Corona Engines Overhaul or Factory Overhaul (or just cylinder replacement)?

[frcabot]

Hi Folks,

I figured I'd start a new thread to get these specific questions answered since the other thread was getting long and a bit off topic. (http://mooneyspace.com/topic/16913-engine-failure)

To sum up:

• I own a Mooney M20J
• The engine has 2100 tach hours SMOH (which is also the total time on engine). It is an IO-360-A3B6D (dual mag)
  • Bottom end was torn down approximately 430 hours ago after previous owner suffered a prop strike.  While it wasn't a complete bottom overhaul apparently, it seemed like a comprehensive inspect & repair job.  The log entry reads as follows:
    • "Disassemble engine & inspect for prop strike. Magnaflux crankshaft & all steel parts. Zyglo case. Check for hidden damage. Counter weights worn. Replace rod nuts & bolts. Replace main & rod bearings. Replace seals, gaskets & c.w parts. Magneto inspection. See listed parts. All current AD's complied with. Reassemble engine, ready for installation."
  • Top was overhauled approximately 1040 tach hours ago.  The Bakersfield mechanic (where the plane is stuck at the moment) says he doesn't consider it an overhaul because the valves were merely "reconditioned" instead of replaced, but I'm skeptical.  The log entry reads as follows:
    • "Removed all cylinders and performed top overhaul.  New pistons and rings installed. Valves and seats reconditioned.  New gaskets and hardware used as needed."  Other stuff too like spark plugs services, oil change, new fuel hose, cleaned fuel nozzles, etc.
• Despite getting an annual inspection in September, I suffered an engine failure a couple weeks ago when an valve broke off and got sucked into the #3 cylinder.
  • At annual, the engine got a clean bill of health and the compressions were 70+ all around.
• The plane is stuck in Bakersfield with a mechanic I'm not really familiar with.  The mechanic stated that there was a lot of aluminum in the oil filter, which is expected since a valve broke off and circulated through.  He says he doesn't feel comfortable just pulling the #3 cylinder and replacing it and thinks I need a major overhaul instead.
  • There is the possibility of hidden damage but he hasn't found any other than to the #3 cylinder piston and the aluminum in the filter.
• Given the high time on engine SMOH, I am leaning towards overhauling the engine (but still could be persuaded otherwise).
• I've narrowed the overhaul down to two options:
  • The first is Corona Engines in Corona, CA.  The price is about $18.6K for a total overhaul.  Does anyone know much about them?  It seems like they are a pretty professional shop, though, and the price is right.  As an added bonus, because they are close they've offered to pick up the engine.
    • That price includes overhauled cylinder (shop says they recommend "fresh ground oversize cylinders," or otherwise plated nickel or chrome, and I'd have the say on any of those options.
    • The price for new cylinders is $23,776
  • The second choice is Air Power, for a factory overhauled engine.  The price is $29,647 (overhauled) or $33,047 (for rebuilt zero time)
    • It would actually be an exchange, as they would replace the A3B6D for an A3B6, with two single mags instead of a dual mag.  This increases reliability.
    • This also includes new roller tappets.
    • I believe both options include new cylinders rather than overhauled cylinders.
    • Round trip freight is an extra $1000, bringing the prices to $30.7K and $34.0K.
  • As you can see, even with new cylinders, there is a significant difference in price.

Questions:

• Given the bottom teardown and top overhaul, and the high time SMOH (2100 hours), does it make more sense to simply replace the #3 cylinder or do an overhaul? I may need to find a new mechanic if I simply pull the cylinder as the Bakersfield mechanic doesn't sound comfortable.  Or at least I'd have to get a second opinion.
  • Does anyone know any reliable mechanics in the Bakersfield area who can give a second opinion?
• Has anyone ever used / heard of Corona Engines?
• Does it make more sense to go with:
  • Replace #3 cylinder only?
  • $18.6K Corona overhaul with overhauled cylinders (but no new roller tappets and keep dual mag system)?
  • $23.7K Corona overhaul with new cylinders (but no new roller tappets and keep dual mag system)?
  • $30.7K Factory overhaul with roller tappets, new cylinders, and upgrade to A3B6 (two single mags)?
  • $34.0K Factory Rebuilt zero time engine and upgrade to A3B6 (two single mags)?

