Rato R300

Rato R300The Rato R300 is a 301 cc (18.4 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 R300 engine has an OHV design; flat suction valve carburetor; recoil starter or electric starter, transistorized magneto ignition (TCI) system and centrifugal mechanical governor system.

The R300 motor has an 80.0 mm (3.15 in) cylinder bore and 60.0 mm (2.36 in) piston stroke with a compression ratio of 8.5:1. It produced 12.0 HP of horsepower at 3,600 rpm and 18 N·m (1.83 kg·m, 13.27 ft·lb) of torque at 2,500 rpm.

General information

Engine Specifications
Model R300
Type 4-stroke, OHV, single cylinder
Displacement 301 cm 3 (18.4 cu-in)
Max. horsepower 12.0 HP at 3,600 rpm
Max. torque (crank PTO) 18 N·m (1.83 kg·m, 13.27 ft·lb) at 2,500 rpm
Carburetor Flat suction valve carburetor
Cooling system Forced-air
Ignition system Transistorized magneto ignition (TCI)
Lubricating system Splash
Starting system Recoil / electric starter
Stoping system Ignition primary circuit ground
Fuel used Unleaded gasoline (octane number 86 or higher)
PTO shaft rotation Counterclockwise (from PTO shaft side)

Cylinder Block and Head

The Rato R300 engine has cast-iron cylinder liner, dual ball bearings and steel forged and hardened crankshaft.

Cylinder block
Compression ratio: 8.5:1
Bore x Stroke 80 X 60 mm (3.15 x 2.36 in)
Sleeve internal diameter 80.000-80.015 mm (3.1496-3.1501 in)
Piston skirt outer diameter 79.975-79.985 mm (3.1486-3.1490 in)
Number of piston rings (compression / oil): 2 / 1
Ring side clearance Top/Second 0.025-0.060 mm (0.0010-0.0023 in)
Ring end gap Top 0.20-0.40 mm (0.008-0.016 in)
Second 0.30-0.50 mm (0.012-0.020 in)
Oil 0.20-0.70 mm (0.008-0.027 in)
Connecting rod small end ID 15.011-15.022 mm (0.5909-0.5914 in)
Connecting rod big end ID 33.025-33.039 mm (1.3001-1.3007 in)
Crankshaft crank pin outer diameter 32.975-32.985 mm (1.2982-1.2986 in)
Cylinder Head
Warpage (limit) 0.10 mm (0.004 in)
Valve Arrangement: OHV
Valves: 2
Stem outer diameter (standard): INTAKE 5.48 mm (0.216 in)
EXHAUST 5.44 mm (0.214 in)
Cam height: INTAKE 6.045 mm (0.2380 in)
EXHAUST 5.766 mm (0.2270 in)
Valve spring free length: 38.5-39.5 mm (1.5157-1.5551 in)
Camshaft journal diameter: 16.166-16.184 mm (0.6364-0.6371 in)

Tightening torque specs

Tightening torque specs
Connecting rod bolt 15 Nm; 1.5 kg·m; 11 ft·lb
Oil dran plug 22 Nm; 2.2 kg·m; 16 ft·lb
Crankcase cover 28 Nm; 2.8 kg·m; 21 ft·lb
Flywheel subassembly 75 Nm; 7.5 kg·m; 55 ft·lb
Cylinder head subassembly 42 Nm; 4.2 kg·m; 31 ft·lb
Rocker shaft bolt 24 Nm; 2.4 kg·m; 18 ft·lb
Cylinder head cover 10 Nm; 1.0 kg·m; 7 ft·lb
Spark plug 28 Nm; 2.8 kg·m; 21 ft·lb
Ignition coil 10 Nm; 1.0 kg·m; 7 ft·lb

Service Information

Maximum speed 3750-3850 rpm
Cylinder compression 11.2 kg/cm2 at 1400 rpm
Valve clearance
Intake valve clearance 0.10-0.15 mm (0.004-0.006 in)
Exhaust valve clearance 0.15-0.20 mm (0.006-0.008 in)
Oil system
Oil type 4-stroke or an equivalent (SJ)
Recommended oil SAE 10W-30, 15W-40
Oil capacity 1.1 L
Ignition system
Spark plug NGK: BPR6ES
Spark plug gap 0.7-0.8 mm (0.028-0.031 in)
Primary ignition coil resistance 0.6-0.9 Ω
Secondary ignition coil resistance 5.6-6.9 kΩ
Ignition coil air gap 0.4 ± 0.2 (0.016 ± 0.008)
Author: Sergei Wers
About: Co-founder and CEO of a multi-brand auto repair shop (engine repair, chassis repair, body repair and painting) for over 15 years. I have been developing internet sites with technical specifications for more than seven years.

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1 Comment

  1. Thanks for the information. Do you has specs on the diameter and the length of the shaft? I am looking to put an equivalent engine in.

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