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Views: 44 Author: Site Editor Publish Time: 2026-07-27 Origin: Site
How To Replace Harvester Cutting Knife, Sieve & Conveyor Chain (Step-by-Step Guide)
A combine harvester’s cutting knife, sieve, and conveyor chain are the three most wearable yet critical components for efficient crop harvesting. Over time, continuous friction, crop residue buildup, and heavy field workloads cause knife dulling, sieve clogging/wear, and chain loosening or damage. These issues directly lead to uneven cutting, grain loss, blockages, reduced harvesting speed, and even unexpected machine downtime.
Regular replacement of these core parts not only restores your harvester’s optimal working performance but also extends the machine’s overall service life and cuts long-term maintenance costs. This complete step-by-step guide will walk you through safe, professional replacement of the harvester cutting knife, sieve, and conveyor chain, suitable for most mainstream combine harvester models. No professional mechanic is required—farmers and equipment operators can finish the whole process independently.
Before starting any disassembly and installation work, strictly follow these safety rules to avoid mechanical injury and equipment damage:
Power Off & Lockout: Turn off the harvester engine, remove the key, and engage the safety lockout device. Wait 5–10 minutes for all rotating parts to completely stop to prevent accidental startup.
Machine Support: Park the harvester on flat, solid ground. Raise the header and threshing device, then fix them with safety brackets to prevent falling.
Wear Protective Gear: Put on anti-slip gloves, safety goggles, and work shoes. Old chains and blades have sharp edges and burrs, which can easily cause cuts.
Prepare Tools & Parts: Ready new matching cutting knife, sieve, conveyor chain, chain breaker, wrench set, screwdriver, lubricant, cleaning brush, and tension gauge. Confirm all new parts match your harvester’s model specifications.
Clean Working Area: Remove crop residues, soil, and dust on the header, threshing chamber, and conveyor system to ensure a clean operating environment.
The cutting knife undertakes all crop cutting work. Dull, deformed, or broken blades will cause crop pulling, uneven stubble height, and increased machine load. Replace it immediately if you notice blade wear, cracks, or edge passivation.
First, unscrew the fixing bolts of the header protective cover and remove the cover to expose the cutting knife assembly. Use a socket wrench to loosen the blade fixing bolts and pressure plates one by one. Take out the worn old knife blade carefully. For integral knife strips, remove the end fixing pins first, then slide out the entire knife assembly.
Use a brush and rag to clean dirt, crop residues, and rust on the knife mounting base, guide rail, and moving gap. Check the guide rail for wear, deformation, or jamming. If the guide rail is severely worn, replace it together to avoid affecting the new knife’s operating stability.
Place the new qualified cutting knife into the mounting guide rail, align the blade position accurately, and ensure the blade fits closely with the fixed cutter gap. Install the pressure plates and fixing bolts in sequence, and tighten the bolts diagonally to avoid uneven stress causing blade deformation.
The standard gap between the moving knife and fixed knife is 0.3–0.8mm (follow the manufacturer’s manual for exact data). Adjust the gap via the guide rail adjusting bolts to ensure no friction or jamming during blade movement. Manually push the knife strip back and forth several times to confirm flexible operation without stagnation. Finally, reinstall the header protective cover.
The sieve is a key part of the grain cleaning system. Long-term use will cause mesh deformation, hole blockage, screen wire breakage, and abrasion, resulting in incomplete grain cleaning, high impurity rate, and grain leakage. Timely replacement ensures clean grain output and reduces crop loss.
After confirming the machine is completely powered off, open the side and top protective covers of the harvester’s cleaning chamber. Remove the grain delivery chute and auxiliary baffles that block the sieve for easy operation.
First, disconnect the sieve vibration connecting rod and fixing clips. Loosen the front and rear fixing bolts of the upper and lower sieves, and slowly pull out the old sieve along the slide rail. Pay attention to prevent residual grains and sundries from falling into the machine interior. Separate the upper coarse sieve and lower fine sieve for individual inspection and replacement as needed.
Thoroughly clean all crop residues, dust, and blocked sundries in the sieve frame, vibration groove, and air duct. Check the vibration spring and connecting rod for fatigue damage or deformation. Damaged vibration parts must be replaced first to ensure the new sieve works with stable vibration frequency.
Place the new sieve (match mesh size with crop type: wheat/rice for fine mesh, corn/soybean for coarse mesh) on the slide rail, push it into place flat, and ensure the sieve fits closely with the frame without skew or gap. Fasten the fixing bolts and clips firmly, and reconnect the vibration connecting rod to guarantee flexible linkage.
Adjust the sieve inclination angle according to crop variety and humidity. Reasonable angle avoids grain accumulation and leakage. Simultaneously debug the fan air volume to match the sieve vibration frequency, ensuring efficient separation of grains, chaff, and impurities. Reinstall all baffles and protective covers after debugging.
The conveyor chain undertakes grain and crop material transportation. Loose chains, worn chain links, broken pins, and rust will cause slipping, jamming, material accumulation, and even chain breakage during operation. It is recommended to inspect the chain every 50 working hours and replace it every 300–500 hours.
Locate the chain tensioning device, loosen the tensioning bolt, and reduce chain tension to create enough disassembly space. Use a professional chain breaker to disconnect the master link of the old chain. After breaking the lock link, slowly take down the old chain from the driving and driven sprockets. Note: The old chain is heavy with sharp worn edges—handle it carefully to avoid injury.
After removing the old chain, check the sprocket teeth for wear, tooth breakage, or deformation. If the sprocket is severely worn, replace it together with the chain to prevent accelerated wear of the new chain. Clean sprocket surface rust and sundries, and check bearing flexibility to ensure smooth transmission.
Check the new chain’s model, pitch, and length to confirm full compatibility with the harvester. Wind the new chain evenly on the driving and driven sprockets, keep the chain vertical and parallel without skew or twisting. Align the two ends of the chain, install the master link and lock spring, and ensure the lock spring is firmly clamped in place to prevent falling off during operation.
Gradually tighten the tensioning bolt to adjust chain tightness. The standard tension is: press the middle of the chain with moderate force, and the sagging distance is 10–20mm. The chain should be neither too loose (causing slipping and jittering) nor too tight (increasing wear and power consumption). Ensure the left and right tension is consistent to avoid chain deviation.
Apply high-temperature and wear-resistant chain lubricant evenly on all chain links and rollers to reduce friction. Manually rotate the sprocket several times to make the lubricant penetrate fully. Then start the harvester at idle speed and run the conveyor system for 3–5 minutes. Listen for abnormal noise, check for jamming, deviation, or loose links. If everything runs smoothly, the replacement is completed.
To maximize the service life of new parts and ensure stable harvester operation, follow these maintenance rules after replacement:
Cutting Knife: Check blade tightness and gap daily before operation; polish blades regularly to keep sharp; replace severely deformed blades in time.
Sieve: Clean mesh sundries after daily work; avoid excessive material impact; adjust angle and air volume according to crop conditions.
Conveyor Chain: Lubricate every 20–30 working hours; check tension and link wear regularly; remove rust and sundries timely.
Replacing the harvester cutting knife, sieve, and conveyor chain is a basic but vital maintenance job for agricultural equipment. Standardized replacement operations can effectively reduce grain loss, improve harvesting efficiency, and avoid costly equipment failures. By following this step-by-step guide, you can complete the replacement safely and quickly, keeping your harvester in peak condition throughout the harvest season.
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