Short upfront: I’ll explain what main bearings are and why they fail, describe every part you’ll touch, and give a clear, step‑by‑step procedure with measurement and inspection techniques a beginner can follow. Do not skip getting the Toyota 2Z factory service manual (FSM) for exact torque specs, bearing part numbers, and clearances — those are engine‑specific and critical.

What main bearings do (analogy + theory)
- Analogy: the crankshaft is a spinning axle and the main bearings are the soft “socks” and “pillows” that let it spin smoothly inside the block while keeping it centered. They create a controlled thin film of oil that carries the load so metal doesn’t rub metal.
- Theory: main bearings are shells (upper and lower halves) that line the engine block’s main journals. When the crank spins, oil pumped under pressure forms a hydrodynamic film between journal and bearing. Proper oil pressure + correct clearance = full fluid film lubrication. Too little oil, too much clearance, bearing damage or debris break the film and you get metal contact, heat, and knocking.
- Thrust bearings control axial (end‑to‑end) movement of the crank; if they’re worn, the crank moves too far forward/back and can damage seals, timing components, and cause chatter.

Components you will see and what each does
- Cylinder block main bores: machined seats in the block for the upper bearing shells.
- Main bearing shells: two half shells per journal (upper shell pressed into block, lower shell installed in cap). They have oil grooves on some positions and a locating tang to fit into a notch.
- Bearing cap(s): heavy machined caps that bolt the crank into the block; they clamp the lower bearing shells against the crank journals.
- Main cap bolts or studs & nuts: clamp the cap to the block and carry preload. They often require replacement or stretch-checking if torque‑to‑yield.
- Crankshaft and main journals: the shiny surfaces the bearings ride on.
- Thrust bearing (or thrust surfaces on main shells/cap): flat surfaces/shells that accept axial loads and limit crank endplay.
- Oil galleries/passages and oil holes in bearings: carry oil from the pump and galleries to the bearing clearance. Bearings must align their oil holes with block oil passages.
- Oil pump: supplies pressure; if it fails, bearings starve.
- Oil pan and pickup: collect and supply oil to pump; pickup gasket/clogging can cause starvation.
- Rear and front main seals: seal crank at ends — damaged by excessive endplay.
- Plastigauge (clearance measuring) or micrometer/telescopic gauges: measuring tools.
- Dial indicator: measures crank endplay.
- Assembly lube: sticky lubricant used to protect bearings on first start.
- Torque wrench, engine hoist/stand (if you pull engine), basic hand tools, cleaning solvents, lint‑free rags.

Symptoms that indicate main bearings need attention
- Loud deep knocking from bottom end, worse under load.
- Very low oil pressure (bearing clearance up or pump worn).
- Metallic particles in oil, oil filter, or on magnetic drain plug.
- Excessive crank endplay (thrust wear) or visible scoring on journals.
- Bearing material embedded on crank journals or caps.
- Rapid oil pressure drop at idle after start.

Common failure modes (what goes wrong)
- Oil starvation: clogged pickup, low oil, pump failure, or long cranking without oil.
- Contamination: dirt/sludge or metal flakes score bearings.
- Overheating: oil breakdown, bearing glazing, seizure.
- Misassembly: wrong bearing orientation, wrong bearing type (use correct ID), improperly torqued caps, dirt under bearings.
- Out‑of‑spec journals: worn or scored journals requiring crank grinding or replacement.
- Thrust wear from clutch/flywheel misuse or incorrect installation.

Tools, parts, consumables you’ll need
- Toyota 2Z FSM (mandatory for torque, clearances, sequences).
- Full metric socket set, torque wrench (capable of required torque range), breaker bar, feeler gauges, screwdriver set.
- Plastigauge (various sizes) or micrometers/inside micrometer and telescopic gauges to measure journal and bearing ID.
- Dial indicator with magnetic base.
- Engine hoist and stand (recommended if you plan to fully rebuild).
- Assembly lube, engine oil, new oil filter, new gaskets (pan, seals), RTV as required.
- Replacement main bearings (OEM or quality aftermarket), thrust bearings if specified separately.
- Clean solvent, lint‑free rags, compressed air (blow passages), bench wire brush, brass/bristle for cleaning (no steel wool on journals).
- Torque angle gauge if FSM specifies angle torquing, nylon brush for bearings, bearing alignment tools if needed.

High‑level procedure (step‑by‑step)
This is the logical workflow. Follow the FSM for exact removal order, torque values, and clearances.

1) Preparation and safety
- Disconnect battery. Drain engine oil and coolant (if you’ll remove timing cover).
- Work in a very clean environment. Any dirt = future bearing failure.
- Decide: if the engine is accessible and simple, you may be able to do this in‑car; for accuracy and thoroughness remove the engine and mount on a stand — recommended for beginners.

2) Remove obstructing components
- Remove intake/exhaust manifolds, accessories, alternator, AC, drive belts, starter, and anything blocking access to timing cover, oil pan and flywheel/flexplate.
- Remove timing chain/belt cover and timing chain/belt components if necessary (follow FSM sequence).
- Remove flywheel/flexplate and torque converter if automatic.
- Remove oil pan and oil pickup tube (clean pickup screen and passages).
- Remove oil pump if needed to access passages and pump mounting.

