Caterpillarwork toolmulching head

Caterpillar HM315

Maintenance schedule, common problems & OEM parts breakdown

The Cat HM315 is a hydraulically driven mulching head attachment, not a self-powered machine - it carries no engine, transmission, or cooling system of its own and runs entirely off the host carrier's hydraulic circuit. The base HM315 has an operating weight of about 1,075 kg (2,365 lb), a 1,450 mm (57 in) working width, and a counter-rotating drum carrying 34 fixed carbide teeth turning at 1,800-2,100 rpm, driven off the carrier's hydraulics through a V-belt reduction to an axial-piston dual-speed motor. It requires a high-flow (XPS) hydraulic circuit on the host, drawing 120-137 L/min (31.5-36 gpm) at 195-350 bar, and mounts through a standard SSQA quick-attach coupler to Cat C-Series and earlier skid steer loaders and multi-terrain loaders. It sits in a family alongside the smaller HM312 and larger HM415B, and was offered with standard carbide or optional chisel teeth, a hydraulic front hood, an adjustable pusher bar, and skid shoes.

Caterpillar carried the mulcher forward as the HM315B and HM315C, which move to a poly-chain (synchronous) belt drive in place of the V-belt and are rated for higher hydraulic flow and pressure, giving faster rotor recovery under load; a later bite-limiter variant added intake-limiting disks and a two-speed motor to reduce stalling in heavy material. The line was eventually succeeded by the HM316 for D3-Series carriers running XPS hydraulics as standard. In the used and parts market the HM315 remains relevant as a low-cost, simple-drivetrain mulcher: value hinges on rotor bearing condition, drive-belt generation (V-belt vs poly-chain parts do not interchange between generations), and whether the buyer's carrier can actually supply the flow and pressure the head needs - undersized hydraulics is the most common cause of poor performance and premature wear reported on these tools.

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 HM315 specifications

Engine

Power source	No onboard engine. The HM315 is a hydraulically driven mulching head, powered entirely by the carrier machine's own hydraulic system.
Hydraulic motor	Axial piston, dual-speed motor, driving the cutter drum through a V-belt drive.
Optimum hydraulic flow	120-137 L/min (31.5-36 gpm)
Optimum hydraulic pressure	195-350 bar (2,828-5,075 psi)
Emissions tier	Not applicable, no engine is fitted to this work tool.

Weights

Operating weight	1,075 kg (2,365 lb)
Later-generation heads	Redesigned Polychain-belt-drive successor heads run heavier, roughly 1,165 kg (2,564 lb) up to 1,342 kg (2,959 lb) depending on series. Treat those as separate models from this base HM315.
Ground pressure	Not published. Mounted work tool with no ground contact of its own; ground pressure is a function of the carrier machine.

Dimensions

Overall width	1,830 mm (72 in)
Working/cutter width	1,450 mm (57 in)
Overall length	1,470 mm (58 in)
Overall height	1,610 mm (63 in)
Mounting/gauge	Universal quick-coupler mount for skid steer and multi-terrain loader work tool systems. No wheelbase or track gauge applies; it is not self-propelled.

Performance

Rotor/drum speed	1,800-2,100 rpm
Cutter teeth	34 fixed tungsten-carbide teeth on a dynamically balanced rotor, single-bolt retention for fast replacement.
Maximum cutting diameter	200 mm (8 in) brush/tree stems.
Material processing	Counter-rotating knife sets re-cut material as it circulates through the drum for a finer finished mulch.
Carrier requirement	Sized for Cat C-Series and earlier skid steer loaders and multi-terrain loaders equipped with high-flow (XPS) hydraulics.
Travel speed / gradeability	Not applicable. Mounted work tool with no self-propulsion; ground travel and grade performance are set by the host carrier.

Service capacities (summary)

Hydraulic oil	No dedicated reservoir. Draws from the carrier machine's own hydraulic tank; the carrier's hydraulic oil type and capacity governs the system.
Fuel tank	Not applicable, no engine or fuel system on this work tool.
Engine oil	Not applicable, no engine is fitted.
Cooling system	Not applicable. Heat rejection is handled by the carrier machine's own hydraulic oil cooler.

