Used Spark Plug Analysis
Chipped Insulator
Use the following illustrations for determining ser-
viceability of spark plug. Spark plug condition also
can suggest a variety of possible engine malfunc-
tions and, therefore, can indicate needed engine re-
pairs. When old plugs are replaced, replace entire
set.Performplugserviceonlyonthoseplugssuitable
for additional service, using the following proce-
dures:
Chipped insulator usually results from careless plug
regapping. Under certain conditions, severe detona-
tion also can split insulator firing ends. Plug must be
replaced.
1.
2.
3.
Remove any oil deposits with solvent and dry
plugs thoroughly.
Openelectrodegapwideenoughtopermitclean-
ing and filing.
Remove combustion deposits from firing end of
spark plug with a plug cleaner. Blow off with com-
pressed air to remove abrasives.
72420
4.
5.
File electrode surfaces to restore clean, sharp
edges. Again remove filings with compressed air.
Reset gap to specifications by bending only side
electrode with proper tool.
Wet Fouling (Oil Deposits)
Plug becomes shorted by excessive oil entering
combustion chamber, usually in engine with many
hours of operation. Worn piston rings, cylinder walls,
valve guides or valve stem seals are causes of oil en-
tering combustion chamber. Only engine repairs will
permanently relieve oil wet fouling.
Spark Plug Analysis
Normal Condition
IMPORTANT: New engines or recently over-
hauled engines may wet foul plugs before normal
oil control is achieved with proper break-in pro-
cedures. Such fouled plugs may be serviced
(clean, file and regap) and reinstalled.
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 elec-
trically and mechanically in good running condition.
With proper plug servicing (clean, file and regap), this
plug can be reinstalled with good results.
72420
72420
Index
1C-2 - TROUBLESHOOTING
90-823224--2 796
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 454 CID, Mercury MerCruiser 502 CID |
| Model Year | 1993, 1994, 1995, 1996, 1997 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
(4 votes, average: 4.5 out of 5)
Marine readers have rated 1993 1997 Mercury-MerCruiser GM V8 454 CID 7.4L and 502 CID 8.2L Marine Engines Service Manual Number 16 4.5 out of 5.0 based on 4 product reviews. Hugely helpful service manual! Perfect. Thank you!
Manuals are all Important for Technician
This book is invaluable if you do your own repairs. Great book.
Could not find a copy until a search brought me here.
Excellent print.
Thank you