Copyright (C) 1994 Gregory R. Travis
The author makes absolutely no claims regarding the accuracy of the
material presented herein.
The author reserves the right to revise this material as the real facts
come in...
------------------------------------
Nomenclatura
Lycoming's specific convention for post-WWII aircraft piston engine
designation is as follows. Note that this convention is fairly standard
and applicable to many other manufacturers.
C-D-M
Where:
C Letters indicating the engine's configuration:
I Fuel injected
O Opposed type (pancake-style)
X X-type engine
R Radial type engine
G Engine is geared
T[S] Engine is turbocharged
S Engine is supercharged, EXCEPT for
most Continental TURBOcharged engines. These
are designated "TS". See below.
L Engine is liquid-cooled or left-turning (ugh!)
A Engine is designed for aerobatics (DRY SUMP)
AE Engine is designed for aerobatics (WET SUMP)
M Engine is designed for unmanned drone (UNCERTIFIED)
H Engine is designed for helicopter installation
V Engine is designed to have the crankshaft in the
vertical, not horizontal, plane. Usually implies
"H"
D The engine's displacement in cubic inches.
M The manufacturer's "data" - often indicating what
types of accessories or engine revisions.
Regarding "L" - it seems that the convention is that if the L is the first
thing in the configuration list, then the engine is left-turning. If it's
the LAST, then the engine is liquid-cooled.
Lycoming and Continental differ in the "manufacturer's data" portion of
the engine designation. For example, a typical Lycoming designation
looks like (from the Lycoming Overhaul manual):
Example:
TIO-541-E1B4D
Where:
TIO - The prefix as described above.
541 - The engine's cubic inch displacement, as described
above. A 1 at the end indicates an integral
accessory drive (e.g. TIO-541) except for the
76 series engines (see below).
E - Power section and power rating for the displacement
1 - Nose section (provisions for a prop governor,
hollow/solid crankshaft, prop governor
location)
B - Accessory section (fuel pump type, accy pad(s), etc.)
4 - Counterweight application (if applicable, see the power
section to determine this)
D - Dual magneto (if applicable)
Continental does not try and describe the engine's configuration or options
in the engine's designation. Considering how confusing Lycoming's
designations can become, this may not be the worst idea!
Instead, Continental lists only what Lycoming considers the "power" section
with a 1 or 2 letter designator. Information about what types of
accessories, counterweights, revisions, etc. are numerically encoded (and the
encoding must be looked up!) on the engine's dataplate.
Example:
IO-360-K
Pancake-style (opposed) engine of 360 cubic inches displacement and
fuel injection. Power section "K."
Glossary:
{Turbo/Super} charging
A method of compressing ambient air via a pump. This
pump is almost always a rotating compressor although other
types have been used (i.e. a Roots blower). The compressed
air is often used to boost engine output, to pressurize an
aircraft's cabin, and to provide pressurized air to magnetos
(to prevent high-altitude arcing).
The different names refer to the power source for the
compressor. A TURBOcharger is driven by exhaust gas from
the engine. A SUPERcharger is driven by a belt or gear
directly from the engine's crankshaft.
Continental, confusingly, calls turbocharging "TurboSuper"
charging. Hence turbocharged Continental engines typically
look like TSIO-XXX-X[X]. I do not know of any recent
Continental engines which incorporate a supercharger - all
their boosted engines are turbocharged as far as I know
Lycoming has made both turbo and supercharged engines
within the last thirty years. You will not see a
TS in a Lycoming engine, instead you will see either:
TIO-540 (turbocharged 540) -or-
IGSO-540 (supercharged 540)
for example.
All supercharged Lycoming engines are also geared.
Turbocharged Lycomings are produced in geared and
direct-drive models.
"Turbo"normalizing
The turbo-(or super!)charger is limited to producing no
more than 29.92 inches (typically) of "pressure" on a
turbonormalized engine. Turbonormalizing is used to
recover lost power due to altitude gain but is not used
to boost the sea level power of an engine. Virtually all
after-market (and quite a few factory-installed) turbochargers
are turbonormalized. This allows ordinary "off the shelf"
engines to be used.
A turbonormalized engine may or may not have a "T" in its
designation. For example, the turbonormalizing on the Cessna
T182 was performed by the Cessna factory, not Lycoming.
The engine in the T182 is an O-540, not a TO-540.
