Why so many top overhauls on Acclaims?

[PaulB]

Do Bravos not have issues with early top overhauls?

[KSMooniac]

Erik's summary is spot-on.  There are numerous well-respected shops in the Beech world that provide very long-lasting engines, and one of their steps is to buy new CMI cylinders, un-box them, disassemble them, and re-work all of the valves.  Years ago CMI deleted the careful steps required for long-lasting valves and opted to just install parts out of the bin with no regard to how well they fit together.  It was good enough to get past the warranty period in most instances.  It does not matter if the operator ran ROP or LOP for this failure mode.

Heat and pressure related failures, though, are certainly influenced by the operator.  I'm sure a lot of the Acclaim issues were due to this and the stupid breather arrangement, but some certainly could have been due to the valve workmanship from the CMI factory as well.

[mike_elliott]

There has been a lot said here that you need to run a conti conservatively to make tbo with the cylinders - and also that the cylinders are crap and that turbos are implicated.

Here is the real story that I have gathered by reading many sources but I will just summarize what I read - and my own direct observation - rather than trying to track down all the sources.

Continental designed a superb engine.  It runs great.  They used to build a great engine but sometime about 20 or 15 years ago they went cheap and made personnel changes that resulted in a much lower quality build.  Specifically relevant to this discussion, they no longer put the care into building cylinders that they should - and the valve assembly was a weak point.  Those valves were not seating well direct from the factory when new.  I read from beechtalk this statement, and he (I forgot which one but it was one of the guys who runs the GAMI-APS program) said that when you have a cylinder with a crappy built valve assembly gasses will leak by and no matter how you run the engine, conservatively, LOP, ROP, or not, you will need to overhaul that (and others too) cylinder by 1000 hrs at least.

So - what do you know - my own engine started showing two bad cylinders at 980 hours - right on schedule (3 years ago ago).  I only owned and operated my airplane since the engine had 750hrs.  It had gone from all good signs and compressions in the low 70s to one very weak cylinder (in the 20s) and one with singificant blow-by sounds and compressions in the 50s.  So overhaul those two at least was called for.  When we got those two cylinders off - I was appalled to see the workmanship on those cylinders.  They were just not seating very well - just like I read from numerous sources.  ANd this is not an issue of it wearing out - this is how it was built- built poorly.  So I decided right there to do a top since i then suspected the other cylinders were probably built the same poor standard.  I decided to buy new cylinders (from a company other than continental since I was mad at them - but in retrospect, that doesnt matter) and furthermore, I decided to have the valves worked by an expert cylinder guy to seat nice and tight (called lapping).  That last step, I will do with every overhaul or cylinder to be installed in my engine henceforth - a little extra spent up front can save I think down the road. 

So that's the main thing for the fleet of conty engines - leaking hot exhaust gases past poorly built valve cylinders directly from the factory.  IF YOU HAVE A POORLY BUILT cylinder - there is NOTHING you can do from the pilot seat that will make that cylinder go to tbo.  This applies to turbo or NA.  According to the material I read by the GAMI-APS guy on beechtalk - he said that even a conservatively operated engine that has a poorly built cylinder with a poorly built valve assembly will not go the distance.

My own continental engine now has about 400 hours on the new cylinders and all compressions were 77 or higher at last check - knock on wood.  The rocket is very easy to keep the cylinders cool - that is the temps are easy to maintain at <380F CHT at all times.  This is one factor in the pilot operating that can help so I hear and I am working hard on it.

They say its controlling CHT's and also ICPs that make cylinders last.  Both of those are controllable by the pilot by knowing how to operate the red knob. And not going crazy with the black knob.  This is true whether its conty or lycosaurus.  But as I said, it also takes a properly built cylinder in the first place and conty for a long stretch had a major workmanship problem in the valves department (supposedly that is fixed now on their factory floor - but I will still be reworking any valve assembly that goes installed into my airplane, new or not).

The Acclaim problem is none of the above, according to the AD, as already stated - it has a special problem related to coking of the breather - a fixable problem.  Once that is fixed, then it will be subject to all the 3 problems above (1) CHTs - keep em under control with the red knob and pitching for enough speed and step climbing if you need (2) ICPs - high power leads to higher chts but also stress on the cylinders - and high power in the winter may not lead to high temps but still high icp - also the red knob controls where in the power stroke (angle) the combustion occurs and that has cht and icp implications.  (3) valves need to be built right and there is nothing the pilot can do about operating the airplane out of this gotcha- only the pilot-owner can fix this by making sure only good valves are in the plane.

