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Thread: IO-520 Compressions

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    Tom3holer's Avatar
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    IO-520 Compressions

    We just started the annual on my 185 and the compression had dropped a good deal from last year.
    Last year they were 73,75,69,70,71,72. This check showed 63,73,60,64,63,62. The engine has 233 hrs. since a 2006 FRM.
    I dd one flight around the patch to warm it up. The plane had flown about 70 hours since last annual and had been running Phillips 20/50 with a bottle of Camguard. Previously it had run Aeroshell.
    Most of the flights were over an hour. I have been running LOP on most all the flights and operating per Gami recommended procedures. My mechanic was in a bit time constraint to leave for an appointment so we didn't have time to do any diagnosing with the scope till he returns on Monday.
    In going through the logbook the previous compressions were fairly consistent over the years. I do have a multiprobe engine analyzer and keep an eye on temps and the cylinder temps run in the low 300's with #1 the highest at 360 in cruise. the EGT's all in the mid to upper 1400's.
    I am questioning the change from AS to Phillips and perhaps the LOP operation but am quite concerned at the big drop almost on all jugs.
    Any thoughts or suggestiosn greatly appreciated.
    Tom
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    skywagon8a's Avatar
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    Tom, The first question that you need to answer is "where are the leaks"? The three possible places are rings, exhaust valves or intake valves. Listen at the breather exhaust, the tail pipe exhaust and the induction air intake while the compression tester is plugged in.
    N1PA

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    Eddie Foy's Avatar
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    A compression check on a big Continental requires a mandatory borescope. That is your next step.

    Also requires that the check be done with a gauge set calibrated against a master orifice. That determines your minimum number. It is not necessarily 60 PSI.

    Was this test done with the same set of gauges by the same mechanic?
    Eddie Foy
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    Steve Pierce's Avatar
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    There are 2 sizes of orifices as well. You should be using the large orifice. My son let the inertia hose reel go with one set of gauges attached, then a customer helping dropped my other set of gauges. I bought a new set and sent the others in for repair and calibration. They read consistantly higher now I believe.

    Read the SB Eddie linked and borescope the cylinders. I assume you had a well broken in engine before you added Cam Guard? I know several engine shops that prefer Phillips X/C over Aeroshell hands down due to corrosion issues. Our testing proved the Phillips stuck to parts longer than Aeroshell.
    Steve Pierce

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    behindpropellers's Avatar
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    TO fuel flow - when was side 97-3 completed?

    Tim
    Last edited by behindpropellers; 11-11-2017 at 09:51 AM.

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    www.SkupTech.com mike mcs repair's Avatar
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    like everyone else says, make sure the gauges are reading correctly, they do change over time or drops... pressurized but with no flow, do both gauges read the same? note discrepancy to compensate.. then use that orifice thing to find lower limit

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    www.SkupTech.com mike mcs repair's Avatar
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    and changes to the air supply pressure/volume/restrictions will mess with readings, thats why using that orifice to calibrate is important

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    aktango58's Avatar
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    233 hours in 11 years is not enough to keep your engine from corrosion. I remember being told by a reputable engine guy that you can get away with flying an internally corroded engine for about 50 hours without much issue; after 50 hours all the friction areas from pitting starts to show.

    May just be a gauge issue, but what does the filter show?
    I don't know where you've been me lad, but I see you won first Prize!

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    Does the engine run differently than it did last year? Using more oil? Different temperatures? Lacking power? Performance is what most of us want. Sometimes we look for numbers to diagnose a change in performance. Barring performance changes? I'd suspect there's something wrong with the numbers.

    That plane's compressions have bothered you since you bought it. Maybe you just ought to top it and get happy? That's not sarcasm. If the numbers are sagging it may be time to start budgeting.
    Last edited by stewartb; 11-11-2017 at 10:51 AM.
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    If only one or two had dropped I would look at the cylinders. With them all dropping I would look at testing procedure/equipment. If bore scope does not show any problem I would treat it with benign neglect and recheck after 50 hours as long as performance has not changed as Stewart noted.
    DENNY
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    I think 3 hole tom has lost confidence in this particular 185 and should sell it to me at a steeply discounted price then buy a different one. I feel that this would be the best solution for the given situation.

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    Someone may have mentioned above that you need to make sure that you have the required take-off power fuel pressure/flow. You will see upper-end wear on your cylinders if you don't have the required fuel. Don't lean above 75% power, continental uses fuel for cooling at high power settings...
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    Tom3holer's Avatar
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    Thank you all for the thoughts and suggestions.
    My mechanic will be back Monday and we will scope the jugs and try and diagnose what is going on.

