1991 Johnson/Evinrude Models "EI" 40 thru 55 Service Manual, Page 314Get this manual
IMPACT RELIEF 1When the engine hits an underwater obstruction, extreme pressure develops above the piston 2The extreme pressure must be vented and the cylinder rod must extend to allow the engine's lower unit to clear the obstruction 3Under extreme pressure, five IMPACT relief valves and one UP relief valve fluid to pass through the piston as the cylinder rod extends
will open to allow