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

HM315 fluids & capacities

System	Capacity	Recommended fluid
Hydraulic system (work tool circuit)	No dedicated reservoir or tank on the tool itself; the mulching head runs entirely on the host carrier's auxiliary hydraulic circuit and shares that machine's hydraulic tank capacity	Matches whatever hydraulic oil the host carrier's own OMM calls for (typically a Cat multi-viscosity hydraulic oil such as Cat HYDO Advanced, graded by ambient temperature per the carrier's chart). The HM315's own manual does not specify a separate fluid because it has no independent hydraulic supply.
Rotor and cutter-bearing lubrication (grease)	Grease-point service, not a fluid chart volume; apply until fresh grease purges from the seal at each fitting. Daily/8-hour servicing is typical for the rotor bearings, with drive-tensioner fittings on belt-driven variants serviced on a longer interval	A multipurpose extreme-pressure grease, NLGI 2 for normal ambient temperatures (e.g. Cat Multipurpose Grease or Cat Advanced 3Moly). For cold-climate operation, step down to a softer NLGI 1 low-temperature grease (e.g. Cat Ultra 5Moly) so the grease still flows to the bearing at start-up.
Rotor drive gearbox or chain case (if equipped)	Not documented in the sources reviewed for this model line, and coverage varies by drive design: some mulching heads in this family use a belt drive with no oil sump, others use a geared or chain reduction with its own oil fill. Confirm which drive configuration your unit has before assuming a capacity	Where a gear or chain reduction case is fitted, Cat's general-purpose gear-case fluid is Cat GO (gear oil), typically an 85W-140 GL-5 grade selected for ambient temperature; this has not been confirmed as an HM315-specific call-out and should be checked against the tool's own maintenance section or your dealer.
Engine, cooling system, fuel tank, transmission/final drives, axles	Not applicable	The HM315 is a hydraulically powered work tool (mulching head) with no onboard engine, cooling system, fuel tank, transmission, final drives, or axles. All power is supplied by the host carrier (skid steer, multi-terrain loader, compact track loader, or compact excavator depending on variant).

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

Caterpillar HM315 maintenance schedule

Service interval	Tasks
Every 10 h	Inspect carbide teeth daily for chipping, wear flats, or missing teeth; replace in matched pairs so the drum stays balanced. Check hydraulic hoses and quick-couplers at the motor daily for leaks, chafing, or loose fittings. Clean packed debris from the hood, rotor housing, and skid shoes daily before it hardens and hides wear. Grease rotor bearings daily at shift end while still warm, applying until grease purges at the seal. Weekly (about every 50 hours), check drive belt tension and sheave alignment; adjust the tensioner if deflection is out of spec. Weekly, inspect skid shoe wear plates and mounting hardware torque; rotate or replace shoes as wear dictates.
Every 250 h	Grease the belt tensioner arm and pivot point. Inspect the mounting plate, wear plates, and coupler pins for play; tighten or shim as needed. Check the hydraulic motor shaft seal area for oil seepage. Inspect hood and pusher bar hinge pins, bushings, and cylinder rod for wear or leaks. Recheck carbide tooth torque on the drum and replace any teeth showing uneven wear.
Every 500 h	Pull the belt guard and inspect sheave grooves for glazing or wear; replace the belt if cracked, glazed, or stretched past adjustment. Hand-check rotor shaft end play and listen for bearing noise or roughness while rotating. Inspect carbide tooth mounting pockets on the drum for cracking or elongation. Torque-check all rotor housing, hood, and frame fasteners. Inspect hydraulic hose runs for abrasion against the frame; reroute or re-clamp as needed.
Every 1,000 h	Do a full inspection of rotor bearing play and seal condition - this is the point where bearing wear commonly becomes noticeable. Replace the drive belt as a preventive step if the tool has been in heavy brush or hardwood duty. Check the drum for straightness and rotating balance; inspect frame weld seams for cracking. Flow- and pressure-test the hydraulic drive motor against spec to catch internal wear early. Repack all grease fittings and replace any zerks that won't take grease cleanly.
Every 2,000 h	Replace rotor bearings and seals as a set rather than waiting for failure. Rebuild or replace the hydraulic drive motor if the flow/pressure test falls below spec. Inspect the drum shaft for wear beyond tolerance and replace if scored or undersized. Inspect the full frame and mounting plate for stress cracking, especially around the coupler and hood pivots.
Every 3,000 h	Perform a complete rotor and drum overhaul: bearings, seals, shaft, and rebalance. Replace the belt-drive component set together - sheaves, tensioner, and belt - rather than mixing worn and new parts. Decide between rebuilding or replacing the hydraulic motor based on accumulated wear history. Inspect the entire structural frame for fatigue cracking; repair or retire the tool if the frame is compromised.

