, rotate crank, remove cap and measure flattened width to get clearance. Ideal clearances are in the manual.
- Crank runout and straightness: mount dial indicator on crank to measure bend/runout; if excessive, crank must be corrected or replaced.
- Endplay: install crank, temporarily torque center main cap(s) and use dial indicator to measure axial movement by prying the crank forward/back and recording travel. Compare to spec and inspect thrust bearings.
- Visual crack checks: magnaflux (flourescent dye) or dye penetrant to check for stress cracks, especially near fillets and counterweights.

Typical outcomes and fixes
- Normal wear within spec: replace bearing shells, clean, reassemble with correct torque and lube.
- Journals slightly scored but within regrind allowance: have crank reground to undersize and fit corresponding undersize bearings.
- Journals badly scored, hollowed, heat‑damaged, or cracked: crank must be replaced.
- Main bores worn beyond spec: block machining (line bore/align hone) or new block needed.
- Thrust bearing wear: replace thrust washers, check cause (improper assembly, misaligned torque converter or transmission input).
- Oil passage clogging: clean and flush; replace oil pump if scuffed/pitted.
- Harmonic balancer failure: replace damper; a failed damper can destroy front of crank.

Reassembly — key principles and steps
1) Cleanliness: block, crank, bearings and all mating surfaces must be impeccable. Any grit kills bearings fast.
2) Bearing orientation and caps: install new bearing shells in block and caps in correct orientation. Match oil hole/slot alignment. Make sure bearings are fully seated.
3) Lubrication: coat bearings and journals with assembly lube before initial startup.
4) Torque sequence: snug main cap bolts in stages in the factory sequence (usually center outward) and torque in multiple steps to final spec. If bolts are torque‑to‑yield, use new bolts.
5) Check crank rotation: after final torque, rotate crank by hand. It should spin smoothly with slight resistance from lube.
6) Check endplay: measure and fit correct thrust washers if required.
7) Install rear and front oil seals properly using a driver to seat without nicking.
8) Reinstall timing gear(s) and set timing marks exactly. If gear train changed, cam timing will be wrong and engine will run poorly or be damaged.
9) Reinstall oil pump and prime it (fill pump and oil galleries with oil or use pre‑lubing tool) before first start. On diesels, crank until oil pressure builds before starting.
10) Final assembly: torque flywheel and harmonic balancer, torque rod caps in sequence, reassemble oil pan, manifolds, turbo (12H‑T), and all accessories.

Startup and break‑in checks
- Before starting: crank engine until oil pressure shows (crank with starter but do not start, if safe) to ensure bearings get oil.
- On first start: watch oil pressure, engine noise, leaks. Run at low load and moderate rpm for a prolonged warm‑up. Do not rev.
- Recheck torque on accessible fasteners per manual after initial heat cycles if recommended.
- Change oil and filter after first few hours of run‑in to remove break‑in debris.

Common mistakes and what goes wrong when you don’t follow the rules
- Reusing old bearings or bolts that are stretch‑type — leads to premature failure and loss of clamp load.
- Mixing up main caps or flipping them — causes misalignment and rapid wear.
- Incorrect bearing clearance (too tight = seizure; too loose = low oil pressure and knock).
- Dirt/metal in oil passages during assembly — oil starvation and bearing failure.
- Damage to journals from careless handling; nicks and scratches embed into bearings.
- Incorrect torque sequence or under/over‑torquing — main cap distortion or bolt failure.
- Incorrect timing gear reassembly — poor engine timing, possible valve/piston contact on interference engines (diesel 2H is generally non‑interference but follow manual).
- Not priming oil pump — dry start causing immediate bearing damage.
- Failing to replace the harmonic balancer or flywheel bolts if specified — catastrophic loosening.

Analogy recap (to remember roles)
- Crankshaft = central axle/spine that converts seesaw pushes into rotation.
- Main bearings = bearings on the axle where it rides in the block (like wheel hubs with thin linings).
- Rod bearings = small bushings where connecting rods attach (like the pivot at each seesaw fulcrum).
- Oil = the thin cushion of water under a boat that keeps the hull from scraping the dock — too thin or gone and metal meets metal.

Final notes and cautions (be safe and accurate)
- Always use the factory service manual for that engine for torque values, clearances, and sequences. If you don’t have it, obtain it before starting.
- Work on a clean bench or engine stand. Label everything. Photograph as you disassemble.
- If you’re unsure about journal measurements or regrinding, consult a reputable machine shop for crank inspection and grinding. Have them check runout and balance after any correction.
- Safety: heavy parts, solvents, and compressed air can be hazardous. Use lifting gear, eye protection, and gloves.

