Time for the Cylinder Farey to Visit

[aviatoreb]

Well, I am in annual since yesterday, and I got "THE CALL" from the shop - compression on one cylinder is very low - 28 and two others are showing signs in the borescope that the valves are getting weak with compressions in the low 60s.  Surprised me since since all cylinders were in the low to high 70s at last compression test last summer.  And she has been running smoothly and burning very little oil.  I am a little surprised, but so it is.

 

3 other cylinders are showing 76 and up for compression.

 

Engine time is 985hrs on my TSIO520NB on my rocket.  I have read that continental cylinders last about 1000hrs and what do you know....  Argh.

 

Discussion was concerning if to replace all cylinders and make it a complete "top" or just to replace the bad cylinders, since the other 3 are showing good health.  By the way, engine has been burning very low oil - like 1 quart per 12 to 15 hrs, and she has been running very smoothly, but oil analysis was showing signs of possible valve problems lately.  Given the good health indicators of the 3 good cylinders, the cylinder shop recommended "if they ain't broke then don't fix them" and my AP concurs, and I tend to concur too.  So unless there is a good counter argument, I am giving thumbs up to reman just the bad cylinders.  These are first run cylinders on this factory new engine, so I see no reason to replace them at greater expense.

 

As for how to break in....they break in cylinders just like an overhaul, right?  I broke in an Lyc-IO360 once and it was fine.....run it hard wot at 3k went nicely.  But who here has broken in a TSIO520 lately?  Obviously not WOT.  My CFI who flies an airline that runs twin 402's (with the TSIO520VB and he has broken in many cylinders over the years with them) asked me what my cruise climb is - 88% on my engine is 35'', 3500rpm, and he said break it in like that.  Really?  I will be going pretty fast and burning lots of fuel like that.  Well I guess that will be fun.

[Alan Fox]

Make sure he is using the correct restrictor in the compression gage.....(continentals use a restrictor in the gage) .....Also low 60s in not out of range for a continental....

[DonMuncy]

Have you read the service bulletin fromTCM that basically says "if you have low compression on a cylinder, fly it for 45 minutes or more and recheck it."  At my last annual, one of my cylinders read some low number (like 46, if memory serves) and the MSC recommended a cylinder overhaul or replacement. I told him to fly it and check again. He did, and it was within specs. I looked back in my logbooks and found about 5 cyoinder replacements due to "low compression". I wonder now how many of them really were bad. 

[BigTex]

A couple of thoughts... Did they fly the plane before checking the compressions? Big Continental engines need to be flown before doing compression checks. There is some folks on this forum that changed out several cylinders only to find out if they flew their plane first, compressions would be right where it should be. If you decide that you need to replace a cylinder, only replace the bad one. It would be worth your time to watch Mike Busch's webinar called "All About Cylinders." He never changes on perfectly good cylinders.

[aviatoreb]

A couple of thoughts... Did they fly the plane before checking the compressions? bore Continental engines need to be flown before doing compression checks.

 

Thanks all.

 

How recently do they need to be flown for a compression check?  He ran it up but did not fly it.  I flew it in to the shop 36 hours before the compression check and I had gone to Burlington then Hartford then SLK during that same flight so roughly 2 hrs.

 

I will ask about the continentals restrictor in the gage - I can say that this particular AP/IA does a lot of work on the airline Cessna 402s and has a lot of experience with those TSIO520 generally.

[aviatoreb]

Have you read the service bulletin fromTCM that basically says "if you have low compression on a cylinder, fly it for 45 minutes or more and recheck it."  At my last annual, one of my cylinders read some low number (like 46, if memory serves) and the MSC recommended a cylinder overhaul or replacement. I told him to fly it and check again. He did, and it was within specs. I looked back in my logbooks and found about 5 cyoinder replacements due to "low compression". I wonder now how many of them really were bad. 

 

Could it really go from 28 back up to the 70+ it was last summer?  It is a surprise to see it drop so much so quickly.

[Seth]

Erik-

 

I hope the flight before checking the compressions again fixes at least one or two of them.  Sorry to hear that you are having Cylinder problems.  As the shop and your A&P state, I'd keep the other three Cylinders as they are indeed seeming strong right now.  Some Cylinders do last, others have issues. 

 

Break in wise, you do use a lot of fuel during break in.  Some will state to break in LOP vs ROP, but I went the ROP way even though it is possible to break in, and evidently cleaner too, using a LOP method - let's not debate this here however.

