Caterpillarwheel tractor-scraperwheel tractor
Caterpillar 657
Maintenance schedule, common problems & OEM parts breakdown
The Caterpillar 657 wheel tractor-scraper is a 1960s mechanical-era earthmover built in the 31G serial series from about 1962 through 1968, before Caterpillar replaced it with the 657B. It paired a D346T turbocharged diesel in the tractor unit with a D343T turbocharged diesel in the towed scraper, a tandem-power layout that put driven power at both ends of the machine to improve traction and bowl fill rate. Combined output ran near 785 flywheel horsepower through a 9-speed powershift transmission. Empty weight sat around 56 tonnes (about 62 tons). Original 657 units carried no factory cushion hitch, so loading depended on a separate pusher tractor working the cut rather than the machine cushioning its own hitch shock.
What set the 657 apart in its day was the tandem-power idea itself: two full diesel engines synchronized through an air-over-oil rotochamber control system that also handled engine starting, ejector operation, and braking, plus a factory choice between gasoline pony-motor and direct-electric starting built on the same serial prefix. Rounded tractor fenders and a rigid drawbar hitch mark an original pre-1968 machine at a glance. In the collector and restoration market today, surviving 31G-series 657s draw interest precisely because of that early mechanical layout, twin engines, powershift gearing, and rotochamber pneumatics, which set them apart as a distinct restoration and parts category from the later cushion-hitch 657B and from the unrelated modern electronic machine that later reused the 657 name.
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 657 specifications
Engine
| Tractor engine | Caterpillar D346T, V-8 diesel, turbocharged. Rated 450 flywheel hp (336 kW) on the original 31G-series machine. |
| Scraper (rear) engine | Caterpillar D343T, 6-cylinder inline diesel, turbocharged. Rated 335 flywheel hp (250 kW) on the original 31G-series machine. |
| Combined output | 785 flywheel hp (585 kW) combined at introduction. Factory literature on this same 31G production run also cites a combined rating raised to about 900 hp later in the run — treat as varies by build date/series and confirm against the data plate. |
| Governor / controls | Mechanical (flyweight-type) governor typical of Cat diesels of this era. Exact governor/control linkage detail is not confirmed in available documentation for this specific serial range — verify against the factory service manual. |
| Starting arrangement | Factory-offered as either gasoline pony-engine starting or direct electric starting of the diesel engines; Caterpillar did not split these two options by a separate serial-number prefix on this series (unlike the earlier DW-series scrapers). The rear (scraper) engine starter used an air-over-hydraulic arrangement that drew oil from the ejector hydraulic circuit to crank the engine, with an over-running clutch disengaging the starter drive once the engine fired. |
| Note on engine family | Later production of this same model line (657B, 68K series, from 1969) moved to 550 flywheel hp D346T at 2,000 rpm and 400 flywheel hp D343T at 2,100 rpm — do not apply those figures to the original 31G-series machine. |
Weights
| Empty/shipping weight | Approximately 62 tons (about 124,000 lb / 56,200 kg) per period equipment-history documentation for the 31G series. Single documented figure only, not independently cross-verified across multiple sources — treat as approximate and confirm against the data plate or factory spec sheet. |
| Operating (loaded) weight | Not documented in available sourcing specific to the original 31G-series machine. |
| Ground pressure | Not published in available sourcing for this machine. |
| Bowl capacity | Struck 32 yd3 (24.5 m3), heaped 44 yd3 (33.6 m3). This capacity figure is documented across the early mechanical-era production run. |
Dimensions
| Transport length/width/height | Not documented in available sourcing specific to the original 31G-series machine. Figures published on modern spec-sheet aggregators are for the later G-series/current tandem-engine reissue and do not apply to this vintage machine. |
| Wheelbase | Not documented in available sourcing specific to the original 31G-series machine. |
| Ground clearance | Not documented in available sourcing specific to the original 31G-series machine. |
| Tires | 37.50 x 39, 44-ply, E3, tubeless. Documented as standard fitment across the early mechanical-era production run. |
Performance
| Transmission | 9-speed powershift transmission (planetary/range type), original 31G series. Later 657B production (68K series, from 1969) changed to an 8-speed semi-automatic powershift — do not apply that spec to the 31G machine. |
| Travel speeds | Not documented in available sourcing specific to the original 31G-series machine. Do not substitute the later 657B's published top speed, which applies to a different (68K-series, 1969-on) machine with different engine ratings. |
| Drawbar pull | Not documented in available sourcing for this machine. |
| Gradeability | Not documented as a discrete published figure in available sourcing for this machine. |
| Design note | Twin-engine (tandem-power) layout: separate tractor and scraper engines synchronized to give combined pulling power without a push tractor, distinct from single-engine scraper designs of the same period. |
Service capacities (summary)
| Fuel tank | Not documented in available sourcing specific to the original 31G-series machine — verify against the factory parts or operation manual. |
| Hydraulic system | Not documented in available sourcing specific to the original 31G-series machine — verify against the factory parts or operation manual. |
| Engine oil (crankcase) | Not documented in available sourcing specific to the original 31G-series machine — verify against the factory parts or operation manual. |
| Cooling system | Not documented in available sourcing specific to the original 31G-series machine — verify against the factory parts or operation manual. |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