That covers the why, the parts, step‑by‑step disassembly/reassembly flow, measurements, what can go wrong, and safety reminders. Follow the manual’s specs precisely for clearances and torques; the procedure above gives the practical sequence and checks a beginner needs to do the job correctly.
rteeqp73

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- Quick overview
- The oil temperature sensor (oil temp sender) on Toyota 2H / 12H‑T engines is an electrical probe screwed into the engine oil gallery or oil filter housing. You do not “oil” the sensor; the normal actions are inspect, clean, lubricate the electrical connector, and replace or reseal the sensor if it’s leaking or giving bad readings. Below are step‑by‑step bullets for a beginner, including every tool, why it may be needed, and how to use it.

- Safety first (read & follow)
- Work only on a cold engine to avoid burns from hot oil and metal.
- Wear safety glasses and gloves.
- Disconnect the negative battery terminal before unplugging sensors to avoid short circuits.
- Have a drip tray and rags ready for spilled oil.
- If you must raise the vehicle to access the sensor, use jack stands on solid ground — never rely on a jack alone.

- Tools you need (with detailed descriptions and how to use each)
- Socket set (metric) with ratchet and extensions
- Purpose: remove the sensor if it is recessed or needs a socket to access.
- Use: pick the correct deep socket size that fits the hex on the sensor, fit the ratchet and extension if tight space, turn counterclockwise to break free. Use steady force; avoid cheater bars on small ratchets.
- Open‑end / flare nut wrenches (metric)
- Purpose: handy for sensors with a visible hex where a socket can’t fit; flare nut wrenches grip more faces to avoid rounding.
- Use: place wrench fully over the sensor hex and turn counterclockwise; keep steady force and don’t slip.
- Adjustable wrench (crescent)
- Purpose: backup if fixed‑size wrench isn’t available; less ideal because it can slip and round corners.
- Use: set jaw tight on hex and turn carefully.
- Penetrating oil (e.g., PB Blaster, WD‑40 Specialist)
- Purpose: frees seized or corroded threads.
- Use: spray around sensor base, let soak 10–20 minutes (longer if very rusty), then attempt removal.
- Wire‑terminal pick / small flat screwdriver
- Purpose: release plastic wiring connector clips gently.
- Use: depress the locking tang while pulling the connector straight off; be gentle to avoid breaking the plastic.
- Dielectric grease
- Purpose: protects electrical connector from moisture and corrosion after reconnection.
- Use: put a thin smear inside the connector, not on sensor probe itself.
- Anti‑seize compound (thread lubricant)
- Purpose: prevents threads from seizing in the engine block and eases future removal.
- Use: apply a thin coat to the sensor threads before installing. Don’t contaminate the tip of the sensor with anti‑seize if the manufacturer warns against it; avoid getting anti‑seize into the oil passages.
- Torque wrench (metric, low range, e.g., 5–50 Nm)
- Purpose: tighten the sensor to correct torque without over‑tightening and damaging the sensor or block threads.
- Use: set torque to manufacturer spec (see note below) and tighten until the wrench clicks. If you don’t have the spec, tighten snugly — about 10–20 Nm for small sensors — but using a torque wrench is strongly recommended.
- Multimeter (digital)
- Purpose: test the sensor for correct resistance or voltage before and after installation.
- Use: set to ohms (Ω) to measure resistance across sensor terminals; or volts to check signal output while engine warms (consult sensor type).
- Small container/drip tray and rags
- Purpose: catch any oil that leaks while sensor out and keep the area clean.
- Use: place under sensor, use rags to wipe oil and clean threads.
- Small wire brush / brass brush
- Purpose: clean the sealing surface and threads if corroded.
- Use: brush gently, then wipe clean with a rag.
- Heat source (propane torch) — optional, only for severely seized sensors
- Purpose: heat the area to expand metal and free stuck threads.
- Why extra tool required: seized sensors sometimes need heat if penetrating oil fails.
- Use: heat carefully, avoid heating near fuel or plastics; let cool briefly and reattempt removal. If uncomfortable with heat, choose a shop.
- Extractor (left‑handed thread extractor) and thread repair kit / helicoil — optional
- Purpose: for a broken sensor stud or badly damaged threads.
- Why required: if sensor snaps, you’ll need an extractor to remove the broken stud and possibly a helicoil to repair the thread.
- Use: these are advanced repairs; if you need these, consider a machine shop unless experienced.

- How to locate the oil temperature sensor (general guidance)
- The oil temp sensor on H‑series engines is typically near the oil filter housing, oil cooler lines, or screwed into the block/pan. It’s usually a brass body with a hex head and a 1‑ or 2‑pin electrical connector.
- Clean surrounding area before disconnecting to prevent dirt falling into oil passages.

