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Fiat Tractor 55-60 60-90 79-90 80-90 90-90 100-90 tractor factory workshop manual download

1) Quick definition and symptoms (so you know what you’re fixing)
- Lifters (tappets) are the interface between cam lobes and pushrods/rocker arms. Two types: hydraulic (self-adjusting, use oil to eliminate lash) and solid/mechanical (require set valve clearance).
- Typical faults: loud ticking/knock over valves, misfire/rough running, loss of power, uneven valve seating (low compression), accelerated cam lobe wear.
- Root causes: collapsed or blocked hydraulic lifter, worn lifter face, clogged oil feed passages, stuck plunger, improper valve lash (mechanical), worn pushrod/rocker or cam.

2) Theory (how the parts work and why faults cause symptoms)
- Hydraulic lifter theory: a body contains a small plunger and a check valve. Engine oil pressurizes the lifter and pushes the plunger out to take up clearance between cam and valve train. When the plunger collapses or oil flow is restricted, clearance appears and the valve train bangs (noise), valve timing/closure changes and compression/power fall.
- Mechanical lifter theory: fixed height tappet that must have a specified clearance (lash) so valves fully close at the right time. Too much lash = noise and late/insufficient valve lift; too little = valves not fully closed, burning, loss of compression.
- How repair fixes it: restoring correct preload or clearance (by replacing/cleaning/setting lifters) removes excess clearance, restores correct valve timing and seating, eliminates the hammering loads that cause noise and cam wear, and restores compression and smooth running. Cleaning/repair also restores oil feed to hydraulic lifters so they can maintain preload.

3) Preparation (tools, parts, safety)
- Required: service manual for your exact Fiat model (torques, clearances, sequence), good quality replacement lifters or a lifter set, new rocker cover gasket, basic hand tools, torque wrench, feeler gauges (for mechanical), clean oil, parts trays, solvent, paper towels, magnetic pick-up, small dial indicator (optional), compressed air/ultrasonic cleaner (optional).
- Safety: disconnect battery, work on cool engine, support tractor securely, keep dirt out of the cylinder head.

4) Diagnosis sequence (ordered checks before teardown)
1. Listen and localize the noise with the engine at idle and at speed (use a long screwdriver stethoscope). Confirm noise comes from valve cover area/cam area.
2. Check oil level and condition; low oil or very dirty oil commonly causes hydraulic lifter complaints.
3. Check oil pressure (service manual spec). Low oil pressure means lifters won’t fill.
4. Remove valve cover(s) and inspect rocker assembly, pushrods and lifter bores for leaks, sludge or metal.
5. Rotate engine slowly by hand to TDC on each cylinder and observe pushrod movement; excessive play indicates lifter problem.
6. Compression or leak-down test on suspicious cylinders to confirm valve sealing problems.

5) Removal and inspection (ordered workshop steps)
1. Drain or catch any oil that will leak; remove air intake components as needed for access.
2. Remove valve cover(s) and gaskets; keep fasteners in order.
3. Mark or photograph rocker arm positions and pushrod locations so each pushrod goes back into its original bore (important).
4. Rotate engine to TDC for cylinder 1 (base circle on cam lobe for that cylinder). This puts lifter on base circle for removal if needed.
5. Loosen and remove rocker arms or the rocker shaft assembly per manual so pushrods can be removed. Keep pushrods in order, standing them upright in order.
6. Remove pushrods and inspect straightness and wear at ends.
7. Extract lifters: either drop them out of lifter bores following manual (some engines require camshaft or lifter retainer removal). Keep lifter bores covered to prevent dirt entry.
8. Inspect lifters:
- Hydraulic: plunger must move smoothly with some resistance and hold position when compressed; look for collapsed units (no plunger travel), scoring, clogged oil holes, or sludge. If you can compress a hydraulic lifter easily with finger or tool and it doesn’t build back up when placed under oil pressure, it’s failed.
- Mechanical: check top face for concavity/wear, measure the length against spec.
- Check cam lobes and follower faces for pitting, glazing or wear; score marks indicate deeper issues.
9. Inspect lifter bores for sludge or scoring; inspect oil feed holes for blockage.

6) Bench testing and decision
- Hydraulic lifters: attempt cleaning (ultrasonic and strong solvent) only if moderately contaminated; if collapsed or pitted, replace. Bench test by filling with clean oil: push plunger down and see if it returns. If sticky or won’t hold oil pressure, replace.
- Mechanical lifters: replace if face worn or out of spec. Replace in matched sets if cam wear is evident.
- If multiple lifters failed, likely oil feed or cam wear — inspect cam and consider camshaft replacement.

7) Repair / replacement procedure (ordered)
1. If cam lobes are badly worn, replace camshaft and lifters as a set. If only a few lifters failed and cam is OK, replace failed lifters and clean system.
2. Clean lifter bores and oil passages thoroughly. Blow out oil galleries to ensure lifter feed holes are open.
3. Fit new or restored lifters into original bore positions (unless replacing cam etc). For hydraulic lifters, prime them: submerge in clean engine oil and compress repeatedly until oil fills the plunger cavity.
4. Reinstall lifters and pushrods in their original order. Ensure pushrods seat properly in lifter cups and rocker ends.
5. Reinstall rocker arms/shaft per manual. Torque fasteners to factory specs and in the correct sequence.
6. Valve adjustment:
- Mechanical lifters: set valve lash cold/hot as specified by the manual with feeler gauge. Typical sequence: rotate engine to TDC and set intake/exhaust clearances per cylinder order.
- Hydraulic lifters (if adjustable rockers): set preload per procedure — commonly: loosen rocker nut, rotate to base circle, tighten nut until slight resistance then back off a fixed amount or tighten to spec then rotate a set amount; follow model-specific hydraulic preload procedure in the workshop manual. If non-adjustable hydraulic systems, simply torque rocker mounting and ensure lifters are primed.
7. Reinstall valve cover with new gasket, torque to spec.
8. Refill/replace oil and filter if oil contamination suspected.
9. Start engine and run at idle. Listen for noise. Re-torque rocker fasteners after warm-up if manual requires.

8) How each repair action fixes the fault (concise cause→fix relationship)
- Replacing a collapsed hydraulic lifter: restores the oil-filled plunger that removes lash; noise stops, valve closure timing returns to spec, compression restored.
- Cleaning blocked oil passages and priming lifters: restores oil supply so hydraulic lifters can operate; prevents starvation-related collapse and noise.
- Replacing worn lifter faces or mechanical lifters and setting correct lash: restores correct valve lift and seating geometry; prevents leakage at the valve seat, restores compression and reduces noise.
- Replacing camshaft when lobes are worn: prevents rapid repeat failure of new lifters and restores correct valve lift profile and timing.
- Replacing bent/worn pushrods or rocker components: ensures accurate transfer of cam motion to valves, preventing misalignment and premature wear.

9) Final checks and prevention
- After repair, verify oil pressure at idle and under load, run the engine through warm-up cycles and recheck clearances where required.
- Recheck for oil leaks, re-listen at different RPMs.
- Prevent recurrence: keep oil and filter changes on schedule, use correct oil viscosity, ensure oil pickup/sump not clogged, keep engine clean to avoid sludge.

10) Notes specific to Fiat tractor series
- These Fiat models use both hydraulic and mechanical setups depending on engine/build year. Use the exact workshop manual for model-specific preload/adjustment sequences and torque values. If cam and lifters are replaced, follow timing and cam phasing procedures in the manual.

That is the ordered workshop procedure plus the theory and exactly how each repair action resolves the symptoms.
rteeqp73

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