[Andy95W]

Just my humble opinion...

If you plan to sell the airplane in the next 500 hours, $18.6k Corona overhaul with overhauled cylinders.

If you plan to keep the airplane for significantly longer than that, or for 10+ years, $29.7k factory overhaul with roller tappets and no dual magneto.  As soon as you get the engine, swap the magnetos for Bendix and never look back.

Good luck, and I wonder how long it will take for thread creep to happen to this topic...

[jetdriven]

Metal in the filter doesn't mean metal through the bearings.  Pull the governor off and check the screen on the gasket.  If there is metal on that screen then you'd be wise overhauling it.  If rd clean, the filter caught it all and since its aluminum, it's soft, stick an overhauled cylinder with new valves in it and roll on, but monitor carefully.   At next annual, replace all exhaust valves.  

[ArtVandelay]

If 1 valve failed, I'd be suspicious of the rest, it's be through a prop strike already, if it were me, I'd get the rebuilt. Too much bad history.

[cliffy]

1) Corona Engines- I had a cylinder done by them a couple of years ago that has done fine on a twin comanche. Good service, easy to deal with.

2) How many hours on the cylinders? Are they first run or on their 3rd go around? Makes a difference in my mind. 3rd time around, I'd go new cylinders otherwise a good grind and overhaul is fine. 

3) Bottom ends are bottom ends. Will it be a "new limits" bottom end or a "service limits" overhaul. New limits is best. Has the engine ever had a prop strike or a gear up landing and it still has the original crankshaft? You may have a bad crank even if an overhaul/repair was made, check into it when its torn down (been there, done that).

4) Resale value may be somewhat better with a factory engine but probably not equal to the investment delta in the factory engine. What do you plan on doing with the airplane? keep it for years? A good Corona overhaul will be good for that.

JMO

[M20F]

The engine has 2100 SMOH (and total time) and in order to be a major overhaul you have to comply with several things.  Because they didn't do all these things when they did the bottom they can only write it as a repair and return.  This is a paperwork thing, for all practical purposes the lower end went through the same process it would have if a full major had been done.  Thus you have a 430 bottom and a 1040 top, the 2100 is totally irrelevant at this point and means really nothing.  Given the case was just done I personally wouldn't pull the engine out and do a full overhaul.  The cylinders are mid-time and they didn't put new valves in, you lost one.  I would personally overhaul the 3 on there and get a new one to replace the trashed one.  The issue you may have is if the mechanic doesn't want to return it to service you are sort of stuck. 

[frcabot]

23 minutes ago, cliffy said:

1) Corona Engines- I had a cylinder done by them a couple of years ago that has done fine on a twin comanche. Good service, easy to deal with.

2) How many hours on the cylinders? Are they first run or on their 3rd go around? Makes a difference in my mind. 3rd time around, I'd go new cylinders otherwise a good grind and overhaul is fine. 

3) Bottom ends are bottom ends. Will it be a "new limits" bottom end or a "service limits" overhaul. New limits is best. Has the engine ever had a prop strike or a gear up landing and it still has the original crankshaft? You may have a bad crank even if an overhaul/repair was made, check into it when its torn down (been there, done that).

4) Resale value may be somewhat better with a factory engine but probably not equal to the investment delta in the factory engine. What do you plan on doing with the airplane? keep it for years? A good Corona overhaul will be good for that.

JMO

1. Thanks, glad to hear this.

2. First run. The TSOH is also TSNEW. It's the original engine and I'm pretty sure the original cylinders.

3. Corona does everything to new limits. Yes to prop strike and I believe yes to original crankshaft (the crankshaft was "magnafluxed" by the repair shop).

4. Keeping it for a few years at least.  Definitely no immediate plans to sell.  As to the Corona overhaul, would you go for O/H cylinders or new, and why?

