Build a Maintenance Bill of Materials for an Excavator Undercarriage

A maintenance bill of materials can describe an installed machine, a model configuration or the parts needed for a particular task. For an undercarriage repair, the planner has to connect those records to one defined job. A list headed “excavator undercarriage” can contain the right components and still produce the wrong order if it mixes both sides of the machine, counts an assembly and its included pieces twice, or leaves quantities detached from their positions.

For a job replacing two right-side rollers, the physical requirement is two assemblies at two identified positions. A supplier may sell them individually or together, and mounting hardware may have its own replacement requirement. The BOM has to connect that physical need to the actual supply units without losing which parts are included in each one.

Define the machine and repair scope

Begin with the identity that controls the parts information: manufacturer, exact model, serial number or serial range, and any undercarriage configuration or option that affects the assembly. A model family can contain more than one arrangement. Field modifications and previous assembly replacements can also leave the installed configuration different from the simplest catalogue assumption.

Keep whole-machine configuration separate from current repair scope. The machine has a left and right undercarriage, but the current work order may cover one failed roller on the right, a complete right-side rebuild, or both sides. If a BOM lists the whole configuration without marking the repair boundary, a reviewer cannot tell whether omitted quantities are mistakes or deliberate exclusions.

A clear header can record:

• machine make, model and serial identity;
• installed track or undercarriage configuration where verified;
• affected side and positions;
• reason for the repair and inspection reference;
• work included in this release;
• related work explicitly deferred or handled under another order; and
• drawing, parts catalogue or service-information revision used.

A maintenance system can contain several kinds of BOM. CHAMPS describes lists tied to equipment, maintenance tasks or a particular make and model. Those scopes serve different purposes. A model list helps locate candidates; an asset list should reflect the actual machine; a task list supports a defined job. Copying one into another without checking the scope is how a plausible parts list becomes the wrong repair order.

The scope should describe physical limits. “Replace worn undercarriage” is not a boundary. “Right side: replace identified lower rollers at positions recorded in the inspection; retain the track, idler and sprocket pending the listed checks” tells the planner which neighbouring components need inspection information and which parts belong in the purchasing request.

Follow the undercarriage assembly hierarchy

An excavator undercarriage is easier to plan when the BOM follows the way the repair is assembled. Start with the major assembly or location, then list serviceable components, attachment hardware and genuine options or variants beneath it. This prevents a top-level assembly and its included children from being ordered twice.

For example, a roller line may represent a complete service assembly. Separate seals, shafts or internal pieces should not be added merely because an exploded diagram shows them; whether they are separately serviced and required for this repair depends on the applicable parts information. Similarly, mounting bolts may be reused, replaced individually or supplied with another item depending on the documented procedure and packaging. The BOM must state what the source establishes rather than infer package contents from an illustration.

Separate installed components from past consumption

An asset's transaction history is a useful source, but it is not automatically a picture of what is installed now. Microsoft's asset BOM documentation explains that work-order consumption can update the record and can include lubricants, bolts and gaskets as well as spare parts. It also distinguishes current entries from expired ones and calls for updates when items are replaced.

For example, two roller purchases for the same position in successive repairs do not mean two rollers occupy that position. One replaced the other. Lubricant consumed on those jobs does not become another permanent assembly beneath the roller. Keep the removed component in service history, identify its replacement as the installed item, and determine the next repair quantity from the current inspection. Otherwise, adding up consumption can quietly inflate the BOM.

The following fictional repair concerns two identified right-side lower-roller positions. It assumes the inspection has selected those positions and the roller identities have been resolved. It deliberately leaves the hardware decision open because its service requirement has not yet been checked; these are not quantities or fitment instructions for a real machine.

The two assembly rows establish the physical need: two complete rollers at two different positions. They do not establish that one supplier package contains two rollers, or that attachment hardware is included. That second question belongs to the actual offer. Keeping it separate prevents an exploded view, a transaction total or a package photograph from deciding the order quantity.

Resolve part identity before quantity

Quantity does not rescue an uncertain identity. Before multiplying a line across positions, establish the item using current applicable information and evidence from the machine. Useful evidence can include the installed marking, part number, casting identifier, measured features taken from defined datums, mounting arrangement, side and position, and photographs that show context as well as detail.

Do not silently translate an original number into a seller number. Supersession, alternate suppliers and aftermarket references each have their own evidence chain. Record the original or installed identifier in its own field, the candidate service part in another, and the source supporting the relationship. If that source is missing, mark the cross-reference unresolved.

For a track roller, retain the installed marking alongside the proposed replacement. If the parts reference identifies different rollers at different positions, keep those lines separate even when the quantities are small. Combining them into “two rollers” would erase the distinction that made the selection valid.

Configuration changes should remain visible. If a complete assembly was replaced previously, preserve both the machine's original parts reference and the identity found on the installed assembly. The current installed state may control service parts, while the original identity explains why older records show different numbers. Deleting one side of that history makes the next repair harder.

Give every quantity a denominator

The number “2” is incomplete until the BOM says two of what, for which boundary. Undercarriage quantities are often described per machine, per side, per assembly, per track chain or per current repair. Seller units add another layer: one listing may be an individual item, another a matched pair, a kit or a set with included hardware.

Record the engineering need first. If the repair requires one component at each of two documented positions on the right side, state “2 each for the current right-side repair.” Then record how the seller supplies the item. If packaging has not been verified, do not assume that “set” means the required two or that a kit contains every pictured item.

This separation makes conversions reviewable:

required repair quantity ÷ verified pieces per seller unit = seller units to request

Rounding and spare policy may change the purchasing quantity, but those decisions should have their own field. They should not overwrite the physical need. A purchase of an extra spare then remains distinguishable from a quantity error.

Return to the two-roller repair example. An offer confirmed to supply one complete roller per seller unit requires two units. An offer confirmed to supply two of the required rollers in one set requires one set. The physical requirement remains two rollers in either case. A listing showing two views of the same roller, however, does not establish that it supplies a pair. The package description must settle that question before the conversion is made.

Give hardware its own evidence

Hardware deserves the same discipline. A note such as “bolts included” needs a source tied to the exact offer. If the service information requires replacement hardware, that requirement should be linked to the appropriate parent assembly. If reuse depends on inspection, the BOM should show the condition and owner of that decision rather than preselect a quantity.

Keep unresolved lines visible

A robust BOM has a status column because uncertainty is part of maintenance planning. Suggested states can be plain language: confirmed, awaiting machine inspection, awaiting current parts information, supplier package not confirmed, or outside approved scope. The wording matters less than ensuring that an unresolved line cannot pass unnoticed into release.

Unknowns should block only the decisions they actually affect. An uncertain bolt package may prevent release of the hardware line while a separately verified roller remains valid. An unknown machine serial range may undermine every fitment-dependent line. The reviewer should be able to see that difference without reading an email chain.

Describe the missing information beside the affected line. In the two-roller example, “hardware quantity pending the specified reuse/replacement requirement and confirmed package contents” explains why the count is open. It also makes clear that the uncertainty concerns the attachments, rather than casting doubt on the two already identified roller positions.

Finally, freeze the release version. If inspection expands the repair from one side to both, revise the scope and quantities rather than editing a printed list silently. If a superseded part is accepted, keep the original candidate, the replacement identity, the supporting source and approval together. The maintenance BOM then becomes a traceable explanation of what was ordered for this repair, not merely a spreadsheet that happened to total correctly.

References

• Champs: Bill of Material
• Microsoft Learn: asset bills of materials