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Monroe, Wa. 360 453 2030 www.longacreracing.com
Engine Leak Down Tester
Digital and Analog Models
Step 1: Warm up motor to operating temperature.
Step 2: Remove all spark plugs, put transmission in neutral, block wheels.
Step 3: Remove rocker arms of cylinders to be checked
10/12
Step 4: Important WARNING: TURN THE MOTOR OVER SO THE PISTON
OF THE CYLINDER TO BE TESTED IS AT BOTTOM DEAD CENTER OR AT
EXACTLY TOP DEAD CENTER (TDC). If not the motor will suddenly turn over
when you connect the air line. This could cause serious injury or death.
Step 5: Screw the included hose into the spark plug hole just tight enough so it
doesn’t leak (
Step 5.5: Digital only: Turn on both gauges and zero if Primary gauge (left) is not at
0.0 and Secondary gauge (right) is not at 100.0. (these read to .5).
after this.
Step 6: Close the lever ball valve. Connect the tester to the hose and then the tester to
your air line (must be over 105 psi).
Step 7: Adjust the regulator knob on the tester until the left gauge reads exactly 100.0
Step 8: Read the leakdown on the right gauge.
It will be somewhere between 3 - 5% (fresh engine) and 20 - 30% (very tired engine). Consult your
engine builder on what to expect or use your own experience. Different ring combinations and
cylinder finishes can give different leakdowns. He will also advise you at what point you need a
rebuild. Of course you can also use your own experience as a guide.
!
ANY leakage will give you a false reading).
DO NOT re-zero
SLOWLY open the ball valve.
Step 8: Close the ball valve. Disconnect the hose to the engine. Repeat all steps
above for the other cylinders to be tested.
Step 8.5: Digital only: Shut off gauges. They do not have an auto-off feature,
Do not drop the unit. Keep it clean and dry. Do not connect to an
airline of more than 175 psi.
Leakdown normally comes past the rings. However if your leakdown is excessive
listen for a leaking valve at the carb (intake valve) or at the exhaust (exhaust valve). It
is a good idea to check several cylinders and keep a record of the leakdown and the
number of laps run.
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