10.1
Section 10
Inspection and Reconditioning
10
Section 10
Inspection and Reconditioning
This section covers the operation, inspection, and
repair/reconditioning of major internal engine
components. The following components are not
covered in this section. They are covered in sections of
their own:
Section 4: Air Cleaner and Air Intake System
Section 5: Fuel System and Governor
Section 7: Retractable Starter
Section 8: Electrical System and Components
Clean all parts thoroughly. Only clean parts can be
accurately inspected and gauged for wear or damage.
There are many commercially available cleaners
that will quickly remove grease, oil, and grime from
engine parts. When such a cleaner is used, follow the
manufacturer’s instructions and safety precautions
carefully. Make sure all traces of the cleaner are
removed before the engine is reassembled and placed
into operation. Even small amounts of these cleaners
can quickly break down the lubricating properties of
engine oil.
Do not scrape the gasket surfaces, as any scratches,
nicks, or burrs can result in leaks. Use an aerosol
gasket remover, paint stripper, or lacquer thinner to
remove any gasket residue. Apply the solvent, allow
time for it to work, and then brush the surface with
a brass wire brush. Clean the surface with isopropyl
alcohol, lacquer thinner, or aerosol electrical contact
cleaner.
Refer to A Guide to Engine Rebuilding (TP-2150-A)
for additional information. Measurement Guide
(TP-2159-B) and Engine Inspection Data Record
(TP-2435) are also available; use these to record
inspection results.
Automatic Compression Release (ACR)
These engines are equipped with an Automatic
Compression Release (ACR) mechanism. ACR lowers
compression at cranking speeds to make starting
easier.
Operation
The ACR mechanism consists of a spring-loaded arm
and sliding pin mounted to the camsha . When the
engine is rotating at low cranking speeds the arm
holds the pin so it protrudes above the heel of the
exhaust cam. This holds the exhaust valve off of its
seat during the fi rst part of the compression stroke.
See Figure 10-1.
Camshaft
Decompression
Weight
Return
Spring
Lever
Cam
Lobes
Figure 10-1. ACR Operation Details.
A er the engine speed increases centrifugal force
causes the spring-loaded arm to move outward
causing the pin to retract. When in this position the
pin has no eff ect on the exhaust valve and the engine
operates at full compression and power.
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