Not just lapping the valves, it is important to get the valve geometry right, so the rocker "rocks" across the top of the valve stem, not slides and pushes laterally on it. Few shops take this extra step.

[Joe Zuffoletto]

Well, I don't have an AcclaimPOH so is there someone who does who could tell me likely true airspeed at 70% power at, say, 18K - 20K?  (With the recent.apparent hypoxia deaths @ 25K I'm a little reluctant to put full faith in my oxygen system at an altitude at which a problem has only minutes to fix).  Thanks.

At my ROP setting at those altitudes I get 220KTAS. LOP is about 205KTAS. I'll have to check my POH to see what % those power settings are. I think they're about 75 and 65, respectively. I know that when I'm running LOP all but one CHT is below 400 degrees.

Edited September 13, 2015 by Joe Zuffoletto

[RobertE]

Thanks for that info, Joe.  Just what I was looking for.

[Bravoman]

Do Bravos not have issues with early top overhauls?

not to my understanding. I researched this before buying the plane. Before the wet head design change it was a different story. The early TLS Mooneys were burning up cylinders and that was why Lyc and Mooney got together on the design change. Now a very hardy engine much like the other IO-540s.

[aviatoreb]

Not just lapping the valves, it is important to get the valve geometry right, so the rocker "rocks" across the top of the valve stem, not slides and pushes laterally on it. Few shops take this extra step.

Quite right - I thought the word lapping included working the geometry.  I went with Victor Aviation since they claimed to spend special attention to shaping the valve geometry and I feel it is well worth it to pay attention to this factor.  So far I have been very happy with the result.

[Tony Armour]

not to my understanding. I researched this before buying the plane. Before the wet head design change it was a different story. The early TLS Mooneys were burning up cylinders and that was why Lyc and Mooney got together on the design change. Now a very hardy engine much like the other IO-540s.

When I bought my TLS at 13xx TT the cylinders were shot (thanks Don Maxwell and the prebuy) I believe this was due to the previous owner running too high of a TIT (1650, more ?) even though it was in spec. I had those cylinders remand'd with the nickel process and never have run over 1615TIT and actual now days I run right at 1600TIT. So far about 600 hrs later I'm still at one quart of oil for 25 hours. 

I am as biased as one could be, but for the money there is NO better airplane out there than a Bravo. Compare the prices and performance against an Acclaim and you just have to really really want a newer airplane to make that jump....AND you get to keep the house :-)

 Take the rear seats out (reference my bicycle post) and it's almost an unbelievable amount of room compared to other airplanes. Something all long body guys should know......you DO know how to take the seats in and out right ? ;-) it takes 3 or 4 minutes. 

[carusoam]

i used to think I was 'passionate' about my engine...

Turbo owners are truely passionate!

in the engine manufacturer wars, All three are equally challenged. All three have had difficulty rolling out their first engine. The P variety never got to their Bravo model.

lycoming needs another update made available for the Long Body.

A ) getting it up to 310hp would be really cool.

B ) being able to run LOP keeps Mooney owners happy.

for the Mid Length guys

A) corrosion kills the Lyc. cam, then nearly requires an OH to swap the cam out...

For the short body guys...

A) lycoming needs a solution for stuck valves in their O360. Talk about serious valve issue.

 

if I were the OP, I would still strongly consider the Acclaim with a real PPI and some how include Erik's experience while checking the engine...

Keep up the passion!

now back to the NA LOP channel,

-a-

 

Edited September 14, 2015 by carusoam

[N177MC]

It could explain why RAM uses new nickel plated cylinders on their engine overhauls.

Clarence

Well,  most Conti "pre-mature" cylinder failures are valve related which is of course not affected by the bore surface treatment. 

[Guest]

Well,  most Conti "pre-mature" cylinder failures are valve related which is of course not affected by the bore surface treatment. 

Not in my 30 plus years of maintenance experience.  If it wasn't cylinder wall and ring issues causing low compressions TCM would not have issued an SB allowing compression reading down into the low 40's.

Clarence

[StevenL757]

Conti cylinders are crap, period.

Lycoming cylinders out last them two to one if not more ...