- Step‑by‑step procedure (for inspection, lubricating connector, testing, and replacement)
- Prepare
- Park on level ground, engine cold, parking brake on.
- Place drip tray under engine area where sensor is located.
- Disconnect negative battery terminal.
- Access and clean
- Clean the sensor and surrounding area with a rag and small brush to remove dirt and oil.
- If access is restricted, remove any obstructing components as needed (note: you may need basic hand tools or to remove an intake hose — only remove what you can confidently reinstall).
- Disconnect the electrical connector
- Use a pick or small screwdriver to depress the connector clip and pull the connector straight off.
- Inspect the connector for corrosion or bent pins.
- Apply a small amount of dielectric grease in the connector and on the pins to protect against corrosion.
- Test the sensor in situ (optional, recommended)
- With the connector off, use a multimeter to measure resistance across the sensor terminals (or between terminal and ground) — compare to expected behavior: most oil temp sensors change resistance with temperature (you can verify by warming sensor in hot water and watching resistance change). If you cannot find exact resistance values for your sensor, look for a measurable change when warmed vs cold. No change or open circuit = faulty.
- Remove the sensor
- Spray penetrating oil around base if it looks corroded; wait 10–20 minutes.
- Fit the correct deep socket or wrench to the hex head.
- Turn counterclockwise steadily until it loosens. Use an extension or universal joint if recessed.
- Catch any dripping oil in your drip tray.
- If it won’t budge after penetrating oil, try heating the area with a torch carefully or seek a shop to avoid damaging threads.
- Inspect sensor and hole
- Check sensor tip for contamination, physical damage, or broken threads.
- Check the engine port for old sealant or debris; clean with a rag/brush.
- Decide on repair vs replacement
- If sensor reads incorrectly on the multimeter (no continuity, erratic or no response), replace it.
- If sensor leaks (oil around connector or threads) or threads/seal is damaged, replace it.
- If sensor is just dirty but otherwise electrically sound and unbroken, you can reinstall after cleaning.
- Install (reused sensor) or install new sensor
- Apply a thin smear of anti‑seize to the sensor threads (avoid the sensing tip).
- Screw sensor in by hand until seated, then tighten with a wrench.
- Torque to manufacturer spec. If you do not have a spec, tighten snugly and do not over‑torque (using a torque wrench is preferable).
- Reconnect electrical connector (apply dielectric grease inside connector first).
- Test after installation
- Reconnect negative battery.
- Start engine and let it idle, watch for oil leaks around sensor.
- Use the dashboard gauge or a scan tool to observe oil temperature reading; compare to expected behavior (should gradually rise as engine warms).
- If you have a multimeter and the sensor provides a voltage signal, check voltage change with temperature if needed.
- Final cleanup
- Wipe up any spilled oil, properly dispose of oily rags.
- Tighten any removed components and remove jack stands if used.

- Signs replacement is required and why
- Replace the sensor if:
- No electrical response when warmed/cooled (open circuit).
- Erratic or false readings on gauge or ECU.
- Visible damage, corrosion, or leaking oil from sensor body or connector.
- Broken or rounded hex that can’t be reused.
- Why replacement matters:
- A faulty oil temp sensor can cause incorrect dash readings, affect engine control (if ECU uses the signal), and lead to misdiagnosis of engine temperature problems.
- Leaks can allow oil loss and contamination.

- What replacement part to buy
- Get the correct oil temperature sensor for the Toyota 2H / 12H‑T engine: ask Toyota parts department or reputable diesel parts supplier for “oil temperature sender/sensor” for your engine model and year.
- Buy OEM or quality aftermarket with matching:
- Thread size and pitch
- Electrical connector type (1‑pin or 2‑pin)
- Temperature range and electrical characteristics
- If unsure, take the old sensor to the parts counter to match physically.

- Common extra tools and why you might need them
- Universal joint and deep socket: if sensor is in a recessed or awkward angle.
- Heat torch: if sensor is seized and penetrating oil alone fails (use caution).
- Extractor / thread repair kit: only if sensor breaks off or threads are stripped — this can become a complex repair and may need a machine shop.
- Diagnostic scan tool: to read ECU fault codes or live oil temp values (useful if your dash doesn’t show an oil temp gauge).

- Quick troubleshooting notes (no fluff)
- Sensor shows no change with temperature → likely failed electrically → replace.
- Oil leak at sensor when tightened → bad seal or damaged threads → replace and inspect threads.
- Sensor difficult to remove → use penetrating oil, proper socket, and heat if necessary; avoid rounding head.

- Final tips
- Don’t overtighten sensor — brass sensors and aluminum blocks can strip.
- Use anti‑seize on threads for future removals and dielectric grease on connector for corrosion protection.
- If you’re unsure about removing a seized sensor or repairing damaged threads, take the vehicle to a professional — removing broken studs or repairing block threads can be difficult without experience.

Done.
rteeqp73