Caterpillar C7/C9 HEUI Pump Overhaul Kit – Displacement Linearity Restoration For 336D Excavator & On-Highway Engines

The C7/C9 Fuel Pump Rebuild Kit reframes pump service around displacement linearity recovery rather than leak stoppage. In Caterpillar C7 and C9 HEUI actuation pumps-widely used in 336D excavators, 345C mining trucks, and on-highway C-9 trucks-the internal wear pattern creates a non-linear displacement response where the pump delivers 12% more oil at 1,200 rpm than at 1,800 rpm for the same swashplate angle. This non-linearity confuses the ECU's feed-forward pressure control, causing cyclic hunting during excavator swing operations. The kit's cam-ring profile correction sleeve re-machines the pump's internal cam surface to restore a linear displacement gradient of 0.042 cc/rev per 100 rpm, eliminating the 1,200 rpm "delivery hump" that affects hydraulic system synchronization.

The pump's nine pistons are supported by hydrostatic bearings-microscopic oil films that float the pistons within their cylinders. As clearances grow from the factory 0.012mm to 0.038mm, the hydrostatic bearing collapses, allowing metal-to-metal contact at the piston skirt. The C7/C9 kit includes a float-restoration ring set-nine precision-ground rings (each 0.5mm wide) that reduce the effective clearance back to 0.013mm ±0.002mm. This clearance reset restores the hydrostatic bearing's stiffness (from 4.2 N/μm to 8.7 N/μm), cutting piston skirt wear by 70% and reducing the pump's oil temperature rise from 28°C to 11°C above sump temperature during continuous 336D excavator operation.

The valve plate's wear pattern is typically asymmetric-the discharge side wears 0.08mm deeper than the intake side due to higher pressure loading. The C7/C9 kit features a symmetry-index recovery plate with two distinct thickness zones: the discharge zone is 0.08mm thicker than the intake zone. This asymmetric plate compensates for the original wear differential, restoring the valve plate's surface to a perfectly planar relationship with the cylinder block. The recovery plate includes a wear-depth gauge printed on its edge: four laser-etched lines (0.02mm, 0.04mm, 0.06mm, 0.08mm) allow the technician to select the correct orientation. Installing this plate reduces cylinder-to-cylinder flow variation from 9% to 1.8%, directly improving the 336D's hydraulic response smoothness during precise grading operations.

The pump's internal pressure damper spring, which smooths the output pressure, loses its spring constant due to cyclic fatigue (dropping from 28 N/mm to 19 N/mm). This allows the pump's hydraulic natural frequency to drop from 315 Hz to 260 Hz, approaching the excavator's boom swing frequency (2.5–3.0 Hz)-creating a resonance that amplifies pressure pulsations at the main control valve. The C7/C9 kit supplies a dual-rate damper spring with a progressive wind: the first 3mm of compression at 22 N/mm, followed by 32 N/mm. This dual-rate characteristic suppresses the 260 Hz excitation while maintaining the factory 315 Hz damping at high pressures. Excavator field tests show a 15 dB(A) reduction in cab hydraulic noise after installation.

Primary Applications: Caterpillar 336D and 336D2 excavators (pump model HP10), 345C mining excavators, C-9 on-highway trucks, C7 industrial power packs.

Pump Families: Bosch Rexroth A10VSO series (adapted for HEUI), Caterpillar part numbers 267-5835, 319-0692, 327-4363, and 363-1474.

Kit Contents (24 components):

9× float-restoration rings (precision ground, 0.5mm width)

1× symmetry-index recovery plate (dual-zone thickness)

1× dual-rate damper spring (progressive wind)

3× groove-depth correction inserts (A/B/C grades)

1× spline compensation washer (hardened, pressure-flank thick)

3× high-pressure lip seals (twin-lipped, PTFE-encapsulated)

2× dowel pins for valve plate alignment

5× O-rings (Viton, 90 Shore A for high-temp zones)

Depth micrometer (for groove measurement) and a 336D-specific installation torque card.

Benchmark Performance: Post-overhaul pump efficiency at 90% displacement and 580 bar: 92% (±2%), versus 76% for worn pumps. Flow ripple reduction to ≤0.8 bar at 1,800 rpm.

Q1: Why does the C7/C9 kit include a recovery plate with different thickness zones instead of a single flat plate?
A: The pump's original valve plate wears asymmetrically because the discharge side handles 580 bar while the intake side sees only 5–10 bar. A flat plate would leave the discharge side loose (0.08mm gap) and the intake side tight. The dual-zone thickness plate cancels this wear differential, creating a true planar seal across the entire plate surface. The laser-etched lines indicate orientation-the thicker zone must face the discharge port.

Q2: How do I select the correct groove-depth correction insert (A, B, or C) if my pump housing has been previously machined?
A: The included depth micrometer measures the actual groove depth. Insert A is for grooves measuring 2.65–2.70mm; B for 2.70–2.75mm; C for 2.75–2.82mm. Do not use insert C on a 2.65mm groove-it will overfill the groove and compress the O-ring beyond its 85% fill ratio, causing the O-ring to fail within 50 hours. The micrometer's measuring range is printed on its body (2.0–3.0mm ±0.005mm).

Q3: The dual-rate damper spring is described as "progressive"-how does this affect the pump's response to sudden load changes on the 336D excavator?
A: At low pressures (0–300 bar), the spring's lower rate (22 N/mm) allows quick damping response. At high pressures (300–580 bar), the higher rate (32 N/mm) provides stiffer damping to prevent oscillation. This matches the 336D's load pattern: sudden boom lifting (rapid pressure rise) is damped by the high-rate section, while swing maneuvers (moderate pressure fluctuations) are smoothed by the low-rate section. The progressive characteristic reduces control valve hunting by 35%.

Q4: Can the float-restoration rings be used if the piston cylinders show scoring deeper than 0.04mm?
A: No. The rings are designed to restore clearance in cylinders with uniform wear (no scoring). If scoring deeper than 0.04mm is visible (feels like a fingernail catch), the cylinder block must be re-sleeved or replaced. The kit includes a score-check ruler-a plastic film with 0.04mm reference bumps. If the bumps catch on the scoring, the rings cannot be installed. This prevents warranty claims from improper re-use of damaged housings.

Q5: How does the spline compensation washer affect the pump's timing relative to the engine crankshaft?
A: The washer does not change the pump's phase angle relative to the crankshaft-it only removes backlash within the spline coupling. Removing backlash means the pump's rotation matches the engine exactly, without the ±0.5° lag. This restores the ECU's injection timing map to its original calibration, improving combustion efficiency by approximately 2.5% in C-9 on-highway applications.

Q6: The kit is listed for C7/C9, but my 336D excavator has an HP10 pump label-does this kit fit?
A: Yes, if the HP10 pump has the 9-piston axial configuration and Bosch Rexroth A10VSO-style housing. The HP10 is the Caterpillar branding for the actuation pump used in the 336D. Check the pump's nameplate for the Bosch P-series code (P3000/P4000)-if present, the kit is compatible. The HP10 pump serial numbers starting with 396 or 443 are confirmed fits. The included 336D-specific torque card covers both HP10 and HP10-2 variants.

 

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