Caterpillarwork toolmulching head

Caterpillar HM312

Maintenance schedule, common problems & OEM parts breakdown

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The Caterpillar HM312 is a hydraulically driven rotary mulching head built as an attachment for skid steer, multi terrain, and compact track loader carriers. It weighs 940 kg (2,070 lb) and cuts a 1,210 mm (48 in) wide swath, sized for clearing brush and stems up to 200 mm (8 in) in diameter. It carries no engine, transmission, or fuel tank of its own; carrier hydraulic flow drives an axial-piston motor that spins the cutter drum through a V-belt reduction at 1,800-2,100 rpm. The head mounts to the carrier through Cat's standard quick coupler with quick-disconnect hydraulic couplings.

Within the mulching-head lineup, the HM312 sits at the compact end alongside the larger HM315 and HM315B, which share the same basic hydraulic drive concept but scale up flow requirements and cutting width for bigger carriers. Because the HM312 carries no fluids beyond grease at its drum bearing, drive shaft hub, and pivot pin, its upkeep centers on wear parts rather than fluid changes or analysis. That grease-only, wear-part-driven service profile keeps running cost predictable and makes belt, tooth, and bearing condition the main things worth checking on a used unit today.

Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.

Caterpillar HM312 specifications

Weights

Operating weight940 kg (2,070 lb)

Dimensions

Overall length1,470 mm (58 in)
Overall width1,640 mm (65 in)
Overall height1,610 mm (63 in)
Cutting width1,210 mm (48 in)

Performance

Hydraulic flow required (from carrier)120-137 L/min (31.5-36 gpm)
Hydraulic pressure required (from carrier)195-350 bar (2,828-5,075 psi). Actual pressure varies by carrier hydraulic setup.
Drum/rotor speed1,800-2,100 rpm
Maximum cutting diameter (stem capacity)200 mm (8 in). Rated for light-duty vegetation clearing, not heavy forestry work.
Drive systemCarrier hydraulic flow powers an axial-piston motor, which turns the cutter drum through a V-belt speed reduction.

Service capacities (summary)

Grease pointsDrum bearing and pivot grease fittings only. No published grease quantity or fitting count in dealer literature — follow the service decal or operation and maintenance manual for intervals.
Gearbox/drive-case oilNone documented. The head has no oil-filled gearbox or sump; drive is by V-belt off the hydraulic motor. All hydraulic oil is carried and serviced in the carrier machine's own circuit, not in the head.

Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.

HM312 fluids & capacities

SystemCapacityRecommended fluid
Grease points (drum/rotary cutter bearing, drive shaft hub bearing, pivot/mounting pin at the cylinder)No fill capacity applies. Apply grease at each fitting per the OMM interval until fresh grease purges from the bearing or pin; no volume is specified.Exact grease name is not confirmed in available source excerpts for this tool. Cat work-tool grease fittings and pivot pins generally call for Cat Multipurpose Grease (MPGM); confirm the exact grease callout on the HM312 lubrication chart in the Operation and Maintenance Manual, since high-speed drum bearings on some Cat mulching heads can call for a dedicated high-speed bearing grease instead of standard chassis grease.

Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.

Caterpillar HM312 maintenance schedule

Service intervalTasks
Every 10 h
  • Inspect the V-belt for glazing, cracking, or slipping and confirm proper tension.
  • Check cutter teeth for wear, chipping, or missing carbide tips.
  • Inspect hydraulic hoses, fittings, and quick-coupler connections for leaks.
  • Clear packed debris from inside the drum housing and hood.
Every 50 h
  • Grease the rotary cutter (drum) bearing per the operation and maintenance manual interval.
  • Grease the drive shaft hub bearing.
  • Grease the pivot pin at the cylinder mount.
  • Recheck belt tension and adjust as needed.
Every 250 h
  • With the head off the carrier, spin the drum by hand and check bearing play and smoothness.
  • Inspect tooth holder pockets for cracking or damage from a worn or missing tooth.
  • Check quick-coupler pins and wear plates for slop.
  • Inspect the hydraulic motor case and shaft seal for leaks.
Every 500 h
  • Replace V-belts as a matched set if glazed, cracked, or stretched.
  • Inspect the hydraulic motor shaft seal and replace if weeping.
  • Service or rebuild the drum bearing housing if play or noise is present.
  • Have a dealer verify carrier hydraulic flow and pressure still match the head's spec.

