ANSWER MAN ARCHIVE...
Swift Engines - general
GETTING READY FOR
From Jerry Swartz (JSw7211963@aol.com):
77759 does not have an engine heater. Have used the Reiff Hotpadd in previous
aircraft, with o.k. results along with 15/50. What system would you recommend
and also what winter engine oil weight and brand do you use. Have put
three hours of pattern work and near wide open use on the engine since
the change to seven qts of mineral oil and cup of marvel. It's now on
six on the dip stick. Stacks are not oily, Will continue until weather
forces me to get the 50 wt out of there. I plan on another couple of hours
on the 50 wt, before I go to the lighter oil, and will then see what happens.
It's at 6 qts on the stick now, so am interested in seeing how long it
takes to get to the minimum 5 qt reading. Would you suggest adding any
Marvel, and if so, how much??
The best engine preheater is a Tanis. They make one tailored for the O-300.
Sorry, I don't remember the price, but its fairly expensive. There are
various units available in the catalogues for $100 - $300. I just use
a kerosene "torpedo" to blow hot air over the engine for 15 - 20 min.
I like the Phillips 20-50 oil, the Shell 15-50 is more expensive, but
my good buddy has a 55 gallon drum of it and gives it to me for nothing,
so guess what I use!
Many guys don't like a multi-grade
oil, even the oil manufacturers are starting to admit that multi-grades
may not be the best for aircraft. Doc Goodlad up here has an IO-360 which
I overhauled 20 some years ago and is now over TBO and still runs great,
he has always used straight 50 in the Summer and 40 in the Winter. He
always pre-heats below 32F. If you had a good pre-heater, maybe you could
use straight 40. The multi-grade allows starts down to about 20 deg. It
sounds to me like your engine is doing pretty good, is that an improvement
on the amount of oil it was using? BTW - the figure of 5 qt min. is mine,
Continental says 4 qt. min. I think as the oil gets black, I suggest you
should chg it to 40, and run it that way for a while. In the cooler weather,
you can run 6 qts right after the chg. Run it normally and see if the
consumption goes down. A friend of mine here has a 145 that has always
taken a qt of oil every 4 hrs or so and his exhaust stacks always run
clean. I don't know if that can be attributed to valve guides or rings.
His bores have several thousands wear & the valve guides are marginal
(he had the cyls off and did a top at one time).
I would suggest flushing
the sump by dumping in a gallon of mineral spirits after the oil is drained,
(available up here in gallons at Menards & Wal-Mart for between a
buck and two bucks a gallon) Then try 6 qts of 40 wt. mineral oil. You
should be able to tell within 5 hrs if all this has done any good. Try
it without adding any Marvel at first. -- Jim
CYLINDER HEAD TEMPS /
FUEL CONTAMINATION... (4399)
From: Yves Starreveld <email@example.com>
My brother and I just finished flying our Swift from Edmonton, Alberta
to London, Ontario. 15 flying hours and 8 airports in 5 days! Was a beautiful
trip, and the airplane performed wonderfully. A couple of questions, though...
What cylinder head temperatures does one normally see? Our OAT was between
+10C and -10C, and the CHT tended to stay around 220-230C regardless.
Probe is on the right back cylinder. Oil... the breather line loves coating
the belly. Oil was kept between 5.5-6 the whole way. I heard rumor of
an air-oil separator. Any thoughts? Finally, the A/C was outside a couple
of nights, in the rain. I have heard that fuel contamination in the Swift
is unheard of (but checked anyway) - anyone have any experiences there?
Thanks for any comments anyone may have... -- Yves
I presume you have a O-300 engine. The cyl.head red line is 275C, but
I don't like over 230 deg continuous. 220-230 are normal readings. There
are so many possible variances in guages, type, accuracy, etc. that I
wouldn't get too worried about any readings. The O-300 is notorious for
throwing oil out the breather, and yes, air/oil separators have been used,
I've got a baffle inside my case now to keep some of the splash away from
the breather, but I can't tell you yet if its working. My EQ oil cooler
adaptor leaks, and I too have oil on the belly! If someone has drilled
a hole in your fuel cap, tape it over when leaving the airplane outside,
othewise, just make sure the cap is tight. -- Jim
FROM THE "I FIND THIS
HARD TO BELIEVE" DEPARTMENT...
I think I put Mike's success with '11Echo in a previous update but don't
remember. Anyway, saw the following in the So-Cal Newsletter...
