Turbo Failure mode! Single turbo Vs. Twin or TN?

[kmyfm20s]

I know there are a lot of happy turbo owners on the forum. With having several friends having turbo failures as well as several on this forum I have always been hesitant of a single turbo engine. I like the idea of a true TN engine because if the turbo fails it is just a NA engine but the factory doesn't offer that. What about a twin turbo like the M20TN? I know its not truly turbo normalized but with it having 2 turbos does that actually add to the redundancy? If one of the turbo fail does the other compensate but with less performance? I keep eyeing them and that might persuade me to go that direction. 

[aviatoreb]

3 hours ago, kmyfm20s said:

I know there are a lot of happy turbo owners on the forum. With having several friends having turbo failures as well as several on this forum I have always been hesitant of a single turbo engine. I like the idea of a true TN engine because if the turbo fails it is just a NA engine but the factory doesn't offer that. What about a twin turbo like the M20TN? I know its not truly turbo normalized but with it having 2 turbos does that actually add to the redundancy? If one of the turbo fail does the other compensate but with less performance? I keep eyeing them and that might persuade me to go that direction. 

Well I'll admit Monday night at around 6:45....I would have preferred to have had a no-turbo airplane.

I would think 2 turbos is not like 2 engines.  I would think that a turbo failure that is burning oil - is a major problem even if you have another turbo.  For example - as it turns out my engine fired back up on its own but because of the burnt oil I had not enough oil to run the engine at normal settings safely and there was burning smell and a small amount of smoke in the cockpit - I could see that happening on a twin turbo model - so in that situation I don't think two turbos would be any better than one.

I do still believe that turbo is a fine way of designing an engine, but I am re-educating myself as to what it takes to manage the inspection and service monitoring for such a unit.

There are a lot of parts on an airplane, any airplane, and they all need to work.

[kris_adams]

Erik I think you have a lot of us pondering turbos. Especially flatlanders like me. Though I readily admit I’d love to be able to more easily climb to 11 or 12k loaded on a hot day. 

[anthonydesmet]

2 hours ago, aviatoreb said:

Well I'll admit Monday night at around 6:45....I would have preferred to have had a no-turbo airplane.

I would think 2 turbos is not like 2 engines.  I would think that a turbo failure that is burning oil - is a major problem even if you have another turbo.  For example - as it turns out my engine fired back up on its own but because of the burnt oil I had not enough oil to run the engine at normal settings safely and there was burning smell and a small amount of smoke in the cockpit - I could see that happening on a twin turbo model - so in that situation I don't think two turbos would be any better than one.

I do still believe that turbo is a fine way of designing an engine, but I am re-educating myself as to what it takes to manage the inspection and service monitoring for such a unit.

There are a lot of parts on an airplane, any airplane, and they all need to work.

Turbo is the way to go....Fly in the teens, smooth air more than down low, less traffic, above Class B, C, ... I change oil every 30 hours (I fly average 140/ year) and when the cowl is off we check turbo blades (for loseness and /or damage, etc) lines, lube waste gate if required, air inlet clamps, air filter, etc.  I don’t know if all turbo owners do this and/or you can isolate or trace turbo failures to maintenance “looks” but I haven’t been surprised.  Had to change a line once and Lao didn’t like the way my air filter clamp was attaching to the turbo inlet one time but I have not been surprised....(knock on wood)....I also watch fluctuations on MP different than when I was flying non-turbo as well.....I don’t know...maybe other turbo owners treat differently...

[aviatoreb]

10 hours ago, anthonydesmet said:

Turbo is the way to go....Fly in the teens, smooth air more than down low, less traffic, above Class B, C, ... I change oil every 30 hours (I fly average 140/ year) and when the cowl is off we check turbo blades (for loseness and /or damage, etc) lines, lube waste gate if required, air inlet clamps, air filter, etc.  I don’t know if all turbo owners do this and/or you can isolate or trace turbo failures to maintenance “looks” but I haven’t been surprised.  Had to change a line once and Lao didn’t like the way my air filter clamp was attaching to the turbo inlet one time but I have not been surprised....(knock on wood)....I also watch fluctuations on MP different than when I was flying non-turbo as well.....I don’t know...maybe other turbo owners treat differently...