Servicing the HM315 beyond the schedule

Predictive Maintenance & Fluid Analysis

The HM315 has no engine oil or reservoir to sample - its only fluid interface is the carrier's hydraulic system. Track drum recovery time and motor temperature as early warning signs of internal motor wear, and periodically flow/pressure-test the circuit against the 120-137 L/min, 195-350 bar spec. Watch rotor bearing grease purge at each greasing - reduced purge or discolored grease signals seal wear. Log carbide tooth wear rate so replacement happens before chipped teeth cause drum imbalance or belt strain.

Corrective & Common Repairs

Most HM315 downtime traces to three items: worn carbide teeth, a loose or glazed drive belt, and hydraulic leaks at the motor or hose fittings. Replace teeth in pairs to hold rotor balance. Re-tension or replace the V-belt at the first sign of glazing, cracking, or slip marks on the sheave. Reseat or replace worn skid shoes and mounting plate wear plates before play develops at the coupler. Chase seepage at the motor shaft seal immediately - it does not self-correct.

Overhaul & Rebuild Points

Rotor bearing wear is the HM315's main rebuild driver, with roughly 1,000 hours as a rule-of-thumb inspection point before play becomes damage. A rebuild typically bundles bearings, seals, and a drum rebalance in one job. Treat belt-drive components as a matched set at overhaul - do not mix a new belt with worn sheaves, and never substitute poly-chain parts from a HM315B/HM315C onto a base HM315. Rebuild or replace the hydraulic motor once a flow/pressure test shows it below spec, and inspect frame welds around the mounting plate for fatigue cracking at every major teardown.

Seasonal & Environment Servicing

Switch grease grade for cold-weather operation - Cat Ultra 5-Moly below freezing, Multipurpose or Advanced 3-Moly in normal temperatures - to keep rotor bearings protected at start-up. In wet or muddy conditions, clear packed debris from the hood and rotor housing more often; trapped mud accelerates belt and bearing wear. Tooth wear runs faster in hardwood or rocky ground than in brush, so adjust inspection frequency to material. Before seasonal storage, relieve residual hydraulic pressure, retract the hood, and coat the exposed motor shaft and coupler faces to prevent corrosion.

HM315 attachments & work tools

Mulcher head (cutting/rotor system)

The HM315 is a forestry mulcher head, not a hammer or bucket. Its drum carries about 34 tungsten-carbide teeth with three sets of counter-rotating knives for a second-stage mulch pass. Cutting/working width runs roughly 1,450-1,600 mm (57-62 in) depending on series, and it processes brush up to about 200 mm (8 in) in diameter.

Carrier compatibility / size class

Built for Cat mid-size skid steer loaders, multi-terrain loaders and compact track loaders, roughly the 246-299 class (for example 246D/262D through 297D2/299D2 and their C-Series/D-Series equivalents of that era). Smaller compact loaders and larger dedicated forestry carriers use different mulcher heads in the same family, not this one.

Coupler / mounting system

Mounts through the standard skid-steer quick-attach coupler plate matched to the host loader's own quick-coupler, so it swaps on and off like any other Cat work tool. No pin-grabber or excavator-style coupler is used on this tool.

Hydraulic kit / flow-pressure arrangement

Requires the carrier's high-flow auxiliary hydraulic circuit (Cat's high-flow/XPS package); standard-flow carriers need a high-flow hydraulic kit conversion before running this head. Optimum flow and pressure vary by series and drive type, with figures spanning roughly 95-140 L/min (25-36 gpm) and 195-350 bar (2,800-5,100 psi) reported across versions -- confirm the exact setpoint for the specific unit and drive type before commissioning.