 

You want to keep temps down by keeping a high mixture while using a high power setting to seat the piston rings.  Follow the instructions and do what the A&P and shop tell you to do.  Also, you'll get a lot of advice from MooneySpace.  I've now broken in a new engine, and then broken in new cylinders during a Top.  Both went well - the most important two flights are the first and second hour.  It also depends on what type of cylinders you are using, but once oil consumption levels off, that's when the cylinders are broken in.  This can range anywhere from a few hours to 25 hours depending on what type fo cylinder.  In both cases, mine were broken in probably before 10 hours, but I conservatively kept the mixture rich and higher power for another 10-25 hours.  You'll also have to change the oil at sooner cycles.

 

1st hour - 75-85% power keeping the cylidners as cool as possible using rich mixture.   Overfly the field for about 15 minutes to make sure everything is operating smoothly and then fly near the field but in longer laps so you're not turning the entire time at 180+ knots.  Land and check for oil leaks.

 

2nd hour - 75%-85% power and every five minutes vary the power settings.

 

3-10 hours - 75% or better power settings keeping everything cool

 

Once oil consumption stabalizes, your engine is broken in.  I kept running 75% plus power until around 20-25 hours.  I also did not try too much manuvering or pattern work - just long legs and cross countries.

 

0-10 hours = oil change

10-25 hours = oil change

25-55/60 hours = oil change

Change the oil every 30-35 hours after that.

 

That's what I do.  My former Mooney had oil changes closer to every 50 hours, but I'm trying to be real conservative to the IO-550.

 

Your engine is different along with a tubro, and thus may have different break in instructions.

 

Good luck!

 

-Seth

[aaronk25]

When the time comes for me to break in new cylinder(s) I'm gonna fly it just like I do now. 75% peak egt or slightly lean of peak and only back off (lean more) if the heads climb above 380.

The only thing your not supposed to do is fly around at low power settings but who cruises around at 50% power any way ? Pipeline patrol I guess.

I always roll my eyes when a mechanic says run it hard to seat the rings like there trying to make some statement when in fact very few mechanics really, truly know about great engine Managment. There great at fixing things though.

I run peak egt at 5-6000ft and still have 74 compressions on jugs with 1400 hours....go figure.

[DonMuncy]

Could it really go from 28 back up to the 70+ it was last summer?  It is a surprise to see it drop so much so quickly.

I don't remember the numbers, but it was low enough he recommended a cylinder replacement and after flying it for 45 minutes or so, he said it was OK. It is apparently TCM's view that the compressions vary considerably.  Mike Busch contends that he would never replace a cylinder for low compression. He thinks compression test are a very poor test of cylinder health. He says that if you find low compression, you should do a borescope and see if you can find out why it is low. If that shows burned valves, then you should fix it. 

[duke]

I agree with Mike Busch. If leakdown shows excessive leakage, listen at oil filler, if you hear excessive leakage there it is going past the rings, listen at exhaust pipe, leakage there it is exhaust valve leaking. If scope does't find anything bad, fly it for an hour and do leakdown again when hot. Excessive ring leakage can show up when leakdown is done when eng is too cold, or excessive ex valve leakage can be caused when a flake of carbon is stuck on valve seat. In either case, another hour of flight and recheck is in order.

[aviatoreb]

Thanks all.  I am bringing these questions to the shop today.  I find it hard to imagine that the 28 cylinder will bounce back to healthy, but you never know!  I was describing to me other signs of bad health in the other two, like blow by and poor valve health as he does use a high quality digital borescope.  So in all likelihood, facing the music, the cylinder farey will be visiting me this annual.  But nonetheless, last ditch effort your advice all and thanks.  I am completely decided to follow AP + cylinder shops advice to leave the 3 good cylinders in place.  By the way, my CFI who I called last night gave me the opposite advice - remember he is the guy who flies Cessna 402s for the local airline so he has lots of experience breaking in TSIO520's (I called him in large part to ask him about engine settings during break in). He said, 1000 hours- thats how long those cylinders last.  So he suggested I should replace all the cylinders since he figures there is no way they will all make TBO so no money will be saved by not just replacing them now while it is all taken apart.  I told him my leaning which is to take the cylinder shops strong advice to leave the good ones in place.  He said he respects that as a fine decision even if it is not the one he suggested.  

