Automatic Compression Release (Acr); Section 10. Inspection And Reconditioning - Kohler CV11-16 Service Manual

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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:
Air Cleaner, Section 4
Carburetor & External Governor, Section 5
Retractable Starter, Section 7
Ignition, Charging & Electric Starter, Section 8
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. Use gasket
remover or paint remover to remove the old RTV from valve cover, cylinder head, crankcase, and oil pan. Do not
scrape the surfaces when cleaning as this will damage the surfaces. This could result in leaks.
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.
Refer to A Guide to Engine Rebuilding (TP-2150) for additional information. Measurement Guide (TP-2159-A) and
Engine Inspection Data Record (TP-2435) are also available; use these to record inspection results.

Automatic Compression Release (ACR)

This engine is equipped with an Automatic
Compression Release (ACR) mechanism. The ACR
lowers compression at cranking speeds to make
starting easier.
Operation
The ACR mechanism consist of a flyweight, spring and
pivoting control pin assembly attached to the gear on
the camshaft. At cranking speeds (700 RPM or lower),
the control pin protrudes above the exhaust cam lobe.
This pushes the exhaust valve off its seat during the
first part of the compression stroke. The reduced
compression results in an effective compression ratio
of about 2:1 during cranking.
After starting, engine speed increases to over 700
RPM, and centrifugal force overcomes the force of the
flyweight spring. The flyweight moves outward, pulling
the arm of the control pin, so it pivots into the ''run''
position. The control pin no longer has any effect on
the exhaust valve and the engine operates at full
power.
Inspection and Reconditioning
Section 10
When the engine is stopped, the spring returns the
flyweight lever and control pin assembly to the
compression release position ready for the next start.
Benefits
Because of the reduced compression at cranking
speeds, several important benefits are obtained:
1. Manual (retractable) starting is much easier.
Without ACR, manual starting would be virtually
impossible.
2. Electric start models can use a starter and battery
size that are practical for the applications in which
these engines are used.
3. ACR eliminates the need for a spark retard/
advance mechanism. A spark retard/advance
mechanism would be required on engines without
ACR to prevent the ''kickback'' that would occur
during starting. ACR eliminates this ''kickback''
making manual starting safer.
CV11-16
Section 10
CV460-465, CV490-495
10
10.1