Rato R420

Rato R420The Rato R420 is a 420 cc (25.63 cu-in) single-cylinder air-cooled 4-stroke internal combustion general-purpose gasoline engine with horizontal shaft manufactured by Chongqing RATO Holding (Group) CO., LTD.

The Rato R420 engine has an (OHV) overhead-valve design; flat suction valve carburetor; recoil starter or electric starter, transistorized magneto ignition (TCI) system and centrifugal mechanical governor system.

The R420 motor has a 90.0 mm (3.54 in) cylinder bore and 66.0 mm (2.60 in) piston stroke with a compression ratio of 8.5:1. It produced 15.0 HP of horsepower at 3,600 rpm and 26.5 N·m (2.7 kg·m, 19.54 ft·lb) at 2,500 rpm of torque.

General information

Engine Specifications
ModelR420
Type4-stroke, OHV, single cylinder
Displacement420 cm 3 (25.63 cu-in)
Max. horsepower15.0 HP at 3,600 rpm
Max. torque (crank PTO)26.5 N·m (2.7 kg·m, 19.54 ft·lb) at 2,500 rpm
CarburetorFlat suction valve carburetor
Cooling systemForced-air
Ignition systemTransistorized magneto ignition (TCI)
Lubricating systemSplash
Starting systemRecoil / electric starter
Stoping systemIgnition primary circuit ground
Fuel usedUnleaded gasoline (octane number 86 or higher)
PTO shaft rotationCounterclockwise (from PTO shaft side)

Cylinder Block and Head

The Rato R420 engine has cast-iron cylinder liner, dual ball bearings and steel forged and hardened crankshaft.

Cylinder block
Compression ratio:8.5:1
Bore x Stroke90 X 66 mm (3.54 x 2.60 in)
Sleeve internal diameter90.000-90.015 mm (3.5433-3.5439 in)
Piston skirt outer diameter89.960-89.970 mm (3.5417-3.5421 in)
Number of piston rings (compression / oil):2 / 1
Ring side clearanceTop/Second0.020-0.060 mm (0.0008-0.0023 in)
Ring end gapTop/Second0.20-0.40 mm (0.008-0.016 in)
Oil0.20-0.70 mm (0.008-0.027 in)
Connecting rod small end ID20.011 mm (0.7878 in)
Connecting rod big end ID36.025 mm (1.4183 in)
Crankshaft crank pin outer diameter35.985 mm (1.4167 in)
Cylinder Head
Warpage (limit)0.10 mm (0.004 in)
Valve Arrangement:OHV
Valves:2
Stem outer diameter (standard):INTAKE6.580 mm (0.2590 in)
EXHAUST6.560 mm (0.2583 in)
Cam height:INTAKE6.59 mm (0.2595 in)
EXHAUST6.07 mm (0.2390 in)
Valve spring free length:39.0 mm (1.5354 in)
Camshaft journal diameter:15.984 mm (0.6293 in)

Tightening torque specs

Tightening torque specs
Connecting rod bolt15 Nm; 1.5 kg·m; 11 ft·lb
Oil dran plug22 Nm; 2.2 kg·m; 16 ft·lb
Crankcase cover28 Nm; 2.8 kg·m; 21 ft·lb
Flywheel subassembly95 Nm; 9.5 kg·m; 70 ft·lb
Cylinder head subassembly42 Nm; 4.2 kg·m; 31 ft·lb
Rocker shaft bolt24 Nm; 2.4 kg·m; 18 ft·lb
Cylinder head cover10 Nm; 1.0 kg·m; 7 ft·lb
Spark plug28 Nm; 2.8 kg·m; 21 ft·lb
Ignition coil10 Nm; 1.0 kg·m; 7 ft·lb

Service Information

Engine
Maximum speed3750-3810 rpm
Cylinder compression12.2 kg/cm2 at 1400 rpm
Valve clearance
Intake valve clearance0.15±0.02 mm (0.006±0.001 in)
Exhaust valve clearance0.20±0.02 mm (0.008±0.001 in)
Oil system
Oil type4-stroke or an equivalent (SJ)
Recommended oilSAE 10W-30, 15W-40
Oil capacity1.1 L
Ignition system
Spark plugNGK: BPR6ES
Spark plug gap0.7-0.8 mm (0.028-0.031 in)
Primary ignition coil resistance0.6-0.9 Ω
Secondary ignition coil resistance5.6-6.9 kΩ
Ignition coil air gap0.4 ± 0.2 (0.016 ± 0.008)
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We try to use verified sources and official documentation, however, differences between sources or errors in entering information may occur. We do not provide advice on technical issues related to the engines operation or repair. We do not recommend using provided information for engines repairing engines or spare parts ordering, use only official service manuals and spare-parts catalogs.

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