Guarding and control features

Standard guarding includes a hydraulically actuated front hood for dense-brush work, an adjustable pusher bar for controlling felled material, and adjustable skid shoes that keep the carbide teeth off the ground. A cutting-head pressure gauge is fitted so drum load can be monitored from the cab.

Tooth/tool configuration options

Standard rotor uses fixed tungsten-carbide cutting teeth; an optional chisel-tooth set is offered for more aggressive processing of vines and soft wood. A later bite-limiter configuration adds limiter discs between teeth to cap material intake per pass and reduce stalling on dense growth.

Series/generation variants

Published specs vary across the HM315, HM315B and HM315C revisions of this head: weight ranges from about 1,070-1,390 kg (2,360-3,050 lb), drum speed from about 1,800-2,400 rpm, and drive hardware changes between V-belt and synchronous (Polychain) belt across updates. Treat exact figures as series-dependent rather than one fixed spec, and keep this model distinct from the larger mulcher heads in the same family and from Cat's separate hydraulic hammer line, which share no parts or specs with the HM315.

All HM315 assemblies by section

Every catalogued assembly group for the Caterpillar HM315. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Frame And Body

308-0202 Frame Gp-Mulching Head

09***97	Pulg	2
17***05	Bolt-Socket Head; (M8x1.25x12-mm)	4
17***11	Locknut; (M16x2-Thd)	6
24***49	Plate As-Skid; (Rh)	1

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308-0203 Guard Gp-Bottom -Bottom Debris

24***85	Chain	104
24***86	Plate-Block	2
30***03	Guard Group-Bottom; -Bottom Debris	1
30***15	Guard	2

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308-0240 Guard Gp-Mulching Head

13***50	Nut; (M18x2.5)	6
24***42	Support-Frame; (Lh)	2
25***33	Bolt	6
30***40	Guard Group-Mulching Head	1

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Hydraulic System

253-6947 Cylinder & Mtg Gp-Mulching Hd

25***47	Cylinder & Mtg Group-Mulching Hd	1
25***48	Cylinder Group-Hydraulic	1
25***49	Kit-Seal	1
26***41	Pin	2

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308-0260 Hydraulic Ar -Mulching Head

30***31	Hydraulic Group-Mulching Head	1
30***55	Lines Group-Connecting	1
30***60	Hydraulic Ar; -Mulching Head	1

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308-0231 Hydraulic Gp-Mulching Head

25***44	Manifold Group-Control	1
25***47	Cylinder & Mtg Group-Mulching Hd	1
25***81	Kit-Seal; (Propel Piston Motor)	1
26***57	Motor Group-Piston	1

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308-0255 Lines Gp-Connecting

09***31	Bolt; (Socket Head) (M10x1.5x120mm)	8
14***48	Fitting As; (Quick Disconnect, Male)	1
14***49	Fitting As; (Quick Disconnect, Female)	1
14***17	Adapter, -12 Orb / -16 Orfs	2

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Service Equipment And Supplies

308-0265 Film Gp

22***69	Film-Warning; (Do Not Operate, Read Omm)	1
24***21	Film-Warning; (Flying Debris)	1
24***19	Film-Warning; (No Clrn, No Hand, Read Omm)	3
24***21	Film-Warning; (Flying Debris, Stay Back)	2

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Work Tool Arrangement

327-3942 Head Ar-Mulching

16***89	Tack-Fastener	4
30***40	Guard Group-Mulching Head	1
30***60	Hydraulic Ar; -Mulching Head	1
30***65	Film Group	1

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308-0250 Head Ar-Mulching

30***01	Head Group-Mulching	1
30***40	Guard Group-Mulching Head	1
30***50	Head Ar-Mulching	1
30***60	Hydraulic Ar; -Mulching Head	1

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Work Tools

327-3944 Cutter Gp-Rotary

25***46	Bolt-Socket Head	34
25***44	Bolt-Socket Head	34
30***19	Washer-Spring	68
30***21	Tooth As-Cutter	34

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308-0225 Cutter Gp-Rotary

24***13	Tooth As-Cutter; (Standard)	32
24***14	Tooth As-Cutter; (Heavy-Duty)	2
25***46	Bolt-Socket Head	34
25***44	Bolt-Socket Head	34

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308-0204 Drive Gp-Mulching Head

