Looking for advice-used Lyc

[szicree]

Dang! Guys, it's only an engine, not a family member.

[Jconard]

"No four stroke builds up pressure? Sir, I suggest you do some homework. A weak cylinder will indeed build up pressure if spun long enough, as opposed to a fresh cylinder will build up pressure immediately. Better read on."

At the end of each compression stroke, there is a power stroke...with no burning fuel, pressure goes to almost zero, followed by an exhaust stroke where the cylinder goes to completely no pressure, followed by an intake stroke where there is actually a vacum....

The compression guages you are talking about appear to "build up" because each compression stroke pressurizes the guage chamber and hose a little more, until the pressure generated anew on each compression stroke is equal to the guage chamber...this is why those guages all have a release valve.

That you do not understand the dynamics of such a spinning test is simply shocking.

Again, every race team I have ever owned or driven for uses the leakdown test as the most precise way to evaluate a piston engine.

I have performed thousands of leakdown and spinning compression tests on various street and race cars I've owned including but not limited to:

911 2.4 MFI converted to 2.7 ltr, RSR Cams and injection (slide valve)
914 2.0 4 carbureted, cammed
3 different VW Karman Ghias with various 1776-2100 cc mod motors
4 different buses with 2.0 fuel injected engines
2 different ITB rabbits
1 FA Cosworth Engine
1 FA Toyota engine
3 FC Single Cam Fords
dozens of 1.6 ltr formula fords


See also:
http://www.avweb.com/news/columns/187037-1.html
Mike Bush's credentials speak for themselves.


No one test is conclusive, but you said each was worthless. They all have value, all I am saying.

[tacchi88]

