AOPA Pilot Magazine - February 2019 - 95

P&E

OWNERSHIP

Heart transplant
DIY engine conversion of a middle-aged Skyhawk
BY PETER A. BEDELL

A FEW YEARS AGO, my brothers and I
came to a decision point with the family's 1975 Cessna 172M Skyhawk when
we invested in new avionics and some
interior restoration (see "Avionics
Upgrade-On a Budget," September 2015
AOPA Pilot, and "Ownership: A New
Lease on Life," August 2015 AOPA Pilot).
After some careful examination of critical parts, we were committed to investing
in it for another 20 to 30 years. It's a sentiment shared by many other owners of
middle-aged airplanes-invest heavily
in your existing airplane or sell it and
move on. Last spring, sagging compression and some intermittent roughness led
us to finally come to a decision to replace
the engine.
Our 150-horsepower Lycoming
O-320-E2D soldiered on for 27 years
and more than 2,000 hours after its last
field overhaul. The engine is the same
one the 172 left the Cessna factory with
in 1975. The choices are plenty when it

comes to engines for popular airplanes
like the 172. Prices, as well, run the gamut
from reasonable to more than the value
of the airplane. While we drooled over
a true 180-horsepower Lycoming O-360
replacement, reality left us with more
affordable choices such as field overhauling our engine a second time or getting
a factory rebuild from Lycoming (see
"Overhaul Terminology," p. 96).
Experience, wisdom, and age have
made us much more cautious pilots than
we were in our teens and 20s when this
engine was last overhauled. Because of
that, and the fact that our kids are now flying this airplane, we elected to go with the
factory rebuild. While the original -E2D is

a fine, reliable engine, we just didn't feel
comfortable pressing our luck for a third
run to TBO, which would bring the lowerend components to the ripe old age of 70
at the rate we fly.
After some research, we found Ram
Aircraft in Waco, Texas, holds a supplemental type certificate to replace the
-E2D with a 160-horsepower O-320-D2J.
The -D2J is a more modern engine with
a more robust design than the alreadypretty-bulletproof -E2D. The -D2J was
stock equipment in the Cessna 172P. Ram
offers a conversion package, including
the STC paperwork, factory-new engine,
and new propeller for around $40,000.
Unfortunately, that put us over budget,
so we elected to purchase just the STC
paperwork for $515 and purchase a factory-rebuilt engine on our own through
Air Power. That put us in the range of
about $29,000-still a sizable purchase.
The core upcharge for trading a -E2D for
the -D2J is $1,500.
In the end, however, we got a modest 10-horsepower boost in performance
with an engine designed from the beginning to be 160 horsepower, as opposed
to modifying the -E2D with highercompression pistons to get the same
result. The -E2D was designed to run on
80-octane avgas, which went extinct in
the late 1990s. The -D2J was designed to
run on 100LL avgas and takes advantage
of the added power that fuel can provide.
The power boost requires repitching the
propeller to absorb the extra power.
Lycoming was working on a six-week
lead time, which gave us time to attend
to other chores, such as removing all the
accessories for overhaul.
Since it had never been sent out
for inspection, the engine mount was
sent to Aero Fabricators for inspection and repaint. Some head-scratching
was required to figure out how to ship
such a huge contraption. Our mechanic

Experience, wisdom, and age have made us
much more cautious pilots than we were back
in our teens and 20s when this engine was last
overhauled.
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AOPA Pilot Magazine - February 2019

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