Absolutely disagree.  The longevity of CMI cylinders has everything to do with good engine management by the flying pilot.  The IO550 is designed to be run LOP, and I've taken one of those engines from ~500 hours to TBO running it that way.  Such good operating habits by pilots of CMI-equipped aircraft in general have contributed, in part, to CMI offering certain engines with a 2200-hour TBO, up from the earlier 2000, including my new IO550N a year ago.

Edited September 15, 2015 by StevenL757

[N177MC]

CMI offering certain engines with a 2200-hour TBO, up from the earlier 2000, including my new IO550N a year ago

And what does that prove ?  Nothing, except that they're confident the bottom-end will go the distance and contrary to cylinders, we know this to be 99.99% true. 

[N177MC]

Here's an idea :  Let's take a poll comparing M20J  (Lyco IO-360)  cylinder life Vs  M20R (Conti IO-550) cylinder life .

They are directly comparable because they have similar compression ratios and displacment.  The big difference is the Conti is probably loafing @ 2300 - 2400 rpm average compared to the Lyco that's by & large probably working harder @ 2500 rpm, average.

I'm willing to bet that Lycos out last Contis, 2 : 1  , hence my original post.

 

[jlunseth]

I don't fly an Acclaim so maybe don't have much to add, but I heard alot about the Acclaim issues a few years ago from just hanging around shops.  At first what you heard was talk about how the engines were being run too hotly, alot of grousing about poorly skilled pilots believing hyped up marketing from the company.  There was quite alot of hyperbole about ill-advised LOP operations mixed in, by people who just didn't like LOP operations.  There were quite a few top overhauls at 200-400 hours being blamed on that.  Then the coking of the oil breather tube was discovered and when it was corrected the top overhauls stopped like magic.  The oil breather plugs, the crankcase can't relieve pressure from blow by, lots of bad things happen including the rings being reverse pressurized (forced into the cylinder walls).  I had an episode with my 231 involving icing of the air oil separator and wouldn't want to wish that on any engine.

I can think of alot of reasons not to buy an Acclaim, the lack of useful load being a major one, but the engine is not one of them.  It is a very good engine with that problem solved.

[StevenL757]

"And what does that prove ?  Nothing, except that they're confident the bottom-end will go the distance and contrary to cylinders, we know this to be 99.99% true.

Here's an idea :  Let's take a poll comparing M20J  (Lyco IO-360)  cylinder life Vs  M20R (Conti IO-550) cylinder life .

They are directly comparable because they have similar compression ratios and displacment.  The big difference is the Conti is probably loafing @ 2300 - 2400 rpm average compared to the Lyco that's by & large probably working harder @ 2500 rpm, average.

I'm willing to bet that Lycos out last Contis, 2 : 1  , hence my original post."

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Answering both of your posts - As far as "what it proves", it speaks to the overall quality of cylinders when paired with good operating habits over time.  You stated flatly "CMI cylinders are crap", so unless you've put time in behind one of these engines, this is your rightful opinion - albeit, with no valid data.

You may or may not have heard of Bob Minnis.  If you have, you may also know he was a chief engineer and then senior leader at then-TCM who contributed heavily to the present-day design and functionality of the IO550 platform.  I've been lucky (and fortunate) to have worked with him regularly over the last few years on a couple of my engines' general maintenance tasks and he's counselled me regularly on my engine operating habits.  In my present airplane (310HP IO550N) this profile is a takeoff at 2700RPM, adjust MP, pull RPM to 2550RPM for cruise, and lean as desired.  IO550G-powered Ovations and Acclaims alike are perfectly happy to take off, climb, and cruise at their full 2500RPM.  At no time does this engine "loaf" - let alone at 2300-2400RPM.

I'm not disputing Lycoming cylinder performance - just challenging your general comments with some real-world collective, solid data.

Edited September 15, 2015 by StevenL757

[jetdriven]

Quite right - I thought the word lapping included working the geometry.  I went with Victor Aviation since they claimed to spend special attention to shaping the valve geometry and I feel it is well worth it to pay attention to this factor.  So far I have been very happy with the result.

Continental, from what I've read, uses a 3 step process to install, cut, and lap the valve seat. 3 different stones to the the 3 angles. then they dont even lap the valves.  but the valve is not centered in the seat and they wont really seal well when new.  Modern, and I mean since about 1985 or so, machine shops use a specialized cutter than does the 3 angles concentric to the valve guide.  A light lapping and it will last forever.