657 fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Tractor engine crankcase w/ filter (front D346/D346T diesel, V8) | Not confirmed for the D346 specifically in sources found. Comparable large Cat industrial diesels of this era typically run roughly 30-40 L (8-10 US gal) with filter change; treat as a rough indication only, not a verified 657 figure. | Straight-grade detergent diesel engine oil, graded by ambient temperature per period practice: SAE 30 above 0C (32F), SAE 10W from -18C to 0C (0-32F), SAE 5W below -18C (0F). |
| Scraper engine crankcase w/ filter (rear D343/D343T diesel, inline-6) | Approx. 38 L (10 US gal), per D343-family engine data corroborated across two independent technical sources. Given as a close estimate for the 657 rear unit, not a machine-specific confirmed figure. | SAE 30 for warm climates, SAE 40 in sustained high heat; SAE 10W in cold weather, per era-standard Cat viscosity-by-temperature guidance. |
| Gasoline pony/starting engine crankcase (only on units built with pony start; direct electric start was the alternative factory option and has no separate crankcase) | Not documented in sources found for this application. Small Cat gasoline starting engines of the era typically held on the order of 1-2 US quarts (about 1-2 L); indicative only, not a confirmed 657 figure. | Automotive-type gasoline engine oil, SAE 30 per period practice, SAE 20W in cold weather. |
| Tractor engine cooling system (front D346) | Not confirmed in sources found. | Water plus a Caterpillar-approved permanent-type antifreeze/corrosion inhibitor; period manuals called for a compounded rust inhibitor when antifreeze was not used. |
| Scraper engine cooling system (rear D343) | Roughly 66-68 L (17.5 US gal) reported for D343-family engines in comparable industrial/marine applications. Treat as an approximate range, not a confirmed 657-specific figure. | Same as tractor engine cooling system: water plus approved antifreeze/corrosion inhibitor, or compounded rust inhibitor if antifreeze not used. |
| Fuel tank | Not confirmed for the vintage 31G-series machine in sources found. A 430 US gal figure appears online but belongs to the modern C18/C15 reissue and does not apply here. | No. 2-D diesel fuel oil, the standard grade specified in period Cat documentation. |
| Powershift transmission (9-speed) | Not confirmed in sources found. | Period Cat lubrication practice used a straight-grade engine-type oil (commonly SAE 30, or SAE 10W in cold weather) for powershift transmissions, predating dedicated TDTO/TO-4-class fluids. Exact period spec should be checked against the data plate or manual. |
| Final drives, each (wheel planetary/final drive housings) | Not confirmed in sources found. | Period Cat gear lubricant, typically the same multipurpose-type oil specified for the transmission, per the era lubrication chart. |
| Drive axle differential (tractor) | Not confirmed in sources found. | Period Cat EP gear lubricant, grade selected by ambient temperature per the era lubrication chart -- heavier EP 90-class oil in warm climates, lighter EP 80-class in cold. |
| Hydraulic/rotochamber control system and tank (air-over-oil actuation for bowl, apron, and ejector) | Not confirmed in sources found. | Period Cat practice used a straight mineral oil for air-over-oil control systems (commonly SAE 10 or SAE 30 depending on climate) rather than a dedicated hydraulic fluid. Exact period spec should be checked against the data plate or manual. |
| Chassis grease points (spec only) | N/A -- applied via grease fittings, no reservoir capacity. | Period Cat multipurpose-type EP grease, NLGI No. 2 for general chassis and pin lubrication, NLGI No. 1 in cold weather for easier gun flow. |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Caterpillar 657 maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 50 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
| Every 4,000 h |
|
Servicing the 657 beyond the schedule
Predictive Maintenance & Fluid Analysis
On a twin-engine 657, oil sampling on both the D346T tractor engine and D343T scraper engine catches problems before they cause a shutdown. Track crankcase oil condition, coolant condition, and powershift transmission oil separately for each power unit, since wear patterns differ between the two engines under tandem-power load. Watch turbocharger boost and exhaust color as an early flag for injection or air-intake trouble. Check rotochamber air pressure and moisture buildup regularly; a slow leak in the air-over-oil circuit shows up first as sluggish ejector or starting response before it fails outright.
Corrective & Common Repairs
Common failure points on the 657 center on the rotochamber air-over-oil system: cracked diaphragms, sticking bendix engagement on the pony-motor starter, and worn ejector linkage all show up as slow or failed engine starts and sluggish bowl ejection. Powershift transmission clutch wear and leaking seals at the tandem-power engine mounts are frequent corrective jobs given the twin-engine torque loads. Because these machines predate the factory cushion hitch, drawbar and hitch-pin wear from pusher-loading impact is a routine repair item, along with tire cuts on the heavy 37.5x39 E-3 tubeless tires.
Overhaul & Rebuild Points
Major overhaul work on a 657 centers on the two separate diesel power units: injector, turbocharger, and top-end rebuilds on the D346T and D343T are scheduled independently, since duty cycles differ between tractor and scraper engine. The 9-speed powershift transmission clutch packs and the final drives at both axles are the other major rebuild items given the tandem-power torque path. Rotochamber diaphragms, the air compressor, and starter bendix hardware get a full teardown at major overhaul, along with bowl wear plates, cutting edge, and gooseneck pivot bushings on the scraper frame.
Seasonal & Environment Servicing
Cold-weather starts on a 657 depend on the pony-motor or direct-electric starting circuit working correctly, so battery condition, pony-motor fuel and ignition, and coolant warm-up checks matter on both engines before winter operation. Drain air system moisture from the rotochamber circuit more often in freeze-thaw conditions to keep starting and ejector control reliable. In hot, dusty cuts, service the oil-bath air cleaners on both diesels more frequently and check the radiator cores on the twin cooling systems for packed dirt that cuts airflow across either engine.