[frcabot]

16 minutes ago, M20F said:

The engine has 2100 SMOH (and total time) and in order to be a major overhaul you have to comply with several things.  Because they didn't do all these things when they did the bottom they can only write it as a repair and return.  This is a paperwork thing, for all practical purposes the lower end went through the same process it would have if a full major had been done.  Thus you have a 430 bottom and a 1040 top, the 2100 is totally irrelevant at this point and means really nothing.  Given the case was just done I personally wouldn't pull the engine out and do a full overhaul.  The cylinders are mid-time and they didn't put new valves in, you lost one.  I would personally overhaul the 3 on there and get a new one to replace the trashed one.  The issue you may have is if the mechanic doesn't want to return it to service you are sort of stuck. 

If I do a top overhaul on it (new cylinders, new valves, etc.), it's still going to have 2100 hours SMOH.  If I'm going to be spending however much it costs to do the entire top overhaul, aren't I just better off doing a major haul and getting a 0 hr SMOH engine?

Also, is it really true that the lower end went through the same process? I don't think they repaired/overhauled the parts to "new limits," as a Corona overhaul (or factory overhaul) would.

[M20F]

Just now, frcabot said:

If I do a top overhaul on it (new cylinders, new valves, etc.), it's still going to have 2100 hours SMOH.  If I'm going to be spending however much it costs to do the entire top overhaul, aren't I just better off doing a major haul and getting a 0 hr SMOH engine?

0 SMOH is something written in a log book and certainly can impact resale value with a lot of people.  Your bottom was overhauled 430hrs ago if there is nothing wrong with it why go through the expense of doing it (and the bottom is where the expense is) given it is not even 25% to 2000hrs?  The issue is the cylinders.  If you intend to keep the plane then a repair and return is just as safe.  Once you start doing things to the engine total time means a lot less.  You have 430hr bottom and 1040 top, 2100 again doesn't really mean anything other than that is the total time on the engine.  Make sense?

[garytex]

One of the kickers if you decide to overhaul the existing top,  on the overhauled cylinders if your cylinders are still good, in other words that they're not metal scored or even if they are  and have to be ground oversized and plated, is to keep YOUR cylinders.   They are first run cylinders, and overhauling them is a much better proposition than taking exchange  overhauled cylinders from a pool.

The angle valve cylinders cost about $2600 New,  so people are inclined to overhaul their old cylinders over and over and over much more so than in the parallel valve cylinder world where you can buy a new cylinder for 1100 bucks. So you really want to keep your relatively low hour first run cylinders if you decide to go the overhaul route.

jet driven's got it right,  my feeling is that you should head towards new exhaust valves,  2100 hrs. is a long life for an exhaust valve.

[N601RX]

6 hours ago, jetdriven said:

Metal in the filter doesn't mean metal through the bearings.  Pull the governor off and check the screen on the gasket.  If there is metal on that screen then you'd be wise overhauling it.  If rd clean, the filter caught it all and since its aluminum, it's soft, stick an overhauled cylinder with new valves in it and roll on, but monitor carefully.   At next annual, replace all exhaust valves.  

That is not the way oil flows in a Lycoming. The oil that goes to the governor comes directly from the oil pump and does not go through the oil filter. 

[cliffy]

JMO but you have a relatively good bottom end BUT I would (as an A&P) be skeptical of just doing a cylinder change given the metal in the engine from the valve failure. Too many nooks and crannies for metal to be hiding for my liking. If it was me it would be a tear down and O/H. Should be no surprises (crank aside, mine "had" a magnaflux also but was cracked). Given they are first run cylinders I'd keep them and have them fully overhauled, Cheaper than new, just as good as new. Either way is fine. Me, I'd grind if necessary with new oversize pistons and rings. They MAY measure out good for standard size and new fits maybe not. You might get lucky and not have to grind them. No big deal if you do. You will still need one more for the replacement one. You may be able to find a first run one to match the others. That would be good.

