Engine Disassembly
DISASSEMBLY/ASSEM
BLY
When complete engine disassembly is necessary, first
remove all complete assemblies. Individual assemblies
such as fuel pump and carburetor can bedisassembled
and repaired at another time.
Suggested Disassembly Order
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
Drain crankcase.
Disconnect all exhaust and electrical lines.
Remove engine from its mountings and place on a
suitable bench or work stand.
Remove all housings, shrouds, blower housings,
etc.
Remove flywheel, using a puller.
Remove ignition trigger and gear cover, being
careful to protect oil seal from keyway damage.
Remove crank gear, using a gear puller and ring.
Remove all accessories such as oil filter, starter,
intake manifold, fuel lines, spark plugs, etc.
Remove oil base, oil pump and cylinder heads.
Remove valves, springs, lifters, etc.
Remove camshaft and gear assembly.
Remove connecting rods and pistons.
Remove rear bearing plate, crankshaft, and front
bearing.
Keep all parts in their respective orders. Keep valve
assemblies together. Return rod caps to their respective
pistons. Analyze the reasons for parts failure.
Suggested Assembly Procedure
Engine assembly is normally the reverse
of
the dis-
assembly procedure, observing proper clearances and
torques. Use a torque wrench to assure proper tightness.
Coat the internal engine parts with oil as they are
assembled. After the internal engine parts are
assembled, the engine should turn over by hand freely.
Use only genuine Onan parts and special tools when
reassembling your engine.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Use
proper bearing driver
to
install front main
bearing after coating
it
with
a
light film of oil.
Insert rear main bearing in rear bearing plate.
Insert crankshaft, rear bearing plate, and crankshaft
gear.
Install pistons and connecting rods.
install camshaft and gear assembly; align crank
gear mark with cam gear mark.
Install valve assemblies, oil pump, oil base, and
cy1
i
nd er heads.
Install all accessories such
as
oil filter, starter, fuel
lines and spark plugs.
Install gear cover with oil seal, trigger ring, and
flywheel.
Check valve clearance.
Install all housings and air cleaner.
Fill crankcase with oil.
Operation
Start engine and check oil pressure. Run for approx-
imately
15
minutes to bring engine to operating
temperatures. Check for oil leaks, fuel leaks, and exhaust
leaks. Adjust carburetor and governor for speed and
sensitivity.
Testing Compression
The compression tester is used to determine the
condition of valves, pistons, piston rings and cylinders.
To check compression:
1.
Run the engine until thoroughly warm.
2.
Stop engine and remove spark plugs.
3.
Remove air cleaner and place throttle and choke in
4.
Insert the compression gauge in one spark plug
5.
Crank the engine and note the reading.
Refer to
SPEClFlCA
TlONS
for compression pressures.
There may be variations due to equipment, temperature,
atmospheric conditions and altitude. These pressures
are for a warm engine at cranking speed (about 300
the wide open position.
hole.
rPm)*
10-1
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