Servicing the HM312 beyond the schedule

Predictive Maintenance & Fluid Analysis

The HM312 has no engine oil or coolant to sample, so its predictive checks are physical rather than lab-based. Track belt tension and glaze, tooth wear pattern, and drum bearing play over time. With the head off the carrier, spin the drum by hand and feel for roughness or side-to-side play at the shaft. Watch for heat at the bearing housing after a run, grease weeping past the seals, or a new whine from the drum center. Catching these signs early flags a bearing or belt problem before it turns into a shaft or housing repair.

Corrective & Common Repairs

Most HM312 repairs are wear-part swaps. Replace V-belts as a matched set rather than mixing a new belt with stretched ones, which loads the new belt unevenly and shortens its life. Rotate reversible teeth to even out wear before they go fully dull, and replace a tooth once the carbide is gone or the holder itself starts contacting material, since running on a bare holder damages the mounting pocket. Check quick-coupler pins and wear plates for slop, since a loose coupler lets the head shift under load.

Overhaul & Rebuild Points

Deeper work centers on the drum and the hydraulic motor. A rotor thrown out of balance by a missing tooth accelerates bearing wear, so a drum or bearing-housing rebuild often follows neglected tooth maintenance. Have a dealer service the axial-piston motor if the shaft seal weeps or the case shows leaks at the fittings, since motor wear shows up as reduced rotor speed even with correct carrier flow. Verify hydraulic flow and pressure against the carrier's high-flow circuit spec before returning a rebuilt head to work.

Seasonal & Environment Servicing

Clear packed debris from inside the drum housing and hood regularly; built-up material traps moisture against the bearing seals and hides tooth wear underneath. In cold weather grease stiffens, so cycle the drum and hydraulic motor briefly before working the head hard, and keep the drum bearing, drive shaft hub, and pivot pin on their normal grease interval even during storage. For extended storage, back off belt tension to reduce set, cap or plug the hydraulic couplers to keep contamination out, and keep the head off the ground to protect the coupler wear plates.

HM312 attachments & work tools

Host carrier class

The HM312 mulching head is built for skid steer loaders, multi-terrain loaders, and compact track loaders in that power and hydraulic-flow class, not for excavators or wheel loaders. Real-world fitments reported for the head include Cat multi-terrain loader and compact track loader platforms such as the 287C and 299D2 size range.

Coupler / mounting system

The head attaches through Cat's standard work-tool quick coupler, an opposing-edge clamping design that locks the tool to the carrier's coupler frame for fast changeouts. Hydraulic hookup uses quick-disconnect couplings on cordura-wrapped hose runs; depending on the carrier's hydraulic circuit and electrical setup, a work-tool conversion kit or machine harness kit can be needed to match line count and control-pin wiring, so exact hookup varies by configuration.

Cutter tooth / tooth-holder options

The rotor uses a fixed-tooth, single-bolt-retention design, with standard carbide teeth as the baseline for general brush and sapling clearing with occasional rock contact. Harder, more wear-resistant tooth styles for rocky or abrasive ground, and narrower cutting-style teeth for faster work in cleaner wood, exist across this mulcher tooth family; exact option availability varies by configuration.

Guarding / debris protection

A hydraulically operated front hood/door encloses the cutting chamber to contain thrown material during normal mulching and opens to feed larger stems into the rotor. An add-on debris barrier package is offered for extra flying-debris protection when the head is run in heavier clearing work.

