HIRTH ENGINES

 

 

Fig. 1-Exploded view of magneto, high tension coils and associated parts used on In-Line Twin.

1. Flywheel 2. Generating coils 3. Lighting coil 4. High-tension coils 5. Lighting wires (yellow) 6. Ground cables (black) 7. Stop cable (brown) 8. Advance weight 9. Crankcase 10. Through bolts

 

MAINTENANCE

CARBURETOR. Tillotson diaphragm type carburetors are used. Refer to TILLOTSON Carburetor section for operation and overhaul in-formation. An external impulse line is used on most models to connect fuel pump diaphragm cover to engine crankcase. Be sure that all passages are open and that vacuum and pressure leaks are eliminated.

IGNITION AND TIMING. Breaker point gap should be approximately 0.4 mm (0.016 in.). Points can be adjusted after removing the recoil starter, starter cup and flywheel cover plate. Most engines are equipped with a centrifugal timing advance which provides retarded spark timing for starting only. When points are serviced, check to see that advance mechanism moves freely without binding. If binding occurs, disassemble and clean the advance mechanism and/or renew the parts concerned.

The fan wheel (flywheel) contains a mark and the letters "OT" on outer rim and a similar mark appears on fan housing. Piston is at top dead center when the two marks are aligned. Static

Fig. 2-High-tension coils on Opposed Twin, properly wired. Numbers (1 & 15) appear on

coils.

A Shorting cable

B. Generator coil wire (Blue)

C. High tension coils timing position may not be marked. Timing position (Piston crown BTDC) is given in specification data for use if timing marks cannot be located.

On alternate firing twins, points must be set to open exactly 180° apart. Twin cylinder engines use energy transfer type ignition system, with a low tension (generating) ignition coil located underneath the flywheel. On alternate firing twin the generating coils are "Piggy-Backed" or stacked as shown at (2-Fig. 1)!and high tension coils (4) are concealed underneath the crankcase and secured by through-bolts (10).

On opposed twin, only one generating coil is required and high tension coils are connected in series as shown in Fig. 2. Coils are located in fan housing and bolted to crankcase casting.

Refer to MAGNETO Section of SERVICE FUNDAMENTALS for overhaul procedures.

LUBRICATION. The engine is lubricated by mixing oil with the fuel. A suitable two-cycle air cooled engine oil is recommended. Standard grade SAE 30 automotive motor oil may be used if two-cycle oil is not available.

Recommended fuel-oil mixture is 25:1. Mix fuel and oil thoroughly using a separate container before pouring mixture into fuel tank. For cold. weather blending, pre-mix the oil with a small amount of gasoline and shake thoroughly until mixture is liquid, then blend the remainder of fuel. Do not use kerosene or fuel oil for pre. mixing.

REPAIRS

TIGHTENING TORQUES. Recommended tightening torques are as follows. Data is given in ft.-lbs. Cylinder Head

Models 170R, 180R     20  Model 171R (Studs)  20  Model 171R (Bolts)  6

Models 210R, 211R, 220R  6  Model 230R  17

 

Crankcase

Model 180R  6  All Other Models  17

Cylinder Base

Models 210R, 211R, 220R, 230R ... 17

Intake Manifold

Models 210R, 211R, 220R      17

Model 230R     6

 

Exhaust Manifold

Model 230R     6

All Other Models          17 15

Fig. 3-Exploded view of Opposed Twin. Refer to Fig. 4 for parts identification.