CYLINDER HEAD AS 2436741 - Caterpillar

Caterpillar: Confidential Yellow
PSP FOR MODIFICATIONS TO ELECTRIC SHUTOFF SYSTEM ON 3500 SERIES - PS0179 WORLDWIDE
  The information supplied in this service letter may not be valid after the termination date of this program.   Do not perform the work outlined in this Service Letter after the termination date without first contacting your Caterpillar product analyst.
PRODUCT SUPPORT PROGRAM FOR MODIFICATIONS TO ELECTRIC SHUTOFF SYSTEM ON 3500 SERIES ENGINES, 7400, PS0179 U-83 A-76 AU-70 B-34 C-77 E-68 O-65 Many of these engines are also included in the July 8, 1 983 Service Letter, Safety PI1007, and the August 10, 1983 Service Letter, PI7009. Problem The electric shutoff system on the listed 3500 Series Engines can cause false engine shutdowns. The false shutdowns are usually caused by moisture or mildew inside the speed sensor causing the sensor to send false signals, or none at all, to the electric speed switch. There have also been some failures of the circuits inside the electric speed switch. Some of the problems which can result are: False overspeed signal will activate both the air and fuel shutoffs during normal engine operation. False engine reversing signal will activate the fuel shutoff, or intermittently activate the fuel shutoff simulating governor surge. No speed signal to the electric speed switch. Without a speed signal, the shutoffs will never be armed (or reset). When the engine toggle switch or remote shutoff switch is activated, the engine will not shut down. Defect in crank termination section of the speed switch. Engine starter will not disengage. A magnetic pickup is now used on the flywheel housing to sense engine rpm instead of the former speed sensor at the tachometer drive. This should eliminate any moisture problems and false signals to the electric speed switch. A new electric speed switch is also used with improved circuits. It does not have the engine reversing feature because this was a problem area and many users believe it is not needed. Affected Engines And Parts Needed All the listed marine engines and generator sets are included in this Product Support Program. The listed industrial engines are included if they have these electric shutoffs as an attachment. Engine Serial Numbers Model * Industrial Marine Generator Sets 3508 95Y1-95Y618 96Y1-96Y612 23Z1-23Z551 3508 68Z1-68Z676 69Z1-69Z254 70Z1-70Z557 3512 49Y1-49Y432 50Y1-50Y539 67Z1-67Z497 3512 65Z1-65Z590 -- 24Z1-24Z841 3516 -- 29Z1-29Z747 25Z1-25Z431 3516 -- 72Z1-72Z316 -- * These engines are included in Program only if equipped with the electric shutoffs. Parts needed for the various applications are listed in the following charts: 1 - 4W2218 Switch Assembly - Speed * 1 - 5N9292 Pickup Assembly 1