Short answer: Boom, arm (stick) and bucket cylinder seal kits are designed for three different hydraulic cylinders on an excavator. They are usually not interchangeable because each cylinder can have different rod and bore diameters, stroke, pressure loading, gland design, seal profiles and OEM part numbers. Always match the exact cylinder position, machine model, serial range and part number before ordering.
“Excavator seal kit” is not a complete application description. One excavator normally uses separate hydraulic cylinders to raise the boom, move the arm or stick, and curl the bucket. Even when the seals look similar, installing a kit intended for another cylinder position can cause poor fit, internal bypass, external leakage or installation damage.
Boom vs Arm vs Bucket Cylinder Seal Kits
| Cylinder position | Main function | Typical operating characteristic | Identification priority |
|---|---|---|---|
| Boom cylinder | Raises and lowers the main boom | Supports and moves a large portion of the front attachment load | Boom cylinder or seal-kit part number, machine model, serial range, rod and bore size |
| Arm/stick cylinder | Moves the arm or stick inward and outward | Controls digging reach and pull through the middle section of the attachment | Arm/stick terminology, exact part number, model suffix and cylinder dimensions |
| Bucket cylinder | Curls and dumps the bucket | Operates through the bucket linkage and experiences frequent direction changes | Bucket cylinder part number, linkage application, model and dimensions |
What Is a Boom Cylinder Seal Kit?
The boom cylinder seal kit services the cylinder—or cylinder pair—that raises and lowers the excavator boom. Depending on the machine design, an excavator may use one or two boom cylinders. The kit can include rod seals, piston seals, wipers, O-rings, backup rings and wear rings, but the exact contents depend on the cylinder.
A boom kit should not be selected simply because the machine model appears in a product title. Confirm whether the machine uses different cylinder revisions, whether the listing is for the left or right cylinder when relevant, and whether the OEM reference matches the installed cylinder.
What Is an Arm or Stick Cylinder Seal Kit?
The terms arm cylinder and stick cylinder often describe the same excavator function. Terminology varies among equipment manufacturers, parts manuals and regions. This cylinder moves the second section of the excavator attachment and controls reach and digging motion.
Do not assume a listing is wrong because one source says “arm” and another says “stick.” Instead, compare the part number, component drawing, machine model, serial number and dimensions. A translation or terminology difference is less important than the actual cylinder identity.
What Is a Bucket Cylinder Seal Kit?
The bucket cylinder operates the bucket linkage, curling the bucket inward for digging and extending it for dumping. It is normally a different size from the boom and arm cylinders and uses its own seal arrangement.
Bucket kits can also be confused with bucket-linkage components or with front-loader bucket cylinders on backhoe loaders. State the machine type and exact cylinder position when requesting identification help.
Why Are These Seal Kits Usually Not Interchangeable?
- Different dimensions: Rod diameter, cylinder bore, groove width and seal cross-section can differ.
- Different seal profiles: The rod seal, piston seal, buffer seal or wiper design may not be the same.
- Different hardware: Gland, piston, wear-ring and backup-ring arrangements vary by cylinder.
- Different part numbers: Each repair position commonly has its own OEM seal-kit or cylinder reference.
- Different revisions: Machines in the same model family can use different cylinders according to serial range, production date or regional configuration.
How to Identify the Correct Cylinder Position
- Locate the cylinder physically on the machine.
- Determine which attachment section it moves.
- Check the equipment parts diagram for the cylinder and seal-kit reference.
- Record the complete machine model and serial number.
- Photograph the cylinder tag, casting marks and hose-port arrangement.
- Compare the rod and bore dimensions when reliable specifications are available.
If the cylinder has already been dismantled, keep the boom, arm and bucket components separated and labeled. Mixing old seals from different cylinders makes dimensional identification less reliable.
Information to Check Before Ordering
| Required information | Example | Why it matters |
|---|---|---|
| Equipment brand | Caterpillar, Komatsu, Hitachi, JCB, Case, Volvo or Doosan | Directs the search to the correct parts system |
| Full machine model | Include LC, -7, V or other suffixes | Similar model names may use different cylinders |
| Serial number or range | From the machine identification plate | Helps identify production changes |
| Cylinder position | Boom, arm/stick or bucket | Prevents selecting a kit for another function |
| Part number | Complete number with every prefix and suffix | Preferred compatibility reference |
| Dimensions | Rod, bore, groove and seal measurements | Supports confirmation when references are incomplete |
Can Rod and Bore Size Alone Identify the Kit?
Rod and bore measurements are valuable confirmation points, but they should not be used alone when an OEM reference is available. Two cylinders can share similar main dimensions while using different gland designs, seal profiles, groove sizes or component revisions.
When no part number is available, follow our hydraulic cylinder seal-kit measurement guide. Measure components without stretching soft seals, record the unit, and provide clear photos of the complete seal arrangement.
Common Ordering Mistakes
- Ordering by excavator model without naming the cylinder position
- Confusing arm and boom terminology
- Assuming all cylinders on one machine use the same kit
- Comparing only product photos
- Dropping letters, hyphens or suffixes from the part number
- Using dimensions from an online source without checking the installed cylinder
- Opening or installing the kit before comparing it with the original components
Examples by Equipment Brand
Brand-specific numbering and model conventions differ, but the selection principle is the same. Browse the relevant application collection and then confirm the exact product:
- Caterpillar excavator seal kits
- Komatsu excavator seal kits
- Hitachi excavator seal kits
- JCB excavator seal kits
- Case excavator seal kits
- Doosan excavator seal kits
Frequently Asked Questions
Are arm and stick cylinder seal kits the same thing?
“Arm” and “stick” commonly refer to the same excavator attachment section, but you must still verify the part number and installed cylinder. Terminology alone does not prove compatibility.
Can a boom cylinder seal kit fit a bucket cylinder?
Normally no. Boom and bucket cylinders commonly have different dimensions, groove designs and seal-kit references. Use the kit specified for the exact position.
Does one excavator model always use one boom seal kit?
Not necessarily. Cylinder designs can change by serial-number range, production version, supplier or regional configuration.
What if I cannot find the OEM seal-kit number?
Provide the complete machine model, serial number, cylinder position, cylinder or gland markings, old-seal photos and accurate dimensions. Read our excavator seal-kit identification guide for the complete process.
What may be included in a cylinder seal kit?
Depending on the application, a kit may contain rod seals, piston seals, buffer seals, wipers, O-rings, backup rings and wear rings. Always check the individual listing because kit contents vary.
Need Help Identifying the Correct Kit?
Contact Fujis Seal with the equipment brand, full model, serial number, boom/arm/bucket position, part number, photos and required quantity. Fujis Seal supplies aftermarket replacement seal kits; manufacturer names and references are used for compatibility identification. Unless expressly stated on a product page, products are not represented as being manufactured or endorsed by the equipment brand.
Technical note: This guide provides general identification information. Confirm the repair against the equipment manufacturer's current parts and service information before ordering or installation.
