Komatsu Part SHIM 421-23-31370

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Product Overview

The 421-23-31370 SHIM is a genuine Komatsu OEM replacement shim from the 421 prefix series. Shims are precision-ground spacers that allow you to adjust clearances, preloads, and alignments to the exact values Komatsu's engineers specified when they designed the assembly. In gearboxes, final drives, and bearing housings, the correct shim thickness can mean the difference between a machine that runs reliably for thousands of hours and one that fails prematurely from incorrect bearing preload or gear mesh.

Part Number: 421-23-31370 Part Name: SHIM Part Type: OEM Komatsu Replacement Shim Availability: In stock — ready to ship

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Why Skipping Shim Measurements Causes Comebacks

If you've ever rebuilt a gearbox or final drive only to have it come back noisy, running hot, or leaking, incorrect shimming was likely the root cause. Every machined component in an assembly carries manufacturing tolerances — allowable variations in dimensions that are part of the production specification. When you stack five or ten components together, those tolerance variations accumulate. A bearing assembly that needs exactly 0.05 mm of preload might end up with 0.15 mm — three times the specification — if the tolerance stack-up isn't corrected by shimming. The machine may run acceptably for a few hundred hours, but the incorrect preload causes the bearing to run hotter than designed, the lubricant to break down faster, and fatigue to accelerate. The failure comes later — often just outside the warranty period on your repair — and the customer blames your work rather than the root cause. Taking the time to measure the assembled clearance, calculate the required shim thickness, and install the correct shim pack is what separates professional, lasting repairs from those that won't survive. Our customers who rebuild Komatsu components regularly know that a shim kit and the discipline to use it correctly protect their reputation as well as their work.

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When to Replace

Replace the 421-23-31370 when the shim is physically damaged — bent, crushed, torn, or its precision surfaces are corroded; when clearance or preload measurements during assembly indicate the existing shim pack is outside the specification range; when the assembly is being rebuilt and all shims must be measured and verified against Komatsu's published values; or when the shim shows uneven wear patterns, which indicates the assembly has been running with incorrect clearance.

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Installation

1. Confirm 421-23-31370 in your Komatsu parts catalog — verify the shim thickness matches what your measurement calls for
2. Clean the shim and all contact surfaces completely — even a thin film of oil or a hair-thin piece of debris affects the assembled dimension
3. Install the shim in the correct position — note the stack order if multiple shims are being used together
4. Measure the resulting clearance or preload with a dial indicator, feeler gauge, or micrometer as specified in the service manual
5. Adjust by adding or removing individual shims until the specification is achieved
6. Record the final shim pack thickness in your maintenance records — this saves measurement time at the next rebuild

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Request a Quote

Need the Komatsu 421-23-31370 SHIM? Contact us through the form on this page, or reach out by phone, email, or WhatsApp. We respond within one business day.