Compression Testing

[sflrainmaker01]

How many times do you crank the motor over before you take the actual compression reading? Cold or warmed up engine?

FYI, this is not for my Marauder, rather a small block Chevy engine in a boat I want to buy...

[fastblackmerc]

How many times do you crank the motor over before you take the actual compression reading? Cold or warmed up engine?

FYI, this is not for my Marauder, rather a small block Chevy engine in a boat I want to buy...

STEP 1 Remove the fuel pump and fuel-injection fuses. Disconnect the main wire to the coil and spark plug wires; remove all spark plugs. Connect a battery charger so you will have the same voltage available for the entire test.

STEP 2 Start the threaded end of the compression gauge in a spark plug hole by hand.

STEP 3 Turn the ignition on, depress the throttle, and crank the engine four revolutions. This should result in a stable reading; if not, crank up to 10 revolutions, but do the same with all cylinders.

STEP 4 Make note of the compression reading.

TIP For a cylinder below 100 psi, pour 1 teaspoon of engine oil into the plug hole and retest. If the reading jumps, the piston rings are worn. If not, think valve problems.