    To answer a few questions now:
    The last reading was done by him with the same equipment.
    If I am not mistaken he is using the smaller orifice but that is what he used last time also.
    We did calibrate the FF with the proper gauges and TO FF is at the redline.
    My mistake on the overhaul date, it was 2009 and it was stored for slightly over a year with the logbooks indicating it was done in compliance with TCM long time storage procedures.
    The plane was kept in a heated corporate hanger since the engine was installed.
    As far as performance it seems to perform just the same as when I received it some 80 hours ago.
    One thing I noticed shortly after I bought it was oil on the belly coming from the breather tube.
    I had not noticed it when I first flew the plane with the original owner but I may have missed it.
    There is a thread here I started on that issue and one of the items on this annual we are addressing is to change the outlet on the breather tube to be vertical sticking just below the firewall with the end parallel to the ground in flight attitude.

    Again thank you all and will report the findings later this week.

    Tom

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    18180's Avatar
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    I find that it takes more than one run around the patch to get everything warmed up good. I like to do my compression checks right after a good hard run. Seems especially true on Continentals.

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    aktango58's Avatar
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    Quote Originally Posted by Tom3holer View Post
    We just started the annual on my 185 and the compression had dropped a good deal from last year.
    Last year they were 73,75,69,70,71,72. This check showed 63,73,60,64,63,62. The engine has 233 hrs. since a 2006 FRM.
    I dd one flight around the patch to warm it up. The plane had flown about 70 hours since last annual and had been running Phillips 20/50 with a bottle of Camguard. Previously it had run Aeroshell.
    Most of the flights were over an hour. I have been running LOP on most all the flights and operating per Gami recommended procedures. My mechanic was in a bit time constraint to leave for an appointment so we didn't have time to do any diagnosing with the scope till he returns on Monday.
    In going through the logbook the previous compressions were fairly consistent over the years. I do have a multiprobe engine analyzer and keep an eye on temps and the cylinder temps run in the low 300's with #1 the highest at 360 in cruise. the EGT's all in the mid to upper 1400's.
    I am questioning the change from AS to Phillips and perhaps the LOP operation but am quite concerned at the big drop almost on all jugs.
    Any thoughts or suggestiosn greatly appreciated.
    Tom
    If all of the compressions had fallen about the same ratio, I would tend to consider equipment. However, number two cylinder only lost two pounds compared to other's as much as 10.

    I am not a fan of LOP, not to be critical but TCM operational data overrides Gami. Just because Gami says it will work fine does not make that so.
    I don't know where you've been me lad, but I see you won first Prize!

  18. #18
    Steve Pierce's Avatar
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    I would check it again, I have had plenty of case where pressures came up after a simple ground run. Like posted above listen to where the air comes from.
    Steve Pierce

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    Will Rogers

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    Tom, what's the history of those cylinders?

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    www.SkupTech.com mike mcs repair's Avatar
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    you don't understand what the orifice is.... it a TEST UNIT that gets hooked to the compression gage to determine the lowest acceptable reading... to calibrate unit occasionally.

    lowest acceptable reading changes depending on air supply fluctuations/obstructions/lines and damage to gauges

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    I find that my small bore compression tester doesn't seat the rings easily on big bore engines. Just switching to the big bore tester will increase the numbers sometimes dramatically. Most often there is a "tink" when a ring seats in its groove with a jump in pressure on the gauge. No "tinks" and the numbers are marginal with air out the breather.

  22. #22
    Eddie Foy's Avatar
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    You need this tester for bores over 5 inches,
    https://www.aircraftspruce.com/catal...EaAu55EALw_wcB
    Eddie Foy
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  23. #23
    Tom3holer's Avatar
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    Again thank you all for the input.
    I am confused now that I see there are two different gauges the E2M and the E2M 1000 for bores 5" and over. The TCM service bulletin SB03-3 makes no reference to two different gauges.

  24. #24
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Tom3holer View Post
    ..
    I am confused now that I see there are two different gauges..
    so am I .... I only have one test unit... wiggle the prop to get rings to seat, unless you are selling the plane and want to make it look like it has good compression...

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    Fly it more...
    "Don't feed the hipsters"

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    skywagon8a's Avatar
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    Quote Originally Posted by OLDCROWE View Post
    Fly it more...
    And harder, stop babying it.
    N1PA
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    Eddie Foy's Avatar
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    One thing puzzles me. Why is this test called a compression test in the aircraft world.

