ENGINE
Page G-5
Repair and Service Manual
Read all of Section B and this section before attempting any procedure. Pay particular attention to all Notes, Cautions and Warnings.
B
B
Allow the water to flow freely over the cooling fins and
through the blower housing. After flushing, dry with low
pressure compressed air.
Fig. 15 Air Drying Cooling System
SPARK PLUGS
Tool List
Qty. Required
Spark plug wrench,13/16" ........................................... 1
Plug gauge, wire type.................................................. 1
Using a 13/16" spark plug wrench, remove the spark
plugs at 250 - 300 hours or annually and replace. All
new spark plugs should be properly gapped (Ref. Fig.
16 on Page G-5). Tighten to 18 ft. lbs. (24 Nm) torque.
Fig. 16 Gapping the Spark Plug
Fouled spark plugs are indicated by a wet, black
appearance. This could be caused by a dirty air filter
element or other restrictions in the air intake system.
Incorrectly adjusted valves, spark plug wires which are
in poor condition or poor quality fuel could also contrib-
ute to the problem.
Use care not to over tighten the plug. Overtightening can
cause damage to the aluminum cylinder head threads.
FOUR CYCLE ENGINE
Engine Specifications
Engine model ......................................... EH29, EH35C
Type............................Four cycle, overhead cam, OHV
Number of cylinders........................................2 (In-line)
Displacement..........................................295 cc, 350 cc
Rated horsepower ........................................... 9.0, 11.0
Spark plug type (295 cc).......................... NGK FR2A-D
Spark plug type (350 cc)......................... NGK BPR5ES
Spark plug gap (295 cc)...................... .0.035" (0.9 mm)
Spark plug gap (350 cc).......028" - .032" (.70 - .80 mm)
Cooling .............................................. Forced air cooled
Oil Filter ...................................... Washable, permanent
Oil Pump............................................................Gerotor
Engine Description
The engine is a four cycle air cooled, in line, twin cylin-
der, overhead cam unit. It incorporates pressure lubri-
cation, a washable permanent oil filter and a counter
rotating balance shaft (Ref. Fig. 17 on Page G-7).
An electronic ignition system fires both spark plugs
simultaneously which eliminates the need for a distribu-
tor. The pistons are aligned together which means that
they both are at TDC (Top Dead Center) and BDC (Bot-
tom Dead Center) at the same time.
Engine Operation
A four cycle engine has a power stroke for each piston
every four strokes or two revolutions of the crankshaft.
Since this engine has two pistons, the engine is timed to
have one power stroke for every rotation of the crank-
shaft. To understand the operation of a four cycle
engine, it is easiest to consider a single cylinder engine.
The first cycle (stroke) takes place with the piston mov-
ing down and the intake valve open (Ref. Fig. 18 on
Page G-8). Fuel is drawn into the combustion chamber
from the carburetor and through the intake valve and is
known as the
intake stroke
. As the piston reaches the
bottom (BDC) of its travel and starts to move upwards,
the second cycle begins. The intake valve closes which
seals the combustion chamber since the exhaust valve
is already closed and causes the fuel air mixture to be
compressed as the piston rises. This is known as the
compression stroke.
Just before the piston reaches
TDC (Top Dead Center) the spark plug fires which
causes a rapid burning of the air fuel mixture. The tem-
perature rises rapidly which causes the air fuel mixture
to expand. The piston has been carried through TDC by
centrifugal force and is now forced downwards into the
Air Hose
295cc
.035”
(0.9 mm) Gap
350cc
.02
8
” - .032”
(.70 - .
8
0 mm) Gap
Pl
u
g
