What else idles like a
six-cylinder Harley-Davidson, roars on takeoff like a dragster, and has
the best bottom end in the business? Here's everything you ever wanted
to know about TCM's ubiquitous big-bore but were afraid to ask.
September 30, 1996
The 0-470 is a rugged engine that's capable of producing solid
and dependable power. It distinguishes itself from other six-cylinder
carbureted engines by its characteristic lope at idle and throaty
exhaust stack burp. When balanced, an O-470 will run at cruise
power without the least bit of burble or vibration.
There are 15 models of the O-470 engine flying around in Beech
Debonairs, Bellancas and Cessna 180s, 182s, 310s and various AG
models. The single common denominator in all models is the bore
(five inches in diameter) and stroke (four inches in length).
Cylinder and crankcase castings are the main differences between
the various models. Other than these, the basic engine has remained
the same with only minor changes made to accessories and peripheral
equipment. To its credit, the engine's magnetos, carburetor, starter
and charging system have all been upgraded and improved over the
The predecessor to the O-470 was TCM's old E-225 series. And though
the E-225 enjoyed a successful career with Bonanzas and some models
of the Navion, an engine that had a better weight-to-power ratio
with a simplified carburetion and lubrication system was needed.
The E-225 had a separate accessory case, dry oil sump and dated
accessory configuration that became a liability to the design
requirements of newer, more streamlined planes. In 1952 that need
was satisfied when the 0-470-A was given its birth certificate:
Type Certificate E-273. The subsequent 14 additions to this TC
include five models which are eligible for an upgrade to a fuel-injection
system in place of the original equipment Bendix pressure carburetor.
Of the 15 originally certificated, only eight models, the O-470-G,
-J, -K, -L, -M, -R, -S, and -U, remain in the current TCM engine
specification list. The most popular of the eight are the 0-470-L,
-R, -S and -U models which power Cessna 180s and 182s. There were
over 21,700 of these planes built between 1953 and 1986, so it
stands to reason that these last four models would comprise the
bulk of the O-470s flying today.
Cases & Cylinders
There are few issues concerning 0-470 crankcases because this
engine is not under the same kinds of stress an I0-520 or turbocharged
engine is. And while all crankcases crack, the O-470's case is
remarkable because TCM's SB #M90-17 — which recommends the replacement
of engine crankcases with newer and stronger styles during overhaul — will
accept any part number and casting number assigned to the O-470
engine without requiring an upgrade. In contrast, larger, higher
horsepower engines have had to change their case design in an
ongoing effort to eliminate deck cracking, (with limited success).
Thankfully, replacement-before- TBO type of crankcase cracks
are somewhat rare on O-470s.
However, while this engine may not need upgraded cases, factory
remans are currently using a reinforced casting which, in large
part, appears identical to the sand-cast 520 case.
Cylinder castings for this engine have changed in style and structure
eight times since the late 60's. Beefed up spark plug bosses,
improved exhaust port walls, combustion chamber profile changes
and threaded barrel engagement areas have all been altered by
subsequent cylinder improvements.
The basic 0-470 engine consisted of two separate configurations
identified by the shape and style of the cylinder head. Models
-A, -E and -J all incorporated a parallel valve (also known as
a straight valve) cylinder head which is easily recognized by
the small rocker box cover and short, thick cylinder fin castings.
Characteristic of these models is the large, round intake port
and the small, two-bolt, exhaust port and stack assembly. These
engines are still seen today on Beechcraft Debonair and very early
Cessna 180 models.
The angle valve cylinder used on all other models is the present
standard issue for O-470 engines. This style cylinder's fin area
is 75% greater than the parallel valve type and the induction
and exhaust ports are standardized with a four bolt pattern. Due
to differences in the deck hold down stud configuration, angle
valve cylinders can't be fitted onto parallel valve cylinder
Cylinders are also classified as light or heavy. A light cylinder
is one that depicts a casting manufactured in the late 60's and
early 70's and is similar to the old E-225's cylinders. Later
models of 470 engines use the heavy style casting made available
around 1978 and subsequent cylinder part numbers are an improvement
on that design. Heavy cylinders are physically identified by a
thicker fin just below the top spark plug hole and a vertical
bridge below the bottom spark plug hole. While these are not the
only identifiers, they serve to assist in a definitive assessment
of cylinder and casting age. You may consider upgrading at overhaul
to a heavy cylinder appropriate for your engine if you are currently
running light cylinders on their second run.
