TROUBLESHOOTING
SERVICE MANUAL NUMBER 24
Engine Noise
Important Information
No definite rule or test will positively determine source of engine noise. Use the following
information only as a general guide to engine noise diagnosis.
1.
Use a timing light to determine if noise is timed with engine speed or 1/2 engine speed.
Noises timed with engine speed are related to crankshaft, rods, pistons, piston pins and
flywheel. Noises timed to 1/2 engine speed are valve train related.
2.
3.
The use of a stethoscope can aid in locating a noise source; however, because noise
will travel to other metal parts not involved in the problem, caution must be exercised.
If you believe noise is confined to one particular cylinder, ground spark plug leads, one
at a time. If noise lessens noticeably or disappears, it is isolated to that particular
cylinder.
4.
5.
Try to isolate the noise to location in engine: front to back, top to bottom. This can help
determine which components are at fault.
Sometimes noises can be caused by moving parts coming in contact with other compo-
nents. Examples are: flywheel or coupler; exhaust flappers rattling against exhaust pipe;
crankshaft striking pan, pan baffle, or dipstick tube; rocker arm striking valve cover; and
loose flywheel cover. In many cases if this is found to be the problem, a complete engine
teardown is not necessary.
6.
7.
When noise is isolated to a certain area and component, removal and inspection will be
required. Refer to proper sections of service manual for information required for service.
If noise cannot be distinguished between engine and drive unit, remove drive from boat.
Run a water supply directly to engine. Run engine without the drive to determine if noise
is still there.
Valve Cover Area
Noise Location
Possible Causes
Rocker arm striking valve cover
Rocker arm out of adjustment
Worn rocker arm
Valve cover area, timed to 1/2 engine
speed, noise could be confined to one cyl-
inder or may be found in any multitude of
cylinders
Bent push rod
Collapsed filter
Index
Page 1C-18
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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