Early Model Lycoming Fuel Pump (40174/40295 low pressure, 40595 medium pressure, 40296 high
In the spring of 1964, AC introduced the first dual diaphragm type
fuel pumps. These pumps were the first models to incorporate the
oil seal integral with the upper diaphragm and a separator ring
for installation of the vent / overboard drain line. These pumps
are characterized by a rocker arm which is an early riveted, laminated
design. Current production in Lycoming pumps will not fit some pre-1978
applications without expensive modifications. You can eliminate
the need for these modifications by ordering an FAA Approved overhauled
early model pump for direct replacement.
Late Model Lycoming Fuel Pump
During August of 1978, AC introduced what is now known as the "late
model" fuel pump which has a "channeled" rocker arm.
This pump is taller than the early laminated arm pump and has a
unitized diaphragm assembly. Because of its increased size some
pre-1978 model aircraft require expensive and time consuming modifications
to carburetors or accessory housings (ref: Lycoming Service Inst.
No. 1110C). These modifications are not required if our smaller,
early model laminated fuel pumps are installed on your aircraft.