Help / Brain Cells Request Continental O-300 Problem

[Dan Thomas]

In 2o year of Alon flying before my 172 now, Never had lead fouling. Frequent oil changes too. The Lyc o235 doen;'t make enough heat to do toast. Its a lead generator.!
Does any one know what Lyc recommends for oil change intervals??
Excuse my long winded ness.

Lyc recommends 25 hours for an engine using a filter screen, 50 for one with a full-flow filter (spin-on filter).

Use the UREM37BY plugs in the O-235. They're the only plugs that will not foul up in that engine.

 

[planewrench]

Lyc recommends 25 hours for an engine using a filter screen, 50 for one with a full-flow filter (spin-on filter).

Use the UREM37BY plugs in the O-235. They're the only plugs that will not foul up in that engine.

Also,, and this always gets missed, QUARTERLY oil changes regardless of hours flown.
carl

 

[Victor Bravo]

My understanding is that it's not the TCM or Lycoming build-ups on the factory floor that are the problem. It's the guys who do it in the field on an engine that's mounted in an airplane.

And it is also my understanding that most of the field work is OK, it's just that there is a higher instance of insufficient thru-bolt stretch and "bearing crush" on field cylinder replacements than "real engine shop" cylinder replacements.

I'm a somewhat inexperienced mechanic... I've never done any of this professionally. So I accept that it takes me 5X longer to do anything than it takes a working mechanic.

I am very glad to have all these opinions from different sources, some of whom are mroe experienced, some of whom are professional mechanics, and some of whom are amateurs. I consider all of these opinions, whether I agree or not.

 

[TFF]

For a big Continental twin, tops are pretty normal fair. It’s where the chromed cylinder made their money. Like everything today, we collectively are scarred to put our name on it. Being an A&P is a stick your neck out business. I went to take a glider intro flight, years ago, and the guy, a lawyer, who signed me in said it’s a solid contract so don’t try to sue it you crash. I laughed at him and said the A&P who signed the logs signed stuff you could never recommend a client to sign.

Nature of the business on both sides. We are forgetting that and wanting to put on goggles so we can pretend. Sloppy mechanicing, worn out parts, just bad luck can happen. If you intentionally work on those issues, bad stuff is rare. For the thousands of topped cylinders that go on this year, it’s the one that only gets the attention. Hmmm, sounds like how we handle all media today. For the guy writing the articles, it only means he is not practicing being a mechanic to pay the rent anymore and can stand back. That’s the kind or writing that keeps new boots on the ground. Wonder why there is a lack of new A&Ps?

 

[planewrench]

For a big Continental twin, tops are pretty normal fair. It’s where the chromed cylinder made their money. Like everything today, we collectively are scarred to put our name on it. Being an A&P is a stick your neck out business. I went to take a glider intro flight, years ago, and the guy, a lawyer, who signed me in said it’s a solid contract so don’t try to sue it you crash. I laughed at him and said the A&P who signed the logs signed stuff you could never recommend a client to sign.

Nature of the business on both sides. We are forgetting that and wanting to put on goggles so we can pretend. Sloppy mechanicing, worn out parts, just bad luck can happen. If you intentionally work on those issues, bad stuff is rare. For the thousands of topped cylinders that go on this year, it’s the one that only gets the attention. Hmmm, sounds like how we handle all media today. For the guy writing the articles, it only means he is not practicing being a mechanic to pay the rent anymore and can stand back. That’s the kind or writing that keeps new boots on the ground. Wonder why there is a lack of new A&Ps?

Exactly, thanks,, sure there is risk, unfortuantely some capitalize on the fear factor to further carreers and reputations. Couple years back, I was doing two cylinders on a Champ c90. After torqueing them down the crank was hard to turn. Bring this only the second time i had done cylinders,, ( in my 40 plus years) i knew exactly where the problem was despite my being very carefull and aware of the job i was doing. Eventually we ended up doing a overhaul due to a spun/misplaced main bearing. Hey, this happens. But Rare. It was a high time engine, mismatch of all the cylinders so it was on borrowed time . Would you rather find this on a maintenance event or over lake Superior?
I love working and helping to train and inform newby mechanics,,, if they want to learn. My experience level is getting rare,,, the mechanic shortage is as epidemic as Covid is. How do you think i feel when i see mechanics doing this? ( see phot) ( yes, thats a shim on a crankshaft ! )
Carl

 

[TFF]

I’m not showing it to a friend. In fun. I watched this friend make two double hops down the runway. I asked him the next day and he said the engine would quilt, and when he landed it would start running and he would try it again until he ran out of runway.

