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20
Noisy Pistons.
FIAT· 850 PASSENGER CARS
The most common piston noise
is
t
slap
t,
due to the piston rocking from side to side
in
the cylinder.
Piston slap causes a hollow, muffled, bell-like sound.
It
is especially audible when driving at low speed
under load.
POSSIBLE
CAUSES
1) Excessive clearance between pistons and cylinder
barrels causes piston «slap
II
or
(I
rocking n.
2) Excessive clearance of rings In piston grooves.
Noisy Piston Pins.
REMEDIES
1) Replace pistons and rebor. cylinders,
If
necenary.
2) Remove and inspect pistons and rings and replace as re-
quired.
The most common piston pin noise
is
the result of excessive pin clearance.
This is
characterized
by
a sharp. metallic, double knock generally audible
with
the engine idling.
POSSIBLE
CAUSES
1) Excessive piston pin clearance In piston
bon.
Noisy Valves and Tappets.
REMEDIES
1) II1.tall over.in
piston pins proceeding
as dlreded
under
«Pistons· Connecting Rods
».
Noisy valve action has a characteristic clicking noise occurring at regular intervals.
The frequency
of this clicking is generally less than other engine noises, because the valves are operated by the
camshaft
running at one-half of crankshaft speed.
POSSIBLE
CAUSES
1) Excessive rocker arm-to-valve stem clearance.
2) Threads stripped on adjusting screw.
3) Broken valve springs.
4) Excessive valve stem-to.gulde clearance.
5) Excessive tappet.to-crankease guide hole clear·
ance.
I)
Excessive wear on one or more camshaft lobe••
REMEDIES
t) Adjust to specified tappet clearance.
2) Check threads on screw and rocker arm seat and replace
as required.
3) Replace valve spring ••
4) Check valve .tem diameter and valve guide Inside diam-
eter, then replace worn parts.
5) Replace tappets by oversize. a. directed In eoverlng
chapter.
6)
Replace camshaft.
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