I very much like flying in the mid and also upper teens on the East coast.  Its quiet despite usually busy in the East - higher than most pistons and lower than most jets, smooth, more direct routing, and lots of options in case of an emergency....although Monday a turbo emergency .  Its hard to balance the risk benefit of flying high versus the extra risk associated with a turbo but my general feeling is that it is in favor of turbo.  I have called altitude my virtual twin, when flying across hostile terrain.  That said - Im still stinging since Monday...

As I said I am re-evaluating all of my maintenance concepts and will better include the kind of checking you just described.

Edited May 3, 2018 by aviatoreb

[gsxrpilot]

As a turbo driver who enjoys flight in the flight levels... Do I think of it this way? If a cylinder comes apart, the engine will quit, so even in my previous M20C, there were four opportunities for catastrophe banging away at all times.  In my TSIO360 I've got 6 cylinders and a turbo, so 7 possible points of failure. 

I'm mitigating as much as I can with good maintenance and a proper engine monitor and knowing how to read it. But in addition, the turbo gives me altitude which certainly adds to the safety factor.  Like Erik says, altitude is like a virtual twin engine.

I'm certainly interested in the best recommendations for inspection to catch turbo issues before they stop my engine.

[anthonydesmet]

53 minutes ago, aviatoreb said:

I very much like flying in the mid and also upper teens on the East coast.  Its quite despite usually busy in the East - higher than most pistons and lower than most jets, smooth, more direct routing, and lots of options in case of an emergency....although Monday a turbo emergency .  Its hard to balance the risk benefit of flying high versus the extra risk associated with a turbo but my general feeling is that it is in favor of turbo.  I have called altitude my virtual twin, when flying across hostile terrain.  That said - Im still stinging since Monday...

As I said I am re-evaluating all of my maintenance concepts and will better include the kind of checking you just described.

I hear you.  Something like that definitely makes you stop and re-evaluate.  I would be interested hear from you and other turbo owners how they consider turbo routine maintenance/inspections.  Just during annual?, periodically between manuals.  M20K Maintenance Manual says: to inspect all brackets and hoses in accordance with SB M83-3.  I have attached the service bulletin if interested.

M83-3.pdf

[tomgo2]

Very good discussion topic gentlemen. I don't know the right answer myself. Based on my own experiences and customer interactions, it seems like there are basically three indicators:

1. No boost after troubleshooting everything else on the plane going from least expensive to most expensive.

2. Visual inspection of the system reveals cracks in any part of the turbocharger.

3. Oil leak that doesn't stop after checking the scavenge pump and check valves.

 

[chrisk]

8 hours ago, kmyfm20s said:

I know there are a lot of happy turbo owners on the forum. With having several friends having turbo failures as well as several on this forum I have always been hesitant of a single turbo engine. I like the idea of a true TN engine because if the turbo fails it is just a NA engine but the factory doesn't offer that. What about a twin turbo like the M20TN? I know its not truly turbo normalized but with it having 2 turbos does that actually add to the redundancy? If one of the turbo fail does the other compensate but with less performance? I keep eyeing them and that might persuade me to go that direction. 

I don't understand your comment about turbo normalized.   If the turbo fails (and doesn't dump your oil), you will have a normally aspirated engine.  A turbo normalized engine just keeps the turbo at 30 inches, instead of 36 or 40 like factory turbo engines.  And a turbo failure in a turbo normalized engine results in a normally aspirated engine.  The only difference is most turbo engines have a lower compression ratio, which means a bit less power until.  But in either case, the engine will run.

[carusoam]

28 minutes ago, chrisk said:

I don't understand your comment about turbo normalized.   If the turbo fails (and doesn't dump your oil), you will have a normally aspirated engine.  A turbo normalized engine just keeps the turbo at 30 inches, instead of 36 or 40 like factory turbo engines.  And a turbo failure in a turbo normalized engine results in a normally aspirated engine.  The only difference is most turbo engines have a lower compression ratio, which means a bit less power until.  But in either case, the engine will run.

Negative captain...

A simple to describe failure... is a loss of pressure from an intake hose coming loose... (no oil loss or other turbo hardware issues)

The CR is the problem... at high altitudes.

The compression is needed for the thermodynamics to work...

without the MP generated by the turbo... there will be an altitude, above which, there won’t be enough compression to burn the fuel properly...

The advantage of the TN, the CR is closer to the CR of the NA engine...

There is probably a technical term for this critical altitude related to the turbo challenge...  the TN’s critical altitude will be higher...