"FASTER AND LIGHTER... OR
Mike Williams checked-out Jim Stribling, Columbus, Ohio, in his new Swift,
N711E, sporting an O-300D and new polish. It lost fifty pounds by removing
the O-320, constant speed prop, and Corbin cowl; and picked-up 15 mph,
at 160 IAS at 4000 MSL."
LYC O-320 VS CONT O-300...
I want to comment on the above before all you O-320 Swifters run out and
trash your engines for O-300s. I sincerely believe that 160 IAS at 4000
MSL is possible with an O-300D. Takes a good clean airframe and a tight
cowl which 711E must surely now have. (Please Mike, tell me how ya did
it!!!) I can speak with some authority about this O-320 vs O-300 issue
because my Swift has an O-300 and my wife's has an O-320. When we are
flying with the same RPM, our climb rates and/or cruise speeds are virtually
indentical. However, I evny Erin's Swift because the O-320 allows the
use of a constant speed prop. I feel that the extra takeoff and climb
performance that the C/S prop gives her Swift outweighs, (no pun intended)
the extra weight of the constant speed prop. You'll get that 150hp at
2700 rpm right from the get-go on takeoff. With the O-300, you certainly
won't get that 145hp at 2700 rpm with a reasonable pitched (57-60) fixed
pitch prop. I'd love to have a constant speed prop on my O-300 but that
just isn't available... (Well, Continental did, I'm told, make a very
small production run of an engine called the O-300E for a constant speed/reversable
prop... for the Goodyear Blimp.)
You have to consider the
type of flying you do and where you do it. In some cases the takeoff and
climb performance gained with a constant speed prop is more of an important
issue than all out cruise speed. If I had to start from scratch shopping
for a Swift to buy, it would have an engine installation that allowed
a constant speed prop. Then I wouldn't sweat those high density altitude
takeoffs as much. Still, the fixed pitch prop Swift will perform in high
density altitude conditions too but ya gotta really be careful. During
my trip to Athens in '93 I took off from Alexander, NM with an 8,000'
plus density altitude and 15 knot direct crosswind. Did OK because I didn't
ask the ol' Swift to do anything before it was ready to and the runway
length and terrain allowed that.
So the fixed pitch just
does not perform as well and THAT limits your options when it comes to
takeoff weight and performance vs safety. Kinda like the difference between
taking a friend along to Lake Tahoe in the summer (O-320) or going by
yourself (O-300). The next engine for my Swift will be one that allows
a constant speed prop.
Just my humble opinion gang.
I'd love to hear others.
BIG MOTORS AND SUPERCHARGERS...
From: Larry Owen <T081763@sphn.com>
Subject: Re: O-470's and IO-470's
This is probably a silly question but.... I have heard of and seen Swifts
having dozens of different engines installed and have never heard of one
with a Cont 470. This engine seems to be available, has the larger HP
numbers that everyone (including myself) wants, and is certainly smaller
than the Cont 550 and varous turbine installations I have seen. Is there
a valid reason that this engine is not used or have I missed something?
You have to understand that I have too much time on my hands with a C-145
with a rate of climb of about 100 fpm on these nice hot El Paso Texas
days. My density alt is often above 7000' and this gives me a lot of time
to think while climbing to any alt that doesn't require air cond. ....and
I wonder if that small British supercharger can be.... well, I'll save
that one for later.... -- Larry
The O-470 is just plain too much iron for the Swift. Even an IO-360, which
is approved, makes it a heavy airplane and it flies accordingly. Steve
Halpern had a 250 hp Franklin installed and now is going to an IO-540
Lycoming. This is not a casual, or easy conversion. It involves moving
the firewall back for CG purposes and changing the whole control system.
Local GC-1A Swift owner Charlie Hoover considers any Swift with an empty
weight over 1100 lbs. too heavy, regardless of engine! Regarding hot El
Past Texas days... There are no easy answers to that problem. You could
(1). Install a big engine, 180 or 200 Lycoming, a 210 Continental or a
220 Franklin. (2). get a different airplane. (3). Install an Aeromatic
prop or a prop pitched for a C-125 and be content with a 120 mph cruise.