Geared:
The engine's crankshaft turns at a faster rate than the
propeller. Used to boost engine power output, which
increases with RPM (within limits) without sacrificing
propeller efficiency, which decreases with RPM.
Pancake:
Term used by many gearheads to describe opposed engines.
==============================================================================
Cessna 172s were manufactured with the following engines (in rough
chronological order):
Engine Make & Model Power TBO Fuel Yrs C172 Models
-------------------- ----- ------ ------ --- -----------
Continental O-300-A/C/D 145HP 1800Hr 80Oct 1956-67 /A->H/T-41A
Continental GO-300-A/C/E 175HP 1200Hr 80Oct 1958-63 C175&Powermatic
Continental IO-360-D 210HP 1500Hr 100Oct 1967-81 R172E&T-41B/C/D
Lycoming O-320-E2D 150HP 2000Hr 80Oct 1968-76 I->M
Lycoming O-320-H2AD 160HP 2000Hr 100Oct 1977-80 N
Continental IO-360-K 195HP 1500Hr 100Oct 1977-78 R172K
Continental IO-360-KB 195HP 2000Hr 100Oct 1979-81 R172K
Lycoming O-360-F1A6 180HP 2000Hr 100Oct 1980-85 C-172RG (Cutlass RG)
Lycoming O-320-D2J 160HP 2000Hr 100Oct 1981-86 P
Lycoming O-360-A4N 180HP 2000Hr 100Oct 1983-86 Q (Cutlass)
Engine breakdown by FIXED GEAR, FIXED PROP model:
(Blank) or models A through H: 145HP, 6 Cyl, 80 Oct Continental O-300-A/C/D
Models I though M: 150HP, 4 Cyl, 80 Oct Lycoming O-320-E
Model N: 160HP, 4 Cyl, 100 Oct Lycoming O-320-H
Model P: 160HP, 4 Cyl, 100 Oct Lycoming O-320-D
Model Q: 180HP, 4 Cyl, 100 Oct Lycoming O-360-A
Military T-41A 145HP, 6 Cyl, 80 Oct Continental O-300-D***
Military T-41C 210HP, 6 Cyl, 100 Oct Continental IO-360-D***
Model 175 A&B: 175HP, 6 Cyl, 80 Oct Continental GO-300-A/C*
Engine breakdown by FIXED GEAR, CONSTANT SPEED PROP model:
Model R172E/H/J: 210HP, 6 Cyl, 100 Oct Continental IO-360-D**
Model R172K: 195HP, 6 Cyl, 100 Oct Continental IO-360-K/KB**
Military T-41B & D 210HP, 6 Cyl, 100 Oct Continental IO-360-D***
Model 175 C & P172D (Powermatic)175HP, 6 Cyl, 80 Oct Continental GO-300-D*
Engine breakdown by RETRACTABLE GEAR, CONSTANT SPEED PROP model:
Model R172RG: 180HP, 4 Cyl, 100 Oct Lycoming O-360-F1A6
===============================================================================
Notes:
* Cessna experienced trouble with the geared engines in the model 175
(also known as the Skylark) and, in 1963, changed the designation
to P172D (also known as the Powermatic) in an attempt to remove the
stigma of the engine. The 175 has always been, basically, a 172 airframe
with some changes. The P172D is even more so: it's a straight 172D airframe.
For more information, see note 1 below.
** The "R" designation (as in R172) is problematic. It sometimes refers
to aircraft derived from Reims designs, as in the "Reims Rocket" AKA
the R172E AKA FR172E, Models derived from the "Reims Rocket"
included the R172E/R172H/R172I/R172J which were all 210HP, and the R172K
which was derated to 195HP. Reims was Cessna's French subsidiary (now
independent). The "R" designation is also applied to the R172RG, for no
apparent reason.
The R172H/R172I/R172J were never produced in any quantity. The
most numerous example of all is the 195HP R172K which is known by
the marketing name "Hawk XP"
*** The T-41-B/C/D models are just militarized R172E airframes (although the
T-41C has a fixed-pitch prop).
The T-41A is a two-seat militarized version of the original (145HP) C172.
It was a training plane designed to lower the cost of "weeding out"
those who just didn't have what it takes to be a pilot. The Air Force
decided that this little bit of learning was too expensive in the T-37
(Cessna twin jet trainer) and sought out the lower-cost T-41A as
a device to accomplish that goal.