The plane had an off field landing before, prop strike, and old style prop strike inspection as in put a new prop on. The crank was bent pretty good. No one looked. The original prop was metal, the first replacement was wood borrowed from someone else. That guy asked for it back so a new metal one went on. The wood dampened everything so no one payed attention. The metal shook and was shaking all the fuel out the float bowl. At idle it would catch up.

He did have a new crank. That was put in. This guy is 90+ and lived a life of aviation. Aviation was not going to be the cause of death for this guy. So the saying forgot more than the next guy knew applied. It’s the people who get his stuff next have to worry.

 

[Victor Bravo]

First, for the highly experienced mechanics here who have been doing engines for many years and know this stuff inside out.... you can have a good laugh at my expense. You can laugh your keester off at how big of a deal I'm making over something that is probably simple or straightforward to you, and then you can laugh your keester off twice over how much of a big discussion this has caused here. I don't take any offense, and I'm very thankful to have people here who can offer some brain cells in areas where I fall short. I'll return the favor somewhere down the road where I'm the one with some useful experience or talent

And with that soaring preamble... Last night before bed I watched the Mike Busch video and looked at his matching website page again.

In terms of mechanical principles and basic physics, I cannot find any fault with his description of why cylinder installations are somewhat higher risk on a "field replacement" basis compared to a new engine build or full shop overhaul.

His reasons are 1) fastener thread wear, 2) loss of the cad plating layer on stud and nut threads, 3) the likelihood of used through-bolts being present instead of new ones, and 4) poor wrench access affecting how smoothly and uniformly you can apply the torque to the base nut.

He also goes on further to postulate that plain engine oil is a poor choice as the fastener lubricant, and other high pressure lubes like Moly grease would yield better pre-load (bolt stretch) which is the root of the problem.

So I made an assessment of what I have going for me and going against me. My cylinder base nuts were new when I started this, and so are "near new" now. My through-bolts are used, likely original, but the threads are in fairly good shape. I removed everything off of the engine that would impede wrench access, except the pushrod housing tubes which are more or less built in to the cylinder. One cylinder base nut has a built-in limit of about 20 degrees of wrench rotation, so if you don't hit the torque in that arc you fall into the "breakout force" issue that Mike speaks about.

On big thing I have going for me is that I will cheerfully use the Moly grease instead of engine oil, which will likely overcome some of the negative factors that result in lower preload. The factory manual procedures were written before Moly grease was in widespread daily use; I'm sure it was considered an exotic material in 1948 or whenever the original O-300 overhaul manual was written.

 

[Dan Thomas]

The factory manual procedures were written before Moly grease was in widespread daily use; I'm sure it was considered an exotic material in 1948 or whenever the original O-300 overhaul manual was written.

Moly grease has been around a long time. I was selling a moly-based oil in the mid-1970s.

From Molybdenum Disulfide -The Ideal Solid Lubricant and Anti-Galling Material | Valin

The United States National Advisory Committee for Aeronautics, the precursor to NASA, the National Aeronautics and Space Administration, initiated research on aerospace uses of molybdenum disulfide in 1946. These investigations resulted in extensive applications in spacecraft3, including the extendible legs on the Apollo Lunar Module. Applications continue to expand as new technologies evolve requiring reliable lubrication and resistance to galling under increasingly stringent conditions of temperature, pressure, vacuum, corrosive environments, process sensitivity to contamination, product life, and maintenance requirements.

If Continental thought it was a good idea, they're be specifying it in their current manuals, but they don't. Their Standard Practices Manual says this on page 10-34:



And from the Lycoming Direct-Drive overhaul manual:



They specify these lubricants because they have a known amount of lubricity, making the torque and stud-strength calculations consistent. Molybdenum Disulfide greases or oils are extremely slippery under pressure, similar to Never-Seize, and the stud can be put under more stress with it at the specified torques. Further, that stuff might allow the nuts to creep loose in operation. Oils will get squeezed out before the engine runs; the moly molecules will stay in there.

