Corn Harvester Chopper Cylinder YM4P.83.01 – 56mm Bore, 130mm Stroke

YM4P.83.01 · Corn Harvester Series

Corn Harvester Chopper Cylinder

High-force, short-stroke actuator for stalk chopper gap adjustment and blade-engagement mechanisms on 4-row corn harvesters.

Bore Diameter

56 mm

Push force ≈ 39.4 kN @ 160 bar

Rod Diameter

50 mm

Rod/bore ratio 0.893 — structural specification

Stroke

130 mm

Covers full chopper gap adjustment range

Mounting Distance

390 mm

C/C retracted — OEM bracket-match dimension

Rated Pressure

160 bar

Continuous working pressure

Surge Pressure

250 bar

Blade-strike shock rating — proof-tested

Rod Chrome

25–30 µm

Hard chrome HV 800+, full rod length

Seal System

PU / PTFE

Quad-ring piston, −25 °C to +100 °C

Port Standard

BSP G3/8″

SAE ORB available on request

Mounting Style

Clevis × 2

Ø20 mm pin bore both ends

Push Force (Extend)

39.4 kN

F = 160 bar × π/4 × 56²

Pull Force (Retract)

8.7 kN

F = 160 bar × π/4 × (56²−50²)

Push / Pull Ratio

4.53 : 1

Chopper engagement demands high push force; spring-return handles retract — this ratio is deliberate, not a compromise.

Why does a 130 mm stroke chopper cylinder need a 50 mm rod — the same diameter as the 300 mm stroke header lift cylinder?

Stroke length does not determine rod diameter — load case does. The chopper cylinder operates in a sustained high-vibration environment: the rotating blade shaft runs at 1,200–1,800 RPM directly adjacent to the cylinder mounting bracket, and blade-on-stalk impacts generate repeating impulsive lateral loads through the chopper frame into the cylinder pivot. A slender rod on a short-stroke cylinder in this position will develop fretting wear at the piston seal and gland under these lateral micro-cycles, not under conventional push-pull loading. The 50 mm rod provides the lateral bending stiffness to prevent rod deflection amplitudes that would accelerate seal fretting — a failure mode that a buckling calculation alone will not reveal because it is fatigue-driven, not static.

The push/pull ratio is 4.53:1 — isn’t that an extreme asymmetry? What does it mean in practice?

It is extreme for a positioning cylinder, but it is correct for a chopper engagement actuator. Here is the mechanism: the cylinder pushes the chopper counter-knife mounting rail against its operating spring preload to set blade-to-counter-knife clearance. This requires 39.4 kN because you are compressing multiple return springs simultaneously while overcoming friction in the adjustment rail guides. Once the position is set, the cylinder holds — it is not continuously cycling. When the operator releases or opens the gap, the spring system provides the retract force — the hydraulic pull of 8.7 kN simply controls the rate of retraction, it does not need to overcome the spring alone.

Trying to use a standard 56/32 mm rod cylinder here — which would give a push/pull ratio closer to 1.75:1 and only 22.5 kN push force — would result in the cylinder being unable to compress the counter-knife spring system to the minimum clearance position. The machine would appear to operate but with an excessive blade-to-counter-knife gap, leading to poor stalk chopping quality and elevated whole-stalk rejection rate.

The surge pressure rating is 250 bar — what is causing pressure surges on a position-holding cylinder?

Blade strikes. When a corn stalk contains a buried stone, an embedded metal fragment from previous tillage, or a dense knot section, the rotating chopper blade impacts it with an energy spike that transmits directly through the blade shaft and frame into the counter-knife mounting. If the counter-knife is hydraulically positioned, that impact energy partially translates into a hydraulic pressure spike in the rod-side circuit. On a short-stroke, high-bore cylinder, the hydraulic stiffness (pressure rise per unit displacement) is very high — a 2 mm rod-side displacement at 50 mm rod, 130 mm stroke generates a pressure spike of several tens of bar above circuit pressure. The 250 bar surge rating is not theoretical headroom: it is the calculated peak from a stone-strike event modelled against the circuit’s relief valve response time. Any cylinder rated below 200 bar surge on this position is inadequately specified.

Why is the internal leakage specification tighter here than on the grain tank lift cylinder?

Chopper blade-to-counter-knife clearance is typically set within a range of 1–5 mm. The operational consequence of exceeding the upper limit by even 2 mm is measurable: stalk particle length increases, the proportion of whole-stalk carryover to the field rises, and in markets where straw quality matters for subsequent soil incorporation, agronomic performance degrades visibly. An internal leakage rate above 5 cc/min on the rod-side port of this cylinder translates to approximately 0.3 mm/min gap increase under the counter-knife spring load. Over a 30-minute field section without readjustment, that is a 9 mm drift — enough to take the machine from optimum to poor chopping quality. The ≤ 3 cc/min specification is tighter because the application demands it, not because it is a standard production specification applied universally.

Cylinder Tube

E355 cold-drawn seamless, honed to Ra ≤ 0.4 µm. Wall 7 mm — calculated for 4:1 yield safety at 250 bar. External: zinc phosphate + PU topcoat, 500-hour salt spray.

Chrome Rod

Ck45 steel, ground Ra ≤ 0.2 µm. Hard chrome 25–30 µm, HV 800+. Post-plate ground to h6. At 50 mm Ø, I = 307,000 mm⁴ — lateral stiffness that matters in high-vibration mounting positions.

Piston & Seals

Cast iron piston, double PTFE guide rings. Primary seal: PU quad-ring + PTFE backup. Rod seal: dual-lip PU. Wiper: PU with steel exclusion lip. Full seal kit available separately as catalogued spare.

End Fixings

Clevis both ends, Ø20 mm pin bore, sintered bronze self-lubricating bush. Grease nipple at each pivot. Clevis wall 14 mm machined steel — rated for lateral bending moments from vibration loading.

QC Protocol

Hydrostatic proof test 250 bar × 60 s per unit. Full-stroke cycle × 5 under rated load. Leakage check both ports. Dimensional audit: C/C, stroke, pin bore. Records retained per batch.

C/C Retracted

390 mm

Primary bracket-match dimension. Measure existing cylinder before ordering.

Pin Bore

Ø20 mm

Both clevis eyes. Verify pin diameter on machine before ordering.

Rod Diameter

50 mm

Do not substitute a thinner rod — see engineering rationale above.

Port Thread

BSP G3/8″

SAE ORB available; specify at order.

Stroke

130 mm

Custom strokes 100–160 mm available on inquiry.

Custom Configuration Enquiry