Mack ASET AC, Service Manual, Page: 263 / 536

Page 250
REPAIR INSTRUCTIONS, PART 1
Valve Yoke Guide Pin Replacement
[213 FH]
Valve yoke guide pins are located only between
each set of exhaust valve guides. There are no
guide pins for the inlet valves which are actuated
by pinless valve yokes.
INSPECTION
Inspect each valve yoke guide pin surface for
cracks or other damage. Also check the pin
diameter and installed height. If the pin is worn or
broken, it can be removed following the
applicable procedure below.
REMOVAL PROCEDURE (INTACT PIN)
To remove an unbroken pin, use valve yoke
guide pin puller kit PT6575 and the 7/16 inch
extractor PT6570-11 as follows:
1. Install the extractor over the guide pin and
position the lock on the extractor
(Figure 273).
2. Using the slide hammer, firmly tap onto the
extractor to lock the puller onto the guide
pin.
3. Next, using the slide hammer, remove the
worn pin from the cylinder head bore.
REMOVAL PROCEDURE (BROKEN PIN)
Remove a broken pin as follows:
Due to the hardness of the valve yoke guide pins,
drilling and tapping must be done slowly with
sharp tools and with plenty of lubrication.
1. Center punch the broken section of the pin
in the cylinder head prior to drilling. The
punch mark MUST BE close to the center of
the broken pin to control the drilling
operation.
2. Using a drill press, drill a 7/64-inch pilot hole
completely through the broken section of the
yoke pin. A drill press is strongly
recommended to keep the drilled hole
straight with the yoke pin hole in the cylinder
head. Use care when drilling to “feel” when
the drill bit passes through the yoke pin and
contacts the cylinder head. Stop drilling at
that point to avoid drilling through the head
and into the water jacket.
3. Drill a 13/64-inch hole completely through
the broken section of the yoke pin.
4. Tap all the way through the broken yoke pin,
using a 1/4-inch -20 tap and cutting oil.
Clean out the cutting chips using
compressed air.
5. Using a slide hammer fitted with a 1/4-inch
extractor, remove the broken yoke pin from
the cylinder head (Figure 273).
Thread the slide-hammer extractor as deep as
possible into the threaded yoke pin. Failure to
install the extractor deep enough will cause the
yoke pin to break again.
6. Clean out any remaining chips with
compressed air and inspect the yoke pin
hole in the cylinder head for drilling or
tapping damage.
273
Figure 273 — Valve Yoke Guide Pin Removal
1. Extractor Lock (Part of PT6570-11)
5-111.bk Page 250 Monday, July 10, 2006 2:26 PM