Going with a supercharger... I'm afraid the O-300 will blow up on its
own occasionally, without the added boost of a supercharger! Several Swifts
have had the TSIO-360 installed, but none to my knowledge have been approved
for a standard airworthiness. You could buy Steve Halperns old Turbo-Franklin
engine, it's for sale! Jim
STICKY RINGS... (12499)
Subject: Re: 1A's
From: Peet King <firstname.lastname@example.org>
What do you recommend for sticky rings?? Enjoy the season, Pete King
For sticky rings, Marvel Mystery oil sometimes works. Also, perhaps numerous
oil changes using light weight oil. Don't fly with really light weight
oil, but run it on the ground and with reasonable oil pressure. Run at
1000 rpm. Change the oil every time it gets dirty. -- Jim
LYCOMINGS AND CONTINENTALS
ARE LIKE APPLES AND ORANGES... (12499)
Subject: Re: Swift Engine Conversion
From: Steve Whittenberg <email@example.com>
I am looking for a Swift with at least a 145. I have found one that has
a Lyc 0-290-C which I understand is a downgraded engine to a 125. . Specifically
can it be upgraded to a 145 or 150 ? What is involved? Major mod or minor
mod? Why did they downgrade the engine in the first place? Since we are
talking engines, if the 125 is not suitable for upgrade - what would it
cost to put in a 145 or a 180? Many thanks -- Steve Whittenberg
We are talking a different animal here. A Lycoming engine and a 145 are
apples and oranges. The Swift as originally certified was approved for
125 hp. So most STC's in following years limited the hp to 125, no matter
what engine was installed. The Lycoming O-290 is rated at 125, 135 and
140 hp in various versions. The 125 hp restriction is a paperwork technicality
for the Swift installation. Don't worry about it. As a matter of practicality,
with a fixed pitch prop, you probably couldn't pull over 125 hp under
any conditions. The airframe can be converted to any of the big engines,
but the O-290 should give comparable performance to the 145 hp O-300 Continental.
Most so called 145 hp Continental engines are likewise restricted to 125
hp. This is no big deal, 125 hp is 86% power for a 145 and it is only
possible to exceed that at sea level with a climb prop. (ok, in Florida
it might be possible to get near sea level, but you would also need a
prop permitting 2700 rpm) My 145 will only turn about 2300 rpm on takeoff,
which is less than 125 hp. At altitude, it will turn 2700 rpm, but the
manifold pressure is down far enough that 125 hp is not exceeded. The
O-290 can be upgraded to 140 hp max. To get 150 hp, you need an O-320.
If you need a lot of power, make up your mind to spend a lot of money,
and go for at least 200 hp. -- Jim
ANOTHER ONE OF LARRY'S
STRANGE QUESTIONS... (010500)
Subject: Re: EGT MONITORS AND MIXTURES
From: Larry Owen <T081763@sphn.com>
WARNING: This area often contains random thoughts! OK, another one of
my strange questions. There are several auto-parts companies offering
small inexpensive, add on, exhaust gas mixture monitors. Most of these
use a "GM" the "O2" sensor to measure if the exhaust is rich or lean.
But...auto engines get 2 to 3 times the mileage because air cooled A/C
engines use fuel to "cool." Does this mean the A/C mixture is considerable
richer (2 or 3 times)? or does the A/C engine have a huge valve overlap
to pull "cooling" air/fuel mixture through? Or something else? In any
case, would a O2 sensor give you a faster, more accurate measurement of
our mixture setting , compared to the A/C EGT gauge which is slower and
more problematic? Or would the O2 sensor be confused by the additional
"cooling" air/fuel mixture? Thanks, Larry Owen, N78287
Short answer. Darned if I know.
Longer answer. Well, I think you have pretty well answered part of your
own question. The "ideal" fuel/air mixture is about 14.7:1 but the engine
will probably run at a range from 5:1 to 25:1.(air/fuel by weight) I remember
30 years ago when the automotive shop at the school I was teaching aircraft
mechanics got their first combustion analyzer, the auto instructor had
to show it off to the aircraft students, who he thought, were mired in
'30's technology. Of course, EGT was not in wide use yet then either.
Remember, auto engines typically run at 10 - 15% power. Aircraft engines
typically cruise at 75% power. At 60 mph my Camaro burns just a little
over 2 gph at 1600 rpm and 12" mp. (a guess, no mp gauge) The engine is
rated at approximately 300 hp and I would guess it's using about 10% power
at 2 gph. An IO-360 Continental or Lycoming will burn 10 - 12 gph at 75%
power. (150 hp) If I could cruise my 300 hp Camaro at 150 hp, I have no
doubt it would take just as much, if not more gas! (if I could cruise
at 100 mph, I think it would get about 5 mpg, or 20 gph). I must confess
I don't know much about O2 sensors, they appeared on the scene fairly
recently. Aircraft technology is sometimes criticized as being behind
the times. Certainly, an aircraft engine, with its 1920's magnetos is
not as sophisticated as a today's automobile engines. But, you must remember,
in aircraft certification, one thing is paramount -- reliability. Can
you imagine the lawsuits if an aircraft engine was computer controlled
and the engine quit and the airplane crashed? Electrical axiom # 1 - a
light bulb will eventually burn out and a computer will crash. That's
why we have two magnetos. Perhaps the answer is two separate computer
controlled ignition systems on an aircraft. But, think about it, two batteries,
etc. etc. I'm sure you'll see something of that sort in the future, but
I'm too old to worry about it! -- Jim Montague
WHAT NEXT... A TURBOPROP?