Geroge,
I have had some experience with dynomometers, with myriads of engine types, and in every case, I have never seen a high time engine, as "strong" as a new or low timer. Run is does, but strong, no way. Would it be safe for flight? In some case why not? In most cases, I would (and have) park it.
As for differential compression, it is not mandatory, and is suggested only. It is the rule in aviation and I can see the benifits which only have to do with safety. As to being conclusive, that is absolutely false.
We perform differential compression by introducing pressurize air artificially in the the cylinder while it is in the TDC position. As it the case of most Lycomings the bores are tapered, and are tightest of the top.
Any type if piston engine will have some normal taper in its bore in due time, and in some case is acceptable, but still the least wear is at the top of the cylinder.
The key is that no piston spends its time at TDC, and had 4 cycles to deal with.
As the piston moves on the intake stroke, excess clearance will stiffle intake due to leaking from wear or accisive clearance. It will not be able to ingest the required amount of mixture to perform to its potential. Like wise on the way up when it's trying to compress what ever it "sucked it" it will lose some of it's ability for complete compression from leakage. On powe.r as the piston goes lower, the access wear/cleareance will allow "blow by" in to the crankcase, and as it exhausts, it will still lose some into the crankcase since it is not able to retain spent gasses above the piston as it is trying to "exhaust " it. And the cycle repeats. Note that in aviation we discuss oil consumption, qt/hr. This is never a topic in any other type of internal combustion engine.
Still the same engine will and can exibit normal differential numbers.
Given the condtion these engines are assembled, and even operated. oil sampling, in order to have some meaning will have to be made from it's inception when new, or rebuillt. Operating a high timer on short hops and high power settings such as T&G, for example, for say 100 hrs, will exibit a higher number pf partices, for the same time at normal setting and long distances, leaned properly, the results on oil samples will be astonishly different. In no case is one sample a good indicator of the engines life. At least six, and at different setting will be far more conclusive, since we would have established a trend, which is the purpose. In addition, I assure you that oils type also plays an important part.
As to tolerances, you will find that most Briggs and Stratton engines (as well as others) operate with with .002 to .003 piston clearance from new, and are considered worn at .005 to .006 depending on model.
Most Lycoming are set up new at .010 to .012, and maximum allowed to .018 to .022 depending on model.
Autos vary, new from .0005 to ,0025 max, some .002 to .006. In other word, most lawnmowers are worn out as well as autos and ready for the scrap heap if they were to see tolerances like a typical Lycoming or Continental.
A Franklin starts at .003 and worn at .005. Rotax 4 cyles AC engines. new .0005 and worn at .005. (lots of wear allowed)
It doesn't take a wizard to see that Lycs and Contis not only are oil burners, right from the factory, but all the time.
Lycoming engineers are stuck in the 30s, and still don't know how to make a crankshaft. The recent AD will bear that out. My engine experience extends when autos use to not live long, didn't spin very fast, (3400 rpms in most cases, 3200 for a helo Lyc). They had many of the problems we see in AC engines, oil consumption, sticking valves, etc, but in all cases, no differential compression method was ever use to determine their lives. It was a spin test. Even as archaic as they once were, they would outlast any AC engine.
As to the auto guys, they have some valid points. If the engine is made to run as it does in the auto it came from, it is a great choice. Albeit with some weight increase, still reliability factor and economy of fuel and oil is an excellenty advantage.
I'd like to tell you about a Corvair, but it's getting too long already.
The choice of straight cut gears, and sloppy backlask had been known to every one except aviation. The only advantages are ease of manufacturing. In racing, although not so much nowadays, straight cut gears require less power to operate, but also wear much faster, but that's racing.
In the real world, and considering oil samples, we would see more steel present than say a typical auto engine
As to air cooled engine requiring more tolerance, I will simply point out the Franklin AC engines( too bad they died) and a typical Lyc or Conti, as I stated previously.
We can also mention motorcycles which typically run in bumper to bumper traffic without the aid of air flow, and most are ready for the scrap heap should thay ever exibit even new tolerances of a Ly/Con.
The Lycoming engineering had a specific mission, but that was in the 1930s. Every internal combustion piston maker, air cooled and other wise has improved, and advanced, while we're still stuck in the 30. Flipping counter weight cranks were discontuned in the auto world in the 20s. Only the high buck luxury cars had them and very few at that.
Yes Lycoming are unecessarily sloppy, the clones not much better. Think of it. The same components are also sold as certified. To do so, must meed the same archaic designs and manufacturing methods. They have improved squat. Case in point is crankshafts. Ever hear of a crank AD for Briggs and Stratton or Ford?
In 28 years invloved with aviation, I have yet to meet a Lycoming or Continental to go 2000 hrs without never, I empahsise "never", having been taken apart. I believe there are a few, but in so many years, nary a one has ever gotten by me.
What engine will I use in my RV10, you guessed it a Lycoming, and I will "tinker" with it.
I always make it a point of reading your comments, they are refreshing, and informative. I do not always agree (obviously) but I enjoy them never the less. After all, this whole chat is an exchange of ideas. Good or bad, we all learn, and benifir. Too bad the FAA, Lycoming and Continental aren't listening.
T88

[tacchi88]

Sorry George I mispelled your name haven't figuired out how to use spell check.
T88

[gmcjetpilot]

QUOTE=tacchi88 in blue

"I have never seen a high time engine, as "strong" as a new or low timer. Run is does, but strong, no way."
No argument, new=better, but my 2200hr Lycs ran great.


"As for differential compression, it is not mandatory, and is suggested only.....As to being conclusive, that is absolutely false."
Again no one said it is conclusive but it is a tool that can root out obvious and not so obvious.


Lycomings the bores are tapered, and are tightest of the top............but still the least wear is at the top of the cylinder.
True but that is where the bang happens and the highest pressure is. Compression rings control, not piston clearance.


"on the way up when it's trying to compress what ever it "sucked it" it will lose some of it's ability for complete compression from leakage."
"Big picture": low static thrust, top speed, climb, not to mention "symptoms" of a weak engine: Diff Comp Check, Oil analysis, Oil use, Oil temps/pressures, CHT and EGT. You mention blow by. Great Check: take oil dip-sitck out, cap with hose to sensitive press gage (some use altimeters) and go fly.