All HM312 assemblies by section

Every catalogued assembly group for the Caterpillar HM312. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Frame And Body
247-5845 Frame Gp-Mulching Head
09***97Pulg2
17***05Bolt-Socket Head; (M8x1.25x12-mm)4
17***11Locknut; (M16x2-Thd)6
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247-5883 Guard Gp-Bottom -Debris Barrier
24***83Guard Group-Bottom; -Debris Barrier1
24***84Shaft-Support2
24***85Chain85
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247-5850 Guard Gp-Mulching Head
13***50Nut; (M18x2.5)6
24***42Support-Frame; (Lh)1
24***43Frame As-Guard1
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Hydraulic System
253-6947 Cylinder & Mtg Gp-Mulching Hd
25***47Cylinder & Mtg Group-Mulching Hd1
25***48Cylinder Group-Hydraulic1
25***49Kit-Seal1
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260-5166 Hydraulic Ar-Mulching Head
16***02Guard; (2m)0
25***50Hydraulic Group-Mulching Head1
26***15Lines Group-Cylinder1
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253-6950 Hydraulic Gp-Mulching Head
25***44Manifold Group-Control1
25***47Cylinder & Mtg Group-Mulching Hd1
25***50Hydraulic Group-Mulching Head1
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260-3616 Lines Gp-Connecting
09***31Bolt; (Socket Head) (M10x1.5x120mm)8
14***48Fitting As; (Quick Disconnect, Male)1
14***49Fitting As; (Quick Disconnect, Female)1
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260-3615 Lines Gp-Cylinder
14***25Connector As.2
15***77Connector Group2
15***81Fitting As; (Quick Disconnect, Male)1
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Service Equipment And Supplies
260-6554 Film Gp
20***25Film-Stripe; (Red)(44cm)0
22***69Film-Warning; (Do Not Operate, Read Omm)1
24***21Film-Warning; (Flying Debris)1
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Work Tool Arrangement
247-5900 Head Ar-Mulching
24***44Head Group-Mulching1
24***50Guard Group-Mulching Head1
24***00Head Ar-Mulching1
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Work Tools
247-5911 Cutter Gp-Rotary
24***11Cutter Group-Rotary1
24***12Drum As-Rotary Cutter1
24***13Tooth As-Cutter; (Standard)26
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247-5887 Drive Gp-Mulching Head
06***27Bearing2
19***34Setscrew; (M12x1.75x110-mm)2
22***30Tube1
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247-5896 Drum Gp-Rotary Cutter
08***17Screw-Hex Socket; (M8x1.25-Thd)12
09***16Ring-Retaining; (External)2
09***56Pin-Spring2
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247-5844 Head Gp-Mulching
24***44Head Group-Mulching1
24***45Frame Group-Mulching Head1
24***83Guard Group-Bottom; -Debris Barrier1
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247-5889 Kit-Guard -Quick Coupler
23***78Plate2
24***89Kit-Guard; -Quick Coupler1
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HM312 serial number reference

The mulching head carries its own identification plate mounted on the tool housing/frame, separate from the carrier machine's engine or chassis plate. The plate lists the full Product Identification Number: a 3-letter prefix identifying the tool model and production block, followed by a sequential unit number. Read the prefix first to confirm the tool family, then use the sequence number to place the individual unit within that production run.

PrefixIdentifies
DJPHM312 Mulching Head

Frequently asked questions

Does the Caterpillar HM312 have its own engine?

No. The HM312 is a hydraulically driven attachment with no engine, transmission, or fuel tank of its own. It runs entirely off the carrier's hydraulic circuit, which powers an axial-piston motor that spins the cutter drum through a V-belt reduction.

What is the operating weight of the HM312?