06***27	Bearing	2
19***34	Setscrew; (M12x1.75x110-mm)	2
22***30	Tube	1
24***88	Shaft-Drive	1

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308-0205 Drum Gp-Rotary Cutter -1500 Mulching Head

08***17	Screw-Hex Socket; (M8x1.25-Thd)	12
09***16	Ring-Retaining; (External)	1
09***56	Pin-Spring	2
1H***14	Bearing-Roller	2

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327-5808 Drum Gp-Rotary Cutter

08***17	Screw-Hex Socket; (M8x1.25-Thd)	12
09***16	Ring-Retaining; (External)	2
09***56	Pin-Spring	2
1H***14	Bearing-Roller	2

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308-0218 Gauge Gp-Pressure

30***17	Gauge As-Pressure	1
30***18	Gauge Group-Pressure	1
30***59	Hose As	1
8T***87	Bolt; (M5x0.8x10-mm)	3

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327-5811 Head Gp-Mulching

30***02	Frame Group-Mulching Head	1
30***03	Guard Group-Bottom; -Bottom Debris	1
30***04	Drive Group-Mulching Head	1
30***18	Gauge Group-Pressure	1

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308-0201 Head Gp-Mulching

30***01	Head Group-Mulching	1
30***02	Frame Group-Mulching Head	1
30***03	Guard Group-Bottom; -Bottom Debris	1
30***04	Drive Group-Mulching Head	1

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247-5889 Kit-Guard

23***78	Plate	2
24***89	Kit-Guard; -Quick Coupler	1

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HM315 serial number reference

The PIN plate on the HM315 mulching head is riveted to the main frame of the head, usually near the mounting plate or hydraulic-motor side where it stays visible with the tool off the carrier. The PIN reads as a 3-letter prefix followed by a 5-digit sequence number (for example TXK00265); the letter prefix ties the unit to its specific work-tool model and generation, and the digits are the build sequence within that prefix.

Prefix	Identifies	Notes
TXK	HM315 Mulching Head - base/first-generation work tool, no engine, hydraulically powered by the host carrier	Full production run is TXK00001 and up; no separate sub-generation breaks found within this prefix. This is the original HM315 mulching head, built for Cat C-Series and earlier skid steer loaders, compact track loaders, and multi-terrain loaders running XPS hydraulics. It is distinct from the later HM315B (revised hydraulic system, paired with high-flow XPS carriers) and HM315C (paired with D3-Series XPS/XE carriers), which are separate generations not covered by this TXK range. HM315C is confirmed under its own distinct prefix in a catalog shared across a family of C-suffix mulching heads, not this one.

Frequently asked questions

What engine does the Cat HM315 have?

None. The HM315 is a hydraulically driven attachment with no engine of its own - it runs entirely off the host skid steer, compact track loader, or multi-terrain loader's hydraulic system, drawing 120-137 L/min (31.5-36 gpm) at 195-350 bar through a high-flow (XPS) circuit.

What is the operating weight of the Cat HM315?

The base HM315 weighs about 1,075 kg (2,365 lb). Later HM315B/HM315C generations run somewhat heavier due to the poly-chain drive upgrade - confirm against the dimension plate on the specific unit, since weight varies by configuration and series.

What replaced the Cat HM315 mulcher?

Caterpillar progressed the line to the HM315B and then HM315C, both moving to a poly-chain belt drive with higher hydraulic flow and pressure capability. For current D3-Series carriers, Caterpillar's mulcher lineup has moved to the HM316 as the direct replacement.

What HM315 owners discuss

What kind of drive does the HM315's rotor use, and what do owners report about it?

The HM315 turns its rotor off the carrier's hydraulic system through an axial-piston hydraulic motor driving a V-belt set into the drum, a design later replaced by a synchronous poly-chain belt on the B and C generations of this mulcher line. Owners running the original V-belt version say the belts need regular tension checks and the belt guard cleared of packed debris, since a slipping belt under load shows up on the carrier as lost cutting power rather than an obvious belt fault. A rotor that has gone out of balance, or a shaft bent from a rock strike, accelerates belt and bearing wear together, so unusual vibration at idle gets treated as a drive-train warning rather than a cosmetic nuisance.