"As to tolerances, you will find that most Briggs and Stratton engines (as well as others) operate with with .002 to .003 piston clearance from new, and are considered worn at .005 to .006 depending on model. Most Lycoming are set up new at .010 to .012, and maximum allowed to .018 to .022 depending on model."
Do you know why? OK its because of the size of the jugs. Thermal expansion. The bigger the jug the more variation is dimension. A small aircooled engine has a small piston. Lyc? 5.125 inch dia! Your tolerance rant holds no sway and makes even less of a point. You have a HANG UP over air cooled engine technology, clearly. It's that way on purpose by design. What can I say to you. It's not lack of technology, it is engineering and material physical limits, which apply as much today as they always have. Get over it, or put a Subaru what ever on. Nuff


"It doesn't take a wizard to see that Lycs and Contis not only are oil burners, right from the factory, but all the time."
You do know what oil control rings do? They expand and keep contact with the cylinder bore. Air cooled engines, BIG BORE ones will always use oil. OIL IS USED TO COOL AS WELL.

Two stokes use oil for lubrication. Rotary engines (Wankel) use oil (to lube seal). In the case of the Lyc it is splashed on the cylinders. In two stokes or Rotary it is mixed with the gas. What I am saying is who cares? It is designed like that, on purpose. A Lyc uses less oil than a Wankel engine.


"Lycoming engineers are stuck in the 30s, and still don't know how to make a crankshaft. The recent AD will bear that out. "
You're talking through your hat. The Crank issue was a communication, manufacturing issue. The metallurgy, the NC machine tools, tolerances and processes are not primitive. They have been updated. Whats your agenda? You are wrong, again.


"no differential compression method was ever use to determine their lives. It was a spin test."
I think someone else addressed you spin test. I agree interesting but useless, as I pointed out to you. I had a perfectly good engine that showed good "spin compression" but the differential test showed a problem with ease. The reason was when the valve slammed shut under load it sealed, static it leaked badly.


"Even as archaic as they once were, they would outlast any AC engine."
You frustrate me because you throw this stuff as fact. Prove it. I know you're and auto engine fan; you think they last longer than a Lycoming. Of course we don't know because few 6,200 RPM machines fly or have gained significant time. A Lyc at 2,400 RPM, cruising 120mph (Cessna), times 2000 hours, you're looking at 240,000 miles. At least ++10 yrs service for typ pvt owned plane. Now take my 225,000mile Acura, still going OK. On the highway it's loping along at 15% power? Now if ran at 75% or more all the time, it would have been junk long ago. Its starting to use more oil & make valve noise. Your logic is faulty, and I disagree.


"As to the auto guys, they have some valid points. If the engine is made to run as it does in the auto it came from, it is a great choice. Albeit with some weight increase, still reliability factor and economy of fuel and oil is an excellent advantage."
Ahaaa, your true colors come out. No it is NOT a GREAT CHOICE. It is a cluster of compromises and make do's. If so great why do they burn more gas, fly slower and are heavier than an antique Lycoming? You are, sadly wrong again.


"The only advantages are ease of manufacturing. In racing, although not so much nowadays, straight cut gears require less power to operate, but also wear much faster, but that's racing. "
Dude, you would not know a straight cut gear to save your life. So I'm dying to know what you think is a superior gear type is? Look at a Lycoming accessory gear. Look at one tooth. Look at the sides. They are have a very precise "involute" curve. You make outrageous claims like "they wear faster". Prove your it. Ridiculous.


In the real world, and considering oil samples, we would see more steel present than say a typical auto engine. "real world" What are you talking about? I have no idea. What's the point.


"As to air cooled engine requiring more tolerance, as I stated previously."
No I am the one who stated it, several times. I am glad you said something I agree with.


"We can also mention motorcycles which typically run in bumper to bumper traffic without the aid of air flow, and most are ready for the scrap heap should they ever exibit even new tolerances of a Ly/Con."
You say all kind of things, wrong. Ever heard of a BMW "Boxer" motorcycle. They go 80,000 before they even break-in and 200,000 to 300,000 miles is not uncommon. They are AIR COOLED. BMW R1150RT AIR cooled engines are also liquid cooled? WHAT! Yes the BMW, like the Lyc are OIL COOLED. That is what cools the valves and the reason for the big oil cooler.


"The Lycoming engineering had a specific mission, but that was in the 1930s."
In 1938 Lycoming developed the O-145 opposed cylinder engine. The O290, O320 and so on came in 1952 and 55 respectively, NOT 1930. So if you want to be correct its based on 1950's technology, about the time the small block Chevy V8 came out. They use computers to manufacture Lycs today.