    It is actually a differential pressure test or a leakdown test in the automotive world.

    It is not a true direct compression test.

    Does anyone do a direct compression test?
    Last edited by Eddie Foy; 11-13-2017 at 07:46 AM.
    Eddie Foy
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    Steve Pierce's Avatar
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    Quote Originally Posted by mike mcs repair View Post
    so am I .... I only have one test unit... wiggle the prop to get rings to seat, unless you are selling the plane and want to make it look like it has good compression...
    I did too until I got into the TCM service buletin. Check out AC 43.13-1B paragraph 8-14. The bigger orifice would be used on O-320 and up, smaller on O-235, 290 and small Continentals.
    Steve Pierce

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    Quote Originally Posted by skywagon8a View Post
    And harder, stop babying it.
    Amen, 24 squared ROP until altitude starts taking away MP and then flat out but always 2400 rpm in cruise. Below 8K I lean to the same 1360-70/320-30 in the hottest cylinder every time and above 9 I run peak...With this engine management all my engine concerns went away (compressions stay put and oil consumption is minimal at 1qt/20 at 700+hours on new cylinders that in the bore scope look better than they did at 100 hours when I was babying it). I got this advise in engine management methodology from a friend who runs a fleet of IO520’s in Canada and once I followed...no regrets well except for his recommendation on Scotch!
    Last edited by OLDCROWE; 11-13-2017 at 07:44 AM.
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    Tom3holer's Avatar
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    For a correction the log books were at the airport when I posted the numbers which were a bit off so here are the actual numbers.
    Last year/This year

    1: 70/60
    2: 72/64
    3: 71/70
    4: 68/68
    5: 72/70
    6: 70/63

    As I read the description for the two gauges one had a .040 restrictor orifice and the larger on has a .060 so it stands to reason it would give a higher reading but where does TCM make mention of this?

    In cruise at 24/24 or WOT. In cruise all egt's are mid to upper 1400's and all head temps are mid 300's except #5 which runs the hottest at 360 ish. I do run LOP in cruise and see right around 160mph in cruise.

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    Eddie Foy's Avatar
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    Interesting article on borescoping by Mike Busch.

    https://www.aopa.org/news-and-media/...ance-borescope
    Eddie Foy
    "Put out my hand and touched the face of God"

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    Steve Pierce's Avatar
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    Was changed in the latest revision of AC 43.13-1B CHG 1 Par 8-14 b:
    (1) For an engine cylinder having lessthan a 5.00-inch bore; 0.040-inch orifice diameter;.250 inch long; and a 60-degree approachangle.(2) For an engine cylinder with 5.00inch bore and over: 0.060 inch orifice diameter,.250 inch long, 60 degree approach angle.
    Steve Pierce

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    mvivion's Avatar
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    Quote Originally Posted by Eddie Foy View Post
    One thing puzzles me. Why is this test called a compression test in the aircraft world.

    It is actually a differential pressure test or a leakdown test in the automotive world.

    It is not a true direct compression test.

    Does anyone do a direct compression test?
    Eddie,

    Its actually called a “differential compression test”. Why is it used in aircraft engines? Only legitimate answer is because it is the “recognized” test, and the one we’ve used forever in aviation.

    the good news is that, properly administered, this test will pick up a lot of engine problems. That said, the specific numbers themselves (60 vs 70) are relative, and so not necessarily meaningful. Trends are more indicative of a problem, or, as others noted earlier, if you can hear where the Air is going, if the cylinder isn’t holding Air.

    I once had an O-360 Lyc that ran hot, didn’t make much power (a REALLY relative function) etc, but it could pass a differential compression test. Just wiggle that prop and fiddle with it to get it to the right spot and it would hold pressure.

    Finally, I called Lycoming Tech help, told them what I had and what we’d done, and first thing he said was go to NAPA and buy an automotive compression tester. Did that, and two cylinders would not pass. They could be made to pass a differential test, but that’s not how an engine works.

    But, differential pressure is the aviation standard, and when properly applied, will reveal many cylinder problems.

    MTV

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    Steve Pierce's Avatar
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    I think the FAA and manufacturers call it a differential compression test and us mechanics call it a compression test. Some of us have a hard time putting a string of long words together.