The T-41B was produced for the Army, to train its fixed-wing pilots and
for other (liaison/scouting) duties. It differs from the standard 172 airframe
in that it has no baggage door, has a strengthened firewall, jettisonable
doors, and long-range (52 gallon) fuel tanks.
The T-41C was produced, again, for the Air Force and is almost identical to
the T-41B except that it has a fixed-pitch prop. It was used as a cadet
motivational (pilot indoctrination) tool. Many T-41Cs were later modified
to T-41D standards by the addition of a constant-speed prop.
The T-41D most resembles the T-41B. It, too, has a constant-speed prop.
It was intended as an "export" T-41 and one that was not just to be
used as a trainer (options included rocket hardpoints!).
**** There are no "J" or "O" model 172s. C172J was intended to be
the designation of what is now known as the Cessna 177 (Cardinal). When
the designation changed to C177, the "J" was retired.
Comments:
1. The geared Continental engines used in the C175 Skylark and
P172D Powermatic have a history of upper-end (cylinder) distress ostensibily
caused by the higher RPMs. It is supposedly becoming very difficult
to overhaul these engines as parts are in short supply, especially
for the gearboxes. Major $$$$$ for gearbox parts.
2. There is also doubt about about continued ability to
economically overhaul "plain" Continental O-300s. Like their smaller
O-200 brothers, the low-compression/output Continentals suffer badly from
valve sticking when run on 100 Octane fuel.
3. Cessna switched to the Lycoming O-320-E2D IN THE 172 after it
became apparent that these engines were NOT going to be powerful enough (even
by Cessna's standards!) for the C177 Cardinal. Unfortunately, Cessna had
pre-bought literally thousands of Lycoming O-320-E2Ds in anticipation of using
them in the C177 (which they also anticipated would replace the C172 line).
Thus they were "forced" to find an alternate use for the -E2Ds; they
put them in 172 airframes, creating the C172I.
Cessna test pilots complained that the 4-cylinder Lycoming was not as
"smooth" as the 6-cylinder Continental engines. Nevertheless, they
liked the 2000 hour TBO and ability to run at higher RPMs (up to
2700 continuous) at altitude.
The O-320-E2D powered 172s are considered very desirable. The engine is
one of the most reliable Lycoming has produced and has few problems except
that it suffers when run on 100 Octane fuel.
4. The 195HP Continental IO-360 powered C172s (C172XP) use a derated
version of the IO-360-D engine. This deration was necessary to meet certain
noise requirements, to keep the plane in the "low performance" category,
and to keep from competing too much with the 230HP C182 line. It is
possible to convert a 195HP C172 into a 210HP C172 at overhaul time.
5. The 1973 172 model M introduced the "Camber-Lift" wing and numerous
aerodynamic improvements. The M and subsequent airframes are thus
considered the "most desirable" with the overwhelming bias going to
the M and N airframes. The P airframe is not as desirable as it was
weakened at the doorposts and other areas in an attempt to reduce weight and
increase interior room. The P airframe is also restricted to 30 degrees of
flaps (as opposed to 40 in all other models). This reduction in flap travel
allowed a 100LBS increase in gross weight (up to 2400LBS). This gross
weight increase is available as a retrofit to the N airframe via an
STC which involves some paperwork and a physical restriction against
more than 30 degrees of flap.
6. The -D2J version of the Lycoming O-320 was introduced to replace
the -H2AD series. It is not considered AS reliable as the -E2D for no
apparent reason. It occasionally suffers from valve sticking.
Switching to the O-320-D2J engine, in the 1981 model year,
was an attempt by Cessna to revive lagging C172 sales. They believed
that these sales lagged because of the growing reputation of the O-320-H2AD
engine (partially true) and that, by "introducing" what is, essentially,
a retrograde design (the -D2J engine) that they could recover their
lost market share. Alas, this was not to be as the early eighties
were actually the beginning of the entire industry's decline. This
development, at least, could not be blamed on the O-320-H2AD!
Note that this was not the first, nor the last time, that
Cessna had felt it necessary to "shake off" a bad reputation. Several
examples of that come to mind including the Skylark->Powermatic name
change and the Cardinal->Cardinal "Classic" name change.
************************************************************************
The O-320-H2AD story:
There is a tremendous amount of hype surrounding the O-320-H2AD engine,
some of it valid, and some of it pure parroting of what one
has heard from others.
