Caution – S&S Cycle Big Twin Engines with 3-1/2 and 3-5/8 Bore Crankcases and Special Application (SA) 4 Bore Crankcases User Manual

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Exhaust Systems
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Drag Pipes - While drag pipes can be used with good results
to establish performance guidelines on 1985 engines, they
are generally not recommended for big twin engines in
street applications. Big twin engines are easier to carburate
with muffled systems.

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Muffler systems - Most stock and many aftermarket exhaust
systems are too restrictive and made exclusively for looks
with little consideration given to performance. Avery good,
economical street system for big twin engines consists of the
stock header pipes with the crossover tube and set of low
restriction mufflers. S&S

offers a series of mufflers that can

be used with stock header pipes that work very well. This
combination will typically produce more horsepower and
torque than drag pipes in the midrange. Since the midrange
is where the vast majority of normal driving occurs, it makes
this system ideal for the street.

START-UP AND BREAK-IN

NOTE - S&S engines require premium gasoline (octane 91 or
higher) for best performance. Octane boosting gasoline additives
may be necessary with marginal gasoline.

Low octane gasoline and hot weather can cause detonation
and extensive engine damage. Never try to power through
ignition knock (“ping,” “rattle,” etc.) by opening throttle.

1. Start engine according to procedure in Carburetor

Instructions. If S&S carburetor supplied with engine is used,
jetting should be approximately correct and engine can be
started and fine tuned according to procedure in carburetor
instructions. Altitudes greater than approximately 4000 feet
above sea level will probably require leaner jets unless high
altitude jetting specified at time of order. If other carburetor
used, it must be rich enough to provide sufficient fuel. In any
case, engine must not be allowed to idle for an excessive
period of time during initial start-up.

Prolonged idling with inadequate air flow over engine will
cause overheating and permanent damage to engine. For this
reason, heavy stop and go traffic and extended idling should
be avoided during break-in.

To avoid damaging heat build-up, engine must not be
subjected to excessive load or strain during break-in period.
Lugging the engine should always be avoided.

Lugging and excessively low idle can cause engine damage.

2. Observe for gas and oil leaks.

3. Break-in according to following guidelines:

A. First 50 miles are critical for new rings and pistons. Most

engine damage occurs during this period. Keep heat
down by avoiding heavy traffic and not exceeding 2500
RPM or approximately 50-60 MPH, depending upon
gearing, during this time. During brake in:

Vary speed and do not lug engine.

Change oil and filter at 50 miles and keep outside
of engine clean.

Do not subject engine to unusual stress or load as
with sidecar or trailer.

Avoid hard acceleration, especially before engine
has reached operating temperature, and do not lug
engine. Vary engine speed and avoid maintaining
steady speed for long distances.

NOTE - On shovelhead engines, cylinder base nuts and head bolts
should be retightened after engine has been run and reached
normal operating temperature. Do not tighten or retorque big
twin head bolts.

B. For next 500 miles, engine may be taken to 3500 RPM or

approximately 65 MPH (depending upon gearing) for
brief periods. Speed should be varied, and lugging and
heavy traffic avoided. Change oil and filter at end of
first 500 miles.

C. Modest increases in speed are permissible during next

2000 miles, but do not exceed 3500 RPM. Engine should
not be given full throttle, and heavy loads such as
trailers and sidecars avoided. Some operation at in-town
speeds (40-45 MPH) is recommended, although
prolonged idling, lugging and heavy traffic should still
be avoided. Change oil and filter at 500 mile intervals
until 2500 miles.

D. The following is mandatory at 2500 miles and

thereafter: HAVE FUN! Oil and filter should be
changed every 2000 miles after break-in, more often if
oil appears dirty or engine is subjected to extreme
temperatures or dusty conditions, ridden for only short
periods of time, or frequently operated in heavy traffic.

PERFORMANCE

Properly tuned and equipped with an efficient exhaust, most S&S
big twin engines produce 1 to 1.1 horsepower per cubic inch at
the rear wheel. The following should be considered in the event
of unsatisfactory dynamometer results or other poor
performance: exhaust system, carburetor jetting, and ignition
timing. Other factors including climate, oil viscosity, gear ratio,
dragging brakes, worn drive chains or belts, gross vehicle weight,
and tire or clutch slippage can affect performance.

S&S has carefully chosen the components in each engine for
reliable high performance use. Substituting another
manufacturer’s product, even one as seemingly insignificant as air
cleaner assembly or pushrods, for one provided by S&S can result
in loss of horsepower, reliability, or both. Additionally, extremely
heavy motorcycles or loads combined with different gear ratios
(61 and 65 tooth rear pulleys) used on newer Harley-Davidson

models will hamper overall performance.

CAUTION