657 fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| Engine coolant temperature gauge (front D346 / rear D343) | Gauge needle enters the high range, indicating an overheating engine on either the front tractor engine or the rear scraper engine. | Low coolant level, plugged radiator core, slipping or worn water pump, or the engine lugging under load in too high a gear. | Stop and check coolant level and radiator core for debris; confirm water pump and fan belt condition before returning to work. |
| Engine oil pressure gauge (front D346 / rear D343) | Needle drops toward zero or into the low range on either engine, signaling loss of lubrication pressure. | Low oil level, worn main or rod bearings, or a failing oil pump. | Shut the affected engine down immediately, check oil level and look for external leaks before restarting or troubleshooting further. |
| Torque converter oil temperature gauge | Converter oil temperature climbs into the high range during operation. | Sustained lugging or stall in too low a gear, low converter oil level, or a plugged converter oil cooler. | Shift to the correct working gear for load conditions and check converter oil level and cooler for restriction. |
| System air pressure gauge (rotochamber / brake circuit) | Air pressure supplying the rotochamber-actuated implement and brake controls reads low or fails to build. | Worn air compressor, a leaking line or fitting, or a worn diaphragm inside a rotochamber unit. | Listen and feel around rotochamber housings and air lines for leaks, check compressor output and governor cut-in/cut-out pressure. |
| Air cleaner service (restriction) indicator | Indicator shows the intake air filter element is loaded and restricting airflow to the engine. | Dust and dirt accumulation on the filter element, common in scraper duty cycles. | Service or replace the element per the indicator rather than waiting for a fixed calendar interval in dusty conditions. |
| Rotochamber sluggish or delayed response (bowl, apron, ejector, or clutch/brake actuation) | The air-over-oil rotochamber actuator moves slowly, only partially, or not at all when the control is worked. | Worn or ruptured internal diaphragm, an external air leak at the chamber, or low oil fill on the hydraulic side of the unit. | Check the chamber and its lines for air leaks, confirm system air pressure is adequate, and inspect the diaphragm and oil fill if response stays weak. |
| Rear engine (D343) unresponsive to gear/control selector | The rear scraper engine's drivetrain fails to shift or respond when the operator works the control, even though the engine itself runs. | Corroded or worn contacts and wiring in the electrical control circuit linking the front tractor controls to the rear engine, rather than a fault in the rear transmission itself. | Check the tandem-power control wiring and switch contacts at the rear engine before pulling the rear transmission. |
| Diluted or fuel-smelling crankcase oil (D343 / D346) | Engine oil level rises unexpectedly or oil smells strongly of fuel, especially after the machine has sat idle for an extended period. | The camshaft-driven fuel priming pump mounted on the cylinder block leaking fuel past its seal into the crankcase. | Check oil level and smell for fuel contamination; inspect or pressure-test the priming pump seal if oil is overfull or unusually thin. |
| Front engine (D346) reaching top-overhaul wear point | Front tractor engine shows rising oil consumption, blow-by, or falling compression as operating hours accumulate. | Valve-train and cylinder wear inherent to the overhead-cam V8 design under sustained heavy tractive load, which owners commonly report needing top-end attention well before the rear D343 does. | Track oil consumption and blow-by over time and plan a top-end overhaul rather than waiting for a failure in the field. |
| Pony motor hard start or no-start (on pony-start equipped units) | The gasoline pony motor used to crank the main diesel fails to start or stalls before it can engage and spin the main engine. | Gummed or varnished carburetor, weak magneto spark, or a pony motor clutch/Bendix that is stuck and not engaging the main engine flywheel. | Check pony motor spark and fuel delivery first, and confirm the clutch mechanism engages freely before suspecting the main engine. |
| Ammeter / battery charge indicator (direct-electric start units) | Ammeter shows a discharge condition or fails to show charge with the engine running. | Slipping charging belt, corroded battery cable connections, or a weak generator/regulator. | Check belt tension and battery cable connections first, then test generator output if the condition persists. |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
657 attachments & work tools
Bowl, Apron & Ejector
The original 657 used an open bowl rated at roughly 34 m3 (44 cu yd) heaped capacity, with an apron and ejector that were hydraulically actuated rather than cable-operated. This was a step up from the cable-controlled aprons used on Caterpillar's earlier, smaller scraper lines.
Apron Hydraulic Circuit
A double-acting cylinder mounted in the gooseneck opened and closed the apron through a multiplier linkage and rod, giving mechanical advantage that direct single-cylinder apron setups on smaller scrapers did not have.
Ejector Hydraulic Circuit
A single double-acting cylinder drove the ejector, which rode on hardened-steel rollers to reduce friction as it swept material out of the bowl during dumping.
Rear-Engine Starting System
The rear D343T scraper engine used an air-over-hydraulic starter that drew oil from the ejector hydraulic circuit: shop air engaged the starter's bendix gear while hydraulic pressure spun the starter motor, with an over-run clutch disengaging it once the rear engine fired.
Push-Loading Arrangement
Pre-1968 machines had no cushion hitch and no factory push-pull capability, so loading relied on a separate pusher tractor working the cut rather than scrapers pairing up. A cushion hitch became an optional factory fitment from 1967 onward but could not be retrofitted to machines already in the field.
Dealer Tandem/Triple Conversion (non-factory)
A California Cat dealer built aftermarket tandem pairs and one roughly 57 m (186 ft) triple hookup of 657 scrapers in the mid-1960s for a large earthmoving project, patenting the steering/control linkage in 1966 and the throttle-interlock system in 1967, so scrapers could push-load each other without a dedicated pusher tractor. The triple proved unwieldy in soft ground and was split back into tandem pairs, which worked well enough for continued use; none of this was ever a Caterpillar factory option on the original 657.
Tires
Standard factory fitment on the original 657 was 37.5x39, 44-ply, E-3 tread tires. Other tread or ply combinations common on large 1960s scrapers may have been available, but no documented alternate factory tire option for this model was found.
Transmission & Engine Starting Options
The tractor used a 9-speed powershift transmission. Period documentation points to a choice of gasoline-assisted or direct electric starting across production, though Caterpillar did not split these into separate serial-number series the way it had on earlier DW-series machines.
Visual/Generation Markers
Early 31G-series 657s are identified by rounded tractor fenders and the absence of a cushion hitch. Squared-off fenders and the optional cushion hitch mark 1967-and-later production still within this original-657 generation, before the separate 657B model took over.