With one cylinder going south at 1000 hrs and just replacing that cylinder would you be riding on borrowed time for another one going bad? Have you looked at the other cylinder's valves with a borescope to see if they are warped or leaking? Have you checked to see if the guides are worn? 

With an O/H you'd be sure things were as good as it gets, if you had to sell your resale price would be better AND your market to sell to would be lots bigger. If I was looking at a plane with a sucked valve and just a cylinder replacement with 2100 TT even considering the bottom end time I'd be walking away. it just doesn't ring good to me. 

[M20F]

7 hours ago, cliffy said:

JMO but you have a relatively good bottom end BUT I would (as an A&P) be skeptical of just doing a cylinder change given the metal in the engine from the valve failure. Too many nooks and crannies for metal to be hiding for my liking. If it was me it would be a tear down and O/H.

Lycoming allows for some fairly large pieces/quantity of metal to be present in the screen/filter.  Assuming the valve parts are found or you are confident they are out of the engine why would you spend $25K plus to take a 400hr case off the plane and break it apart?  That's a lot of money and what it gets I am not sure is anymore piece of mind than just flushing out the engine/governor/etc.

7 hours ago, cliffy said:

With one cylinder going south at 1000 hrs and just replacing that cylinder would you be riding on borrowed time for another one going bad? Have you looked at the other cylinder's valves with a borescope to see if they are warped or leaking? Have you checked to see if the guides are worn? 

The cylinders were done at 1000hrs but the valves and seats were reconditioned, not replaced.  Here is where I would definitely be concerned because those valves are 2100hrs now.  Overhauling the cylinders definitely needs to be done. 

7 hours ago, cliffy said:

With an O/H you'd be sure things were as good as it gets, if you had to sell your resale price would be better AND your market to sell to would be lots bigger. If I was looking at a plane with a sucked valve and just a cylinder replacement with 2100 TT even considering the bottom end time I'd be walking away. it just doesn't ring good to me. 

If you spend $30-35K+ to overhaul you won't get that back out of the sale price and probably wouldn't have to discount much if anything if you did the 4 cylinders.  It also depends on how it gets written into the logbooks.  If you looked at this plane and it said cylinders overhauled 1000 and valves reconditioned, case overhauled 1600, cylinders overhauled at 2100 in the book for a total time of 2100 would you run from it?    

[Yetti]

I would follow Jet Driven

1. Check Prop governor screen - if OK then 

2. Buy a new Cylinder from Air power and ship to Mechanic have him install. Flush oil system

3. Fly it home.

4. Send old #3 cylinder out for overhaul $500 or so.  

5. When you have an off week swap out your next lowest compression cylinder with the overhauled. Change oil and review filter.

6.  You may also have Mechanic ream the exhaust valve guides on all the other cylinders while he is replacing the #3

7. Keep working through your cylinders till you have a top overhauled engine.

.

[ArtVandelay]

Is no one bothered by the fact this engine needed a top overhaul after only 1060 hrs? You got to wonder what kind of abuse it took to require a overhaul at that point.

To answer M20F, yes I would run from it.

[ryoder]

1 hour ago, teejayevans said:

Is no one bothered by the fact this engine needed a top overhaul after only 1060 hrs? You got to wonder what kind of abuse it took to require a overhaul at that point.

To answer M20F, yes I would run from it.

Isn't this somewhat common for the IO360 200hp angle value engines?  The top doesn't always make TBO right?

[mike_elliott]

1 hour ago, ryoder said:

Isn't this somewhat common for the IO360 200hp angle value engines?  The top doesn't always make TBO right?

If it is abused, it wont make it, otherwise should easily make tbo.

[ryoder]

7 minutes ago, mike_elliott said:

If it is abused, it wont make it, otherwise should easily make tbo.

What about the 0360?  Does it have a greater chance of making it to tbo even if abused?  To me, abuse could be climbing out at 400 plus cht and only flying once in a while.  I do both by necessity sometimes.  

[mike_elliott]

3 minutes ago, ryoder said:

What about the 0360?  Does it have a greater chance of making it to tbo even if abused?  

