Checking The Spark Plugs - Yamaha TDM900 Owner's Manual

PERIODIC MAINTENANCE AND MINOR REPAIR

Checking the spark plugs

The spark plugs are important engine
components, which should be checked
periodically, preferably by a Yamaha
dealer. Since heat and deposits will
cause any spark plug to slowly erode,
they should be removed and checked
in accordance with the periodic mainte-
nance and lubrication chart. In addition,
the condition of the spark plugs can re-
veal the condition of the engine.
The porcelain insulator around the cen-
ter electrode of each spark plug should
6 be a medium-to-light tan (the ideal col-
or when the motorcycle is ridden nor-
mally), and all spark plugs installed in
the engine should have the same color.
If any spark plug shows a distinctly dif-
ferent color, the engine could be defec-
tive. Do not attempt to diagnose such
problems yourself. Instead, have a
Yamaha dealer check the motorcycle.
If a spark plug shows signs of electrode
erosion and excessive carbon or other
deposits, it should be replaced.
EAU01880
Specified spark plug:
DPR8EA-9 (NGK) or
X24EPR-U9 (DENSO)
Before installing a spark plug, the spark
plug gap should be measured with a
wire thickness gauge and, if necessary,
adjusted to specification.
a. Spark plug gap
Clean the surface of the spark plug
gasket and its mating surface, and then
wipe off any grime from the spark plug
threads.
6-7
Spark plug gap:
0.8–0.9 mm
Tightening torque:
Spark plug:
18 Nm (1.8 m·kgf)