Large excavator track undercarriage with tightening cylinder

Large Excavator · 4th of 4 · Final

Large Excavator Tightening Cylinder

Not a digging cylinder. Not part of the arm. This cylinder lives inside the track frame — hidden, rarely discussed, but responsible for keeping the entire undercarriage running. It pushes the front idler forward, stretching the track chain to the correct tension. Get it wrong, and the track derails or the rollers die early.

280–380mmBore

3,967 KNThrust

≤700mmStroke

×2Per Machine

A Completely Different Job — Track Tension, Not Digging Force

Track tightening cylinder mechanism

The bucket (#6), boom (#7), and stick (#8) cylinders are all part of the excavator's arm — they dig, lift, and load. The tightening cylinder has nothing to do with digging. It sits inside the track frame (one per track, two per machine), pushing the front idler wheel forward along a slide rail to tension the track chain.

A crawler excavator's track chain is a continuous loop of forged steel links — 30–50 tonnes of chain per side on a 100-tonne machine. The track wraps around the drive sprocket (at the rear), the front idler (at the front), and 5–8 carrier rollers (on top) and 7–12 track rollers (underneath). The tightening cylinder pushes the front idler outward, stretching the chain to the correct tension. A grease-charged accumulator behind the cylinder maintains this tension as the track chain wears and lengthens over time.

Korea Ever-Power manufactures the tightening cylinder as the fourth and final cylinder in the large excavator hydraulic cylinder family — completing the full machine system from arm tip to undercarriage.

Technical Specifications

Parameter	Specification
Product	Large Excavator Tightening Cylinder
Function	Control the action of track tension
Bore Diameter	280 mm – 380 mm
Rod Diameter	170 mm – 300 mm
Stroke	≤ 700 mm
Max Thrust	3,967.4 KN (bore 380 mm / 35 MPa)
Application	Large Excavator (track undercarriage)
Certification	ISO 9001 · 100% hydrostatic tested

Too Loose vs Too Tight — Why Correct Track Tension Is the Most Expensive Maintenance Decision

Too loose — derailment and accelerated wear

A slack track sags between the idler and the first roller, flaps during travel, and can jump off the sprocket during sharp turns — derailing the track. A derailed track immobilises the excavator until a maintenance crew re-tracks it (1–4 hours of lost production). Even without derailment, a loose track allows the links to hammer against the rollers — accelerating roller bearing wear and chain pin wear by 30–60%.

Too tight — premature bearing and bushing failure

An over-tensioned track presses the chain pins into the roller bushings with excessive force — accelerating bushing wear and increasing the power consumed by undercarriage friction (reducing fuel efficiency by 3–8%). The idler bearings, carrier roller bearings, and track roller seals all suffer from the higher contact forces. Over-tension shortens undercarriage component life by 20–40%. Contact Korea Ever-Power for tightening cylinder specifications.

Track undercarriage with properly tensioned track

Manufacturing Process

The tightening cylinder bore (280–380 mm) is honed to Ra 0.2–0.4 µm. Unlike the digging cylinders which cycle rapidly, the tightening cylinder moves infrequently (only during tension adjustment) but must hold its position under extreme static load for months. The grease accumulator behind the piston maintains the tensioning force as the track chain elongates with wear — the cylinder compensates automatically without operator intervention.

Chrome plating 80 µm (the cylinder lives inside the track frame, exposed to the most abrasive undercarriage environment: packed mud, rock debris, and continuous vibration). Seals rated -40 °C to +100 °C. Hydrostatic tested at 52.5 MPa. Position-hold tested under full track tension force for a defined static period to verify zero drift.

OEM & ODM

What You Provide

Excavator model and weight class, track chain pitch and link count, required tensioning force, idler slide travel, grease accumulator volume, bore/rod/stroke, system pressure (grease or oil), temperature range, and the track frame assembly drawing.

What the Factory Delivers

Matched pair with engineering drawing, bore, rod, stroke, grease accumulator provisions, 80 µm chrome, -40/+100 °C seal specification, and mounting dimensions. Hydrostatic + position-hold test. Seal kits. Browse the mobile machinery hydraulic cylinder family and the Korea Ever-Power catalogue.

Workshop

FAQ

Why is the bore so large (380 mm) for a cylinder that barely moves?

Because the track chain on a 100-tonne excavator weighs 30–50 tonnes per side. Tensioning this chain — stretching forged steel links against their own friction and weight — requires enormous force. The 380 mm bore at 35 MPa produces nearly 4,000 KN — the force needed to push the front idler forward and stretch the chain to the correct sag measurement.

How does the grease accumulator maintain tension automatically?

As the track chain wears, the links elongate slightly — loosening the track. The grease accumulator (a reservoir of compressed grease behind the tightening cylinder piston) releases grease into the cylinder, extending it by a fraction of a millimetre to compensate for the chain elongation. This maintains constant tension without manual adjustment between service intervals.

Can Korea Ever-Power supply all 4 large excavator cylinders as a set?

Yes — bucket (#6), boom (#7, matched pair), stick (#8), and tightening (#9, matched pair) cylinders are available as a complete system for large excavator OEMs. All share the 35 MPa pressure rating, 80 µm chrome, and forged rod eyes. Browse telescopic cylinders and industrial engineering cylinders.