TROUBLESHOOTING
SERVICE MANUAL NUMBER 24
Used Spark Plug Analysis
Use the following illustrations for determining serviceability of spark plug. Spark plug condi-
tion also can suggest a variety of possible engine malfunctions and, therefore, can indicate
needed engine repairs. When old plugs are replaced, replace entire set. Perform plug ser-
vice only on those plugs suitable for additional service, using the following procedures:
1.
2.
3.
Remove any oil deposits with solvent and dry plugs thoroughly.
Open electrode gap wide enough to permit cleaning and filing.
Remove combustion deposits from firing end of spark plug with a plug cleaner. Blow off
with compressed air to remove abrasives.
4.
5.
File electrode surfaces to restore clean, sharp edges. Again remove filings with com-
pressed air.
Reset gap to specifications by bending only side electrode with proper tool.
Normal Condition
Few deposits are present and probably will be light tan or gray in color. This plug shows that
plug heat range is compatible with engine, and engine is electrically and mechanically in
good running condition. With proper plug servicing (clean, file and regap), this plug can be
reinstalled with good results.
72420
Chipped Insulator
Chipped insulator usually results from careless plug regapping. Under certain conditions,
severe detonation also can split insulator firing ends. Replace spark plugs.
72420
Index
Page 1C-2
90-861327--1 OCTOBER 1999
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 305 CID, Mercury MerCruiser 350 CID |
| Model Year | 1998, 1999, 2000, 2001 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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