WHAT? THAT'S BEEN DONE TOO? oh... yeah... (020100)
Subject: Re: IO-540
I'd like to know if anyone has ever modified a Swift by putting an IO-540
in it? If you know of some, could you let me know who they are and contact
info if you have them? Thanks.
Yes, Steve Halpern is having an IO-540 installed right now as we speak.
The engine installation is being done by Merlyn Products of Spokane, WA.
Steve is listed on our Swifter Email addresses list and also in the Swift
Membership directory. I don't know if Steve wants to talk about it until
the job is complete and has the FAA's stamp of approval. (Editor's note:
That is correct... Steve has promised us a full report when all is said
and done.) This is not a do-it-yourself type conversion! Steve's airplane
has the firewall moved back for CG purposes and a different control system
installed. This kind of work costs serious money. Steve was once told,
"You coulda had a P-51 for the same money". Steve's reply was, "Yes, but
I didn't want that... I wanted this Swift". A Swifter who has investigated
the various O-540's and their suitability for installing in a Swift is
Snap Lemon. firstname.lastname@example.org For me, an IO-360 is plenty exciting and
I feel the IO-540 is overkill. -- Jim
MONTY'S BREAK-IN ADVICE...
Subj: Engine Break In.
From: Jerry Swartz <JSw7211963>
Jim: After your overhaul and you cowled up and went flying, what power
setting did you use while waiting for the temps to stabilize? Some are
telling me to leave it wide open in a gradual climb and others are telling
me to power back a little. -- Jerry
I used full throttle only long enough to get the gear up and get a few
hundred feet of altitude. The then throttled back to 24" and climbed at
a very shallow angle to get the best airspeed and highest rpm possible.
The cylinder head temperature seemed to level off at 230C so I decided
to not let it rise above that temp. even though the limit is 275C. After
something less than 2 hours at 24" x 2400 rpm the cylinder head temperature
dropped to 210C indicating the rings had seated. It has run 210C ever
since in normal cruise. -- Jim
ALTERNATIVE ENGINES TO
THE O-300 CONTINENTAL... (080200)
Subj: Engine Options
From: Mike Brown <email@example.com>
I would appreciate some advice on the issue of alternative engines to
the 0-300 Continental. My "new" Swift ZS-BCE (s/n1270) has a major bearing
problem, requiring extensive overhaul. It may be prudent at this stage
to consider spending the money on a bigger powerplant, as I will be operating
from highish altitude airfields at reasonably warm temperatures (elevation
4800'; days +16 winter, +25/30 summer, length 2000 feet).
The options available at
Lycoming 150HP, possibly rebored to 160HP
Lycoming 200HP (Arrow motor)
Lycoming 220HP - turbo (Seneca motor).
Why is the Continental 210HP
so favoured - is it an easier installation, or are there definite benefits
over other installations?
What info is available re
STC's, changes required for mounting and C of G maintenance, props (fixed
pitch or CSU), cruise speeds for the different combinations? Best of all
- what would you advise? Many thanks for your assistance. Regards, Mike
Brown, South Africa
There are no engine conversions cheaper than overhauling or replacing
your O-300. I am amazed if you have operated a 145 Swift at that field
elevation from a 2000' runway! To address your question on specific engines:
150 hp - better than the 145hp for takeoff performance because of the
constant speed prop. Once off the ground, there is not much difference.
The 150 and 160 Lycomings have the same cylinders and bore. The 160's
have a slightly higher compression ratio, due to piston design. 180hp
- the 180 Lycoming makes a nice conversion. None of the "big engine" conversions
are exactly cheap but this may be one of the most economical. 200hp -
The IO-360 Lycoming makes the airplane perform! 220hp Lycoming - I don't
know of this engine being used in a Swift. 210 Continental - I don't know
if a US STC is of concern to you in South Africa, but this engine is STC'ed
and is generally thought to provide the most "bang for the buck". (US
expression meaning most performance for the money) Merlyn Products of
Spokane, WA USA has STC's and engine mounts for the 200 hp Lycoming and
the 210 Continental. They have a link off the Swift Home Page. Our Swift
Association now has an STC for the 180 Lycoming engine conversion. I don't
know if they have parts, like engine mounts, available as of yet. You
will have to contact them.
