Rato R390

Rato R390The Rato R390 is a 389 cc (23.7 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 R390 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 R390 motor has an 88.0 mm (3.50 in) cylinder bore and 64.0 mm (2.50 in) piston stroke with a compression ratio of 8.0:1. It produced 13.0 HP of horsepower at 3,600 rpm and 25 N·m (2.54 kg·m, 18.43 ft·lb) of torque at 2,500 rpm.

General information

Engine Specifications
Model R390
Type 4-stroke, OHV, single cylinder
Displacement 389 cm 3 (23.7 cu-in)
Max. horsepower 13.0 HP at 3,600 rpm
Max. torque (crank PTO) 25 N·m (2.54 kg·m, 18.43 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 R390 engine has cast-iron cylinder liner, dual ball bearings and steel forged and hardened crankshaft.

Cylinder block
Compression ratio: 8.0:1
Bore x Stroke 88 X 64 mm (3.5 x 2.5 in)
Sleeve internal diameter 88.000-88.017 mm (3.4645-3.4652 in)
Piston skirt outer diameter 87.965-87.985 mm (3.4631-3.4640 in)
Number of piston rings (compression / oil): 2 / 1
Ring side clearance Top/Second 0.015-0.045 mm (0.0006-0.0018 in)
Ring end gap Top/Second 0.20-0.40 mm (0.008-0.016 in)
Oil 0.20-0.70 mm (0.008-0.027 in)
Connecting rod small end ID 20.005 mm (0.7876 in)
Connecting rod big end ID 36.025 mm (1.4183 in)
Crankshaft crank pin outer diameter 35.985 mm (1.4167 in)
Cylinder Head
Warpage (limit) 0.10 mm (0.004 in)
Valve Arrangement: OHV
Valves: 2
Stem outer diameter (standard): INTAKE 6.590 mm (0.2594 in)
EXHAUST 6.550 mm (0.2579 in)
Cam height: INTAKE 33.6-33.8 mm (1.3228-1.3307 in)
EXHAUST 32.90-33.10 mm (1.2952-1.3031 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 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

Engine
Maximum speed 3750-3810 rpm
Cylinder compression 14.0 kg/cm2 at 1400 rpm
Valve clearance
Intake valve clearance 0.15±0.02 mm (0.006±0.001 in)
Exhaust valve clearance 0.20±0.02 mm (0.008±0.001 in)
Oil system
Oil type 4-stroke or an equivalent (SJ)
Recommended oil SAE 10W-30, 15W-40
Oil capacity 1.1 L
Carburetor
Main jet 0.92
Float height 13.2 mm (0.52 in)
Pilot screw opening 1-7/8 turns out
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)
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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.

3 Comments

  1. I have this motor on my generator Rato R390 is a 389 cc, it is a Pull start unit, does your company have a “electric start (12 volt) conversion kit available to purchase?
    Rato R390 is a 389 cc

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