Service Manual
Engine
Disassembly
DISASSEMBLY/ASSEMBLY
1.
Use proper bearing driver to install front main
bearing after coating
it
with a light film of oil.
When complete engine disassembly is necessary, first
2.
Insert rear main bearing in rear bearing plate.
remove all complete assemblies. Individual assemblies
3.
Insert crankshaft, rear bearing plate, and crankshaft
such as fuel pump and carburetor can be disassembled gear.
and repaired at another time.
4.
Install pistons and connecting rods.
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.
5.
Install camshaft and gear assembly; align crank
6.
Install valve assemblies, oil pump, oil base, and
7.
Install all accessories such as oil filter, starter, fuel
8.
Install gear cover with oil seal, trigger ring, and
9.
Check valve clearance.
gear mark with cam gear mark.
cylinder heads.
lines and spark plugs.
flywheel.
10.
Install all housings and air cleaner.
11.
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.
the wide open position.
hole.
Refer to
SPEClFlCATlONS
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
rpm).
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