 

I did ask him by the way if he would fly dual with me, for hire, for the first hour or two of break in to make sure I fly during those first few hours correctly - seems like money well spent since he has so much experience with this specific engineering ops flight with this (almost same) engine and the cost of doing it poorly can be high.  Not to mention it never hurts to take on a little extra dual time.

[aviatoreb]

What is your collective wisdom on overhauling my first run cylinders vs buying new cylinders?  I figure I only need these things to go max another 1000hrs.  (TBO is 1600 and I am at 985 now).

[danb35]

You say compression in these cylinders is low with leakage past the valves.  Have you seen any indication of this on your engine monitor?  You should see EGTs rising and falling by 30-50 degrees every minute or so, IIRC, on the affected cylinders.  I concur with the suggestion to fly it for an hour or so, and then recheck the compression immediately after shutdown.  If there's still evidence of leakage at the valves, I'd look at repairing the cylinders rather than a full OH or replacement with new.

[Cruiser]

Continental claims that low compression, defined as a number below the reading obtained on the calibrated Master Orifice (MO) should be combined with borescope analysis to determine where the leakage is occurring. IF the borescope shows scuffing on the cylinder walls and uneven, discolored valves coupled with increases in oil consumption then a decision to replace may be in order. It sounds like your mechanic is doing it right.

 

see http://www.avweb.com/news/savvyaviator/188758-1.html

 

see http://www.tcmlink.com/pdf2/SB03-3.pdf

[aviatoreb]

You say compression in these cylinders is low with leakage past the valves.  Have you seen any indication of this on your engine monitor?  You should see EGTs rising and falling by 30-50 degrees every minute or so, IIRC, on the affected cylinders.  I concur with the suggestion to fly it for an hour or so, and then recheck the compression immediately after shutdown.  If there's still evidence of leakage at the valves, I'd look at repairing the cylinders rather than a full OH or replacement with new.

 

Hi.  I have not seen signs of this on the engine monitor since I have not been downloading logged data.  I need to start doing that.  I have a JPI 700 that came with the airplane and I do not see where any cable would plug into it - and I have been dragging my feet on figuring that out.  Where is the plug in anyone? Looks like there is a nice usb downloader lately.

 

I just got off the phone with the AP.  He says the 28 cylinder shows an ugly asymmetric pattern on the valve in borescope.  Another cylinder is sounding significant valve leaking while listening at the exhaust and another cylinder is sounding significant ring leakage.  He said he would be okay with releasing cylinder number 3 to monitor but I decided to go ahead and replace it too since in a rocket it is a pain in the arse to get the exaust lifted to get into the cylinder (everything is super tight firewall forward in a rocket) and so if it is on its way out, and I am replacing two cylinders it makes sense to do the third now rather than in a hundred+ hours from now.

 

Decision is to go with rework my own cylinders OH.

[aviatoreb]

Continental claims that low compression, defined as a number below the reading obtained on the calibrated Master Orifice (MO) should be combined with borescope analysis to determine where the leakage is occurring. IF the borescope shows scuffing on the cylinder walls and uneven, discolored valves then a decision to replace may be in order. It sounds like your mechanic is doing it right.

 

see http://www.avweb.com/news/savvyaviator/188758-1.html

 

Thanks.  I do believe he is.

[KSMooniac]

I'm late to the thread, but think you're making a prudent decision.  If your mechanic has good borescope pics of the asymmetric pattern on the valves, then that is the best reason to take them off.  Overhauling or even just IRAN what your first-run jugs is a good choice IMO.  There is a good chance a savvy cylinder/engine shop will do a BETTER job seating the new valves than what TCM/CMI did at the factory, and that should ensure a long service life if you do your part with the red knob correctly.

 

I advise high power, LOP break-in flights per the Tornado Alley Turbo/GAMI recommendations.  You want high power to seat the rings, a clean combustion chamber to keep from interfering with the ring seating process, and cooler head temps.  Running high power LOP accomplishes all three goals while high power ROP only does one.  I did this successfully on my IO-360 and the break-in was done in less than 5 hours.  Do your research and consider all of the options and especially *why* the instructions are important...don't just follow random advice.  

[duke]

Sounds like your A&P did the proper diagnosis. There is nothing wrong with rebuilding your cylinders if done properly.