CG considerations are addressed
by moving the battery back and possibly adding lead ballast in the tail
area. All of the big engines use constant speed props. Cruise speeds vary
considerably, due to differences in details, such as cowling. The airframe
is red lined at 185 mph (161 knots) and the faster airplanes can exceed
this figure. I like the 210 Continental, I like a 6 cylinder engine. --
SWIFT ENGINE OPTIONS
PART II... (080200)
Subj: RE: Engine Options
From: Mike Brown <MIKE.BROWN@Roche.COM>
Many thanks for your prompt response. No, I haven't been operating this
Swift from the airfield described! In fact, I bought the aircraft subject
to certain conditions, one of which was that the oil pressure problem
be rectified. It turns out that the problem was due to totally shot bearings,
requiring a new crankcase, regrinding the crankshaft, new conrods, camshaft
and hydraulic lifters. In addition, the cylinders are oversize and slightly
conical so the AMO has a significant repair job on it's hands. I'm negotiating
the option of replacing the shot motor with them, and contributing to
the additional costs, which is why I'm looking at the options available.
As I plan to base the aircraft at this airfield, I think it may be prudent
to invest in some extra horses up front! I'll check out the links to Merlyn
Products, as well as the Swift Association site.
I also like the idea of
6 cylinders, but there's more to maintain! The SA Register has two categories
for registration, the general one requiring US or similar STC's, and the
restricted one being less stringent and allowing restricted personal maintenance
options. In the case of a vintage aircraft, I don't suppose it makes much
difference either way in terms of resale value, but I'd prefer to keep
the machine in the general category. Many thanks again for your assistance
- I'll probably be calling on you again quite soon! Kind regards, Mike
The only way that a 145 will perform well enough to operate out of a short
strip at high altitude is too use a non-standard prop. A 76 x 51 perhaps
modified to a "JetFlow" profile would work. This prop has too much diameter
and not enough pitch but would get off the ground pretty good. To get
any decent cruise, high rpm, like 2700 would be needed. With your certification
system, it might be worth a try. A 6 cylinder Continental indeed has 2
more cylinders than a 200 Lycoming, but 6 Continental pistons and exhaust
valves cost less than 4 Lycoming pistons and exhaust valves! -- Jim
Subj: Leaking Thru-Studs
From: Tom Numelin <firstname.lastname@example.org>
One of the through-studs for cylinder/crankcase connection is leaking
oil fairly badly. The oil is coming making its way along the threads and
coming out the end of the nut. There is very little oil coming from under
the cylinder flange. There is a small amount of leakage from the same
stud on the opposite side of the crankcase. I've tried rotating the stud
in hopes of re-seating the seal but it didn't help. My mechanic thinks
that we would have to split the case to replace the O-ring seals. Is there
some way to seal the stud without splitting the case? The obvious way
is to clean it up and then attempt to seal the threads with silicone but
I'm hoping you might know a better way. Tom Numelin
Several of the thru studs can be driven out and new "O" rings installed.
Obviously, not the ones with a cylinder at each end! (unless you remove
a cylinder) Worst case scenario, to replace all the "O" rings, you have
to remove several cylinders. But removing cylinders should not be necessary,
you should be able to put some sealant under the nuts and that should
stop the leakage. Rather than use common silicone, use a Locktite sealant
or GM "Goodwrench" gasket maker. PR 1422 is a 2 part sealant which will
hold up well also. -- Jim
IO-470 IN A SWIFT? SURE
WOULD BE NICE. HOWEVER...(010201)
From: Mike Brown <MBrown@cromedica.com>
Subject: Replacement engine - ZS BCE
I'm still looking for a suitable replacement for my shot Continental 300,
145 HP engine. Do you know whether an STC exists for a Continental IO
470S, 260 HP engine? Or, is this just too much power/weight for the airframe?
