MONTY THE ANSWER MAN ARCHIVE...
Swift Engines - general

GETTING READY FOR WINTER...
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??

Jerry,
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 <ystarrev@julian.uwo.ca>
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

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...  (12399)
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

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 <peetking@earthlink.net>
What do you recommend for sticky rings?? Enjoy the season, Pete King

Pete;
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 <jssjwhitt@email.msn.com>
Jim,
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

Steve,
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

Larry,
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
To: MPapenthien@aol.com
Jim,
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.

Mike,
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. swiftsnap@aol.com For me, an IO-360 is plenty exciting and I feel the IO-540 is overkill. -- Jim

MONTY'S BREAK-IN ADVICE... (040500)
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

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 <mike.brown@roche.com>
Dear Monty
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 present are:
Lycoming 150HP, possibly rebored to 160HP
Lycoming 180HP
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

Mike,
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. -- Jim

SWIFT ENGINE OPTIONS PART II... (080200)
Subj: RE: Engine Options
From: Mike Brown <MIKE.BROWN@Roche.COM>
Dear Monty,
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

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

LEAKING STUDS... (080400)
Subj: Leaking Thru-Studs
From: Tom Numelin <tom@electrodesign.to>
Jim,
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

Tom,
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
Dear Monty,
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

Mike,
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.

Jerry
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.  --  Jim

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 W

TURBOPROP SWIFT...(020201)
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

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 <edlloydaustin@juno.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 the case.

Ed
"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

PS
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. Jim