The 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) |
Author:
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
UNLESS YOU PLAN TO CHANGE THE FLYWHEEL TO ONE WITH A RING GEAR, THERE WOULD BE NO WAY TO MAKE IT ELECTRIC START.
I have an R390 engine with 12 Volt electric start. Do you offer an 120 volt electric starter motor?
Anybody know what size oil drain plug this engine uses?
Are there any after market air filters?