"Every internal combustion piston maker, air cooled and other wise has improved, and advanced, while we're still stuck in the 30."
What are you talking about specifically? FADEC, electronic ignition, composite engine parts, ceramic coatings, water-cooled heads, CNC machining? Lyc Check!


"Flipping counter weight cranks were discontinued in the auto world in the 20s. Only the high buck luxury cars had them and very few at that."
You know just enough to be dangerous. Do you know why counter weights are used on SOME engines? (not on 150-180hp 320's, 360's and some 540's). The reason is ENERGY. Direct drive engines with big HP have large power pulses and torsional vibrations in the crank. The counter weights solves that problem. Has nothing to do with cars. Again you're wrong. A Subaru would explode with a prop bolted direct to its puny crank.


"Yes Lycoming are unnecessarily sloppy, the clones not much better...........must meed the same archaic designs and manufacturing methods. They have improved squat."
You have clearly drank too much cool-aid sir:
http://www.eci2fly.com/pages/products_titan_cyl.aspx
http://www.eci2fly.com/pages/products_titan_320.aspx
http://www.superiorairparts.com/piec...Crankshaft.asp
http://www.superiorairparts.com/piec..._Camshafts.asp
http://www.superiorairparts.com/piec...stons&Rods.asp
http://www.superiorairparts.com/pieceParts_Sumps.asp

Superior applies to ECI and Lycoming, so your comment, "They have improved squat", is........well bull. You have facts? You have bought into auto engines for airplane sales pitch. If auto engines are great, they would stand on their own merits. They don't.


Case in point is crankshafts. Ever hear of a crank AD for Briggs and Stratton or Ford?
A batch of cranks from 1999 to 2002. Second it was a service bulletin. The recent AD was for 300 cranks. There have been few to NO failures. Stuff happens, does not take away from design, performance or efficency.


In 28 years involved with aviation, I have yet to meet a Lycoming or Continental to go 2000 hrs without never, I emphasise "never".
Flying freight, CFI, corporate in the smallest SE to large turbo charge twins for years and years in 30 plane fleets, with no major issue, consistently going to TBO. Not to mention 5 planes I'v owned. I guess its YOU, the way you fly and maintain your plane? So there.


What engine will I use in my RV10, you guessed it a Lycoming, and I will "tinker" with it.
You are wrong you got it backwards. You will NOT have to tinker. Auto engines = endless tinkering.


I do not always agree (obviously) but I enjoy them never the less. After all, this whole chat is an exchange of ideas. Too bad the FAA, Lycoming and Continental aren't listening.

Well I got to be honest, I think your comments are wacko and exaggerated, but hey at least they where frustrating. You retired from brewing beer? Right. G

[jdmunzell]

Wow, guys! Come on settle down and stop trying to get the last word. You are both letting it get personal. Disagreements can be healthy, but keep it in check fellas. Besides, when we all meet at OSH or wherever, it would be nice to be able to shake hands and head for the beer tent.

Jeff
8 wings

[Deuskid]

Thank you George and others -

Alternatives are the future [imho] but the aren't the present.

until there is a clear, empherical, verifiable advantage [advantage being defined as a 10% or > improvement in performance, frugality or safety] to an alternative over what is now conventional it is really a matter of taste not a matter or science or principle. I welcome all who are 'blazing' the way but I'll error on the side of convention for myself and loved ones [and appreciatively watch with keen interest those who are bravely blazing the way].

Please, Plez... Paleze.... somebody ... make a fwf installation for a 160 hp auto diesel ... i will all at your feet and repeat "I'm not worthy... I'm not worthy"...

off my soap box

John

[tacchi88]

George,
I know damned well what I'm talking about, but for your info, Lycoming uses straight cut gears (if you understand the term), bore size and clearance have little to do with how much clearance is required. Franklin aircraft engines, you have heard of them, have 5 inch bores and only have .003 worn at .005 not .012 worn at .020 as in Lyc.
Anyway you cut it, Lycoming cranks are abysmal. Still making the same stuff, in the same old method, and lots of ADs, which you and I are obliged to pay for, whenever they screw up.
Come on George, now it's getting under your skin. I won't comment on the rest of your "notes', suffice it to say, they are fun to read.
Have a nice day.
Remember this is a learning/information forum, Lets leave it at that.
BTW, yes I worked for the world's largest brewer, and no George I never drank on the job. However, your ramblings are suspecious..........Hmmm, I even spelled your name correctly. I'm learning.
T88