How do the carbide teeth wear, and how do owners choose between tooth styles?

The rotor carries tungsten-carbide teeth around its face, and operators judge wear by how rounded or flush the carbide insert has gone rather than by a fixed hour figure, since wear rate depends heavily on soil contact and rock content in the material being cleared. Standard flat-face carbide teeth are the default for general land clearing and underbrush with occasional rock contact, valued for pulverizing action and resistance to chipping. Chisel-style teeth get run instead for faster, cleaner cuts through standing brush, vines, and softer wood, but owners note they chip more easily on rock or buried debris, so the choice comes down to ground conditions on a given job rather than hours on the head.

What hydraulic flow and pressure does the HM315 actually need from the carrier?

Community-reported flow figures for this head cluster around 120-136 L/min (31.5-36 GPM), though exact requirements vary by series and hydraulic configuration and should be checked against the specific unit's rating plate. Running the head on a standard-flow circuit in the 80 L/min (22 GPM) class leaves it short even in light brush, and operators who tried it describe the rotor bogging down on material that should cut easily. Some Cat skid-steer carriers also need an electrical high-flow signal enabled before they deliver full flow to an attachment; without it the machine defaults to standard flow and the mulcher underperforms even though the plumbing itself is correct. Matching carrier-rated flow and pressure to the head before buying or renting is treated as the single biggest factor in whether an HM315 performs as advertised.

Since there's no engine, what electrical or hydraulic-sensor issues come up on these heads?

The HM315 has no engine or engine control module; the closest thing to an instrument is the pressure gauge on the control block that shows the operator cutting-head load. Owners have chased a case where hydraulic temperature climbed toward 93-96 degrees C (200-205 degrees F) while the pressure needle sat in the normal band, which looked like a bogging or dragging rotor but traced back to worn O-rings in the control block's relief valve letting oil bypass internally and generate heat without doing cutting work. Because that failure mode mimics a flow shortage or carrier problem, owners check the control-block relief valve and case-drain circuit before blaming the carrier or the belt. Have your dealer verify relief-valve and case-drain condition before returning a head to service after this kind of overheating complaint.

What wear pattern should I expect on the rotor bearings over time?

Reported bearing life varies widely with ground conditions and material mix, but a commonly cited service life under normal brush-clearing use runs roughly around 1,000 hours per bearing set; heavy rock content or a history of rotor imbalance shortens that considerably. The field check owners rely on is simple: with the head disconnected from hydraulic pressure, spin the drum by hand and feel for roughness, grinding, or side play. Any of those is treated as a sign the bearings are already on borrowed time rather than something to keep monitoring. Because bearing replacement means working around a heavy rotor assembly, have your dealer verify the drum is properly supported and depressurized before the bearings are pulled.

Do the HM315, HM315B, and HM315C need to be treated as different machines for parts and specs?

Yes. Owners and dealers treat these as distinct generations rather than one continuously updated model. The original HM315 uses a V-belt rotor drive; the B and C generations moved to a synchronous poly-chain belt paired with a two-speed axial-piston motor for faster recovery under load, and later versions in the line add a bite-limiting feature to cap how much material the rotor engages at once. Carbide-tooth and wear-part listings for one generation are commonly flagged as not interchangeable with the others, so confirming which generation is on hand before ordering teeth, belts, or motor components avoids a mismatched part.

What should I check before buying a used HM315?

Start with the frame and mounting welds, sighting down each seam for cracks or repair welds, since a cracked frame usually means the head was overloaded or dropped at some point. Disconnect hydraulics and spin the rotor by hand, checking for roughness, grinding, or play in the bearings, and look over the carbide teeth for how much carbide remains versus rounded-off steel. Check the hydraulic motor and hose fittings for weeping oil, since even minor seepage is treated as early seal failure. On the original V-belt HM315, pull the belt guard and check belt condition and tensioner movement; on later poly-chain-drive heads, check the chain belt and idlers instead. Finally, confirm what flow and pressure range the head is rated for and weigh that against the wear you're seeing, since years on an underpowered carrier show up as accelerated belt and bearing wear even at moderate hour counts. Have your dealer verify hydraulic motor and relief-valve condition with a flow test before finalizing any purchase.

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

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