Record the first stroke reading as well as the final reading to
determine cylinder condition.Deciphering the readings
Low-compression readings can be caused by various conditions. The
most obvious is the engine is old and worn out. Older engines,
manufactured prior to 1972, were not designed to be run on unleaded
gasoline. Tetraethyl lead, which has long been phased out of gasoline in
the United States, serves as a lubricant, thus hardened seats were not
necessary in vehicles manufactured during the period in which
Tetraethyl lead was in use. Running a pre-1972 engine that requires lead
on modern unleaded fuel without lead additive can produce low
readings due to engine wear/damage.
A misfire at idle, accompanied by the clicking of a lifter, can indicate a
bad valve seat. Engines requiring frequent valve adjustments, where
valve clearances rapidly tighten, can indicate a receding valve seat or a
stretching valve stem. Either condition immediately should be attended
to in order to avoid other problems. If it is necessary to pull the cylinder
heads, have the machinist install hardened valve seats to avoid future
problems with unleaded fuel. One vintage truck group has had good
results overcoming excessive valve seat wear by opening up the exhaust