Model Spotlight

Case 680K Construction King Backhoe Loader: Specs, Parts & Common Issues

Produced 1986–1988, the 680K is the engine-architecture watershed of the 680 line. Out went the long-serving Case 336 ci four-cylinder used on the 680E/G/H; in came the Case 6-590 — a 5.9-liter six-cylinder diesel (same bore/stroke geometry as the Cummins 6BT B-series, 101 HP gross / 90 net) that brings smoother power delivery and substantially more torque under load.

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Broken Tractor Editorial Team• Updated May 2026• 9 min read

The Case 680K is the engine-architecture watershed of the 680 line. It came to market in 1986 and ran through 1988, replacing the 680H. The defining 680K change is the engine: Case retired the long-serving 336 cu in four-cylinder used on the 680E, 680G, and 680H, and replaced it with the Case 6-590 — a 5.9-liter six-cylinder diesel with the same 4.02 × 4.72 in bore-stroke geometry as the Cummins 6BT B-series industrial engine. The result is a smoother-running, higher-output machine with substantially more torque under load: 101 HP gross / 90 HP net at 2,200 rpm and 260 lb-ft of torque at 1,200 rpm.

Beyond the engine change, the 680K kept the 24V electrical system carried from the 680H, retained the open-center hydraulic architecture (with refinements), and updated the cab and operator station. Production was relatively short (three years) before the 680L took over in 1989 with a turbocharged version of the same 6-590 block. That short run, combined with the cross-fit of many service parts with the longer-running 680L (1989–1993), 780C, 780D, and other Case industrial machines of the era, makes parts availability surprisingly good for a machine this old.

At-a-glance specifications

The 6-590 engine — what changed and why it matters

The step from the 680H's 336 cu in four-cylinder to the 680K's 6-590 six-cylinder is the biggest powertrain change in the 680 line's history. The numbers tell part of the story (90 HP net vs the 680H's 85 HP — a modest gain), but the practical-performance impact is much larger:

• Smoother power delivery — six cylinders running at the same rpm have half the power pulse interval of four cylinders, producing noticeably less engine vibration and a smoother feel under load.
• More torque at lower rpm — the 6-590 makes 260 lb-ft at 1,200 rpm; the 336-class engine on the 680H made its 261 lb-ft peak at 1,500 rpm. Peak torque arriving 300 rpm earlier means the engine pulls harder out of the dig at low rpm — a real-world digging-power improvement.
• Cummins B-series lineage — the 4.02 × 4.72 in bore-stroke geometry of the 6-590 matches the Cummins 6BT 5.9L industrial six-cylinder exactly. Case branded the engine as their own, but the lower-end architecture is shared with the Cummins block that powered countless Case, Dodge, and Ford industrial applications of the era. The result is broad service-parts availability through the Cummins B-series aftermarket.

24V electrical system

The 680K carried forward the 24V electrical system from the 680H — the same dual-battery, 24V-starter, 24V-alternator configuration that runs on the 780B / 850C / W14 family of Case industrial machines. The 24V starter is a high-current device that handles cold-weather starting on a 5.9L six-cylinder diesel without the cranking voltage drop a 12V system would see.

Practical implications: when the starter fails, source a verified 24V replacement rather than attempting a 12V conversion. Charging system maintenance is critical — corroded battery cables drop charging voltage and can lead to chronic discharge problems.

Hydraulics and cab

The 680K's open-center hydraulic system added a dedicated hydraulic oil cooler (A171963 in our catalog, cross-fits 680K and 680L) that helped manage heat from the higher-output engine and faster cycle times. The cooling system itself is the A172138 combined radiator and transmission oil cooler — a cross-fit part that covers 680K, 680L, 780C, and 780D. That four-machine cross-reference is one of the most useful in the Case industrial parts ecosystem.

Cab equipment was refined at the 680K, with optional factory A/C using the York-type compressor (A141060) shared with the 580D, 780C, and W14 through W36 wheel loaders.

Verified parts in stock

The 680K is over 35 years old. Parts availability is moderate-to-good, supported by cross-fit with the 680L (which had a substantially longer production run) and several other Case industrial machines. The items below are confirmed in stock at Broken Tractor with verified 680K fitment.

Common issues and what to expect

Cummins B-series-derived 6-590 engine

The Case 6-590's Cummins B-series lineage is good news for service: pistons, rings, bearings, head gasket sets, water pumps, and oil pumps are widely available through both Case sources and Cummins B-series channels. Common items: head gasket failure (between cylinders or weeping at the deck), valve seat recession on heavy-duty service, and injection pump wear on machines with long fuel-system service intervals.

24V starting and charging

The 24V system is durable but vulnerable to neglect. Corroded battery cables, marginal connections, and failed starter solenoids account for the majority of "won't start" complaints. Inspect at every service.

Hydraulic cooling and oil cleanliness

The dedicated hydraulic oil cooler (A171963) is essential to managing heat on the higher-output 680K. Cooler blockage from external debris or internal corrosion causes hydraulic oil overheating, which accelerates seal degradation throughout the system. Inspect and clean the cooler at every major service.

Power shuttle wear

The 4-speed power shuttle in the 680K has the same general architecture as earlier 680-line shuttles. Hydraulically actuated clutch packs wear with age, the shuttle valve gets sticky, and the torque converter charge pump weakens over time.

Cab seal and glass aging

35-plus-year-old cab seals are typically hard and brittle. The F44629 upper rear glass and matching glass items are common replacement parts. Replace the rubber seals when you replace the glass.

Where it sits in the 680 family

The 680K opens the 6-590 engine generation of the 680 line. After 1988 the 680L took over with the same engine block in turbocharged form — adding meaningful output and continuing through 1993 as the final 680-line backhoe loader. The 680K and 680L share most non-engine service parts, making the 680K's relatively short production run less of a parts-availability problem than it might otherwise be.