 

Somebody probably has an emergency procedure that covers engine restarts in the air...

Also, Take a look at the lowest MP entries in the usual power charts...

If the lowest MPs are 20” or less, Expect that you can generate partial power when below 10k’ with a failed TC...

 

getting below this particular altitude where compression can work... this is where the mixture sweep should come in handy... the mixture that is going to work is going to be leaner than usual...

 

I studied this a bit when trying to determine if a TC was going to be helpful for my mission.  I just happened to notice that having a hose failure over tall rocks would be... unfortunate...

Reading up on Homebuilts and hose issues was eye-opening... they have quite a few compared to factory built installs...

Keep an eye on the hose clamps and V-bands (on the hot end)....  simple failures that can cause some heartache...

 

+1 for altitude being a friend...  310hp to get you there in less time under ordinary conditions...

 

Anybody have some power chart data for the low end of the MP scale?

Anyone have a restart procedure for high altitudes... that says attempt restart below 10k’ or something like that?

PP thoughts only, not a TC pilot...

Best regards,

-a-

[jlunseth]

There is a restart procedure in the 231 POH.  It says restart may not be possible until below 12k.  Can’t find it tonite but maybe someone can, or I can find it for you tomorrow.  

[chrisk]

6 hours ago, carusoam said:

Negative captain...

A simple to describe failure... is a loss of pressure from an intake hose coming loose... (no oil loss or other turbo hardware issues)

The CR is the problem... at high altitudes.

The compression is needed for the thermodynamics to work...

without the MP generated by the turbo... there will be an altitude, above which, there won’t be enough compression to burn the fuel properly...

The advantage of the TN, the CR is closer to the CR of the NA engine...

There is probably a technical term for this critical altitude related to the turbo challenge...  the TN’s critical altitude will be higher...

 

Somebody probably has an emergency procedure that covers engine restarts in the air...

Also, Take a look at the lowest MP entries in the usual power charts...

If the lowest MPs are 20” or less, Expect that you can generate partial power when below 10k’ with a failed TC...

 

getting below this particular altitude where compression can work... this is where the mixture sweep should come in handy... the mixture that is going to work is going to be leaner than usual...

 

I studied this a bit when trying to determine if a TC was going to be helpful for my mission.  I just happened to notice that having a hose failure over tall rocks would be... unfortunate...

Reading up on Homebuilts and hose issues was eye-opening... they have quite a few compared to factory built installs...

Keep an eye on the hose clamps and V-bands (on the hot end)....  simple failures that can cause some heartache...

 

+1 for altitude being a friend...  310hp to get you there in less time under ordinary conditions...

 

Anybody have some power chart data for the low end of the MP scale?

Anyone have a restart procedure for high altitudes... that says attempt restart below 10k’ or something like that?

PP thoughts only, not a TC pilot...

Best regards,

-a-

Thanks.  I understand the concern now.  Basically the critical altitude of the plane when the turbo has failed.   As jlunseth mentions, this is somewhere around 12k based on the re-start procedure in the 231.  For me, that is high enough to not be a concern, even in most mountainous regions. That said, I expect the most common "turbo failure" is running a tank dry.   I am quite careful about running a tank dry at higher altitudes due to the fear it might not restart without going lower.  

Now the question of how the critical altitude differs between a TN and TC engine.  I'm sure it depends on the compression ratio, and there is no guarantee that the compression ratio is significantly higher on the TN engine.  --Most TN implementations I have seen are high compression, but I also recall some older engines that were quite happy with 80 octane fuel.  If there are TN variants of these engines, I would expect them to have lower compression.

[aviatoreb]

1 hour ago, chrisk said:

Thanks.  I understand the concern now.  Basically the critical altitude of the plane when the turbo has failed.   As jlunseth mentions, this is somewhere around 12k based on the re-start procedure in the 231.  For me, that is high enough to not be a concern, even in most mountainous regions. That said, I expect the most common "turbo failure" is running a tank dry.   I am quite careful about running a tank dry at higher altitudes due to the fear it might not restart without going lower.  

Now the question of how the critical altitude differs between a TN and TC engine.  I'm sure it depends on the compression ratio, and there is no guarantee that the compression ratio is significantly higher on the TN engine.  --Most TN implementations I have seen are high compression, but I also recall some older engines that were quite happy with 80 octane fuel.  If there are TN variants of these engines, I would expect them to have lower compression.