Older O-470 cylinders were equipped with aluminum-bronze intake
and exhaust valve guides. And while the intake guide performed
well and is, in fact, still used today, the exhaust guide didn't
hold up to the heat created in the exhaust port. When 100LL fuel
was used, the exhaust guides failed even faster due to the prolonged
burning process of higher octane fuels. The exhaust valve guide
was then changed to a Ni-Resist steel guide which is better suited
to the higher temperatures encountered. After some years of success
with the Nitralloy guide in the 520 series engines, the 0-470
was given the option of using the same top end parts as the 520.
As a result, the use of the pre-sized Nitralloy guide, pre-sized
aluminum-bronze intake guide (with seal) and improved four-ring
pistons became the standard at engine overhaul.
In recent years, the Nitralloy guide has been replaced with a
new version of the old Ni-Resist guide due to some concerns about
accelerated stem wear and isolated cases of valve sticking due
to corrosion in the guides of inactive engines. TCM's SB #M90-13
talks about the corrosive environment in which exhaust valves
must operate and states that accelerated stem wear is caused by
these elements. More to the point would be the elevated temperature
the working Nitralloy guide creates by virtue of the nitrided
surface on the guide's inside diameter. This higher temperature
tends to flash (carbonize) the lubricating oil — especially at
shutdown — and can cause immediate and permanent valve seizure in
Current issues of TCM's SB #M85-8 and #M85-19 define the options
for superseded piston assemblies and valve guide combinations.
It's important to be aware that older, outdated parts can still
be purchased but they are probably not the best option given the
expectations put on our engines today.
Pistons And Rings
The biggest change in pistons occurred with the issuance of the
four-ring piston with semi-keystone (half-wedge) compression rings.
This affected most of the 470 series with the exception of the
0-470-U. The -U model uses a cam-ground, steel-inserted piston.
Clearance between piston and barrel became a serious concern with
this cam-ground piston and SB #M90-5 R1 was issued to clarify
concerns for skirt clearance on affected engines. Field experience
found that these cam-ground pistons would vary on skirt diameter
as much as 0.0015 of an inch. This caused problems when setting
up clearances during reassembly. If skirt-to-barrel clearance
on a steel barrel drops below 0.008 of an inch, the piston will
rub in the bore causing scoring, metal contamination and a number
of other unpleasant things. (Burnt paint on the barrel is sometimes
an outward indication of the piston rubbing in the bore.) The
old, all-aluminum piston used in all other O-470 engines doesn't
have the same close-skirt clearance and thus, isn't susceptible
to this problem to the same degree.
Another problem associated with older cylinder castings is discussed
in SB #M85-9 R1. (This SB identifies cylinder combustion chambers
that are not compatible with newer, high profile pistons.) The
piston's outer circumference contacts the cylinder head's inner
bore when at top-dead-center (TDC) on some 470 models. This is
a particular concern for the 0-470-U which uses a tall, high compression
steel-insert piston rather than the domed, low compression style.
If you change your cylinder or piston model during overhaul, be
sure to check component compatibility.
As with many Continental engines, TCM SB #M85-15 should be used
to establish acceptable criteria for cylinder compression checks
and this is particularly true for the O-470-U engine. The -U engine
is a low RPM, high compression ratio (8.6:1) engine which develops
230 HP at only 2400 RPM. This added stress on the ring and barrel
has accelerated a wear pattern commonly found in all 47Os and
results in sagging compressions much like those found in the IO
and TSIO-520 engines. As always, if valve leakage is present,
repairs must be made, but if ring blowby is experienced and falls
within the guidelines of the Service Bulletin, then the cylinder
is considered a serviceable part.