3) Access the mains and remove bearing caps
- Clean around caps. Mark cap orientation and location (cap #1, #2, etc.) — caps must go back in the same place and orientation.
- Remove cap bolts/nuts in sequence recommended by FSM.
- Carefully pry caps off straight down to avoid damaging block faces. Keep upper and lower shells paired and labeled.

4) Inspect crank and bearings
- With caps removed, inspect bearing shells for wear patterns, scoring, embedded metal, crushed metal, or missing material. Remove shells and set aside.
- Inspect crank journals for scoring, blueing (overheat), or out‑of‑round. Clean with solvent.
- If journals are scored beyond light polishing, the crank must be ground undersize or replaced. This is a shop job — send to machine shop.

5) Measure journals and bearings
- Using micrometer, measure journal diameter at multiple points (front/middle/rear and circumferentially). Measure to thousandths/microns. Determine if crank is within spec.
- Either measure bearing shell inside diameter (after installing new shells) or use plastigauge for clearance measurement.
- Using Plastigauge method: cut a strip to fit journal length, lay across journal, reinstall the lower bearing shell and cap with new shells in place, torque caps to final spec, then remove cap and compare flattened Plastigauge width to scale to read oil clearance. Replace bearing caps once measured.
- Alternatively, compute clearance: bearing ID minus journal diameter = clearance. Compare to spec in FSM.

6) Check crank endplay (thrust clearance)
- With all main caps torqued, use a dial indicator on a fixed block surface to measure crank axial movement by prying forward and backward. Compare with FSM spec. Excessive endplay indicates worn thrust bearing surfaces — replace thrust shells or machine surfaces.

7) Replace bearings / machine work decision
- If journals are within spec and clearances correct with new bearings, you can reuse crank unground. If journals are out of spec (scored beyond polishing), send crank to machine shop for grinding to undersize and fit matched undersize bearings.
- Always fit correct bearing size (standard or undersize) per measured journals.

8) Bearing installation best practices
- Ensure block and caps are spotless and dry. Do not grease block locating dowels.
- Position upper shells in block and confirm tangs are seated; position lower shells in caps.
- Apply a thin coat of assembly lube to bearing surface or engine oil where FSM instructs.
- Align oil holes and grooves — bearing oil holes must match block galleries. Verify alignment visually.
- Install caps in correct orientation and order. Tighten in FSM specified sequence and in stages: snug, intermediate, final torque (or torque + angle). Do not exceed specified torque.
- After torquing, attempt to rotate crank — it should turn smoothly by hand with a small, consistent resistance (from assembly lube). Hard spots or binding = problem.

9) Final checks before reassembly
- Recheck bearing clearances with Plastigauge or micrometers if you changed bearings.
- Check endplay again.
- Inspect oil passages for debris; blow out with compressed air.
- Replace rear main seal and front seal as required.
- Replace oil pump if worn or if it was disassembled; torque pickup and pump bolts correctly.

10) Reassembly
- Reinstall oil pickup and oil pan with new gasket/sealant; torque to spec.
- Reinstall timing components, chain/belt, covers, accessories, and flywheel/flexplate.
- Refill with clean oil and new filter. Prime lubrication system if possible (turning oil pump with drill or cranking engine with fuel/ignition disabled to build oil pressure recommended by some shops).
- Start engine and immediately check oil pressure and listen for knocks. If low pressure or knocking persists, stop and re‑inspect.

Break‑in and follow up
- First start: run at low RPM for several minutes, then shut down and recheck oil and filter for metal shavings. Change oil and filter after initial break‑in run (per FSM or bearing maker).
- Recheck torque on accessible fasteners per FSM after initial hours of operation if recommended.

Common mistakes and how to avoid them
- Not cleaning parts thoroughly — contamination kills bearings.
- Reusing caps out of order or wrong orientation — always mark and reinstall in exact position.
- Using wrong bearing size or mixing brands — always use matched sets for the whole crank.
- Incorrect torque sequence or skipping torque staging — leads to distortion and uneven clearance.
- Not aligning oil holes — causes bearing starvation.
- Not measuring before assembly — guessing clearances = risky.
- Failing to address root cause (oil pump, oil pick-up clogging, cooling issues) — new bearings will fail again if cause remains.

Troubleshooting after assembly
- Low oil pressure: check pump, pickup, clearance (bearings too loose), oil viscosity.
- Knocking persists: check clearances, check for misassembled caps, check for crank runout.
- Smoke or metal in oil: stop engine and inspect immediately.

Where a beginner should draw the line
- Light reconditioning (removing and replacing bearings, measuring clearances, installing new bearings) is doable with patience and correct tools. But if crank journals are severely scored or require grinding, send the crank to a machine shop and get guidance on undersize bearing selection and machining limits.
- If you’re not confident with measurement tools (micrometers, dial indicator) or with torque procedures, get a professional to inspect critical steps.

Final checklist (before first start)
- All bearing caps in original positions and orientation.
- Oil holes in bearings aligned with galleries.
- Caps torqued in specified sequence and to FSM torque/angle.
- Endplay checked and within spec.
- Assembly lube applied.
- Oil pump and pickup clean and installed.
- New seals and gaskets installed.
- Engine primed or oil pressure confirmed immediately on first cranking.

That covers the why, the what, the how, what tools you need, and the common pitfalls. Follow the Toyota 2Z FSM for exact values, part numbers, and torque/angle specs.
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Toyota 2Z Engine View Enjoy :D.

Toyota 2z engine dismantle

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