Chris consider that the failure I just had - a turbo gone bad - was not a situation where you would want to run your engine.  My engine did restart at about 8 but I retarded it because there was a burning smell and a faint smoke in the cockpit.  I was treating that as if I had an active fire in the cockpit and must get down asap.  I think that could be the same with a twin turbo, or a TN, that if you had the kind of turbo failure I had, you would not want to be running that engine.

[aviatoreb]

9 hours ago, anthonydesmet said:

I hear you.  Something like that definitely makes you stop and re-evaluate.  I would be interested hear from you and other turbo owners how they consider turbo routine maintenance/inspections.  Just during annual?, periodically between manuals.  M20K Maintenance Manual says: to inspect all brackets and hoses in accordance with SB M83-3.  I have attached the service bulletin if interested.

M83-3.pdf

Thanks for that SB - I have seen it.

But I am not going to make any comments on maintenance right now - I am only asking questions for a little while since I am re-evaluating from scratch.  I was not inspecting between annuals.  I think I will be designing some new-to-me (I am aware others do) inspection routine for at least every oil change or whenever the cowl comes off.

How long do people run there turbos?  DO they change them on condition or do you run them by a particular service life?  I found somewhere someone said they will change them every 800 hours regardless of condition - what is the collective wisdom?

[chrisk]

58 minutes ago, aviatoreb said:

Chris consider that the failure I just had - a turbo gone bad - was not a situation where you would want to run your engine.  My engine did restart at about 8 but I retarded it because there was a burning smell and a faint smoke in the cockpit.  I was treating that as if I had an active fire in the cockpit and must get down asap.  I think that could be the same with a twin turbo, or a TN, that if you had the kind of turbo failure I had, you would not want to be running that engine.

First, you did an awesome job putting your plane down on a runway with an engine failure.  Second if I were in that situation, I would have done the same thing with shutting off the engine.  That said, if I found myself 1 or 2 miles short of the runway for what ever reason, I would have restarted. --Nice to know it probably would have restarted, even if the engine would need an overhaul afterwards due to the oil loss.

[aviatoreb]

54 minutes ago, chrisk said:

First, you did an awesome job putting your plane down on a runway with an engine failure.  Second if I were in that situation, I would have done the same thing with shutting off the engine.  That said, if I found myself 1 or 2 miles short of the runway for what ever reason, I would have restarted. --Nice to know it probably would have restarted, even if the engine would need an overhaul afterwards due to the oil loss.

Thank you.  

I would also definitely restart if I could if I were coming up short if I had not thought it might be a fire.  In this case I thought it might be a fire so being a rural airport I would have chosen a field instead of restarting the engine.  So thoughts of saving the engine were not on my mind but rather worries of fire in the cockpit.   In my narrative I mentioned this sort of thing went through my mind where I was still at 3k during my last turn to loose altitude and I decided then to only make the one more turn even if that left me still high, which it did, so pointing the nose at the runway from there I was something like 100kts still coming to the numbers and I was willing to take that as an over run landing if it worked out that way but thanks to a lot of wind (cross wind too!) speed brakes and the rest I was able to stop with room to spare.

[Marauder]

5 minutes ago, aviatoreb said:

Thank you.  

I would also definitely restart if I could if I were coming up short if I had not thought it might be a fire.  In this case I thought it might be a fire so being a rural airport I would have chosen a field instead of restarting the engine.  So thoughts of saving the engine were not on my mind but rather worries of fire in the cockpit.   In my narrative I mentioned this sort of thing went through my mind where I was still at 3k during my last turn to loose altitude and I decided then to only make the one more turn even if that left me still high, which it did, so pointing the nose at the runway from there I was something like 100kts still coming to the numbers and I was willing to take that as an over run landing if it worked out that way but thanks to a lot of wind (cross wind too!) speed brakes and the rest I was able to stop with room to spare.

Erik - I really appreciate your transparency on your thought process through this emergency. Many, many, many owners have flown for years without nothing more than the occasional rough running engine or the infamous “automatic rough” when flying over inhospitable terrain. 

For those who have never experienced an emergency, I hope you never do. For those of us who have, it is hard to express how the survival instinct takes over. 

