To overhaul or not?

[healthfx]

Twenty year old, factory overhaul engine on m20C, with 400 hours.  Needs two new cylinders.  Is it wise to just replace them or get overhauled engine?  Could the bad cylinders be an indication of future problems with existing engine?

[LANCECASPER]

I know your engine is a Lycoming, but here's what Continental says regarding years since overhaul and hours of use since overhaul:

Reason for Revision: Addition of engine to TBO listing. Clarification to Note 1.

SUBJECT: TIME BETWEEN OVERHAUL PERIODS

PURPOSE: PROVIDES TIME LIMITS BETWEEN MAJOR OVERHAULS

MODELS

AFFECTED: ALL

Teledyne Continental Motors (TCM) and the aircraft manufacturers provide operational limitations and instructions for your engine along with the requirements for continued airworthiness as specified in the engine Operators, Maintenance and Overhaul Manuals and Service Bulletins. TheTime Between Engine Overhaul (TBO) provided in this Service Information Letter apply only to engines that have been operated and maintained in accordance with these instructions. Engine

mounted components and accessories require overhaul at the same hourly and calendar intervals as the engine, unless otherwise specified by the component or accessory manufacturer.

An engine’s published TBO DOES NOT mean that every engine will operate the number of hours or years listed without requiring component replacements and unscheduled maintenance events. Non compliance with TCM’s instructions for continued airworthiness, operational and environmental factors may necessitate repair or replacement of the engine, engine components and accessories.

 

TCM recommends that the following information be used, along with the engine’s published TBO, in determining the engine’s continued airworthiness:

1. Whether the engine has been operated regularly or has been in storage; gaskets, seals synthetic and natural rubber goods deteriorate over time. Environmental corrosion can occur internally and externally on the engine. This naturally occurring process can inevitably affect continued airworthiness of the engine and engine mounted components and accessories. For these reasons, overhaul the engine at least every twelve (12) years, or on accumulation of the operating hours listed for the engine model.

2. For aircraft used in aerial spraying, overhaul the engine after the accumulation of 1200 hours or twelve (12) years whichever occurs first.

 

3. Aircraft used in parachute jumping, glider towing, banner towing, etc., may require more frequent engine overhauls than listed for the specific engine.

 

4. The quality of parts, accessories and workmanship utilized during routine maintenance, engine top overhaul and major overhaul directly affect the service life of the engine. The TBO’s listed are predicated on the engine having been maintained in accordance with TCM’s FAA approved instructions for continued airworthiness specified in the engine Maintenance Manual, Overhaul Manual, and Service Bulletins and operated within the limitations published in TCM’s Engine Operators Manual and the aircraft manufacturer’s Aircraft Flight Manual / Pilots Operating Handbook (AFM / POH)

 

5. TCM cannot provide a TBO for engines that: 

 • Have been assembled with non-TCM approved parts.

• Have been assembled with parts that do

not conform to the original type design

for the engine.

 

• Have been modified from the original

type certificate configuration.

 

• Have been overhauled or repaired in a

manner that is inconsistent with the

specifications, limits, and instructions

provided in the TCM engine overhaul

manuals, service bulletins, parts catalogs,

and FAA Air Worthiness Directives.

[danb35]

What's wrong with the two cylinders?

[jetdriven]

TCM and Lycoming both advise every 12 years or 2,000 hours.  Some TCM engines are lower, like 1,800 or 1,600 hours.  This is a recommmendation only and is their best guess.  My McCauley prop says every 1,500 hours or 6 years, guess what, both have 11 years on them.  Im not overhauling either until they show signs of needing it.

Mike Busch says why waste its useful life?  A cylinder is a bolt on item, treat it like an accessory such as a magneto or alternator.  Cylinder goes bad, replace that cylinder, not all of them. Busch has several Savvy Aviator colums that are good reading and has webinars at www.savvymx.com as well. I do not work for him, although I do agree in his philosophy. 

If the engine is not making metal and is good otherwise, put two rebuilt or overhauled cylinders on there.  Those are around 500$ each. If you can get a shop to overhaul yours and send them back, all the better.  You will be into the job for 2K and if the engine lasts 200 hours longer, which it should, the cylinders (and the engine time) are free.

 

[1964-M20E]

I’m with jetdriven if you are not seeing any other signs of trouble replace the two cylinders and keep on flying.  I’m not a metallurgist but as far as I know if steel and aluminum are not experiencing corrosion or extreme temperatures they have the same properties they had the day the left the foundry or manufacturing process.  Steel and aluminum do not age like us.

[tony]

I agree with jetdriven;  another vote to make the repair and keep going

[N601RX]

Quote: healthfx

Twenty year old, factory overhaul engine on m20C, with 400 hours.  Needs two new cylinders.  Is it wise to just replace them or get overhauled engine?  Could the bad cylinders be an indication of future problems with existing engine?

[Skybrd]

Quote: healthfx

Twenty year old, factory overhaul engine on m20C, with 400 hours.  Needs two new cylinders.  Is it wise to just replace them or get overhauled engine?  Could the bad cylinders be an indication of future problems with existing engine?

