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Jeep Grand Cherokee 1999-2004 WJ WG Factory Workshop Service Repair Manual download

Role: experienced automotive technician. Procedure: remove/replace pistons on a Jeep Grand Cherokee WJ/WG (general step‑by‑step workshop method). This is a major engine job — read the factory service manual for exact torque specs, clearances and engine‑specific procedures before starting.

Tools and consumables
- Full metric and SAE socket set, extensions, swivel, breaker bar
- Torque wrench (range to cover small and large bolts)
- Engine hoist or support (if removing engine)
- Engine stand (if removing engine)
- Harmonic balancer puller, crankshaft pulley tool
- Screwdrivers, pliers, pry bars
- Floor jack and stands, wheel chocks
- Ratcheting piston ring compressor (sized to pistons) or adjustable band type
- Piston ring pliers
- Ring filing tool (if adjusting ring gaps)
- Cylinder bore micrometer, telescoping gauge or dial bore gauge
- Outside micrometer, piston skirt micrometer (to measure piston)
- Plastigage for bearing clearance checks
- Feeler gauges
- Valve spring compressor (if removing heads/valves)
- Torque angle tool if needed (for torque‑to‑yield bolts)
- Dead blow hammer / wooden haft or soft mallet
- Shop rags, parts trays, labels, marker
- Solvent, brake cleaner, compressed air
- Assembly lube and engine oil
- New gasket sets: head gasket(s), intake/exhaust, oil pan gasket, front/rear seals
- New piston rings (engine‑specific), pistons (if replacing), wrist pin clips
- New rod bearings, main bearings (recommended), rod bolts (replace if stretch/T‑Y), head bolts (if TTY)
- New oil filter, ~6–12L fresh motor oil (qty depends on engine)
- Shop manual (torque specs, sequences, clearances)

Safety precautions (non‑negotiable)
- Disconnect negative battery.
- Work on level surface; use jack stands rated for the load. Never rely on a jack.
- Use engine hoist/stand if removing engine. Do not let engine hang from fragile components.
- Wear eye protection and gloves.
- Keep work area clean. Prevent dirt/metal chips entering oil passages.
- Use proper lifting technique and get help for heavy parts (crankshafts, heads).
- Dispose of fluids and parts per regulations.

High‑level plan
1. Remove whatever is necessary to access cylinder heads (and oil pan) — could be done with engine in vehicle or easier with engine out.
2. Remove cylinder heads and valve train to access pistons from top (or remove oil pan and rod caps to push pistons out from bottom if head removal not desired).
3. Remove pistons and rods, tag and bag everything by cylinder.
4. Inspect crank journals, bores, pistons, bearings. Measure, determine if machining (bore/hone, resurface, crank grind) is required.
5. Install new rings/pistons or re‑install existing pistons with new rings & rod bearings per specs.
6. Reassemble in reverse order with correct torques and clearances. Prime oiling system and follow break‑in.

Detailed step‑by‑step

A. Preparation and disassembly
1. Drain coolant and engine oil; remove intake air box, intake manifold (if necessary), accessory drive belts, alternator, AC compressor (support/leave lines attached if not removed), power steering pump (support), radiator and fan shroud if needed for room.
2. Label and disconnect all wiring harness connectors, vacuum hoses and fuel lines (relieve fuel pressure first). Cap fuel lines to avoid contamination.
3. Remove exhaust manifolds or exhaust Y‑pipe as required to remove cylinder heads.
4. Remove valve covers; note rocker/shaft orientation and mark components if the valve train will be reinstalled. If you are removing heads, follow factory procedure: remove head bolts in sequence, lift heads with helper/hoist, place heads on stand.
5. If keeping engine in vehicle and you remove heads, you can remove pistons from top. Otherwise remove oil pan, pickup tube, and windage tray so you can access rod caps and push pistons up and out.

B. Removing pistons
1. Number and tag each connecting rod/cap and piston top. Keep caps paired to their rods and orient them the same way on reassembly.
2. Remove rod caps (loosen evenly if multiple bolts). Keep caps in cylinder order and note orientation (usually a stamped mark faces the same side).
3. With head removed, compress rings and carefully push pistons out the top of the bore using a wooden dowel or handle of a hammer on the crank journal — push evenly. If removing from bottom, support the piston and withdraw upward.
4. Remove wrist pin circlips with snap ring pliers and slide out pins; separate piston from rod if replacing piston. Keep wrist pins with their original piston if reusing (they are often matched).
5. Place each piston/rod assembly in labeled trays in order.

C. Inspection and measurement
1. Clean pistons and rods. Inspect for scoring, cracks, piston crown damage, ring lands. If pistons are damaged, replace.
2. Measure cylinder bores with bore gauge to determine taper and out‑of‑round. If beyond spec, you will need machine shop boring/honing or overbore pistons.
3. Measure piston diameter and skirt clearance. Compare to bore measurement to determine piston‑to‑wall clearance.
4. Inspect crankshaft journals for wear or scoring. If journals are damaged, crank grinding may be required.
5. Inspect and measure rod and main bearing clearances with plastigage or micrometers—replace bearings if worn.
6. Decide: new pistons vs reuse, hone or bore, new rings, and replace bearings and rod bolts as required.