All 657 assemblies by section
Every catalogued assembly group for the Caterpillar 657. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Attachments
7m914 Air Filter Service Indicator Group
4d7140 Alternator Arrangement--24 Volt, 40 Ampere
| 4B***20 | Clip; - For Orange Wire To L.H. Side Of Alternator Fan Shroud | 1 |
| 4B***58 | Screw (Identification Plate) Mounting | 4 |
| 4D***65 | Wire Assembly; -- Alternator Ground | 1 |
7m9174 Alternator Assembly--24 Volt, 40 Ampere--Type 1
| 7M***74 | Alternator Assembly | 1 |
7m9606 Alternator Group--24 Volt, 40 Ampere--Type 2
| 7M***06 | Alternator Group | 1 |
7m9606 Alternator Group--24 Volt, 40 Ampere--Type 1
| 7M***06 | Alternator Group | 1 |
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 3 Of 4--Type 3
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 2 Of 4--Type 3
| 4D***30 | Battery, Wiring And Lighting Group | 1 |
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 4 Of 4--Type 1
| 4D***30 | Battery, Wiring And Lighting Group | 1 |
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 1 Of 4--Type 1
| 4D***30 | Battery, Wiring And Lighting Group | 1 |
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 3 Of 4--Type 2
| 4D***30 | Battery, Wiring And Lighting Group | 1 |
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 2 Of 4--Type 1
| 4D***30 | Battery, Wiring And Lighting Group | 1 |
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 2 Of 4--Type 2
| 4D***30 | Battery, Wiring And Lighting Group | 1 |
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 1 Of 4--Type 3
| 4D***30 | Battery, Wiring And Lighting Group | 1 |
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 1 Of 4--Type 2
| 4D***30 | Battery, Wiring And Lighting Group | 1 |
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 4 Of 4--Type 3
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 4 Of 4--Type 2
| 4D***30 | Battery, Wiring And Lighting Group | 1 |
4d7130 Battery, Wiring And Lighting Group--24 Volt--Part 3 Of 4--Type 1
| 4D***30 | Battery, Wiring And Lighting Group | 1 |
2s3025 Protection Cover Group--Oil Filler Cap
Cylinder Head Assembly--L.H.--Type 1
Cylinder Head Assembly--R.H.--Type 2
Cylinder Head Assembly--R.H.--Type 1
Cylinder Head Assembly--L.H.--Type 2
9m4819 Direct Electric Starting Arrangement--24 Volt
| 0L***51 | Bolt Starting Engine Fuel Tank Bracket To Diesel Intake Manifold | 2 |
| 0S***94 | Bolt (1 In. Long 3/8 In. Dia.); Plate Assembly To Support Assembly | 4 |
| 2M***89 | Glow Plug And Wiring Group | 2 |
9f740 Discharger
7m2134 Electric Starter Group--24 Volt
4m4615 Electric Starting Motor Assembly--24 Volt--Part 2 Of 2
4m4615 Electric Starting Motor Assembly--24 Volt--Part 1 Of 2
4d7270 Ether Starting Aid Group
Flywheel--Type 2
7m3854 Fuel Priming Pump Group
| 7M***54 | Fuel Priming Pump Group | 1 |
9m2346 Glow Plug And Wiring Group--24 Volt
2m1389 Glow Plug And Wiring Group--24 Volt
8f9866 Grease Gun--Second Type
| 8F***66 | Grease Gun As | 1 |
8f9866 Grease Gun--First Type
| 8F***66 | Grease Gun As | 1 |
8m9858 Tool Group
| 8M***58 | Hand Tool Group | 1 |
4d5910 Hood Side Door Group--R.H.
4d5477 Instrument Panel Protection Group
4s7967 Light Signal Receiver Group--24 Volt
4s7602 Light Signal Receiver Group--12 Volt
Name Plates And Transfers
| 1S***88 | Film-- Drain Valve; --On Each Side Of Radiator Support | 1 |
| 2D***12 | Plate- Seat Adjustment Instructions | 1 |
| 2M***31 | Plate; Serial Number On R.H. Side Of Cylinder Block And R.H. Side Of Loader Frame | 2 |
2d284 Rear Flood Light Group--24 Volt
4m1812 Solenoid Switch Assembly
Tools
3d9330 Windshield Wiper Group--24 Volt
Wiring Diagram--24 Volt System
Diesel Engine
Aftercooler
Air Cleaner
Air Compressor
Air Compressor Drive
Breather, Oil Filler And Fumes Disposal
Camshaft
Camshaft Drive--Top View
4d6377 Rotochamber
| 4D***77 | Chamber As | 1 |
5m8271 Air Compressor Assembly
| 5M***71 | Compressor As | 1 |
Connecting Rod And Piston--8 Required
Crankcase And Lines Guard
Crankshaft And Damper
Crankshaft Bearing Replacement Groups
Cylinder Block And Covers--End View--Part 2 Of 2
Cylinder Block And Covers--Side View - Part 1 Of 2
Cylinder Block And Covers--End View - Part 2 Of 2
Cylinder Block And Covers--Side View--Part 1 Of 2
8m521 Cylinder Block Assembly
| 8M***21 | Cylinder Block Assembly | 1 |
Cylinder Head And Valve Mechanism--L.H. Front View
Cylinder Head And Valve Mechanism--R.H. Front View
Diesel Engine Support
Exhaust By-Pass
Fan And Shroud
Fan Belt Tightener
8h7204 Fuel Filter Group
| 8H***04 | Filter Group-Fuel | 1 |
Flywheel
Fuel Filter
Fuel Injection Valves And Lines
Fuel Injection Valves And Lines--Top View
7m3854 Fuel Priming Pump Group
| 7M***54 | Fuel Priming Pump Group | 1 |
Fuel Pump And Governor Drive
Fuel Pump Housing And Rack Limiter
Fuel System
6d2590 Fuel System--Rapid Filling--220 U.S. Gallon
| 6D***90 | Fuel System Group | 1 |
Fuel Transfer Pump
7m3906 Fuel Transfer Pump Group
| 7M***06 | Fuel Transfer Pump Group | 1 |
Gasket Kits