For reasons unknown, Aviation Consumer seems to be on a vendetta
against the engine, although I've noticed that even they seem to be
mellowing on the issue. For example, their latest "Used Plane
Buyer's Guide" states that it's a tossup between an O-300 powered
172 and a O-320-H2AD powered one, at this point. They also, reluctantly,
concede that the engine has proven reliable in service.
In the mid 1970s, AVCO Lycoming purchased several million dollars
worth of automated milling machinery. Operational considerations of
this equipment, as well as a desire to improve both the production
AND serviceablity of their engines led to a major crankcase and head
redesign.
Engines resulting from this redesign were designated "76" series
engines. Some of them still have "76" stamped on the valve covers.
All of them have "76" as part of the engine serial number (except
for the O-360-E series, which have 77 as part of the serial number.
Nevertheless, the O-360-E engines are generally called "76"
series engines).
Lycoming made a deal with Cessna to purchase the O-320-H2AD variant as
well as with Piper to use the {L}{T}O-360-E engines (in the Piper Seminole).
The "new design" engines were supposed to be much cheaper to build and
buy, as well as being easier for a mechanic to service. For 172 applications,
the O-320-H2AD also offered 10 more horsepower as well as the ability to
burn 100 octane gasoline.
Other variants of the -H engine are the -H1AD, H1BD, H2BD, and
H3AD.
Current "76" series engines include:
O-320-H and {T}O-360-E series engines. Lycoming considers these engines
different enough from all their other engines that they publish completely
separate ("76" series) engine operating handbooks for them. As far as
I know, these engines are still in PRODUCTION (i.e. one can buy one
NEW).
Practically, the "76" series differ in that they:
1. Have removable (non-mushroom style) tappets
2. Have no separate accessory case - the case is cast with the block
3. Use automotive-style "canoe" rockers on studs, as opposed to rocker
shafts and arms.
4. All use Bendix dual magnetos as opposed to two separate mags.
Points 1 & 2 are shared with other Lycoming engines, in particular
the 541 series. They're also a major feature of MOST Continental engines.
Point 4 is common in many Lycomings.
Point 3 is a characteristic of the 76 series only.
Unfortunately, the early life of the engines was not rosy. Both the
engines and the magnetos suffered from some serious teething problems.
Briefly, serious early problems with the "76" series engines included:
Crankshaft assembly. The gear retaining design was inadequate.
An AD came out necessitating replacement of the crankshaft.
Oil pump problems. This necessitated replacement of much of the
oil pump (note this problem has afflicted MANY Lycomings)
Valve rocker, retainment, and spring seat problems.
Virtually all of these problems were taken care of early on and later
engines were manufactured with the fixes in place. They can be considered
evolutionary teething pains, as might happen to any new design.
Then, the big one, problems with camshaft and tappet spalling began to occur:
One theory:
The "76" series was introduced just as GA began to decline. The result
was a lot of aircraft spending a lot less time in the air. Camshafts
dried out and tappets spalled. Especially on the "76" series where, in
order to allow removable tappets, tappet face diameter was reduced.
Lycoming worked on several fixes to this, including progressively
larger and larger tappets. The final fix is the so-called "T" mod,
which was incorporated in all 1980 and later engines during
production as well as being a field retrofit. This mod improves
top end lubrication and involves even larger tappets.
(As an aside: Apparently both Lycoming and Cessna had difficulty reproducing
the camshaft failures in-house. I imagine that's because they probably
RAN the engines, looking for failure, as opposed to letting them sit
around)
The FAA went ahead and promulgated an AD as well, requiring use of the
Lycoming TCP oil additive or a lubricating oil containing the additive
(such as AeroShell 15W-50) in ALL "76" series engines. This additive
is highly effective and the key to ensuring that your O-320-H2AD delivers
a long and productive life.
-------------------------------------------------------------------------
Questions one might ask about the O-320-H2AD:
1. Is it a safe engine?
Absolutely. The O-320-H and O-360-E engines are certificated
aircraft engines with a long history of very reliable operation, often
in commercial (pipeline-patrol) or training role.
Operationally, there are several engines that come to mind
that I consider more "dangerous". For instance, I might feel a bit
uneasy flying behind a non-K model, non-VAR crank Continental TSIO-360 at
night. The same thing goes for the overstressed TSIO-520-BE used in the
early Piper Malibus.
Anecdote time:
One flying school down in Florida ran their O-320-H2AD to 3400 hours
before they overhauled it. I have personally witnessed several
O-320-H2AD engines with over 6,000 hours (total, not SMOH) of
trouble-free flying time (pipeline patrol).
