Lycoming O-290 Operator's Manual page 67

LYCOMING OPERATOR'S MANUAL
O-235 AND O-290 SERIES
d. Removal of Hydraulic Tappet Sockets and Plunger Assemblies (O-290-D2 Series) – It will be
necessary to remove and bleed the hydraulic tappet plunger assembly so that dry tappet clearance can
be checked when the cylinder assembly is reinstalled. This is accomplished in the following manner:
A special Lycoming tool is available for removal of the sockets and plunger assemblies. In the event
the tool is not available, proceed as described below.
The hydraulic tappet socket may usually be removed by inserting the forefinger into the concave end
of the socket. The socket will usually stick to the finger firmly enough to be pulled out of the tappet
body. If the socket cannot be removed in this manner, it may be removed by grasping the edge of the
socket with a pair of needle nose pliers. However, care must be exercised to avoid scratching the
socket. To remove the hydraulic tappet plunger assembly, use special Lycoming service tool. In the
event that the tool is not available, the hydraulic tappet plunger assembly may be removed by bending
a hook in the end of a short piece of lock wire, inserting the lock wire around the edge of the plunger
assembly, and turning the wire so that the hook engages the spring of the plunger assembly. Draw the
plunger assembly out of the tappet body by gently pulling the wire.
NEVER USE A MAGNET TO REMOVE HYDRAULIC PLUNGER ASSEMBLIES FROM
THE CRANKCASE. THIS CAN CAUSE THE BALL TO REMAIN OFF ITS SEAT,
RENDERING THE UNIT INOPERATIVE.
e. Assembly of Valves in Cylinder – Prelubricate valve stems with Molytex Grease O or equivalent and
insert each valve stem in its respective valve guide. Place cylinder over a block of wood so that the
valves are held against the seats and assemble the lower valve spring seat, auxiliary valve seat and
outer valve spring over the valve stem and guide. Place the upper valve spring seat on top of the
springs.
When installing valve springs, place the dampener end of spring (close wound coils marked
with dye or lacquer) toward the cylinder.
Using a valve spring compressor, compress the valve springs and place the split keys in the groove
around the upper end of the valve stem. Slowly release the pressure on the valve spring compressor
and allow the upper spring seat to lock itself in place around the valve keys.
f. Assembly of Hydraulic Tappet Plunger Assemblies (O-290-D2 Series) – To assemble the unit, unseat
the ball by inserting a thin clean bronze wire through the oil inlet hole. With the ball off its seat, insert
the plunger and twist clockwise so that the spring catches.
g. Assembly of Cylinder and Related Parts – Rotate the crankshaft so that the connecting rod of the
cylinder being assembled is at the top center position with both tappets on the low side of the cam in a
position that corresponds with both valves closed.
(1) O-290-D2 Series – Place each hydraulic tappet plunger assembly in its respective body and
assembly socket on top of plunger assembly.
CAUTION
NOTE
MAINTENANCE PROCEDURES
SECTION 5
5-7