Tennant 255 Series II, Operator'S Manual, Page: 88 / 128

MAINTENANCE
255 SERIES II MM189 (12---89)
3-28
IGNITION SYSTEM
SPARK PLUGS
Clean or replace and adjust spark plugs after every
400 hours of operation. Spark plug gaps are best
checked with a wire gauge unless the plug is
dressed to obtain a correct reading with a flat gauge.
The adjustment should always be made on the side
electrode and never on the center electrode, which
may cause a broken porcelain.
“Gapping” the electrode tip is more easily done with
the proper tools.
A
B
01471
GAPPING SPARK PLUG
A. Spark Plug
B. Gapping Tool
The proper spark plug gap is 0.035 in (0.9 mm) for
machines below serial number 038000. The proper
spark plug gap is 0.039 in (1 mm) for machines
serial number 038000 and above.
Spark plugs must be correctly installed in order to
obtain good performance. It is a simple but
important matter to follow these procedures when
installing plugs:
1. Clean the spark plug seat in the cylinder head.
2. Use a new seat gasket and screw the plug in
by hand.
3. Tighten the spark plugs to 22 to 28 ft lb
(30 to 38 Nm) with a socket wrench of the
correct size.
DISTRIBUTOR (For machines below serial number
038000)
The distributor operation is vital to the operation of
the engine. The following items should be carefully
inspected after every 400 hours of normal operation;
however, dirt, dust, water, and high speed operation
may cause more rapid wear and necessitate more
frequent inspections:
1. Remove the distributor cap. Clean the cap and
examine for cracks, carbon runners, or
corroded terminals. If the vertical faces of the
inserts are burned, install a new cap. If the
horizontal faces of the inserts are burned,
replace the cap and the rotor as this condition
is caused by the rotor being too short. Inspect
cap to distributor seal and the distributor
housing breather.
2. Check the centrifugal advance mechanism for
“freeness” by turning the breaker cam in the
direction of rotation and then releasing it. The
advance springs should return the cam to its
original position.
ENGINE IGNITION TIMING (For machines below
serial number 038000)
The engine ignition timing must be checked with a
timing light, using the timing points located on the
front of the engine and the timing marks located on
the crankshaft pulley. Distributor ignition timing
should be checked after the first 50 hours of
operation and after every 400 hours of operation
thereafter.
To check and adjust the ignition timing with a scope,
refer to the scope manufacturer’s instructions. To
check and adjust the timing with a timing light,
proceed as follows:
TO CHECK AND ADJUST IGNITION TIMING (For
machines below serial number 038000)
NOTE: Dwell angle must be correct or timing will not
be accurate.
1. Stop the engine and set the machine parking
brake.
FOR SAFETY: Before leaving or servicing
machine; stop on level surface, set parking brake,
and turn off machine.