In terms of trouble, there are many, many other engines that
are likely to give more trouble. Just about ANY geared engine, for
example. Most turbocharged engines, if not operated properly, for
another.
Yet the HYPE behind the O-320-H2AD is (arguably) much higher.
2. Why don't I hear about problems with the {L}{T}O-360-E engines?
Beats me. It is, essentially, the same engine as the
O-320-H2AD, although the displacement is larger and it has provisions
for a constant speed prop.
All of the problems attributed to the O-320-H engines are present
in the {L}{T}O-360-E engines, including the AD for TCP additive. Yet no
one cautions (at least not usually) against buying a Seminole because
of the ENGINES. And there is no a rash of SDRs about the Seminole's
engines. We also don't hear about Seminoles losing engines and augering in.
Why? See the next section...
3. What about continued SDRs on tappet spalling in O-320-H engines?
The O-320-H engine, with T mod and additive, continues to generate
SDRs detailing tappet spalling problems in numbers slightly ahead
of other Lycoming O-320 engines.
My thoughts (which are worth what you paid) on this are twofold:
a. There are not enough to statistically demonstrate a trend,
therefore the conclusions are invalid.
b. They're finding them BECAUSE people are looking for them:
Removing tappets and inspecting same and camlobes is fairly trivial in
"76" series engines. Unlike most other Lycoming designs, it does not require
cylinder removal. Add to this that people REGULARLY inspect their cams
on these engines both during use and during a prebuy, along with the
predisposition for mechanics to find such problems and it's possible
to account for the "blip."
If you're a mechanic, and you find, say, a spalled O-320-E2D, you might
not write up an SDR. But say you find a spalled O-320-H2AD? You'll
probably want to add it to the statistical database. Thus mechanics
are more INCLINED to report spalled O-320-H2AD engines. Just my opinion,
of course.
4. What about sudden in-flight stoppage (i.e catastrophic engine failure)?
This was a concern before the AD came out on the crankshaft
gears (1978 I believe). The post-AD crank, indeed the whole bottom-end,
of the -H2AD is as stout as any other O-320 series engine. As long
as the engine was manufactured after the cranks were changed, or has had
its crank changed (as required by law) there is no problem.
Tappet spalling, while still a potential problem (see below), does not
result in sudden engine failure unless the spalling has gone on
so long that metal clogs vital oil passages. Note that this is possible
on just about ANY engine, especially Lycomings.
4a. But, what about the dual magnetos?
They are, electrically, two separate magnetos. However, it
is possible for the drive gear to fail, which would result in sudden
engine stoppage. Some people feel uncomfortable about this. Note
that the same condition can occur INSIDE a "traditional" engine's
accessory case, obviating the advantage of two physically separate
magnetos.
Note that the "76" series is also not the only engine to incorporate
dual mags, they are (were, actually, until Continental bought the
Bendix magneto business) quite popular in Lycoming engines.
When looking at an engine with the dual mag (any engine), you should be
wary of the 2000 series. The 3000 series is MUCH improved over the 2000.
The equivalent 3000 series mags can directly replace an older 2000 series.
If you find one with a 2000 series, think about replacing it with a 3000
series (rebuilt 3000 series mags run about $600-700 with a core refund).
5. Is spalling still a problem?
Yes and no. One must understand that, eventually, ALL Lycoming
engines will spall. Therefore, one should be aware of several ways of
avoiding it as long as possible (hopefully beyond TBO!):
1. Use Lycoming's additive or AeroShell 15W-50 in ALL
Lycoming engines.
2. Pre-heat ALL Lycoming engines whenever the temperature
is below freezing.
3. FLY all Lycoming engines often, preferably at least once
a week.
4. Change oil often. I recommend every 25 hours.
5. INSPECT the tappets regularly - every 500 hours. Removing
and inspecting the tappets on a "76" engine is trivial (about
an hour of shop time total). Inspection of the tappets should
be considered a mandatory prebuy step.
If you follow the above advice, you can seriously limit your chances of
having camshaft troubles. I'll go even farther and say that, if
you have a T-modded O-320-H2AD engine and if you follow the above advice,
your chances of making it to TBO and beyond are extremely good.
Likewise, if you take an O-320-H2AD, leave it in a barn and come out
in -30 degree weather the NEXT YEAR and start it, well, I can pretty
much guarantee that you've just turned the engine into garbage.