Tools & consumables (minimum)
- Full metric socket/ratchet set, extensions, breaker bar
- Torque wrench (range to cover low and high torque — e.g. 5–200 Nm)
- Micrometer (0–25 mm) or outside mic for crank journals
- Dial bore gauge or telescoping gauge (optional, for bearing ID/journal)
- Plastigauge (appropriate width) and scale
- Engine stand or secure engine support / hoist
- Piston support tool or wooden dowel to hold pistons from above
- Soft-jawed vice, brass drift, feeler gauges
- Clean lint-free rags, solvent (brake cleaner), wire brush
- Assembly lube (engine oil or moly assembly lube)
- New rod bearing set(s) (correct part numbers for ZD30 / KA23DE)
- New rod bolts/nuts (if OEM are torque-to-yield or recommended to be replaced)
- New oil, oil filter, sump gasket/sealant
- Pry bar, plastic or wooden mallet
- Safety: gloves, eye protection, shop towels, drip pans

Safety precautions
- Work on a flat surface, use jack stands if vehicle is raised. Never rely only on a jack.
- Disconnect negative battery terminal.
- Drain engine oil and coolant as needed; capture fluids and dispose properly.
- Support engine securely if removing engine mounts. If engine stays in car, ensure trunk/hood clearance and engine support.
- Keep work area clean; small debris kills bearings.
- Use eye protection when cleaning/using solvents. Avoid inhaling fumes.
- Do not smoke — solvent + oil are flammable.

Overview of procedure (general for Nissan ZD30 and KA23DE)
1) Service data first
- Obtain the factory service manual for the exact engine (ZD30DD or KA23DE). Get the rod bearing clearance spec, rod cap bolt torque (and torque-angle if TTY), crank journal diameters, and rod bearing part numbers.

2) Strip to bottom end
- Drain engine oil.
- Remove intake/exhaust, accessories, possibly the timing cover and lower front cover if needed for crank rotation access.
- Remove oil pan (sump). On ZD30 you may also need to remove oil cooler lines, baffles, and pickup.
- Remove oil pump/strainer if blocking access (follow manual).

3) Identify & mark
- Rotate crank to access the rod you’ll work on.
- Mark each connecting rod and cap with a unique ID number and orientation arrow (cap-to-rod, direction to front of engine). NEVER mix caps or flip them.
- Note piston orientation if you remove rods/pistons.

4) Remove rod caps
- Clean around the rod caps to prevent debris entry.
- Loosen rod bolts evenly if necessary, then remove rod cap.
- Support the piston from above (wooden dowel from top of bore or piston stop tool) so the piston doesn’t fall into the crankcase if the rod is pushed down.

5) Inspect bearings & journals
- Remove bearing shells and inspect for scoring, glazing, embedded debris, discoloration (overheating). Light polished look may be normal; deep scoring or heat discoloration is not.
- Clean journals with solvent and lint-free rags (no abrasives).
- Measure crank journal diameter with micrometer in three places (axial positions) to check for taper and ovality. Compare to factory spec.
- If journal is damaged beyond limits, crankshaft machining or replacement is required.

6) Bearing replacement & fitment
- Match new bearing shells to their location (upper/lower, thrust if applicable). Bearings often have oil hole/slot orientation—ensure alignment with oiling holes.
- Do not interchange bearing halves between different rods or journals.
- Clean rod cap and rod mating surfaces; they must seat properly.

7) Measuring clearance — Plastigauge method (detailed)
- Clean journal and bearing shells thoroughly and dry.
- Place a single narrow strip of plastigauge across the width of the journal on the journal surface (not on the bearing shell).
- Install the bearing shell in rod cap (lower half installed in cap, upper half in rod) making sure oil holes and tangs are aligned.
- Apply a very small dab of assembly lube on the bearing surface to hold it briefly if desired, but do not smear plastigauge.
- Carefully install the cap and hand-start the bolts. Torque progressively in the specified sequence and increments to final torque. IMPORTANT: Do not attempt to rotate the crank with plastigauge in place.
- Remove cap carefully (do not smear plastigauge).
- Use the Plastigauge scale to measure the flattened width; compare to factory clearance spec. Record results.

8) Interpreting results & corrective actions
- Clearance within spec: good — replace with new bearings (if you used old shells only for measuring) and reassemble using assembly lube and correct final torque.
- Clearance too tight: check bearing thickness and journal size; possible causes are wrong bearings, oversized bearing, or journal oversize. Solutions: fit correct standard-size bearing or undersize bearing after crank grinding. If crank is oversized (worn undersize), grind and fit undersize bearings or replace crank.
- Clearance too loose: often caused by worn journals or wrong bearing halves. Recheck measurements; may require machining or new bearings of correct size.