Erik’s comment about the smell of adrenaline hits home. My DPE for my private checkride was a WWII pilot. He offered an observation that still sticks with me today “the first thing you will notice in an emergency is the smell of raw adrenaline”. The first time I smelled adrenaline was my first night flight in my Mooney when the gear wouldn’t come down. Being new to retracts, I had visions of a fire ball skidding down the runway. Fortunately I recalled the guy who sold me the Mooney making a comment that sometimes the landing gear breaker pops. 

My second real emergency was over the “Bermuda Triangle” of the Northeast. Flying above a solid cloud deck that went from mountain obscurations to 6000’. I went from noticing a fluctuating EGT to riding a Harley in a minute. It is hard to describe the transition from the moment of initial panic, to acceptance to survival mode. That flight changed my risk acceptance. I will no longer fly over extended areas of low conditions in a piston single. 

These threads are really helpful as reminder that what we do has inherent risks to it. We can stack the deck in our favor through training, maintenance, equipment and thorough preparation, but at the end of the day, it can and unfortunately still happens. 

Be safe out there!

 

[peevee]

On the tornado alley twin setup I have had one turbo completely fail. You don't notice it. Turbo 2 can maintain sea level power to the high teens or better.

We didn't know anything was amiss until the bearing failed and dumped a bunch of oil out the exhaust.

 

Edited May 3, 2018 by peevee

[jlunseth]

Here are the Turbo Failure checklists for my 231:

TURBOCHARGER FAILURE (Loss of Power, Engine Runs)

Beware of Fire

Throttle	AS LITTLE AS POSSIBLE
Prop	AS REQUIRED
Mixture	ADJUST TO OBTAIN FUEL FLOW APPROPRIATE TO MN & RPM
Land	As soon as practicable

 

 

TURBOCHARGER FAILURE (Engine Fails)

>12000’ overrich mixture may result and engine may fail

Mixture	IDLE CUTOFF
Throttle	FULL OPEN
Prop	NORMAL CRUISE RPM
Throttle	RETARD TO CRUISE POSITION
Mixture	ADVANCE SLOWLY TIL ENGINE START
Mixture	ADJUST TO OBTAIN FUEL FLOW APPROPRIATE TO MP & RPM
LAND AS SOON AS PRACTICABLE

 

There is another one that applies as well, if the engine quit at high altitude, the pilot descends below 12k or whatever works, and the engine restarts after a prolonged outage.  The problem is that the engine and oil will be cold, so this checklist would apply, or at least the last half of it that requires low throttle and warm to operating limit (240 CHT and 100 OT):

AIR START AFTER EXTENDED SHUTDOWN

Mixture	Idle Cutoff
Fuel Selector	Switch Tanks
Throttle	1/3 Open
Prop	Minimum RPM
Mixture	Slow advance towards rich
Oil Pressure	Monitor
Prop	Minimum RPM
Throttle	16-18 in. Hg MP
Oil Tem	Warm to operating limit
Engine Power	Readjust to cruise
If engine Does Not Start	Proceed to power-off landing

 

These are from the checklist I made and keep on my iPad, but they came from the POH, these are the crib notes version. I should add, I have never had occasion to use any of them, the turbo has been very durable, knock on wood.  I do open the inspection door, apply a little pressure to the tailpipe, and watch for any movement, during every pre-flight, and every now and then I run my finger around inside the exhaust to see if it is cry or oily.

Edited May 3, 2018 by jlunseth

[Marcopolo]

5 hours ago, aviatoreb said:

 I think I will be designing some new-to-me (I am aware others do) inspection routine for at least every oil change or whenever the cowl comes off.

How long do people run there turbos?  DO they change them on condition or do you run them by a particular service life?  I found somewhere someone said they will change them every 800 hours regardless of condition - what is the collective wisdom?

1981 M20K TSIO360 GB(3) Original Engine with 1650hrs since new.  Original Rajay fixed wastegate Turbo! (yikes)

My maintenance routine (as it applies to the Turbo Charger)

 

  Every Pre-Flight includes opening the Turbo inspection panel and visually inspecting the 3 v-band clamps and turbo general condition.  Grabbing the exhaust pipe and moving it to show any looseness and listen for any noises that shouldn't be there.

 

  During oil changes (30hrs) In addition to the above I will run a boroscope up the exhaust pipe to inspect the turbine blades and turbine housing.  I will also remove the air filter and try the wiggle test on the compressor end of the turbine shaft.  I also spin the compressor and check for binding, scraping noises and how freely the shaft spins (it should have very slight resistance, a smooth solid feel).  I apply mouse milk to all exhaust and bypass joints.

