Summary
An engine is essentially reassembled in the
reverse of the order in which it was disassem-
bled. First, bearings and seals are installed in
the crankcase and the crankcase cover. In an L-
head engine, the valve assemblies are reinstalled
in the block. In an overhead valve engine, the
valves will be reinstalled in the cylinder head
before the head is reinstalled.
The journals of the crankshaft are then coated
with assembly lube and the crankshaft is installed
in the crankcase. The valve lifters are installed
in their bores, and then the timing marks on the
crankshaft and camshaft are aligned and the cam-
shaft is installed. The governor gear or oil slinger
is installed next.
The piston is reinstalled on the connecting rod.
Check the marks on the rod and piston to ensure
that the piston is installed in the right orientation.
Next, the piston rings are installed on the piston.
The oil control ring is installed fi rst, and then the
two compression rings are installed. The piston
and rings are lubricated with engine oil, and then
the piston and rod assembly is installed in the
cylinder. If the rod uses insert-type rod bearings,
they are installed next. Rod bearing clearance is
checked using Plastigage, and then the connecting
rod cap is installed on the rod. Matching marks on
the rod and cap should be aligned to ensure that
the cap is put on in the right orientation.
Next, the cylinder head is installed on the cyl-
inder block. Always use a new cylinder head gas-
ket and tighten the head bolts in the manufactur-
er’s recommended pattern. On an overhead valve
engine, the valve assemblies must be installed in
the cylinder head before the head is installed on
the cylinder block. Then, the pushrods and rocker
arm assemblies can be installed and the proper
valve clearance can be set.
The crankcase breather is reinstalled next.
Then, any needed crankshaft endplay adjustments
are made and the crankcase cover is reinstalled.
Before the cover is installed, the keyway in the
crankshaft should be taped in order to prevent the
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Chapter 19 Engine Reassembly and Break-In
oil seal from being damaged by the sharp edges of
the keyway.
Next, all of the engine’s external components
are reinstalled, including the carburetor, intake
manifold, muffl er, gas tank, air fi lter, governor
linkages, shrouds, ignition module, and starter.
Mount the engine on a test stand or reinstall it
in the implement. Gap, install, and connect the
spark plug.
Check the engine for leaks, and then start it. Be
prepared to stop the engine immediately if there is
any indication of over speeding or engine troubles.
Allow the engine to reach operating temperature
and then make any necessary carburetor or gover-
nor adjustments. Change the oil after the fi rst hour
of operation and retorque the cylinder head as di-
rected by the manufacturer.
Review Questions
1. True or False? Valves should be installed so the
dampening coils are on the same side as the
valve caps and retainers.
2. Briefl y list the results of excessive ring end
gap and a lack of ring end gap.
3. Piston rings can be one of two basic types.
Can you name them?
4. Name the tool used to squeeze the piston rings
together so they can be installed in the cylinder.
5. Properly fi tted friction bearing ends protrude
slightly above the parting surface of the
connecting rod cap. This characteristic
produces what is commonly called .
A. bearing crush
B. bearing spread
C. bearing seat
D. bearing swell
6. Bearing caps must never be when being
replaced on the rods.
7. What tool must always be used to tighten
rod caps?
8. What is the name of the special plastic
substance used to measure bearing clearance?