It should be noted that the steel-insert piston allows for a steel
ring to ride in a steel ring land. This combination stays amazingly
free from any real carbon buildup and allows the ring to float
freely in the ring land. However, because of this condition, compression
checks on the -U engine will be somewhat erratic and can vary
substantially from previously recorded compressions. 470 engines
using the all-aluminum piston don't seem to have this problem
and compression results are generally higher and more consistent.
The lower compression and stability of the piston ring in the
ring land due to normal carbon buildup around the ring also probably
contributes to the higher results.
Accessories, Coolers And Pumps
Oil cooler configurations have allowed for the installation of
a variety of oil coolers. There are five manufacturers of oil
coolers for the 0-470 and four different styles to choose from.
Originally, a small, congealing cooler was installed for early
-L models. The subsequent need for additional cooling brought
about a large capacity short cooler, then a large capacity, tall
cooler and finally, a large style, short and long non-congealing
It's rather confusing but the easiest way to order a cooler is
by engine specification number — i.e. 0-470-R spec (1) — or just call
your local oil cooler facility and explain to them what you have
and what you want by bolt configuration and cooler dimensions.
Oil pump assemblies have also made some advancements in the O-470
engine. Early model -L and some -R engines were produced with
oil pumps supporting an acorn-style relief valve which didn't
allow for oil pressure adjustment. Later versions incorporated
an oil pressure plunger and jack screw arrangement which allowed
for easy oil pressure adjustment.
Current production offers as optional equipment a new one-piece
pump assembly which, in addition to an adjustable oil pressure
relief valve, houses an oil filter pad as an integral part of
the casting. During overhaul, we recommended that either of these
oil pumps be used in place of the older nonadjustable style.
When Continental purchased the Bendix line of magneto ignition
systems, it became necessary to request which magneto type you
wanted when purchasing an engine. Both Bendix and Slick magnetos
work well with the engine, however, in our opinion, you're better
off going with Slicks. Bendix mag ADs have been coming out with
annoying regularity over the years and there's no reason to believe
we've seen the last of them.
The ignition timing indicator plate attached to the starter adapter
should be removed in accordance with SB #M84-8 and setting the
magneto timing should be accomplished per SB #M88-8 R1. (This
uses a timing degree wheel to verify piston position and can be
much more accurate than the plate and starter adapter pulley marking.)
SB #M87-15 requires the use of a ground strap on alternators that
are shock-mounted to the engine.
There are several bulletins regarding Marvel-Schebler carburetors
and part throttle mixture control. Service Bulletin #M90-18 discusses
replacing the composite float installed in the early 80's with
a newer metal version.
Also, some Cessna 180s and 182s are experiencing a greater than
normal amount of automatic leaning after the engine comes off
of full power. Some owners are finding cruise conditions that
will not allow for any leaning at all. This problem surfaced in
the early 70's and Service Bulletin #M74-15 revised the economizer
setting for the carb. However, the problem began resurfacing over
the last two or three years. Some in the industry believe that
changes in 100LL are the cause. (If you think it may be the venturi,
forget it. The O-470's MA4-5 carb has had a one-piece venturi
for over eight years.)
Operation and TBO
Graphic engine monitors, EGT/CHT analyzers, fuel-flow transducers
and digital tachometers give exact readings for every engine parameter
measured and can be great aids when trying to troubleshoot engine
problems. However, a single-point EGT is the only tool needed
to sufficiently lean your carbureted 0-470 engine. This is because
fuel and air distribution in the engine's induction system is
grossly inefficient and monitoring of single-degree changes and
measuring fuel in ounces rather than gallons is unnecessary. Adjusting
the fuel mixture for a particular power setting can be easily
accomplished with a single-point EGT using TCM Service Bulletin
#M89-18 as a guideline. Percent power and knowing where you are
in relation to peak EGT is then all that's necessary for adjusting
the mixture on an 0-470 engine. (Keep in mind that too much fuel
is as destructive as too little fuel.)
As one would expect when such a large displacement engine draws
its air through a carburetor, O-470s have a propensity for carb
ice. The large volume of air that passes through the carb's venturi
causes a significant temperature drop along with the desired pressure
drop. In fact, many owners install a kit to read direct carb venturi
temps in an effort to keep the icing condition down to a minimum.
