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
Type4-stroke, OHV, single cylinder
Displacement301 cm 3 (18.4 cu-in)
Max. horsepower12.0 HP at 3,600 rpm
Max. torque (crank PTO)18 N·m (1.83 kg·m, 13.27 ft·lb) at 2,500 rpm
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 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 Stroke80 X 60 mm (3.15 x 2.36 in)
Sleeve internal diameter80.000-80.015 mm (3.1496-3.1501 in)
Piston skirt outer diameter79.975-79.985 mm (3.1486-3.1490 in)
Number of piston rings (compression / oil):2 / 1
Ring side clearanceTop/Second0.025-0.060 mm (0.0010-0.0023 in)
Ring end gapTop0.20-0.40 mm (0.008-0.016 in)
Second0.30-0.50 mm (0.012-0.020 in)
Oil0.20-0.70 mm (0.008-0.027 in)
Connecting rod small end ID15.011-15.022 mm (0.5909-0.5914 in)
Connecting rod big end ID33.025-33.039 mm (1.3001-1.3007 in)
Crankshaft crank pin outer diameter32.975-32.985 mm (1.2982-1.2986 in)
Cylinder Head
Warpage (limit)0.10 mm (0.004 in)
Valve Arrangement:OHV
Stem outer diameter (standard):INTAKE5.48 mm (0.216 in)
EXHAUST5.44 mm (0.214 in)
Cam height:INTAKE6.045 mm (0.2380 in)
EXHAUST5.766 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 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 subassembly75 Nm; 7.5 kg·m; 55 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

Maximum speed3750-3850 rpm
Cylinder compression11.2 kg/cm2 at 1400 rpm
Valve clearance
Intake valve clearance0.10-0.15 mm (0.004-0.006 in)
Exhaust valve clearance0.15-0.20 mm (0.006-0.008 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)
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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