Thanks for your assistance, Kind regards, Mike Brown
The O-470 is just too heavy. If there was a 260hp, 260 pound engine that
would be great, but there isn't.... except a turbine! The 210hp Continental,
200hp Lycoming and 220hp Franklin remain the biggest practical engines
for the Swift. There is a special O-540 Lycoming being installed in a
Swift, but it is well above the investment in effort and money that most
folks would want to make. -- Jim
CREEPING THROTTLE... (020101)
Subj: Throttle (N77759)
From: Jerry Swartz <JSw7211963@aol.com
Jim: My throttle is creeping open and it is getting worse. The tensioner
works, but that is really a pain when taxiing. I have been told that the
reason for this happening is that my throttle cable is wearing out???
If this is true, what is the correct length that I will need for my 0300.
Easier to ask you from the warmth of my house, then to try to do the measuring
in this sub freezing weather. Jerry S.
That is a common problem and easily fixed. Your throttle cable is mis-rigged.
Disconnect any clamps on the throttle cable. Close the throttle. Reclamp
the cable allowing about 1/4" "springback". When the throttle
is closed the stop on the carburetor should make contact first and the
throttle should be able to be brought back slightly further. An extra
clamp may help. If you do in fact need a new throttle cable at some point
I forget the exact length. Remove your old cable and measure it, adding
a couple inches may make it easier to avoid the creeping problem.
And Steve Wilson adds...
Sounds like Jerry got a handle on this, but my first answer was to look
for a throttle spring on the carb. Some carbs have the spring; some do
not. The idea of the spring was a safety backup should the throttle cable
break. The idea was that you would go farther with full throttle, than
with no throttle. I like that! If the internal friction of the throttle
cable is high (read ... old cable), then the spring probably would not
have much effect; however, when I replaced the throttle cable on N77753
with a new "Teflon sheath" cable from AS&S, WA la, I found
I had to use the friction lock to keep it from creeping. Jim is right
about rigging. I ended up putting a cable lock at the firewall in an attempt
to stop the creeping. No workie, though... Just too slick to prevent the
creep. I've gotten so used to working the lock with my thumb and forefinger
and the throttle with the palm of my hand that it has become second nature.
I do think the throttle spring is a good idea and would not remove it,
but just a thought if anyone else is experiencing this problem.... Steve
Subj: Allison 250-C18
From: Steve Lopez <Dangomax@aol.com>
Has anyone put the allison 250-C18 (Model T63-A-700) turbine on a swift.
It is rated at 317shp and weights 136 lbs. Just was wondering if you know
anyone who may have tried this yet. Thanks Steve
To my knowledge a turbine engine was only installed one time in a Swift.
That was the "Swiftfire" by LoPresti. It was displayed at Oshkosh
around 1990. I'm not even sure which engine it was, but I believe it was
the Allison. I'm sure others will remember. -- Jim
(Editor says: See photos of the "Swiftfire" on the GTS Homepage.
Go direct via the following link: "Swiftfire"
WHAT IS A "ZERO TIME" ENGINE... (110201)
From: Ed Lloyd <email@example.com>
What has to be done to an engine to call it a '0" time engine? What
is done to an engine to call it an overhauled engine? If you pull the
jugs and rods, and the crank checks ok, would there be any reason to split
"0" time is not an "official" term like "new"
"remanufactured" "rebuilt" or "overhauled".
Those terms have specific FAA requirements. "0" time means the
engine has not been run, but since what? A true "0" time engine
is a new engine that has not been run. No one but the manufacturer or
certain repair stations can call an engine "remanufactured"
and start the engine time over
from "0" and furnish
a new log book. To overhaul an engine it is necessary to disassemble it
completely and clean and inspect all it's parts and replace those parts
as mandated by the manufacturer and reassemble to certain limits and tested.
For certain engines, the TCM IO-360 for example, the mandated replacement
parts include the crankshaft if it is not a VAR crank. Even if it has
a VAR crank, at overhaul it is necessary to magnaflux the crank, replace
the counterweight pins and bushings and replace the main bearings. Also
the camshaft and associated parts must be inspected so splitting the case
is absolutely mandatory. Plus the crankcase itself must be cleaned and
inspected. -- Jim
If the cylinders are overhauled, but the case is not split, that is commonly
called a "top overhaul". A "top overhaul" has no FAA
significance and is just a repair to get the engine to it's normal overhaul
time. Most current engines will make their recommended TBO with no problems
if the time is put on in a short period. If a 2000 hour TBO engine for
example, has only acquired 1000 hrs in 20 years, it may be necessary to
remove the cylinders and grind the valves at some point. The TCM O-300
will rarely make it to it's 1800 hour TBO without having cylinders removed.