[gmcjetpilot]

Originally Posted by tacchi88

George, Have a nice day. BTW, yes I worked for the world's largest brewer, and no George I never drank on the job. However, your ramblings are suspicious..........Hmmm, I even spelled your name correctly.T88

Have a nice day,

Since you are into learning: Gears. Lycoming uses "Spur" gears. You keep saying "straight" as if crude, low tech or there's something better. Trust me I know gears. Seemingly simple on the surface, these spur gears are remarkably powerful and quite complex. Spur gears used in the Lycoming use the "latest" gear technology. To be fair many call them straight, but there is nothing "straight" except that it means the gears are parallel, not at angles. The differential in you car can not use spur gears. The accessory gears in the Lyc has to use "straight" gears.



When gear axis are parallel there are only 3 gear "types" available: Spur, Helical, Herringbone or double helical gears. The Spur gear is the way to go, produces no axial loads, and for the low speed and low loads here, it's ideal.

The teeth shape used in spur gears is what's called "involute". In the late 1800's early 1900's many gears had a "cycloidal" tooth design (which where poor). Involute came around the 1890's and dominated after the 1920's. It is still the "state of the art" in gears. There is nothing crude, simple or LESS as you imply when you say "they use straight gears!", OK. There not straight, they are spur gears, high strength steel, proper hardness and very powerful "involute" (curved) teeth.

There are differnt types of gear designs, but they are not suitable for this parallel application:

Bevel gears: Straight bevel, "Zerol" bevel, Spiral bevel;
Hypoid gears: Crossed helical gears, Worm gears
and the special Rack and Pinion, to name a few.

T88, another thing you mention is backlash. Backlash, depends on operation velocities, lubrication, loads, tooth pitch and gear center to center. Trust me the Lycoming accessory case gears as designed are a work of art. It could not be done better if designed from scratch today. Trust me. The backlash is what the design manual calls for. They could make it "tighter" but it would serve little purpose and only increase cost. The "slop" is normal and needed with any gear set, including spur gears.

Nuff said on gears, but please don't keep saying STRAIGHT GEARS!, Backlash! like it is bad or primitive. It is anything but. Gear design is something that seems simple on the surface, is remarkably complex in practice, and by no means is it elementary. Those engineers in the 50's knew their stuff, and I was not even born than. Basic machine elements has not changes much or at all in 50 years (100 years). You insult the engineering profession and the men that designed these engines when you willy-nilly throw comments out implying the design is deficient. With all due respect you don't know. Same with car engines, they are a modern marvels, but they where designed for cars, not planes. Can they be adapted? Yea. It is not the engine itself, it's the adaptation in the airframe.

If you never designed anything, than trying to explain the design trade-offs and compromises in an engine is impossible. It's like trying to explain what sex is like to a virgin. A direct drive aircraft engine with a prop bolted direct to the crank is an engineering challenge. These cranks are OVER BUILT. The reason for the AD's is everything has to be perfect. That is why they recall them, to err on the side of conservatism. Also its good there being monitored so close, not that the recent screw ups (from 1997 on) are OK.

As far as cranks AD's you throw it out like an insult. Yep it sucks and is screwed up, but don't spin it, put it in perspective. We are talking about +50 years of service, and most of the problems have been with NEW parts built-in the last 8 years! The other crank problems are with a few older cranks that where corroded. NOT a design or manufacture fault, dis-use and poor maintenance.

