Caterpillar 320 Residual Lift Shim Selection Kit – 2.40–2.20mm Graded Pack (10 Steps × 5 Units) For HEUI Stroke Restoration

In a Caterpillar 320 HEUI injector, the intensifier piston does not directly drive the needle-it acts through a hydraulic link filled with high‑pressure oil. The initial clearance between the piston and this oil column, known as residual lift, determines the effective stroke available for injection. Over time, the piston face and the hydraulic link seat erode by fractions of a micron, increasing the residual lift and reducing the usable piston travel. For every 0.02 mm of extra clearance, the injector delivers roughly 2.5 mm³ less fuel per stroke-enough to drop engine power by 3 % and raise exhaust temperature by 15 °C. The only practical way to restore the original stroke is to insert a precision shim that compensates for this wear. But because each injector wears differently, a workshop needs a broad range of thicknesses to match each unit individually. The Caterpillar 320 Residual Lift Shim Kit (2.40 – 2.20 mm) delivers ten exactly spaced thickness grades, five shims per grade, giving you the flexibility to dial in each intensifier assembly with 0.02 mm resolution-without waiting for special orders.

New or low‑mileage injectors usually require shims near the upper end (2.36–2.40 mm) because the wear is minimal. As the piston and link bed in, the clearance grows, and you must decrease the shim thickness to bring the residual lift back to the factory spec (typically 0.35–0.45 mm). The kit covers the full service life of the injector:

Wear Stage	Typical Shim Range	Effect of Wrong Choice
Low wear (new rebuild)	2.36 – 2.40 mm	Too thin → residual lift too high → reduced stroke
Moderate wear (100k km)	2.28 – 2.34 mm	Too thick → residual lift too low → piston bottoms out
High wear (overhaul)	2.20 – 2.26 mm	Mismatch → uneven cylinder output, rough idle

The 0.02 mm step is fine enough to bring the residual lift within the OEM tolerance of ±0.01 mm, yet coarse enough to keep the kit manageable.

The residual lift shim sits directly under the intensifier spring retainer, experiencing a static preload of ~180 N and additional dynamic loads during each injection. Ordinary mild steel would "creep" and lose thickness over time. Our shims are stamped from DIN 1.3505 (100Cr6) bearing steel, vacuum‑hardened to 58–60 HRC, then double‑disc ground to:

Flatness ≤ 2 µm

Parallelism ≤ 3 µm

Surface finish Ra 0.2 µm

This ensures the shim does not deform, embed, or introduce angular misalignment into the intensifier stack, even after millions of cycles.

Each of the ten thickness grades (2.40, 2.38, 2.36, … down to 2.22) is sealed in a separate transparent poly‑bag with a large, color‑coded label. The bag colour follows a spectrum: red for 2.40, orange for 2.38, yellow for 2.36, green for 2.34, blue for 2.32, indigo for 2.30, violet for 2.28, pink for 2.26, grey for 2.24, white for 2.22. Additionally, each shim is laser‑engraved on its outer edge with the nominal thickness-so even after the bag is opened, you can instantly verify the value without reaching for a micrometer.

You don't need a complicated test bench. With the injector assembled (without the spring retainer), use a dial gauge to measure the distance from the top of the intensifier piston to the retainer shoulder. Then:

Subtract the target residual lift (consult your engine spec, usually 0.35–0.45 mm).

The result is the required shim thickness.

Select the closest grade from the kit (if between two, choose the thicker one, as you can fine‑tune with a thinner shim later).

A quick‑reference card with the formula is included in the storage case.

Q1: Can I stack two thinner shims to get a thickness not in the kit?
A: Stacking is not recommended. The contact faces are ground for single‑piece use; stacking introduces micro‑movements and uneven load distribution, which can alter the residual lift unpredictably. Use a single shim of the correct thickness.

Q2: How do I know if an old shim is still usable?
A: Measure its thickness with a micrometer. If it deviates more than 0.005 mm from the marked value, or if you see surface scoring or indentations, replace it. The new shims in our kit are guaranteed within ±5 µm.

Q3: I have a mix of injectors-some need 2.32, others 2.28. Is the kit cost‑effective?
A: Yes. With 5 shims per grade, you can service up to five full 6‑cylinder engines (30 injectors) without running out of the most common sizes. The kit eliminates the need to buy individual grades at inflated prices.

Q4: What happens if I choose a shim that is 0.02 mm too thick?
A: The residual lift will be too low, meaning the intensifier piston will bottom out before delivering full stroke. This reduces fuel delivery and may cause a knocking sound. Always measure and select carefully.

Q5: Is the laser marking durable enough to survive solvent cleaning?
A: Yes. The engraving is deep (0.05 mm) and resistant to diesel, brake cleaner, and ultrasonic bath solutions. It will remain legible for the life of the shim.

Q6: Can I use this kit for the CAT 3126B if my service manual specifies a different range?
A: The 3126B often uses a similar 8 mm guide pin, but the required thickness may fall outside 2.20–2.40. We recommend checking the manual. If you need a wider range, we offer complementary kits (e.g., 2.60–2.40 and 2.00–2.20).

 

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