[Guest]

it's not just limited to NA cylinder.  You could do the same comparison with a Navajo and a 340/ 414/421.  Cylinder life would be the same Lycoming lasts longer than TCM.

Clarence

 

[aviatoreb]

Continental, from what I've read, uses a 3 step process to install, cut, and lap the valve seat. 3 different stones to the the 3 angles. then they dont even lap the valves.  but the valve is not centered in the seat and they wont really seal well when new.  Modern, and I mean since about 1985 or so, machine shops use a specialized cutter than does the 3 angles concentric to the valve guide.  A light lapping and it will last forever.

So I have read too - that continental factory new valves don't seal properly and that is needed and everything for longevity.  I don't know how they do it but there are certain shops that will work the valves so they have excellent geometry, and that is exactly what I had done when I needed a top - and as i said I was mad when I saw how poorly built all those valves were in my engine in what was a "zero time" engine.

[N177MC]

Answering both of your posts - As far as "what it proves", it speaks to the overall quality of cylinders when paired with good operating habits over time.  You stated flatly "CMI cylinders are crap", so unless you've put time in behind one of these engines, this is your rightful opinion - albeit, with no valid data.

You may or may not have heard of Bob Minnis.  If you have, you may also know he was a chief engineer and then senior leader at then-TCM who contributed heavily to the present-day design and functionality of the IO550 platform.  I've been lucky (and fortunate) to have worked with him regularly over the last few years on a couple of my engines' general maintenance tasks and he's counselled me regularly on my engine operating habits.  In my present airplane (310HP IO550N) this profile is a takeoff at 2700RPM, adjust MP, pull RPM to 2550RPM for cruise, and lean as desired.  IO550G-powered Ovations and Acclaims alike are perfectly happy to take off, climb, and cruise at their full 2500RPM.  At no time does this engine "loaf" - let alone at 2300-2400RPM.

I'm not disputing Lycoming cylinder performance - just challenging your general comments with some real-world collective, solid data.

Well, I'm no "expert", just an airplane owner for over 20 years (present Lancair Columbia 300 & 177RG, notice the 1st is a 310hp Conti and the later is a Lyco).

 I'm also an A&P/IA and I look after a couple dozen airplanes, half dozen are Mooneys. Needless to say, I see a fair amount of engines, first hand, day in & day out ...

[mike_elliott]

So I have read too - that continental factory new valves don't seal properly and that is needed and everything for longevity.  I don't know how they do it but there are certain shops that will work the valves so they have excellent geometry, and that is exactly what I had done when I needed a top - and as i said I was mad when I saw how poorly built all those valves were in my engine in what was a "zero time" engine.

They do it by setting the proper assembled spring height, seat pressures, as mentioned a 3 angle valve job cut perpendicular to the valve guide lateral dimension, matching rocker arms with the right valve and having the right rocker arm ratio. Some shops also take it a step further by unshrouding the valves a bit, and cleaning up the intake ports, along with port matching exhausts.

[jetdriven]

When I bought my TLS at 13xx TT the cylinders were shot (thanks Don Maxwell and the prebuy) I believe this was due to the previous owner running too high of a TIT (1650, more ?) even though it was in spec. I had those cylinders remand'd with the nickel process and never have run over 1615TIT and actual now days I run right at 1600TIT. So far about 600 hrs later I'm still at one quart of oil for 25 hours. 

I am as biased as one could be, but for the money there is NO better airplane out there than a Bravo. Compare the prices and performance against an Acclaim and you just have to really really want a newer airplane to make that jump....AND you get to keep the house :-)

 Take the rear seats out (reference my bicycle post) and it's almost an unbelievable amount of room compared to other airplanes. Something all long body guys should know......you DO know how to take the seats in and out right ? ;-) it takes 3 or 4 minutes. 

isn't useful load the problem with long bodies? What's yours ?

[jlunseth]

Tony-

TIT is not directly related to what happens to the cylinders.  TIT measures the temperature of the gases that drive the turbocharger, not the gases that go into the cylinders, and it is there to protect the turbo, not the cylinders.  It is true that the turbo as a unit will be somewhat hotter at 1650 than at 1615, and therefore will heat the induction gases somewhat more, but it is the Induction Air Temp that counts as far as the cylinders are concerned, and the intercooler cools the induction air quite a lot.  It is not whether the TIT was run at 1650 or higher, but why it was that hot.  If someone ran the engine dead in the red box that would certainly hurt the cylinders, not because of the TIT though, but because of the high pressure combustion process in the cylinders.  Mind, I am not saying go ahead and run your turbine at redline or more -  that is not a good idea for the turbo's sake.  But simply cutting the TIT to a lower number, like 1615 instead of 1650, doesn't mean the cylinders are any better off.  It is the mixture, and the degrees LOP or ROP that does that.  If you are running at 1615 and dead in the red box (i.e. right at peak) you are still hurting the cylinders. 

