Ryobi 990r - Manual (Page 23)

23
MAINTENANCE AND REPAIR INSTRUCTIONS (Continued)
CHECKING / ADJUSTING VALVE TO
ROCKER ARM CLEARANCE
Every 50 hours of operation, remove the rocker arm
cover and check the valve to rocker arm clearance, using
a flat feeler gauge.
NOTE: The engine must be cold when checking
or adjusting the clearance.
Check / adjust the clearance as follows:
1. Remove the four (4) screws from the engine cover
(Figs. 48 and 49).
2. Remove the engine cover.
REPLACING THE SPARK PLUG
Use a Champion RDZ19H spark plug. Correct air gap is
.025 in (0.635 mm). Remove plug after every 50 hours of
operation and check its condition. Allow the engine to
cool before removing the spark plug.
1. Stop the engine and pull the wire off of the spark
plug.
2. Clean around the spark plug and remove it from the
cylinder head.
NOTE: Replace a cracked, fouled or dirty spark
plug. Do not sand blast, scrape or clean
electrodes because the engine could be
damaged by grit entering the cylinder.
3. Set the air gap at .025 in (0.635 mm) using a wire
feeler gauge (Fig. 47). Install a correctly gapped spark
plug into the cylinder head. Torque to 100-110 in•lb
(11.3-12.3 N•m).
Fig. 47
.025 in
(0.635 mm)
Fig. 49
Screw
Screws
Fig. 48