[wishboneash]

Cyl #1 in my Lycoming went to 0 compression within a month or so after annual (where all the cylinders were at mid 70s). First sign of trouble is when compressions are low at low power. Not obvious under the borescope. Engine ran smoothly at high power or cruise. Eventually had to have the valves lapped and put in a new rod to account for the change in the dimensions. So far so good.

[aviatoreb]

 

I advise high power, LOP break-in flights per the Tornado Alley Turbo/GAMI recommendations.  You want high power to seat the rings, a clean combustion chamber to keep from interfering with the ring seating process, and cooler head temps.  Running high power LOP accomplishes all three goals while high power ROP only does one.  I did this successfully on my IO-360 and the break-in was done in less than 5 hours.  Do your research and consider all of the options and especially *why* the instructions are important...don't just follow random advice.  

 

I am a big fan of LOP but have not been able to run LOP with reasonable TiT above 72% (75% somedays).  NOT to make a debate folks about LOP here please.  I simply have a how-to-question regarding LOP break in.

 

I have read about LOP break-in at 85% or so - I forgot where and I cannot seem to find it on google right now. Help anyone?  The thing that always confused me about that - don't you need really well balanced injectors to run LOP at higher power settings like 85%?  But on a major overhaul one is unlikely to have balanced injectors straight out of the box except by great luck, and there is not time to do a full gami test to the put gami injectors as one needs to run high power one way or another ROP or LOP during those first hours.  So how do they do that?

 

I presume on the other hand, my engine was well balanced injector-wise before new cylinders and I am hoping it still will be....or am I wrong?

 

There is a small chance that something will have changed and my TiT will not rise to high allowing me to indeed now be able to run higher power settings during break in.  If not - I will be doing it in ROP mode.

[aviatoreb]

Cyl #1 in my Lycoming went to 0 compression within a month or so after annual (where all the cylinders were at mid 70s). First sign of trouble is when compressions are low at low power. Not obvious under the borescope. Engine ran smoothly at high power or cruise. Eventually had to have the valves lapped and put in a new rod to account for the change in the dimensions. So far so good.

 

What made you look 1 month after annual?  And what do you mean low compressions and low low power? You are not taking compressions with the engine running.

 

I can say that oil analysis was indicating something wrong with valves even as of 50 hours ago and to keep an eye out, which we did.  Then compressions and borescope both agreed this week that something is wrong.  I am still waiting for the post-mortem email with photographs probably tomorrow of the valves with the cylinders off.

[aviatoreb]

But the strange thing - it never started using more than a little bit of oil.  I would have thought that oil consumption would have become high but it was very very modest.

[jetdriven]

Continental cylinders lately often last only 900 hours, especially on factory engines. They don't machine the valves concentric with the seat and guide, and they eventually start to burn and fail. it doesnt matter of you run ROP or LOP, etc.

[wishboneash]

What made you look 1 month after annual?  And what do you mean low compressions and low low power? You are not taking compressions with the engine running.

 

I can say that oil analysis was indicating something wrong with valves even as of 50 hours ago and to keep an eye out, which we did.  Then compressions and borescope both agreed this week that something is wrong.  I am still waiting for the post-mortem email with photographs probably tomorrow of the valves with the cylinders off.

 

I should clarify. I have a JPI-700 engine monitor. At around the annual, the EGT on all cylinders were fairly close to each other at low power (idle/taxi etc, typically under 1500 rpm). Normally a difference of 100 - 200 deg is not an issue under these conditions. I talked to the MSC  and they said it was not a reason for concern for this difference. But after a month or so, the engine started to run rougher than normal at low power settings and the EGT difference was more like 400 or 500. I wasn't comfortable with that. So my interpretation is that the EGT is low on cyl #1, then I am not making much power, hence possible loss of compression. Then I had the compression check done to verify this - turned out it was 0. The engine ran fine under high-power settings.

[AndyFromCB]

Continental cylinders lately often last only 900 hours, especially on factory engines. They don't machine the valves concentric with the seat and guide, and they eventually start to burn and fail. it doesnt matter of you run ROP or LOP, etc.

 

That's sad but on the other hand, they are not $2800 a pop like they are on the Bravo, so as they say, you can pay now, or you can pay later. Mine looked brand new at 1100 hours during overhaul and the previous owner always hauled ass at 32/2400. Could have kept them as is, but I elected to redo them at $1200 a pop with all new running gear.

 

I still think the Lycoming with wet heads is a superior high altitude engine to the Continental.