Determining State Of Engine From Spark Plug Appearance - BMW K75 Repair Manual

Determining state of engine from spark plug
appearance
The colour and nature of deposits on the spark plug and
insulation reflect the engine 's condition and the
combustion pattern.
Spark plug: normal
Insulator base light grey to fawn.
The spark plug's thermal value is correct and the engine
in good cond ition. No faults in ignition and fuel injection
system .
Spark plug: sooted
Spark plug coated in soft , dry soot deposits.
Potential causes: mixture too rich, air filter contam inated,
spark plug too cold (wrang thermal value).
Light (white)
Electrade and insulator a snowy white colour.
Potential causes: mixture too lean, incorrect ignition
timing (too early), deposits in combustion chamber, spark
plug too hot (wrong thermal value) .
Oily
Electrodes and spark plug interior coated in a black oily
film.
Potential causes: oi l in combustion chamber, piston ring
gap too large, score marks in cylinder, valve stem seal
leaking, excessive valve stem play in valve gu ides .
8.87
00050
. ..
00052
00053
00 - 33.0