When an auto engine guy post a NTSB report of a rare crank or rod failure and says, "SEE", I shake my head. Many an auto engine has come out of the sky involuntarily. When a 1000 auto engines fly a total of a million hours, lets talk. I guess I'll fall back on my old, flying is dangerous, the engine internal mechanics is the least of any single engine airman's worries, lycoming, mazda, or subaru. There is no doubt the crank on a Lycoming is complicated and critical, but it is designed for it. (see tongue in cheek picture): Crank me-up Subaru makes a nice crank and has 5 main journals, but that is because its small bore (displacement) engine and there's room to fit them in with out making the engine too long. However clearly its not designed to take torsional loads of a prop directly bolted to the crank, which is fine since its designed for a car. (I don't say enough nice things about Mazda or Subaru, but others do that; the engineers designed these engines well with "compromises" for an automotive application. They can be safely converted to aircraft use, but there are other issues outside the engine case that are still a challenge.)


An AD caught the 660 affected cranks made after March 1999. Lycoming paid for all cost in full. I believe there was a failure on a brand new late model C182. What really started it was a Piper Warrior that had a crank flange fail due to corrosion in the early 1990's. Again not a defect, just poor maintenance. This put the spot light on cranks, even if unrelated.

Than there is the SB, which as you know is not mandatory. Lycoming calls for the retirement of 5100-serial-number specific crankshafts made between 1997 and 2002. Lycoming says it has found no failures in this lot of crankshafts but, nonetheless, wants owners to replace them at the first opportunity? Whisky Tango Foxtrot? Lycoming will sell you the crank and parts kit for $2000, with no labor. I agree this sucks, but again its not the design, it was a failure of "modern" manufacturing in the late 1990s.

The last AD was for 300 late model engines with counterweights. Again to Lycomings credit all cost are paid in full. Also in this case there where no failures attributed to this AD.

To put it in perspective, very few Lyc cranks have failed in the millions of hours flown over the last 50 years. My circa 1970's O360A1A is a brick house, a proverbial "bullet proof" engine. If you look up the history, up to about 8 years ago, the record was pretty awesome on cranks. I am not sure but the "fatigue life" of the cranks are like 30,000 hours. In large commercial aircraft fleets (freight) cranks go 3 or more rebuilds, but they have to made per design and material specs. There is no almost, it has to be perfect. Made correctly the cranks are robust and reliable.

Teledyne Continental had the Airmelt / "vacuum arc remelt" (VAR) mess in the early 90's. Here they changed process to the better VAR and had problems. They tried this NEW and improved high tech process. See what you get. If it ain't broke don't fix it. Its also a tribute to the fact the engineers and craftsman that made these engines knew what they where doing. Just because it is OLD does not make it bad, take you for example.

T88 the point I am trying to drive home is this is an AIRCRAFT ENGINE designed for aircraft use. To get a light weight, direct drive aircooled engines took lots of skill and cunning to achieve a "balanced design". What you see as a huge design fault, is really a clever combination of choices. Same with auto engines. They have their unique qualities that well suited for a car, but in a plane they may be of less importance or even a liability.

If you where building a scratch aircraft engine and had to balance all design requirements, you very well may end up with an aircooled, direct drive, horizontal opposed engine. Not sure what all the Lyc ax grinding is about. As far as backlash and piston clearances being lawn mower loose, LOOSE is good baby, let her rip, because my Lyc will "mower" right over you.

As far as piston clearance, we went over that several times so no need to repeat, but the rings seal, not the piston. The piston clearance does not affect the oil use or compression. As you know the rings are "compressed" when installed and are sprung against the cylinder wall, so the gap is as thick as the oil film. As the cylinder wears the rings will adjust some what. After a while the rings wear too much or they cylinder, producing less compression. However with modern materials the wear of the cylinder is very small. Most Ring/Cylinders have compatible materials so the ring is "sacrificial" more than the cylinder. However you can bring a cylinder back up to specs. In the old days they used chrome, but it was hard to break in. The good part was it lasted. Now with new cylinders being cheap you just replace them many times. So Piston Cylinder clearance is for thermal expansion and proper oil control. To say the clearance is somehow crude or bad is just incorrect. To make tighter tolerances, which they could, would only cause more heat and wear. Loose is good. (see page 12, plasma coated top compression ring)
http://www.eci2fly.com/pdf/titanbooklet.pdf

Last never said you drank on the job, and I am a tea totaler, but I think you are driving me to drink. Just kidding T88, have a great week. George

[AllanB]

Whatever happened to the old adage "If it aint broke, don't fix it".