9) Final assembly
- Replace rod bolts if specified. Many Nissan rods use stretch bolts that must be replaced or torqued with angle method.
- Clean all oil passages and bearing surfaces. Light coating of assembly lube on bearing surfaces before final assembly.
- Torque rod bolts to factory spec in staging increments (e.g., 30%, 60%, 100%) or apply torque + angle if specified. Use a calibrated torque wrench.
- After torquing, rotate the crank by hand at least two full revolutions. It should turn smoothly without binding. If you feel tight spots, stop and re-evaluate.
- Check crank endplay if main work was done (with dial indicator). Replace oil pump and pickup if removed.
- Reinstall oil pan with new gasket/sealant, refill with new oil and oil filter.

How to use critical tools (short instructions)
- Torque wrench: set to desired torque, tighten smoothly to stop, do not use cheater bars. For torque-angle bolts: first torque to preliminary value, then rotate bolt the specified additional angle using an angle gauge.
- Plastigauge: cut single strip, lay across journal, torque cap to spec, remove cap carefully, measure flattened width against supplied scale. Do not reuse plastigauge. Do not rotate crank while installed.
- Micrometer: zero before use; measure crank journal in at least two axial positions and two diametral orientations to check ovality/taper. Record to 0.01 mm (0.0005 in).
- Dial bore gauge: used to measure bearing ID or bore roundness. Set gauge to a calibrated ring or micrometer reading then measure.

Replacement parts commonly required
- Complete rod bearing kit (upper & lower shells) for the engine and any undersize sets if crank is ground
- Rod bolts / nuts (replace if they’re torque-to-yield or manufacturer recommends)
- Oil pan gasket, oil filter, fresh engine oil
- Oil pump/strainer gasket or seals (if removed)
- Possible crankshaft (if journals beyond machining limits) or machine work (grind/polish) plus matching undersize bearings
- Any damaged rod bearings or rods if bent/scored

Common pitfalls and how to avoid them
- Mixing or flipping bearing shells: always mark and keep rod/cap pairs together and oriented correctly.
- Not replacing rod bolts that are TTY: if bolts are torque-to-yield, always replace them — reusing can fail.
- Using wrong bearing part numbers or incorrect orientation (oil hole misaligned): verify oil holes and tangs.
- Rotating the crank with plastigauge in place — it smears and gives false readings and ruins the gauge.
- Not cleaning thoroughly — debris causes immediate bearing failure.
- Over- or under-torquing bolts: use a calibrated torque wrench and correct sequence; follow angle specs.
- Not checking crank journals for out-of-round/taper: this leads to incorrect clearance even with new bearings.
- Trying to “fit” clearance by shimming or reusing damaged bearings — do the correct corrective action (replace or machine).
- Failure to lubricate bearings at assembly — initial start-up starvation will score new bearings.
- Not checking oil pressure after reassembly — low pressure at first start indicates an issue; have a method to prime oil and monitor pressure.

Specific engine notes (ZD30DD and KA23DE)
- ZD30 diesel: heavy-duty diesel crank and bearings; often uses specific bearing sets and larger rod bolts — follow the ZD30 service manual for correct bearings and torque-angle procedure. Diesel engines can show heat discoloration indicating contaminated oil or turbo failures — inspect oil supply and pump.
- KA23DE (KA-series): earlier Nissan four-cylinder — rod bolts may be conventional or TTY depending on year; check manual. Less robust journals than diesel; careful measurement is important.

Final checks & break-in
- Prime the oil system (crank with fuel pump disabled or use an oil pump priming tool or repeatedly crank with ignition disabled to build pressure) before starting to avoid dry-start damage.
- On first start, monitor oil pressure and listen for bearing noise. Check for leaks.
- Do not put heavy loads on the engine for the first 500–1000 km; follow break-in oil-change interval per manual.

Summary
- Get the factory manual for exact torque and clearance specs.
- Cleanliness, correct parts, correct torque procedure, and accurate clearance measurement (Plastigauge or gauges) are the keys.
- Replace bearings and rod bolts as recommended; machine or replace crank if journals are out of spec.
- Follow safety procedures and verify everything (rotation, oil pressure) before returning the engine to service.

No further questions.
rteeqp73

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