Probably what the prior owner did was run leaned to peak, which is what some of the POH's authorize, and that is a bad place for the engine to be operated.

I use EGT and CHT, primarily, to manage the engine.  I use TIT when I operate LOP, just to keep the power being produced at a level that does not hurt the turbo because of high temps.  I try to keep it at or under 1600 (the redline is 1650 for continuous ops.).

[Tony Armour]

isn't useful load the problem with long bodies? What's yours ?

980 lbs

Probably what was meant was payload. 89+ gallons full and a fuel burn of 27gph in climb and 19-20gph in cruise. And remember, those numbers (if not dialed back for, say tooling around local) stay the same no matter if you are at 3,000' or 23,000'. No discount for altitude because you are still making the same power but that equals speed too. Figure the numbers and it still sounds worse then it really is. The speed difference in my Bravo vs the 83' J I owned for seven years offsets at least some of the fuel used. 

Edit, my above statement got me curious and is probably good for its own thread. On the flight I just did, North Ga. to Baltimore (still here) My TLS compared to my J flight planning. I burned 17 more gallons and saved thirty minutes. 53g vs 36g and 2:34 vs 3:01, 14,000' vs 8,000' (used even altitudes for comparison) So when talking weights and comparing, I needed 100 pounds more fuel for the same trip. I will say..so I have been TOLD, the Bravo (and probably an Ovation) will carry an extra 100lbs much better than a 201. If I messed anything up, well, it's 3AM :-)

Edited September 19, 2015 by Tony Armour

[Tony Armour]

Tony-

TIT is not directly related to what happens to the cylinders.  TIT measures the temperature of the gases that drive the turbocharger, not the gases that go into the cylinders, and it is there to protect the turbo, not the cylinders.  It is true that the turbo as a unit will be somewhat hotter at 1650 than at 1615, and therefore will heat the induction gases somewhat more, but it is the Induction Air Temp that counts as far as the cylinders are concerned, and the intercooler cools the induction air quite a lot.  It is not whether the TIT was run at 1650 or higher, but why it was that hot.  If someone ran the engine dead in the red box that would certainly hurt the cylinders, not because of the TIT though, but because of the high pressure combustion process in the cylinders.  Mind, I am not saying go ahead and run your turbine at redline or more -  that is not a good idea for the turbo's sake.  But simply cutting the TIT to a lower number, like 1615 instead of 1650, doesn't mean the cylinders are any better off.  It is the mixture, and the degrees LOP or ROP that does that.  If you are running at 1615 and dead in the red box (i.e. right at peak) you are still hurting the cylinders. 

Probably what the prior owner did was run leaned to peak, which is what some of the POH's authorize, and that is a bad place for the engine to be operated.

I use EGT and CHT, primarily, to manage the engine.  I use TIT when I operate LOP, just to keep the power being produced at a level that does not hurt the turbo because of high temps.  I try to keep it at or under 1600 (the redline is 1650 for continuous ops.).

I agree.

Using TiT was just simplifying my statement. EGT's make up the TiT, don't you agree that they are kinda the same. Move one or the other up or down and they move together. The TiT redline on mine is 1750 !! No wonder so many cylinders were burnt up before the Bravo mod.....and........probably why many cylinders were burnt up afterwards too :-) Oh yea, and 500 CHT :-O

If someone asks me how hot I run mine, I'm not going to quote each EGT. I'll just say 1615 TiT. And that's what I use to set the mixture while watching the EGT's and cylinder temps as well as the oil temp. Knowing that if all else is good then I'm fine with dialing in on a TiT number. For that not to work something has to be wrong. I would never own an airplane, at least an injected airplane without an engine analyzer.

On the back of my kneeboard I have my "normal" EGT's, CHT's, and corresponding TiT laminated and taped. So if I ever question that there is an issue I have quick access to good data to use for comparison.

I forget exactly where mine peaks but it is above 1650 and it will actually run LOP quite smooth but I don't do that except to play with it every few years (briefly)