    Compression test (differential pressure) is only one test. You listen to where the air is going, borescope, read the spark plugs, look at the color of the oil, oil usage, screens, filter, engine temps etc. The engine will normaly tell you when something is amiss if you pay attention to it.
    Steve Pierce

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    Eddie Foy's Avatar
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    Steve,
    I understand all of that. Do you ever do a direct compression test on an engine with a subpar “differential compression” test??
    Eddie Foy
    "Put out my hand and touched the face of God"

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    Quote Originally Posted by Tom3holer View Post
    For a correction the log books were at the airport when I posted the numbers which were a bit off so here are the actual numbers.
    Last year/This year

    1: 70/60
    2: 72/64
    3: 71/70
    4: 68/68
    5: 72/70
    6: 70/63

    As I read the description for the two gauges one had a .040 restrictor orifice and the larger on has a .060 so it stands to reason it would give a higher reading but where does TCM make mention of this?

    In cruise at 24/24 or WOT. In cruise all egt's are mid to upper 1400's and all head temps are mid 300's except #5 which runs the hottest at 360 ish. I do run LOP in cruise and see right around 160mph in cruise.
    I understand they are all different (and this is my first 520) but mine really didn't like LOP operations (and the wife really didn't like leaning it through the rough cough and sputter part) as I had oil consumption issues (1 in10 with new cylinders following break in) and had to steak a valve twice but all that went away with the "run it like you stole it" operations but I also think my flight profile really helps... I typically blast off and climb hard WOT with RPM at the top of the green and begin leaning at 5K, 7K and as I go above that then level off and heat it up for at least and hour, usually two these days and plus I fly it 220-250 hrs/year.

    I think its about finding the pressure/heat combination that makes you and your engine happy and then sticking with it. You might give ROP a try for a few months and see, mine methodology is not per book but is based on 40-50 ROP baseline temps also I run cruise temps in decent.
    Last edited by OLDCROWE; 11-13-2017 at 11:21 AM.
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    skywagon8a's Avatar
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    I've also tried squeezing the fuel flow. It doesn't work in the long run. Maintenance hours (expense) are higher and more frequent. I had a turbo inter-cooled engine for a while and was very careful to lean it correctly. That engine was continually causing something to happen. When I increased the fuel flow one gallon per hour the issues disappeared.

    Tom, Airline pilots are notorious tightwads. I've known a few. Remember I used to be one. Spend just a little bit more money on gas and the maintenance issues will diminish.
    N1PA
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    Cub Builder's Avatar
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    A differential compression test or leakdown test will show problems with a cylinder long before a dynamic compression test. With a whirling propeller out on the front, the differential test is safer and easier to do as well. A dynamic compression test has so many variables like speed of the starter, throttle position, battery condition, etc, that comparing one year vs the next usually isn't a very valid comparison. As Steve said, with a differential compression test, where it's leaking is often times much more important than the numbers you read on the gauge. If one does a dynamic compression test, you get a final compression number, but if there is a problem, that number doesn't tell you whether you have a valve or ring problem. On a differential compression test, that's what the mechanic is looking and listening for.

    As a A&P, when I'm inspecting an engine, I am doing the inspection to detect potential problems before they become flight safety problems, which is why a compression differential test is used. People are number driven, and the numbers are all you see in the logs when looking at history, but the actual inspection process is a bit more involved.

    -Cub Builder
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    The two most disagreed upon topics in aviation with big Continentals? Low compressions and LOP operations. Funny, the big proponents of low compressions not being a problem are also the big proponents of LOP operations. Tom's owner reports of excessive oil discharge from the breather support sagging compression findings and blow-by. It doesn't sound like his rings are seating well with combustion pressures or compression test pressures. If I was to try a Hail Mary I'd put some MMO in the oil and run it hard for a couple of hours and test it again, just in case, but it's a low percentage play.

    MMO's probably the third most disagreed on thing in aviation.
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    aktango58's Avatar
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    Quote Originally Posted by stewartb View Post
    The two most disagreed upon topics in aviation with big Continentals? Low compressions and LOP operations. Funny, the big proponents of low compressions not being a problem are also the big proponents of LOP operations. Tom's owner reports of excessive oil discharge from the breather support sagging compression findings and blow-by. It doesn't sound like his rings are seating well with combustion pressures or compression test pressures. If I was to try a Hail Mary I'd put some MMO in the oil and run it hard for a couple of hours and test it again, just in case, but it's a low percentage play.

    MMO's probably the third most disagreed on thing in aviation.
    Would you use the MMO in a downwind turn?
    I don't know where you've been me lad, but I see you won first Prize!
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