Chief Aircraft (800-447-3408) has an OAT/Carb Temp gauge kit for
about $330. San-Val (800-423-3281) has two Carb Ice Detectors
available, both are around $280. Give them or the other dealers
in Trade-A-Plane a call for more information.
Another design drawback of the O-470 is that the front two cylinders
tend to run excessively rich. This is due to residual fuel that
collects in the balance tube located across the front of the engine.
In the late 70's, a Cessna kit, now discontinued, was made available
which wrapped this tube in insulation for winter use. The kit
usually helped to alleviate the problem somewhat. (If you plan
on installing a kit of your own design, be sure to use insulation
All 0-470 engines carry a TBO of 1500 hours except for many 0-470-U
models. TCM SB #M89-13 (note four) is very specific about which
-U engines hold a 2000-hour TBO and what requirements must be
met to allow for the extension on other -U engines. This means
that the -L,-R, -S and any other models you choose to list will
always be 1500-hour engines. Period.
Also note: The 2000-hour TBO extension is only allowed for engines
using cylinders equipped with steel barrels, not chrome. If your
engine was originally manufactured at Continental as a 2000-hour
engine, then, presumably, chroming of those cylinders would be
considered acceptable. But plan to use new steel cylinders if
making the change up to the 2000-hour TBO with an originally 1500-hour
TBO -U engine.
And Now The Problem Areas
Probably the deterioration most expected with the 0-470 would
involve sagging cylinder compression and high oil consumption.
Exhaust valve deterioration, exhaust guide wear and piston ring
and barrel wear contribute to high crankcase pressure, oil blowing
from the breather tube, fouled plugs and high oil consumption.
Continental has changed a variety of cylinder parts in an effort
to keep these calculated wear patterns to a minimum but the average
engine will face a certain amount of deterioration. Enough, in
many cases, to require top end attention between 900-1100 hours,
especially for those engines which take many years to acquire
that much time in service.
Oil consumption in O-470s can be particularly annoying, and in
our opinion, especially for engines fitted with channel chrome
cylinders, with a quart every three or four hours being common.
Cermichrome, Nu-Chrome or any of the silica-carbide processes
seem to perform well from the standpoint of oil consumption. A
quart every 12-20 hours is not out of the ordinary, at least in
the initial hours after overhaul. However, after accruing 600-800
hours, many times these chrome barrels see an oil consumption
increase of as much as 50% or greater, depending on engine model.
The -U engine, for instance, with the higher compression piston,
has a better-than-average potential to wipe the barrel clean of
the impregnated silica-carbide, thus increasing oil consumption
and decreasing compressions. Generally speaking, the -L, -R and
-S engines do fine with silica barrels and have much less of a
potential for silica failure.
If the option is there, steel cylinders are preferred over any
chrome process. Oil consumption will run one quart in 18-25 hours
until midway through TBO at which point consumption might deteriorate
to one quart each eight to twelve hours.
In contrast to a Lycoming engine, camshaft failure is not expected
but it happens with at least some frequency. The 470 has no greater
potential for this kind of failure than does any other Continental
and in most cases, the 470 engine will continue in normal service
without recognizing cam profile loss due to the slow rate of wear
and the very small particulate produced. When cam failure does
occur, the front shared lobe between the number five and six cylinder
is usually the culprit. More often than not, this wear pattern
begins with minor pitting of the cam and follower due to corrosion.
This degradation of the hardened surface continues until the soft
layer beneath the hardening is breached. At this point, spalling
occurs and material removal accelerates in rate of wear and particulate
Some speculate that the front cam lobes are affected because of
the proximity of the breather tube to this area of the cam. Whatever
the cause, the cam can be checked by removing the pushrods and
cam followers and visually inspecting it for wear.
What's New For the O-470 Engine?
Aside from changes to some accessories and the possible installation
of some form of electronic ignition, the basic O-470 will probably
remain the same for many years. And I, for one, hope that the
changes that do come are minimal. You see, my first airplane ride
as a kid was in a barn-stored Cessna 180B that roared as it took-off
from a small grass strip less than five miles from my home. It's
an adventure I relive each time I hear that high, throaty rumble
from a passing Cessna powered by the venerable 0-470.