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Service
Trained technicians with precision gauging and proper assembly fixtures carefully
assemble all Cobra engines to specific tolerances. If you feel you have the skills,
and the appropriate tools, to perform the following service tasks please follow the
instructions closely. The part numbers are listed throughout to help you when
ordering parts from your local Cobra dealer.
If you do not feel comfortable with the service work log on to:
www.cobramotorcycle.com
to find a cobra dealer or call 517-437-9100.
Engine Service
One method for determining whether the top end of your engine needs rebuilt is
to perform a wide open throttle kicking compression test. Before performing the
procedure please read the caution notes below.
CAUTION:
•
There is a large wide range of variability in reading compression gauges.
•
The head volume of this Cobra Motorcycle is very small and requires 20 kicks
before you establish the most accurate reading possible.
•
Because of the geometry of the spark plug used in this Cobra Motorcycle, the
adapter used with your compression tester must have a similar volume
protruding into the combustion chamber to establish an accurate value.
•
Length of hose on the compression tester will affect the reading. The shorter
the hose length the more accurate your reading will be.
Because of these difficulties in measuring an
absolute
compression value, a
useful
relative
value can be achieved by testing your bike’s compression with
your own particular gauge after a new top end or when the bike is new so that
you know what your particular gauge reads on a ‘fresh’ engine. When it has
dropped to 90% of its original value the engine will be down on power and would
benefit from a rebuild. When it’s dropped to 80% it really needs rebuilt! Using the
table below will help you determine monitor the condition of your top end.
Engine is Fresh
Measured Value
Engine Down on Power
Measured Value * 0.9
Engine NEEDS Rebuilt
Measured Value * 0.8
Example
110 psi
110 psi * 0.9 = 99 psi
110 psi * 0.8 = 88 psi
Your Values
Procedure for Compression Testing
1. Shut off the fuel petcock.
2. Install the compression gauge into the spark plug hole.