Parts commonly replaced
- Piston rings (always with piston service)
- Bearings: rod and main bearings (recommended)
- Rod bolts and head bolts if they are torque‑to‑yield (TTY) — usually replaced once
- Wrist pin clips (cheap, replace)
- Gaskets and seals: head gasket(s), intake/exhaust, oil pan, front/main seals
- Oil pump (recommended if engine has high miles or contamination)
- Pistons if damaged or out‑of‑spec
- Pushrod(s), valve springs if removing heads and worn

D. Machining requirements (if applicable)
- If bores are scored or out of spec: machine shop to hone or bore to next oversize and fit oversized pistons.
- If crank journals scored: crankshaft reground and undersized bearings fitted.
- If heads removed: check head flatness and have resurfaced if warped.

E. Piston/ring preparation and ring gap setting
1. Install rings on new pistons dry to check orientation. Stagger ring gaps: typically top compression ring, second compression ring, and oil ring components should be rotated 120°–180° apart—not aligned.
2. Insert piston into bore to check ring end gap: insert one ring at a time into the bore bottom with piston used as a square, push ring down with a piston to full depth and measure gap with feeler gauge. File ring ends if gap is too small (follow ring manufacturer spec).
3. Clean ring grooves on reused pistons; replace pistons if grooves are worn.

F. Reinstalling pistons
1. Lubricate piston skirts, ring surfaces, wrist pins, and rod bearings with assembly lube or engine oil.
2. Install wrist pin and retainers per piston orientation.
3. Fit new rod bearings into rod and cap halves, ensuring correct shell orientation.
4. Place ring compressor around piston rings. Explain tool usage:
- Ratcheting/compression band type: place compressor around rings just below piston crown, tighten evenly with ratchet or wrench so rings are compressed flush with piston skirt. Ensure compressor is concentric and rings are fully compressed.
- Spring‑type compressors: spread the compressor and slide over piston, then compress the rings. Ensure no rings are sticking out.
5. Lower piston and rod assembly into bore squarely. Use a wooden handle or soft mallet to tap the crown of piston to seat it into bore while supporting the rod so it lines up with the journal on the crank.
6. Once piston is in place and rod is on the crank journal, install rod cap (match identification marks), and torque the rod bolts to factory spec using a torque wrench (replace bolts if TTY). If spec requires angle torque, use torque angle tool.
7. Rotate crank to ensure smooth movement and that piston clears valve pockets as applicable.

G. Final checks before reassembly
1. Check bearing clearances with plastigage if unsure; confirm oil passages are clear.
2. Ensure ring gaps are not aligned and that piston orientation arrow points to the front (follow piston marking).
3. Replace oil pump pickup O‑ring/seal if removed. Prime oil system: fill oil pump with oil and crank engine without spark to build oil pressure (or use drill adapter on oil pump if engine out).
4. If heads were removed, install head gaskets and tighten head bolts in correct sequence and to specified torque/angle.

H. Reassembly and start procedure
1. Reinstall intake, accessories, exhaust, reconnect wiring harness, fuel lines, coolant hoses.
2. Install a new oil filter and fill with fresh oil to correct level. Fill coolant.
3. Reconnect battery.
4. Pre‑start checks: ensure no tools left in engine bay, vacuum lines connected, coolant and oil levels correct.
5. Initial start: crank until oil pressure builds (watch for oil pressure, no knocks). Let idle and monitor for leaks, abnormal noises, and coolant temp.
6. Break‑in: follow piston/ring manufacturer recommendation. Typical break‑in: avoid heavy loads for first 500 miles, vary RPMs, change oil at 500 miles (or 50–100 miles for initial flush then again at 500), use recommended break‑in oil if supplied.

Common pitfalls and how to avoid them
- Mixing up rod caps / orientation — always label and keep matched pairs.
- Reusing TTY bolts — they stretch; replace them.
- Not checking ring end gaps — too small gaps cause rings to butt and break; too large causes blowby.
- Incorrect piston orientation — follow arrow/mark to front of engine.
- Not priming oil pump — immediate scuffing on first start if oil not circulating.
- Dirt, metal chips in oil passages — clean thoroughly; use compressed air to clear passages while preventing debris fall.
- Over‑torquing or under‑torquing fasteners — use calibrated torque wrench and correct sequence.
- Not measuring bores and journals — leads to premature wear or failure if tolerances exceeded.
- Using wrong ring compressor size — can break rings or damage piston.
- Forcing piston past rings — ensure compressor compresses rings fully and piston enters straight; use wooden hammer handle to seat.
- Forgetting to stagger ring gaps — causes blowby and oil consumption.

Notes on engine specifics
- WJ/WG engines differ (4.0L I6, 4.7L V8). Cylinder head removal, timing gear/chain procedures, torque specs and TTY bolts vary. Always use factory service manual for that engine’s torque values, ring gap specs, bearing clearances, and piston orientation instructions.

Final recommendations
- Replace rings and rod/main bearings whenever pistons are serviced.
- If engine has high miles or any scoring on bores or journals, send to machine shop for accurate boring or grinding.
- Keep meticulous labeling and cleanliness; most failures come from assembly errors or contamination.

End.
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