 

[Victor Bravo]

So which "Parker Thread Lube" product does Lycoming specify?

Google shows dozens of Parker and Parker-Hannifin lubricants listed for threaded fasteners.

Is the Continental manual lubrication call-out calibrated for re-installation of a cylinder in the field, or is this the manual that they assume will be used in an engine shop with brand new through-bolts? Physics tells us that there should and must be a difference.

 

[TFF]

The manual has everything. Some things are obvious and some are not. Changing the kind of oil will change the torque from how the factory calibrated the fastener. Percentage of difference, who knows without testing. Are we changing better because we think something is better? Do we have new torque specs? The torque is calibrated to certain conditions. No oil, correct oil, super slippery oil will stretch the same bolt different. Some under, some over,and some just right.

Independent shop overhaul verses sending it to Continental or Lycoming is going to see a lot of these fasteners be reused. If case fasteners are not on the Lycoming parts overhaul list, it’s on condition. A factory overhaul is essentially a new engine. Quality control is the same, and the factories know the backlash of something wrong out of the factory is way worse than getting Bob to overhaul your engine. The definition of overhaul from the FAA is different from what the factory wants you to do. It’s the mechanics job to reconcile both. The flip side is I have to be Bob for my airplane. I have to look at it and make a call. How good Bob studies it is how good Bob is. A customer aircraft is always in between. Some stuff is not worth it. New or it’s not getting fixed. Sometimes it’s getting to the goal line. 200 hours to TBO on something a company will use up in six months, is different from 200 hours for the next thirty years. One you can monitor, one is same as forever. Both require correct repair, but they are not necessarily the same repair. Is this an A-65 on a Flybaby or is this a Barron owner who like to fly to Europe when the season is right?

 

[TFF]

http://pceonline.com/wp-content/uploads/2017/04/M-0standardpractice2017-01-15.pdf

Chapter 3.

 

[Victor Bravo]

Thanks TFF, the OEM overhaul mannual does not give me the cylinder base nut torque'ing sequence and this manual does

 

[Dan Thomas]

FAR 43:

43.13 Performance rules (general).

(a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator, except as noted in § 43.16. He shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices. If special equipment or test apparatus is recommended by the manufacturer involved, he must use that equipment or apparatus or its equivalent acceptable to the Administrator.

This is where so many problems arise. Just doing it however one wants to. I have spent too many years fixing airplanes "repaired" by people who didn't consult the manuals. Probably didn't even have them.

Flight control rigging is another area that gets thoroughly messed up when the manuals aren't followed. Fix them, and see the owner's face when he comes back after a test flight.

 

[Victor Bravo]

One FAA approved Continental maintenance and overhaul manual had a different amount of information than the other FAA approved Continental general practices manual that was referenced above.

The O-300 overhaul manual says to tighten the cylinder base nuts to the torque listed in the appendix. Not in any order. Not in any number of steps. Not using any technique or approach.

The much larger and more thorough "practices" manual referred above refers the mechanic to the cross-pattern tightening sequence listed in an appendix, and then tells the mechanic to tighten all the nuts halfway to final torque (in another appendix), then go back and tighten them fully, using a certain technique (in one smooth motion) which is in keeping with the way Mike Busch's video suggests.

So it looks like it would have been perfectly legal to either have the overhaul manual on the bench and do it one way, or have the practtices manual on the bench and do it another (more thorough) way.

 

[proppastie]

Any mechanic having worked on car or motorcycle engines should know about cross pattern and incremental torque.... often it seems like those with no experience will tackle an aircraft engine because of cost considerations.... often successfully... sometimes not. Understanding that a current overhaul manual and the phone number for the factory representative is needed often escapes the inexperienced. The really hard part is as you said there is vital information scattered around in service bulletins and service instructions.

 

[Dan Thomas]

One FAA approved Continental maintenance and overhaul manual had a different amount of information than the other FAA approved Continental general practices manual that was referenced above.