| 2S***93 | Torque Converter | 0 |
| 2S***94 | Transmission | 0 |
| 9M***94 | Gasoline Starting Engine Clutch Mechanism Control | 0 |
Governor--Side View - Part 1 Of 2
Governor--End View - Part 2 Of 2
Governor--End View--Part 2 Of 2
Governor Control--Front View - Part 1 Of 2
Governor Control--Front View--Part 1 Of 2
Governor Control--Side View--Part 2 Of 2
Governor Control--Side View - Part 2 Of 2
Governor Torque Spring
Manifolds
Oil Filter
Oil Lines--Rear View--Part 2 Of 2
Oil Lines--Part 1 Of 2
Oil Lines--Rear View--Part 1 Of 2
Oil Lines--Part 2 Of 2
2s1826 Oil Pump Assembly
| 2S***26 | Oil Pump Assembly | 1 |
8m7636 Pressure Ratio Control Assembly
| 8M***36 | Pressure Ratio Control Assembly | 1 |
2s80 Pressure Ratio Regulator Assembly
| 2S***80 | Pressure Ratio Regulator Assembly | 1 |
5d1920 Protection Cover Group--Fuel Tank Cap
| 5D***20 | Protection Cover Group-Fuel Tank Cap; Protection Cover Group | 1 |
8m1601 Rack Limiter Group
| 8M***01 | Rack Limiter Group | 1 |
Radiator--Rear View--Part 1 Of 2
Radiator--Side View--Part 2 Of 2
Rear Power Take-Off Drive
8m3550 Service Meter And Tachometer Drive Group
| 8M***50 | Service Meter And Tachometer Drive Group | 1 |
4d6401 Throttle Valve Assembly
| 4D***01 | Throttle Valve Assembly | 1 |
5d3384 Throttle Valve Assembly
| 5D***84 | Throttle Valve Assembly | 1 |
Torque Converter And Engine Oil Cooler
Transmission And Steering Pump Drive
2s879 Turbocharger Assembly
| 2S***79 | Turbocharger Assembly | 1 |
2s2835 Turbocharger Assembly
| 2S***35 | Turbocharger Assembly | 1 |
8m1742 Turbocharger Assembly
| 8M***42 | Turbocharger Assembly | 1 |
2m7938 Valve Assembly
| 2M***38 | Valve Assembly | 1 |
4d7695 Control Valve Assembly
| 4D***95 | Valve Group-Air; (Air Control) | 1 |
Water Lines
Water Pump Belt Tightener
7m1080 Water Pump Group
| 7M***80 | Water Pump Group | 1 |
Starting System
Battery, Wiring And Lighting System--24 Volt--Part 1 Of 4
Battery, Wiring And Lighting System--24 Volt--Part 2 Of 4
Battery, Wiring And Lighting System--24 Volt--Part 3 Of 4
Battery, Wiring And Lighting System--24 Volt--Part 4 Of 4
Camshaft And Governor
7m6038 Carburetor Assembly
| 7M***38 | Carburetor Assembly | 1 |
8m8420 Clutch Group
| 8M***20 | Clutch Group | 1 |
Connecting Rod And Piston--2 Required
Crankshaft
Cylinder Block, Cylinder Head And Valve Mechanism--Part 1 Of 2
Cylinder Block, Cylinder Head And Valve Mechanism--Part 2 Of 2
9m1250 Electric Starter Group--24 Volt
| 9M***50 | Electric Starter Group | 1 |
9m1468 Electric Starting Motor Assembly--24 Volt
| 9M***68 | Electric Starting Motor Assembly | 1 |
7h7188 Electric Starting Motor Group--24 Volt
| 7H***88 | Electric Starting Motor Group | 1 |
4d1920 Fuel System Group
| 4D***20 | Fuel System Group | 1 |
Generator--24 Volt, 20 Ampere
4m9102 Generator Assembly--24 Volt, 20 Ampere
| 4M***02 | Generator Assembly | 1 |
8m2577 Ignition System Group
| 8M***77 | Ignition System Group | 1 |
5d793 Indicator Lamp Assembly
| 5D***93 | Indicator Lamp Assembly | 1 |
1m3379 Head Lamp Assembly--24 Volt
| 1M***79 | Lamp Group | 1 |
1m3387 Dash Lamp Assembly--24 Volt
| 1M***87 | Lamp Group | 1 |
1m1882 Flood Lamp Assembly--24 Volt
| 1M***82 | Lamp Group | 1 |
3s2986 Magneto Assembly
| 3S***86 | Magneto Assembly | 1 |
8m5152 Magneto Assembly
| 8M***52 | Magneto Assembly | 1 |
1s3351 Magneto Assembly
| 1S***51 | Magneto Assembly | 1 |
Manifold, Carburetor, Air Cleaner And Exhaust Extension
8m2573 Manual Starting Crank Group
| 8M***73 | Manual Starting Crank Group | 1 |
8m5042 Oil Pump Assembly
| 8M***42 | Oil Pump Assembly | 1 |
9m1713 Oil Pump Assembly
| 9M***13 | Oil Pump Assembly | 1 |
1s4153 Rain Cap Group--Starting Engine
| 1S***53 | Rain Cap Group | 1 |
4m9349 Regulator Assembly--24 Volt, 20 Ampere
| 4M***49 | Regulator Assembly | 1 |
4d2510 Starting Engine Control Group--Part 2 Of 2
| 4D***10 | Starting Engine Control Group | 1 |
4d2510 Starting Engine Control Group--Part 1 Of 2
| 4D***10 | Starting Engine Control Group | 1 |
Starting Engine Support
7h7290 Disconnect Switch Assembly
| 7H***90 | Switch As-Disconnect | 1 |
8m6301 Transmission And Starter Pinion--Part 2 Of 2
| 8M***01 | Transmission And Starter Pinion Group | 1 |
8m6301 Transmission And Starter Pinion Group--Part 1 Of 2
| 8M***01 | Transmission And Starter Pinion Group | 1 |
8m6301 Transmission And Starter Pinion Group--Part 2 Of 2
| 8M***01 | Transmission And Starter Pinion Group | 1 |
8m2578 Water Lines Group
| 8M***78 | Water Lines Group | 1 |
Wiring Diagram--24 Volt System
Transmission And Chassis
7m8392 Accumulator Body Group
| 7M***92 | Accumulator Body Group | 1 |
Air Compressor And Supply Tank Lines
Air Supply Tank And Lines
Bevel Gear And Differential--Top View
4j8388 Brake Chamber Assembly
| 4J***88 | Brake Chamber Assembly | 1 |
4j2743 Brake Chamber Assembly
| 4J***43 | Brake Chamber Assembly | 1 |
6d6365 Brake Shield Group
| 6D***65 | Brake Shield Group | 1 |
4d3279 Retarder Valve Assembly
| 4D***79 | Brake Valve Assembly | 1 |
Brakes
Bumper