[jetdriven]

The labor to R&R 4 cylinders is twice what it costs to replace 2 of them.  Plus the other two are fine so why be so invasive, and spend money.  Further, if you turn the crank with all 4 cylinders off the through-studs that hold the main bearings together are not torqued so you run the risk of ruining the crank when the bearings spin.

watch this webinar, we saw Mike at OSH in person he is the real deal. 

http://www.eaavideo.org/video.aspx?v=991490765001

Now ask yourself this, do you R&R 2 cylinders and go on flying?  All 4?  Or major the engine?  And based on what?  Facts or old wives tales and "my mechanic said so".

Quote: N601RX

There is very little labor difference in removing and replacing 2 cylinders or 4.  I would go ahead and remove all 4 and get a good look at the camshaft and lifters. This will also let you get a good look at the 2 cylinders that are still belived to be good.  If the cam and lifters looks okay there is no reason to replace the engine.  Get some quotes for overhauling your cylinders and decide if you want to replace the 2 bad ones or go ahead and replace all 4 of them.

[rbridges]

let me ask a stupid question.  Don't most engines have a recommended overhaul based on hours and years (like the continental guideline above)?  Is it just a guideline to cover the manufacturer in case an issue arises?

[fantom]

There are no (OK, a few) stupid questions.

YES, and YES http://www.mooneyspace.com/clipart-4260.html'>

 

[MARZ]

Quote: danb35

What's wrong with the two cylinders?

[Gunderbear]

just bought a plane with 2 bad cylinders and one at low 70's.  the fourth was high for one reason, the cam lob was wore down so much it couldn't open the valves.  high compressions do not mean all is well under the hood.  Oil test showed no metals from the cam either!  My sweet buy turned bitter quick.  The engine is now at Mena Aircraft.  The reason for the bad condidtion??? only 100 hours in 10 years.  don't let your planes sit!  at least start them every week.

[N601RX]

Quote: Gunderbear

just bought a plane with 2 bad cylinders and one at low 70's.  the fourth was high for one reason, the cam lob was wore down so much it couldn't open the valves.  high compressions do not mean all is well under the hood.  Oil test showed no metals from the cam either!  My sweet buy turned bitter quick.  The engine is now at Mena Aircraft.  The reason for the bad condidtion??? only 100 hours in 10 years.  don't let your planes sit!  at least start them every week.

[jetdriven]

Running the engine on the ground doesnt extend its life any at all either.  You are spreading oil around inside the engine but are also adding water vapor (condenses into water and sludge) inside it as well, which increases corrosion.

Fly the aircraft every 14 days or less and use camguard.  Low engine use in Arizona isnt the same as low use in Florida.

Quote: Gunderbear

just bought a plane with 2 bad cylinders and one at low 70's.  the fourth was high for one reason, the cam lob was wore down so much it couldn't open the valves.  high compressions do not mean all is well under the hood.  Oil test showed no metals from the cam either!  My sweet buy turned bitter quick.  The engine is now at Mena Aircraft.  The reason for the bad condidtion??? only 100 hours in 10 years.  don't let your planes sit!  at least start them every week.

[DaV8or]

In addition, I have also read that you have to fly the plane for about an hour to boil off the acids. Ground running doesn't work because it doesn't get hot enough and less than an hour or so flight isn't enough time to thouroughly boil it all off.

Seems like someone could invent an oil cooker to keep in the hangar for those that don't fly often enough. It would work like this, when you put your plane away, you would hook up a hose to you quick drain and drain all the oil into the cooker. It would be electric and on a timer. It would then heat and circulate your oil to get all the harmful things out. Then, when you want to go fly again, during preflight you would just pour the same oil back in. 

Any reasons why this wouldn't work?

[Hank]

Dave,

That would certainly work if cooked oil is what you want. Personally, I prefer an oiled-up engine, and don't see how draining the oil out will keep the inside of my engine from corroding. Maybe an oil recirculating pump, from the quick drain back to the fill tube, and pass it through a dessicant chamber to remove moisture. Then all it will need is an internal method to get it to the top of all four cylinders, so it will coat the walls and the pistons . . . Oh, the internal distribution should be even around the cylinder walls, not just a single-location drip in each one.

Getting the moisture out of the oil is not the only target--gotta keep the moisture-free oil distributed throughout the engine.

[jetdriven]

The Mooneyland guy has an idea for a dessicant device you put in the tailpipe and the dessicant beads absorb moisture.  But face it, the only way to prevent corrosion damage to you engine is to fly it every 10-14 days minimum, and for at least 20 minutes I have read but an hour is better.  IF not, Lycoming has a procedure to fill the case with preserving ol and squirt this oil in the spark plugs andf use dessicant plugs.

[healthfx]

Thanks for the tips.  They really helped.  The problem was a cracked exhaust valve, and a burnt one. Once pulled we looked closer at engine.  No corrosion, as also show my constant oil analysis.  Rebuilt cylinders.  Putting on now.  Will be running Marvels Mystery oil.  Looked into overhaul based on years on engine, and only having 400 hours on it. 

According to Lycoming any engine that is over  2000 flight hours or 12 years since overhaul must be overhauled. Using that criteria the engine is over TBO. That being said this is something mandated by the manufacturer, not the FAA, so it is not required for part 91 operators.  Updated pics coming soon!  Anything I should look for in particular when flying out of this annual for the first few times?