The HM312 weighs 940 kg (2,070 lb) and cuts a 1,210 mm (48 in) wide swath, with overall dimensions of about 1,470 x 1,640 x 1,610 mm (58 x 65 x 63 in, L x W x H).

What carriers is the HM312 compatible with?

It mounts on skid steer, multi terrain, and compact track loader carriers fitted with a high-flow auxiliary hydraulic circuit, roughly 120-137 L/min (31.5-36 gpm) at 195-350 bar (2,828-5,075 psi), using Cat's standard quick coupler and quick-disconnect hydraulic couplings.

What HM312 owners discuss

How often should the drive belts on an HM312 be checked, and what does normal wear look like?
Check belt condition and tension at the start of each shift, more often in dusty or wet ground conditions. V-belts glaze and stretch with heat and slip; look for a shiny, cracked belt face and check the pulley grooves for uneven wear. A belt that's too loose lets the rotor slip under load and drops cutting speed well before it actually breaks. Replace belts as a matched set rather than swapping a single belt, since pairing a new belt with stretched ones loads it unevenly and shortens its life.
What's the tooth wear pattern like, and when do you replace versus rotate?
In softer material, brush and softwood with little rock, teeth can run a long season with very little wear; some operators have gone over a year in rocky ground while changing only a single tooth. In abrasive or rocky ground, wear shows up much faster, with carbide tips rounding off or chipping in a fraction of that time. Rotate reversible teeth to even out wear before they go fully dull, and replace a tooth once the carbide is gone or the holder itself starts contacting material. Running on a bare holder damages the mounting pocket and turns a simple tooth swap into a drum repair.
How long do the drum/rotor bearings last, and what are the early failure signs?
Bearing life depends heavily on rotor balance and greasing intervals; a rotor thrown out of balance by a missing or broken tooth accelerates bearing wear substantially. With the head off the carrier and shut down, spin the drum by hand and feel for roughness, grinding, or resistance, and check for side-to-side play at the shaft. Heat at the bearing housing after a run, a new whine or knock from the center of the drum, and grease weeping past the seals are all early warning signs. Catching it early saves the shaft and housing; running it to failure usually doesn't. Have your dealer verify bearing play and seal condition if you notice any of these signs.
What hydraulic flow and pressure does the HM312 need, and how do you know if a carrier is a good match?
This head is built for a high-flow auxiliary circuit, in the low-to-mid 30s gpm at roughly 4000 psi, not a standard-flow skid steer circuit. Running it on a carrier that can't supply that flow starves rotor speed; the drum keeps turning but lacks the momentum to shear material cleanly, so it tears rather than cuts. Confirm the carrier's high-flow package and relief pressure setting before pairing the two, rather than assuming any skid steer or track loader aux circuit will work. Have your dealer verify flow and pressure match before running the head, since mismatched hydraulics also risks motor cavitation and overheating.
What normally causes reduced cutting performance if the head still spins?
The usual causes, roughly in order, are worn or missing teeth, low rotor speed from insufficient carrier flow, a slipping belt, and debris packed inside the drum housing. Ragged, torn material instead of a clean cut usually points to tooth condition before hydraulics. A head that used to cut well and has gradually gotten worse is more likely wearing teeth or a stretching belt than a sudden hydraulic fault. Work through teeth, belt condition, and drum cleanliness first before suspecting the pump or motor.
What should you check before buying a used HM312?
Pull a tooth and check carbide condition and the holder pocket for damage, not just remaining tooth length. Check belt condition and pulley groove wear, and look for oil or grease weeping from the drum bearing seals. Spin the drum by hand for roughness or play at the bearing, and check the hydraulic motor for leaks at the shaft seal and case fittings. Check the quick-coupler pins and wear plates for slop, since a worn coupler lets the whole head shift under load. Ask for hour history and whether the unit worked mostly in brush or in rocky ground; that tells you more about remaining life than the hour meter alone. Have your dealer inspect the motor and bearings before buying if anything looks questionable.

Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.

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