3j9955 By-Pass Valve Group
| 3J***55 | By-Pass Valve Group | 1 |
5j5272 Brake Chamber Assembly
| 5J***72 | Chamber As-Brake | 1 |
3j7585 Control Lever Housing Group
| 3J***85 | Control Lever Housing Group | 1 |
4j3100 Control Lever Housing Group
| 4J***00 | Control Lever Housing Group | 1 |
5d1900 Protection Cover Group--Hydraulic Tank Cap
| 5D***00 | Cover Group-Protection; Protection Cover Group-- Hydraulic Tank Cap | 1 |
Differential Case And Covers--Part 1 Of 2
Differential Case And Covers--Part 2 Of 2
4d8592 Differential Cylinder Assembly
| 4D***92 | Differential Cylinder Assembly | 1 |
Differential Lock
4d9990 Differential Lock Group--Field Installation
| 4D***90 | Differential Lock Group | 1 |
2d8913 Double Check Valve Group
| 2D***13 | Double Check Valve Assembly | 1 |
Drive Shaft
3j5308 External Control Valve Group
| 3J***08 | External Control Valve Group | 1 |
Fenders
Final Drive And Wheels--37.50 X 39 Tubeless Tires
Flywheel--Type 1
Foot Control And Lines
Gauges--Part 1 Of 2
Gauges--Part 2 Of 2
1s122 Governor Group
| 1S***22 | Governor Group | 1 |
Hand Control Valves And Lines
Hood And Exhaust Extension--Part 1 Of 2
Hood And Exhaust Extension
Hood And Exhaust Extension--Part 2 Of 2
4d2960 Hydraulic Oil Filter Group
| 4D***60 | Hydraulic Oil Filter Group | 1 |
3j9461 Hydraulic Oil Filter Group
| 3J***61 | Hydraulic Oil Filter Group | 1 |
4j1707 Hydraulic Oil Filter Group
| 4J***07 | Hydraulic Oil Filter Group | 1 |
4j823 Hydraulic Pump Assembly
| 4J***23 | Hydraulic Pump Assembly | 1 |
4j2271 Hydraulic Pump Assembly
| 4J***71 | Hydraulic Pump Assembly | 1 |
4d724 Hydraulic Pump Assembly
| 4D***24 | Hydraulic Pump Assembly | 1 |
4j9354 Hydraulic Tank Group
| 4J***54 | Hydraulic Tank Group | 1 |
4d1800 Hydraulic Tank Group
| 4D***00 | Hydraulic Tank Group | 1 |
3d6520 Hydraulic Tank Group
| 3D***20 | Hydraulic Tank Group | 1 |
Hydraulic Torque Converter
5d1854 Link Group
| 5D***54 | Link Group | 1 |
9m2000 Manual Switch Group
| 9M***00 | Manual Switch Group | 1 |
8s6713 Muffler Group
| 8S***13 | Muffler Group | 1 |
5m5757 Override Selector Valve Group
| 5M***57 | Override Selector Valve Group | 1 |
Planetary Transmission--Part 1 Of 2
Planetary Transmission--Part 2 Of 2
9f1996 Pneuphonic Horn
| 9F***96 | Pneuphonic Horn | 1 |
Pneuphonic Horn And Lines
8m8249 Pressure Control Valve Group
| 8M***49 | Pressure Control Valve Group | 1 |
7m8517 Pressure Control Valve Group
| 7M***17 | Pressure Control Valve Group | 1 |
8m8235 Range Transmission Arrangement
| 8M***35 | Range Transmission Arrangement | 1 |
4f6941 Quick Release Valve Assembly
| 4F***41 | Release Valve Assembly | 1 |
8m8253 Relief Valve Group
| 8M***53 | Relief Valve Group | 1 |
5j923 Relief Valve Group--Type 2
| 5J***23 | Relief Valve Group | 1 |
5j923 Relief Valve Group--Type 1
| 5J***23 | Relief Valve Group | 1 |
1s3249 Relief Valve Group
| 1S***49 | Relief Valve Group | 1 |
9m8192 Relief Valve Group
| 9M***92 | Relief Valve Group | 1 |
3j2764 Relief Valve Group
| 3J***64 | Relief Valve Group | 1 |
4d6862 Retarder Assembly
| 4D***62 | Retarder Assembly | 1 |
4d7730 Retarder Assembly
| 4D***30 | Retarder Assembly | 1 |
4d4779 Retarder Valve Assembly
| 4D***79 | Retarder Hand Valve Assembly | 1 |
Retarder Lines--Part 1 Of 2--R.H. View
Retarder Lines--Part 2 Of 2--R.H. View
Retarder Oil Cooler--Part 2 Of 2
Retarder Oil Cooler--Part 1 Of 2
8s3683 Retarder Oil Cooler And Lines Group--Field Installation
| 8S***83 | Retarder Oil Cooler And Lines Group | 1 |
3d2744 Rotochamber
| 3D***44 | Rotochamber | 1 |
Rotochamber And Lines
2m3409 Safety Reset And Converter Hold Valve Group
| 2M***09 | Safety Reset And Converter Hold Valve Group | 1 |
Scavenge Pump
9m6162 Scavenge Pump Group
| 9M***62 | Scavenge Pump Group | 1 |
8m2597 Scavenge Pump Group
| 8M***97 | Scavenge Pump Group | 1 |
1s3201 Scavenge Pump Group
| 1S***01 | Scavenge Pump Group | 1 |
Scraper Control
4j5829 Scraper Control Valve Group--Part 1 Of 2
| 4J***29 | Scraper Control Valve Group | 1 |
4j5829 Scraper Control Valve Group--Part 2 Of 2
| 4J***29 | Scraper Control Valve Group | 1 |
4j3102 Scraper Control Valve Group--Part 2 Of 2
| 4J***02 | Scraper Control Valve Group | 1 |
4j3102 Scraper Control Valve Group--Part 1 Of 2
| 4J***02 | Scraper Control Valve Group | 1 |
Scraper Pump, Lines And Tank
Seat Frame And Platform--Part 2 Of 2
Seat Frame And Platform--Part 1 Of 2
2d5722 Seat Suspension Assembly
| 2D***22 | Seat Suspension Assembly | 1 |
7m8391 Selector Body Group
| 7M***91 | Selector Body Group | 1 |
8m7325 Selector Valve Group
| 8M***25 | Selector Valve Group | 1 |
5m4599 Selector Valve Group
| 5M***99 | Selector Valve Group | 1 |
4j8327 Single Lever Bowl And Apron Control Group--Type 2
| 4J***27 | Single Lever Bowl And Apron Control Group | 1 |
4j8327 Single Lever Bowl And Apron Control Group--Type 1
| 4J***27 | Single Lever Bowl And Apron Control Group | 1 |
2j2181 Slack Adjuster Assembly
| 2J***81 | Slack Adjuster Assembly | 1 |
5d333 Slack Adjuster Assembly--R.H.
