Mack ASET AC Service Manual Download

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REPAIR INSTRUCTIONS, PART 1

Page 189

SALVAGING A DAMAGED VALVE LIFTER
BORE

Occasionally, a failure will result in severe wear
and breakage of the roller and roller axle. These
parts will then separate from the lifter body.
Subsequently, the lifter legs (which had retained
the axle in the lifter body) become bent-outward
and are driven up into the lifter bore by the cam
lobe. This action damages the bottom 1/4 to
3/8 inch (6.35 to 9.52 mm) of the bore and will
prevent installation of the new lifter. It is
necessary to clean up the damaged bore area
with a file, stone or emery paper using care to
remove

all

high spots from the bore. The goal is

to clean up the areas of raised metal, but not to
enlarge the bore diameter. Any remaining nicks
or scores (low spots) do not inhibit proper
function of the parts and will cause no problem.
After removing any raised metal, use a flex-hone
to lightly hone the bore.

Another condition sometimes encountered is a
small amount of scuffing or foreign particle
scoring in a lifter bore. This condition can inhibit
static-free movement of a lifter. This will not
cause a lifter hang-up in engine operation, but is
sometimes noticed during lifter removal or
installation. If this condition is encountered, use a
flex-hone to lightly hone the bottom area of the
lifter bore, trial-fitting the lifter until the high spots
have been removed and free movement is
re-established.

Whenever a lifter bore is reworked or honed, be
sure that all the metal and honing debris is
cleaned from all affected areas by flushing with a
fresh supply of suitable brake/parts cleaner.

LIFTER BORE CLEANING AND LIFTER
CHECKS

While the camshaft is removed and lifter bores
are relatively accessible, it is a good practice to
clean all the lifter bores and then trial-fit all the
lifters into their respective bores and H-rings.
Clean and trial-fit lifters as follows:

1. Clean all lifter bores with a fresh supply of

suitable brake/parts cleaner. Ensure all
Loctite

residue and dried contamination

has been removed from the lifter bore and
H-ring area.

2. Trial-fit a lifter back into its original lifter bore

by aligning the lifter flats with the H-ring flats.
Use only light finger pressure when installing
the lifters. Verify that the lifter has complete
freedom of movement in the bore and H-ring
in both the upward and downward
directions. When the lifter is seated, it should
be possible to rotate it slightly from left to
right. If the lifter is sticky or tight, or if
additional force was required to install the
lifter, proceed as follows:

Try the lifter in another lifter bore. A
stack-up of component tolerances can
result in a lifter being free in another
bore. This is acceptable.

If the problem persists when the lifter is
tried in another bore, replace the lifter.

If the problem is confined to a particular
bore, determine if the lifter tightness is
due to the lifter or the H-ring. If the bore
is the problem, perform a bore clean up
and hone as described in “SALVAGING
A DAMAGED VALVE LIFTER BORE”
on page 189. If the lifter is tight in the
H-ring, replace the lifter or H-ring as
determined by a trial-fit of another lifter.

Mack ASET AC, Service Manual

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