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IO-520 Compressions

Tom3holer

Registered User
Cape Cod
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
 
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.
 
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?
 
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.
 
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
 
and changes to the air supply pressure/volume/restrictions will mess with readings, thats why using that orifice to calibrate is important
 
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?
 
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.
 
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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
 
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.
 
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...
 
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
 
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.
 
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 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.
 
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
 
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.
 
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.
 
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?
 
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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.
 
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!
 
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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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