| 5D***33 | Slack Adjuster Assembly--R.H.,Slack Adjuster Assembly--L.H. | 1 |
Steering Gear--Part 1 Of 3
Steering Gear--Part 3 Of 3
Steering Gear--Part 2 Of 3
Steering Pump And Lines--Part 1 Of 2
Steering Pump And Lines--Part 2 Of 2
8m1071 Three Speed Planetary Torque Divider Group
| 8M***71 | Three Speed Planetary Torque Divider | 1 |
Three Speed Planetary Torque Divider And Converter
Three Speed Torque Divider Hydraulic Control
8m6434 Throttle Pressure And Control Valve Group
| 8M***34 | Throttle Pressure And Control Valve Group | 1 |
8m8251 Torque Divider And Retarder Arrangement
| 8M***51 | Torque Divider And Retarder Arrangement | 1 |
Transmission Control--Rear View--Part 2 Of 2
Transmission Control--Side View--Part 1 Of 2
Transmission Control-Rear View--Part 2 Of 2
Transmission Hydraulic Control--End View--Part 2 Of 2
Transmission Hydraulic Control--Top View--Part 1 Of 2
Transmission Pump And Lines--Part 1 Of 2
Transmission Pump And Lines--Part 2 Of 2
4d2287 Valve Assembly
| 4D***87 | Valve As; -Parking, Service | 1 |
4j8500 Control Valve Assembly
| 4J***00 | Valve As-Control | 1 |
5d3056 Double Check Valve Assembly
| 5D***56 | Valve As-Double Check; -Brakesaver Air Supply | 1 |
3d9943 Horn Valve
| 3D***43 | Valve As-Horn | 1 |
4d1669 Three Way Control Valve Assembly
| 4D***69 | Valve Assembly | 1 |
4d1084 Brake Valve
| 4D***84 | Valve Group | 1 |
Windshield
657 serial number reference
On mechanical-era 657/657B the serial plate is a stamped tag riveted to the tractor frame rail near the operator platform; later 657E/657G machines carry a PIN plate on the tractor frame near the cab entry. Tractor and scraper are separately serialized components, so each carries its own prefix: on the original 657 the tractor uses 31G (or the smaller 46M run) and the scraper uses 19G; on the 657B the tractor uses 68K and the scraper uses 47M or 53K. Read the first three characters as the prefix identifying model/generation and plant; the digits after it are the sequential unit number within that component's run.
| Prefix | Identifies | Notes |
|---|---|---|
| 31G | 657 (original, mechanical era) | Original 657 wheel tractor-scraper, built 1962-1968, tractor-unit serial series. Tandem-power layout: D346T tractor engine rated about 450 flywheel hp (336 kW) and D343T scraper engine rated about 335 flywheel hp (250 kW), 9-speed powershift transmission. Pre-1968 units have rounded tractor fenders; cushion hitch became a factory option from 1967, not standard. Cat did not split this prefix by gasoline-start vs electric-start option. |
| 19G | 657 (original, mechanical era) | Scraper-unit serial series paired with the 31G tractor unit on the original 657. Tractor and scraper are separately serialized components on this machine, each with its own prefix; 19G identifies the towed scraper unit, not a separate model or production run. |
| 68K | 657B | 657B, introduced 1969, produced roughly 15 years; tractor-unit serial series. Same D346T/D343T tandem-power engine family as the original 657 but uprated: tractor about 550 flywheel hp (410 kW), scraper about 400 flywheel hp (298 kW), 8-speed powershift. Cushion hitch became standard equipment partway through the range (documented at a mid-range serial point), followed later by ROPS and an electric service meter as running production changes. |
| 53K | 657B | 657B scraper-unit serial series, paired with the 68K tractor unit. Catalog coverage for this range also spans the tail end of original-657 scraper production. Same uprated scraper engine and running gear as other 657B scraper units. |
| 47M | 657B | 657B scraper-unit serial series, paired with the 68K tractor unit. Documented in the same parts-catalog family as the 53K scraper range. |
| 46M | 657 (original, mechanical era) | Small tractor-unit serial series for the original 657, separate from the main 31G tractor run. Same D346T tractor engine pairing as 31G. Limited production; confirm this range with your dealer before using it for parts lookup. |
| 6MB | 657E | 657E wheel tractor-scraper. Tractor engine 3412E rated about 550 hp, scraper engine 3408E rated about 400 hp. One of several serial ranges documented for this model generation. |
| 87Z | 657E | 657E wheel tractor-scraper, same 3412E tractor / 3408E scraper engine pairing as other 657E serial ranges. |
| 86Z | 657E | 657E wheel tractor-scraper serial range, part of the same documented group as 87Z, 90Z, 91Z, 6MB. |
| 90Z | 657E | 657E wheel tractor-scraper serial range, part of the same documented group as 86Z, 87Z, 91Z, 6MB. |
| 91Z | 657E | 657E wheel tractor-scraper serial range, part of the same documented group as 86Z, 87Z, 90Z, 6MB. |
| 6PR | 657E | 657E wheel tractor-scraper serial range, part of the same documented group as 86Z, 87Z, 90Z, 91Z, 6MB. |
| W1E | 657G, open (standard) bowl | 657G wheel tractor-scraper, standard open-bowl configuration, powered by a Cat C18 tractor engine (about 564/600 hp, dual rating by drive mode) and a C15 scraper engine (about 410/451 hp, same dual-rating logic). Replaced the 657E starting around 2006. |
| W1F | 657G, coal bowl | 657G wheel tractor-scraper, coal-bowl configuration, same C18/C15 dual-rated engine pairing as the open-bowl W1E range. |
Frequently asked questions
What is the engine configuration of the Caterpillar 657?
