mtv wrote:Differential compression checks are pretty much a waste of time, and not required by the FAA. A better test of a cylinder's health is to use an automotive type compression tester. You connect it to a cylinder, then motor the engine through with the starter. You're verifying that the cylinder actually MAKES compression, as opposed to fiddling with a cylinder to see if you can get it to HOLD compression at one particular point in its cycle. A pretty useless test.

MTV

Wrong!
Differential testing is not a useless test!
Continental and Lycoming specify this test for a reason.

You can tell where the cylinder is loosing compression. Intake, exhaust, rings, or a crack.

While you can tell some things with an automotive tester there are too many variables.
Such as battery voltage, starter condition, compression ratio, throttle open vs closed. etc, etc.

TangoFox wrote:

mtv wrote:Differential compression checks are pretty much a waste of time, and not required by the FAA. A better test of a cylinder's health is to use an automotive type compression tester. You connect it to a cylinder, then motor the engine through with the starter. You're verifying that the cylinder actually MAKES compression, as opposed to fiddling with a cylinder to see if you can get it to HOLD compression at one particular point in its cycle. A pretty useless test.

MTV

Wrong!
Differential testing is not a useless test!
Continental and Lycoming specify this test for a reason.

You can tell where the cylinder is loosing compression. Intake, exhaust, rings, or a crack.

While you can tell some things with an automotive tester there are too many variables.
Such as battery voltage, starter condition, compression ratio, throttle open vs closed. etc, etc.

Well, then why, when I was having difficulties with an O-320 Lyoming, and differential testing showed high 70s in every cylinder did a Lycoming tech rep tell me to get an automotive compression tester and test the engine with that. Two cylinders had major problems but the differential tester allowed the mechanic to "fiddle" with the position of the prop to get it to hold pressure, a routine part of the test.

The automotive test verifies that the cylinder is MAKING compression, not just that it's holding compression at one particular point in the rotational cycle.

The tech rep said, and I quote: "The differential compression test is done because we've always done them, and they are not the best test of cylinder integrity. And, in fact, there is no requirement in the regulations to routinely conduct this test at routine inspections, though everyone does."

Yes, the differential test MAY indicate a problem, but I've seen several engines that passed a differential test just fine, but had significant problems....mine being one of them....I wound up overhauling a 400 since "major overhaul" engine that was essentially junk.

FWIW

MTV

CapnMike, with the right engine mount, biscut mounts, and prop, your 185 with the 520 can also be as smooth as a turbine. Most 185 aircraft with the two blade and standard mount are what I call a shaker, just the way they are. Mine was this way for 22 years and two different engines. In 1998 under my I/A's watchful eye I installed a TCM reman, bigfoot 3 blade 88 inch prop, new Kossla heavy duty mount with two of the biscuts being the larger size. It was turbine smooth and still is today with 16 years and closing on 900 hours.

If your 185 has a 3 blade and heavy duty seaplane mount you have something going on causing it to shake. Glad to see you added the 185 to the hanger collection, they are a great plane.
Ron

To bad a permold 520 with the IO520 "D" induction isn't approved for the 185.... Built one for my Bearhawk. Three blade square tip McCauley prop. With assistance from Alaska Aircraft engines came up with a counter weight arrangement with no restrictions on RPM. Gami injectors.... May install the insight engine monitor with the vibration monitor.... Mark M. Platinum, Ak.

mtv wrote:

TangoFox wrote:

mtv wrote:Differential compression checks are pretty much a waste of time, and not required by the FAA. A better test of a cylinder's health is to use an automotive type compression tester. You connect it to a cylinder, then motor the engine through with the starter. You're verifying that the cylinder actually MAKES compression, as opposed to fiddling with a cylinder to see if you can get it to HOLD compression at one particular point in its cycle. A pretty useless test.

MTV

Wrong!
Differential testing is not a useless test!
Continental and Lycoming specify this test for a reason.

You can tell where the cylinder is loosing compression. Intake, exhaust, rings, or a crack.

While you can tell some things with an automotive tester there are too many variables.
Such as battery voltage, starter condition, compression ratio, throttle open vs closed. etc, etc.

Well, then why, when I was having difficulties with an O-320 Lyoming, and differential testing showed high 70s in every cylinder did a Lycoming tech rep tell me to get an automotive compression tester and test the engine with that. Two cylinders had major problems but the differential tester allowed the mechanic to "fiddle" with the position of the prop to get it to hold pressure, a routine part of the test.