Why would it? The angle valve design is more conducive to longevity in the first place, in spite of the lack of valve lubrication :)

 

To me, abuse could be climbing out at 400 plus cht and only flying once in a while.  I do both by necessity sometimes.  Fix the underlying cause of the high temps and stop this.

 

[aviatoreb]

Corona seems to have pretty good prices across the board of engines they service, compared to other shops - how is product - how well do their engines turn out?

[ArtVandelay]

Has anybody run their io-360 past TBO without any major cylinder,engine work?

[cliffy]

M20F_ too many aluminum pieces running around the engine from the piston for me to be comfortable with a "flush" only

cylinders at 2100 hrs is why I recommend an O/H Being first run they could be overhauled except for the damaged one. 

It would also look better in the log book. It's time for all the exhaust valves to be replaced.

Short of a well documented overhaul I would advise anyone on a pre-buy to run away.

The engine is 33 years old and never been fully overhauled. It's time 

 

 

[Andy95W]

5 hours ago, ryoder said:

What about the 0360?  Does it have a greater chance of making it to tbo even if abused?  To me, abuse could be climbing out at 400 plus cht and only flying once in a while.  I do both by necessity sometimes.  

It has always been my experience that the standard O-360 was generally more "bullet proof" than the IO-360 angle valve 200 hp. If nothing else, the 180 hp O-360 seems like it is more forgiving of mild abuse.  The IO-360, with its greater horsepower output per cylinder, needs to be run correctly or it stands less chance of making it to TBO. 

Ryan, the mere fact that you care enough to ask the question means it's unlikely you are abusing your engine.  

"Only flying once in a while" is a little ambiguous.  Every 6 months? Probably not good.  Weekly, with an occasional 2-3 week break?  Probably not bad.  The fact that you are concerned means you are flying as much as you can to take care of your engine.

"400 plus CHT" is also kind of ambiguous.  If you regularly climb out at 430-450 CHT, that would probably be a problem.  Occasional 405-410? Probably not.  40 years ago, before people had fancy engine monitors, the redline CHT was (and still is) 500°.  People used the inaccurate factory gauges, leaned the mixture until the engine ran rough then pushed it back in a little bit, and made it to TBO.  

Perhaps ignorance really was bliss.

[Jim Peace]

My engine has a corona overhaul and it is running strong. Many oil analysis to prove it. About 650 hours into it. I think it was done in 2007  I will have to check  

Running shell 15w50 

1964 m20c

[ryoder]

12 hours ago, N1395W said:

It has always been my experience that the standard O-360 was generally more "bullet proof" than the IO-360 angle valve 200 hp. If nothing else, the 180 hp O-360 seems like it is more forgiving of mild abuse.  The IO-360, with its greater horsepower output per cylinder, needs to be run correctly or it stands less chance of making it to TBO. 

Ryan, the mere fact that you care enough to ask the question means it's unlikely you are abusing your engine.  

"Only flying once in a while" is a little ambiguous.  Every 6 months? Probably not good.  Weekly, with an occasional 2-3 week break?  Probably not bad.  The fact that you are concerned means you are flying as much as you can to take care of your engine.

"400 plus CHT" is also kind of ambiguous.  If you regularly climb out at 430-450 CHT, that would probably be a problem.  Occasional 405-410? Probably not.  40 years ago, before people had fancy engine monitors, the redline CHT was (and still is) 500°.  People used the inaccurate factory gauges, leaned the mixture until the engine ran rough then pushed it back in a little bit, and made it to TBO.  

Perhaps ignorance really was bliss.

After I get to 1000 feet the CHT is primary for pitch   Unfortunately it does get up to 400 which is still in the green.  Also I fly with cowl flaps partially open to keep it below 380 or so when flying with more than 20 inches of MP or so.  I think the guppy mouth is a problem and I also think my doghouse could use some sealant.

I have had some weeks where I didn't fly at all.  Like right now I am having some minor procedures and won't fly until the stitches are removed.