Komatsu 6D105 Engine Rebuild Parts Checklist: Liner, Piston Rings, Gaskets and Valve Train

A successful Komatsu 6D105 rebuild starts before the first part is ordered. The engine designation narrows the family, but the correct liner, piston, rings, bearings, gaskets and valve-train parts still depend on the complete model, serial information, existing part numbers, measured wear and any previous machining. This checklist organizes the inspection and ordering work so the parts list follows evidence from the actual engine.

When does a Komatsu 6D105 need an overhaul or partial rebuild?

An overhaul decision should be based on diagnosis and measurement. High oil use, heavy blow-by, low or uneven compression, coolant in the oil, oil in the coolant, persistent low oil pressure, bearing noise, abnormal exhaust smoke or metal in the lubricant can justify deeper inspection. None of these symptoms identifies one failed component by itself. A damaged turbocharger, injector problem, restricted breather, external leak or cooling-system fault can produce similar observations.

Start with service history, fluid condition and external checks. Then use the correct shop manual for the exact engine and machine serial range to plan compression, leak-down, oil-pressure and cooling-system tests. If teardown is required, preserve the position and orientation of pistons, bearings, valves and related hardware. The wear pattern often explains whether a complete rebuild, a cylinder-head repair or a narrower component replacement is appropriate.

If piston damage is present, identify the cause before replacing the assembly. Our guide to common diesel-engine piston failure causes explains why lubrication, cooling, combustion and clearance problems must be corrected with the damaged part.

Confirm the exact Komatsu 6D105 configuration before buying parts

The 6D105 name is a family identifier, not a complete parts key. Historical technical references describe the family as an inline six-cylinder diesel with a 105 mm bore, 125 mm stroke and approximately 6.49 to 6.5 L displacement, and they distinguish naturally aspirated 6D105 and turbocharged S6D105 forms. Those facts help identify the family, but they do not prove the installed piston crown, liner specification, bearing grade, gasket version or external assembly.

Use the complete engine plate and machine plate. Then compare the old components and measurements with the correct parts book or service manual. For family specifications and a detailed identification workflow, see the 6D105 Komatsu engine guide before preparing the rebuild order.

Model, serial number and old-part evidence

Photograph the engine plate in place so the surrounding engine features are visible, then take a close image that makes every character readable. Record the machine serial number separately. Clean removed parts only enough to expose stamped, cast or printed marks, and photograph both the full part and the marking. A casting number may identify a raw casting rather than the complete service assembly, so keep the image context.

Piston, liner, bearing and gasket variables

Internal parts require measured evidence. The block may have been bored, the crankshaft may have been ground, the cylinder head may have been machined, and an earlier rebuild may have introduced repair-size components. Ask the machine shop for actual bore and journal readings and for the required finished sizes. Confirm piston bowl and crown details, pin diameter, ring-groove count and thickness, liner profile and sealing features, bearing size or grade, and the head-gasket identification used by the correct service information.

Komatsu 6D105 rebuild parts checklist

Top-end rebuild parts checklist

Head gasket and overhaul gasket set

The cylinder-head gasket seals combustion, coolant and oil passages, while an overhaul gasket kit may include multiple seals for different engine areas. Do not assume a complete kit automatically contains the correct version of every seal. Compare the kit packing list with the teardown list and keep the old gaskets available for visual and dimensional comparison. The live 6D105 head-gasket listing and 6D105 overhaul-gasket-kit listing are useful references, but compatibility still needs to be confirmed from the serial and part evidence.

Valves, guides, seats and related valve-train parts

Check valve stems, guide clearance, seat contact, spring condition and cylinder-head machining history as a system. Replacing one part without measuring the mating components can leave poor sealing or incorrect geometry. The 6D105 valve-guide listing provides a live product reference. Confirm the guide dimensions and related valve and seat requirements from the actual cylinder head before ordering.

Bottom-end rebuild parts checklist

Pistons, piston rings and cylinder liners

Treat the piston, rings and liner as a matched wear and sealing group. Record the piston crown, combustion bowl, pin diameter, clip arrangement, ring count, ring profile and groove thickness. Measure liner dimensions and inspect the block register and sealing areas. Useful live references include the 6D105 piston kit, 6D105 piston-ring set and 6D105 cylinder liner. These are product options to verify, not proof of universal fit.

Main bearings, connecting-rod bearings and thrust parts

Bearing size is controlled by measured crankshaft journals and the required oil clearance, not by the engine name alone. Keep every removed shell identified by location, check the back markings and ask whether the crankshaft has been ground. Inspect rod and main housing condition and measure thrust clearance using the correct manual procedure. The available 6D105 connecting-rod bearing is a relevant live listing; the machine-shop report must determine the final size or grade.

Cooling, lubrication and fuel-system parts worth inspecting

A teardown provides access to components that can damage a fresh rebuild if their condition is ignored. Pressure-test or inspect the oil cooler as specified, examine oil passages and pickup components, check the water pump and cooling passages, and review hoses and seals for hardening or contamination. If coolant and oil have mixed, find the source and clean the system before start-up. The live 6D105 oil-cooler assembly should be matched by old number, ports and mounting details.

Fuel-system parts should be tested by a qualified shop when symptoms or inspection justify it. A rebuild cannot compensate for incorrect injection, restricted fuel supply or air-system faults. Preserve identification numbers on pumps and injectors and use the manual for the exact configuration.

Complete rebuild kit vs individual parts

A complete kit can simplify purchasing when the engine identity, included components and required sizes are already confirmed. It can also reduce the chance of forgetting common seals or related wear parts. However, the words "rebuild kit" or "overhaul kit" do not define one universal contents list. Ask for a written packing list and compare it with the teardown report.

Individual parts make more sense when the repair is limited, when the block or crankshaft needs a non-standard size, when several original components remain serviceable, or when the required configuration is not represented by one package. Many rebuild orders combine a gasket set with separately verified pistons, rings, liners and bearings. For an additional model-specific example of how to organize the decision, see the engine rebuild parts checklist and buying guide; use its workflow, not its Kubota-specific parts, for a 6D105.

Part-number verification workflow before placing an order

Prepare one evidence package for the supplier rather than sending scattered messages. Label the photos, measurements and old numbers so each item can be matched to the correct cylinder, journal or assembly. If a number is unreadable, say so instead of guessing. State which parts are definitely required and which are still subject to inspection. This gives the supplier a clear basis for checking the proposal and gives the rebuilder a record that can be reviewed before payment, shipment and installation.

1. Record the full machine model and machine serial number.
2. Record the complete engine designation and engine serial number.
3. Photograph each old part, its number and its mounting context.
4. List the confirmed failure cause and all related parts that require inspection.
5. Obtain bore, liner, piston, crankshaft journal and bearing measurements from the machine shop.
6. State standard or repair size only when the measurements support it.
7. Compare gasket and kit contents line by line with the teardown list.
8. Confirm quantities, related seals, clips and hardware before approval.
9. Ask the supplier to verify the proposed parts against the submitted evidence.

A repeatable identification process is more reliable than visual similarity. Our engine-model identification guide before ordering parts shows the same evidence-first method in another engine family.

Frequently asked questions

Sources consulted: JCMA historical 6D105/S6D105 development reference; Komatsu machine-specific quick-reference parts guides; Komatsu model- and serial-number-based parts ordering. Exact limits, clearances, torque values and procedures must come from the correct service manual for the machine and engine serial range.