Honda HHT31S Owner's Manual page 39

Spark Plug Service
Recommended spark plugs:
HHT25S CMR5HSB (NGK)
HHT31S CR5HSB (NGK)
U16FSR-UB (DENSO)
NOTICE
Incorrect spark plugs can cause engine damage.
1. HHT25S model: Remove the 5 x 12 mm hex
bolt and top cover.
2. Disconnect the spark plug cap, and remove
any dirt from around the spark plug area.
3. Remove the spark plug with a 5/8-inch spark
plug wrench.
4. Inspect the spark plug. Replace it if the
electrodes are worn, or if the insulator is
cracked or chipped.
5. Measure the spark plug electrode gap with a
suitable gauge. The gap should be
0.024 ~ 0.028 in (0.60 ~ 0.70 mm). Correct
the gap, if necessary, by carefully bending the
side electrode.
6. Install the spark plug carefully, by hand, to
avoid cross-threading.
7. After the spark plug seats, tighten with a
5/8-inch spark plug wrench to compress
the washer.
If reinstalling the used spark plug, tighten
1/8 ~ 1/4 turn after the spark plug seats.
If installing a new spark plug, tighten
1/2 turn after the spark plug seats.
NOTICE
A loose spark plug can overheat and damage
the engine. Overtightening the spark plug can
damage the threads in the cylinder head.
8. Attach the spark plug cap.
HHT25S model: Install the top cover and
5 x 12 mm hex bolt and tighten securely.
TORQUE: 51.6 in-lb (1.09 N•m)
SERVICING YOUR HONDA TRIMMER
SPARK PLUG
SPARK PLUG CAP
5/32 in (4 mm) HEX WRENCH
(commercially available)
5 x 12 mm
HEX BOLT
SPARK PLUG
CAP
SPARK PLUG CAP
SIDE ELECTRODE
HHT31S
HHT31S
HHT25S
SPARK PLUG
HHT25S
SIDE ELECTRODE
GAP
0.024 - 0.028 in
(0.60 - 0.70 mm)
SEALING
WASHER
HHT25S
TOP
COVER
37