The original Caterpillar 657 runs a tandem-power, twin-diesel layout: a D346T turbocharged engine rated around 450 flywheel horsepower in the tractor unit and a D343T turbocharged engine rated around 335 flywheel horsepower in the scraper unit, for a combined output near 785 flywheel horsepower through a 9-speed powershift transmission.
What was the operating weight of the Caterpillar 657?
Empty weight on a 31G-series 657 ran around 56 tonnes (about 62 tons). Loaded weight climbs well beyond that once the bowl is filled, which is one reason the original machine relied on a pusher tractor for loading rather than a factory cushion hitch.
What succeeded the Caterpillar 657 in Caterpillar's lineup?
Caterpillar replaced the original 657 with the 657B around 1968-1969. The B-series added a factory cushion hitch to control the bouncing that plagued the rigid-hitch original, along with other running changes, ahead of later updates further down the model line before Caterpillar eventually reused the 657 nameplate decades later on an unrelated modern electronic machine.
What 657 owners discuss
Do owners report anything unusual about starting the two engines on a vintage 657?
Original 657s left the factory with a choice of two starting setups for the diesel engines, a small gasoline pony-motor starter or direct electric starting, and Caterpillar did not split these into separate serial-prefix runs. Two machines built close together can start differently. Operators also describe the rear engine's own starting circuit as unusual: cranking it uses an air-over-hydraulic arrangement that borrows oil from the scraper's ejector circuit to spin the starter, with air only used to engage the starter drive. The ejector needs to be fully retracted before cranking the rear engine or the circuit has no oil pressure to work with. Have a qualified tech verify this circuit before returning a stored machine to service.
What's it like running two engines and two throttles at once on this machine?
Tandem-power scrapers of this size give the operator two accelerator pedals, one for the front tractor engine and one for the rear scraper engine, and coordinating both takes practice. The rear engine's throttle runs on pressurized air rather than a direct mechanical link, so there is a slight lag; operators describe it as a tap-and-wait feel rather than the smooth response of a cable throttle. Experienced operators work the two pedals independently, one foot per engine, to keep power synced through cuts and hills without tiring one leg.
Did the original 657 ride rough compared to later versions?
Yes, this is the machine's best-documented quirk. Without a cushion hitch, the rigid tractor-to-scraper connection let the machine bounce, or 'lope' as period operators called it, hard enough that the higher transmission gears couldn't be used without it getting worse, and the repeated pounding stressed the frame and hitch over time. Caterpillar did not offer a cushion hitch (a linked hydraulic and nitrogen-accumulator hitch) until partway through the model's production run, and it could not be retrofitted onto machines already built. A 657 built before that point rides hard by design, not because something is worn out.
How can you tell whether a 657 predates the cushion hitch?
Check the tractor fenders and the hitch area. Pre-cushion-hitch machines have rounded tractor fenders and a simple rigid connection between tractor and scraper, with no hydraulic cylinder or accumulator visible at the hitch. These earlier machines also shipped without the later push-pull loading option, so an original example needed a separate pusher tractor working the cut rather than being able to load against a sister machine.
What do the twin diesels need to stay healthy long-term?
Both the tractor and scraper engines are pre-combustion-chamber diesels, and owners note they do not tolerate being lugged along at low rpm to save fuel; running them slow just lets them oil up instead. They also need real heat to start reliably, glow plugs threaded into the pre-chambers help, but a cold engine with weak glow plugs will fight the starter. On a machine that has sat unused for years, check the crankcase oil for fuel dilution before the first start. The camshaft-driven fuel transfer pump on the block can leak into the crankcase over a long idle period, which shows up as an overfull, thin-smelling dipstick. Have a qualified tech verify oil condition and glow-plug function before starting a long-dormant engine.
What kind of wear or damage shows up on a well-used bowl and hitch area?
On at least one long-served example, the recorded damage was to the sides of the scraper bowl where rocks worked their way between the draft arms and the bowl side plates over years of loading, marking up the sheet metal there. That, along with missing or replaced body panels, is treated as ordinary wear from decades of production use rather than a sign of abuse or neglect.
What should a buyer check before committing to restoring a used vintage 657?
Confirm which starting setup the machine has, gasoline pony motor or direct electric, since the parts and procedure differ between the two. Check whether it has the cushion hitch or the earlier rigid rounded-fender hitch; that alone tells you the production era and what ride-quality issues to expect. Inspect the bowl side plates and draft-arm area for rock-wear damage, look for missing or replaced panels, and check the crankcase oil for fuel contamination if the machine has sat idle for a long stretch. Sourcing decals, panels, and hard parts for a machine this old usually means working from old parts manuals and dealer channels rather than off-the-shelf stock, so budget extra time for fabrication. Have a qualified tech verify both engines' mechanical condition and the tandem-power control circuits before putting a restored unit back to work.
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
Serial-range & configuration variants
This page covers the Caterpillar 657. Related factory variants of the same model family:
657
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