That's why the FARs require the most current manuals. I have seen the same thing in Lycoming and Cessna manuals. Problems crop up, and so they revise the manuals to correct the problem. Cessna and Lycoming and Continental, among most others, send out revisions to subscribers to their manual programs.

Airplanes are aging. They corrode, they fatigue and crack, vibration loosens stuff. When Cessna brought out the 172 in 1956, aviation was only 53 years old. The guys that designed and built these airplanes had no idea that we would still be using them 66 years later. They likely figured that the phenomenal advances in airframes and piston engines between 1930 and 1950 would continue at that pace, making their designs obsolete in a few years. The technology didn't advance like that, though, and we're still buying and selling and using ancient airplanes, mostly because new airplanes are so expensive. So the manufacturers of airframes, engines and propellers issue revisions to their manuals as problems show up. The O-300 is an old engine and hasn't been produced in a long time, but Continental still updates its overhaul manual. The manual you have is likely an older version.




O-300 manual last revised in 2011. Even the much older E-series engine manuals were updated in 2011. If there are differences between the 2011 O-300 manual and the 2021 M-O Standard Practices Manual, it just means that they haven't gotten around to revising the O-300 manual yet. They will. Even then, Human Factors says that there will be discrepancies, most of them minor. Nobody is perfect. Not even Continental.

Many larger manuals will have a List of Effective Pages right up front, to show which pages were revised and when.

Cessna will issue Temporary Revisions to their manuals, and then once in a while they will issue a new manual that incorporates all those revisions. Their manuals are getting thicker all the time. One that probably applies to your airplane is addressed here on another discussion forum: The International Cessna 170 Association • View topic - ALERT: Failed Landing Gear Spring Strut (ACS)

Some serious stuff. I've had to deal with it.

 

[Victor Bravo]

Update Friday night:

Tonight was Official Torque Wrench Night. I had a conversation with a local IA with years of engine rebuild experience,a nd he agreed with one of the recent posts in this thread that using too slippery of a lubricant is problematic on its own. He strongly supported the "clean 50 weight engine oil" in the factory manual, so I did that. Applied a liberal coating of new Aeroshell 100 with alittle brsh on the threads, nut face, and cylinder mount flange.

The book specs for O-200 and O-300 cylinders are the same, 35 foot pounds on the small nuts and 42 pounds on the large nuts, plus or minus half a foot pound. I went to 50% of torque on all nuts, including the "undisturbed side" nuts on the through bolts. Then I went back and reset the wrench to 100% and final-torqued them, then went back and made the wrench click one more time to be certain.

The 2nuts on the "undisturbed side" through bolt did rotate 1/3 of a turn, so it proved that removing the cylinder did in fact allow the through bolts to relax or move a few thousandth on the undisturbed side.

 

[Victor Bravo]

Update 4-8-2022

I have about five or six hours on the O-300 after all this long and lurid soap opera you all had to put up with.

It seems to run well, makes all the right noises, doesn't make any inappropriate noises, and in general so far it gives off that same "all's well in the engine room!" vibe that the O-300 is so beloved for.

Removing and re-installing the one cylinder was not necessary in hindsight, and I'll be kickinig myself in the butt over it for a while. But the reinstallation and torquing seems to be holding together well.

The one and only downside so far is that it's using a little more oil than it used before. It always used a modest amount, which I believe was part weeping, part leaking, part burning, part blowing. Now after this work, and removal of the cylinder, it is using a little more. Not catastrophic, but measurable.

The three more experienced engine builders I spoke with have agreed that it might very well break itself back in and come back to the previous amount of oil usage... and it also may not come all the way back. Their best advice seems to be run it for 10-20 hours and see if it starts using less oil.

But so far it is flying well and reliably.

I'm going to go to the next oil change (12-13 hours from now) and do a compression check. I'm also going to put some sort of absorbent pad next to the crankcase breather outlet, and see if and how much oil is leaving that way.

 

[TFF]

Good it’s flying.
While the rings can rotate, if they have been in a while they pretty much build camp in one place. If you repositioned them before you put the cylinders on, they are not in their last home, so to speak. They may even out or find their space back. Other than that you have to ride it out. Sometimes fixing compression leaks at the valves makes the rings have to work harder, when they haven’t been.