 

  At annual inspection in addition to all the above, the turbo may be removed and a more thorough inspection completed to include inspecting the turbine housing for cracks at the inlet area (usually not visible by boroscope through exhaust), Scavenge check valves removed, checked and cleaned, new turbine mating surface gasket installed, replace any suspect v-band clamps (check time or torque cycle replacement requirements).

 

  This is my maintenance routine, I'm posting it so it can be used or critiqued ( @M20Doc please correct any mistakes or fill in any blanks)

 

 Ron

[jlunseth]

Ron, another simple pre-flight test that Bruce Jaeger taught me is to run your finger around the inside of the exhaust to see if the grit is dry or grimy.  Grimy/oily may be an oil leak in the turbo.  I don't do it every pre-flight just because it means having to wash my hands afterwards to get the grit off, but I do it every few pre-flights.  Obviously, this is not something to do if the pipe is hot.

[Bennett]

Ive been quiet about Erik’s turbo failure as we hsve been talking privately since the date of tge incident. He did a great job, and i csn enphatize with him as i had a similar situation some years ago starting at FL 210 over mountains in winter, and like Erik, i declared an emergny, and made a power off landing at an airport. I, too, used the commercial spiral tk descend rapidly, as i was concerned about a potential fire. I assumed it was was a turbo failure, but ultimately that proved incorrect as i had failures of both the engine driven fuel pump  and the dual electric back-up pump. Amazingly there was no panic here - just fly the airplane, and since I knew I could spiral down over an airport, I spent my time on concentrating on the commercial spiral, rather than trying a restart.  

In another situation near the same area, I had the straight mineral oil (newly bebuilt engine in breakin) freeze and watched the oil pressure drop to the point to where I put the engine to idle and headed down from the flight levels to a nearby airport. This time at about 8000’ the oil pressure started back up, and I increased power to the point where I could make a normal landing.

in another instance I had to dead stick  a Piper Dakota into an airport.

I mention these situations as things break even with great maintenance, and complacency is the enemy. Recurrent training, and practice at “what if” thinking on every flight can save you, and your passengers.

To return to the theme of this tread, after 2 231s and a 261 conversion I decided that I didn’t really need to fly in the flight levels - even out West.  Over the years I spent a great deal of money in turbo maintenance and replacement with LASAR. At every annual I had the turbo serviced to new specifications, and had many components replaced.  I always was careful about TITs, and always kept the engine cooling for 5 minutes after landing - maybe an old wife’s tale, but couldn’t hurt  I did replace the turbos at 800 hours, and when I had the engine of the 261 rebuilt.  The J I now fly in incapable of the Flight Levelx, but with careful routing I can still cross the country with reasonable speed, and without subjecting my self and the engine to the harsh conditions of the flight levels, and concerns about turbo failures. Life is full of compromises, and after decades of flying, I prefer the the simplicity of the J.  Of course your needs may differ.  

 

[kmyfm20s]

2 hours ago, peevee said:

On the tornado alley twin setup I have had one turbo completely fail. You don't notice it. Turbo 2 can maintain sea level power to the high teens or better.

We didn't know anything was amiss until the bearing failed and dumped a bunch of oil out the exhaust.

 

That is comforting and nice redundancy! 

[MARZ]

1 hour ago, kmyfm20s said:

That is comforting and nice redundancy! 

and expensive. 

[peevee]

2 hours ago, kmyfm20s said:

That is comforting and nice redundancy! 

Yes and no.

 

In our case the turbo ingested something after overhaul. The problem manifested itself about 8 or 10 hours later when the main bearing failed and it plastered the plane with oil and smoke when I went to get fuel for a trip the next day. There was no noise or indication anything was wrong. Had that happened in flight it would have probably lost the crankcase worth of oil pretty quickly with no indication until you started to see a drop in oil pressure. End result could be the same if the engine seized before you found an airport.

 

I had flown the airplane to 17,5 the day before and there was no problem maintaining power and no oil in or dripping from the exhaust before I went for fuel. I always check for a failed check valve and the security of the vband clamps in preflight 

 

We overhauled our turbos at about 1700 hours and main turbo thought they were pretty long in the tooth. It's not just the bearings you have to worry about, the turbine blades get gunked up and blasted and eroded by exhaust gasses too.

Edited May 3, 2018 by peevee