The automotive test verifies that the cylinder is MAKING compression, not just that it's holding compression at one particular point in the rotational cycle.

The tech rep said, and I quote: "The differential compression test is done because we've always done them, and they are not the best test of cylinder integrity. And, in fact, there is no requirement in the regulations to routinely conduct this test at routine inspections, though everyone does."

Yes, the differential test MAY indicate a problem, but I've seen several engines that passed a differential test just fine, but had significant problems....mine being one of them....I wound up overhauling a 400 since "major overhaul" engine that was essentially junk.

FWIW

MTV

Actually you are required to perform a compression test per the FAR's.
And why doesn't Continental or Lycoming specify an automotive tester?
You can get something that doesn't jive with any test on just about anything.
Still doesn't mean the test is useless!

Sounds to me like if you are getting a good reading from the diff tester you may have had possibly some cam issues?
Just a guess though.

Nope, broken rings and a bad valve. Point is, you could screw around by moving the prop enough to get it to hold compression but it couldn't MAKE compression.

I've been told by several mechanics that a differential compression test is a routine and common test, but not specifically required.

I should not have said that it's a useless test, because it in fact can and often does suggest problems.

And, again, it was a Lycoming tech rep who recommended the automotive tester. This was reinforced by the instructor at the Lycoming Piston Engine Service School.

That's all I know, not an A & P.

MTV

FAR 43 appendix D does require a compression test, but doesn't specify what type of compression test. On Rotax annuals we were trained to and used automotive style compression testers and that satisfies the requirement.

Either style test is legal, but a differential leak test will usually show some problems such as a leaking valve or rings at an earlier stage where an "automotive" style wont. That being said I'm sure someone will argue that. Way back in A&P school, we were taught to use both if necessary. I haven't used an "automotive" style since I left school.... I think I have one somewhere in the bottom drawer of my tool box. Any test can be cheated, but then you're not doing the test right, are you...
John

I think the problem with differential compression tests is that there are mechanics that don't do it properly. Automotive testers don't show ring or valve damage as soon as a leak down test will. It's pretty hard for a mechanic to listen for air blowing by valves or rings while using an automotive tester. You can also squirt a little oil in a cylinder with an automotive tester and it will show great compression.
That being said, I think people put too much faith in compression tests. It's pretty easy for a dishonest person to get great compression out of something they are trying to sell. It also doesn't give any indication of the health of the bottom end.

ajfriz wrote:I think the problem with differential compression tests is that there are mechanics that don't do it properly. Automotive testers don't show ring or valve damage as soon as a leak down test will. It's pretty hard for a mechanic to listen for air blowing by valves or rings while using an automotive tester. You can also squirt a little oil in a cylinder with an automotive tester and it will show great compression.
That being said, I think people put too much faith in compression tests. It's pretty easy for a dishonest person to get great compression out of something they are trying to sell. It also doesn't give any indication of the health of the bottom end.

Truer words were never spoken.

MTV

I've been listening to some of Mike Busch's Webinars. While listening to "how to destroy your engine in one minute" I thought of this thread. Was the root cause of this cylinder failure ever determined? Does this plane have a digital engine monitor? I in know way want stones thrown at csstricker, I just think it could be interesting to see what the cause was and if it could have been prevented in the cockpit.

A scenario I'm thinking about is maybe there was some detonation going on and when WOT was applied violent pre-ignition occurred which could easily blow the head off a cylinder in seconds.

Note: Sorry for my rambling...I'm just jonesing for an aviation fix.

Hey Whee,

This is the 182 that I flew for years and it belongs to the flying club that I used to be active in and used to be the treasurer for. It does not have an engine analyzer. Carey and I flew up together and I'm familiar with how he flies the aircraft. We've also talked a lot about how to run it, especially with what I have learned from watching Mike Busch's webinars and reading his articles after getting my 205. To my knowledge, he was running it 100-120 ROP around 2100-2200 RPM and, at that altitude, 19-20" MP. I used to run it at peak EGT when I knew it was below 65% BHP, which is specifically allowed in the AFM, and has been discussed here at length. Carey may have done this too. He can speak to that. We flew up to JC this day together and I believe that he had the above power settings which matched mine.

In my opinion, here are the real issues.

1) It's a flying club plane being flown by numerous people, none of them flying the plane the same way. And in my opinion, most of them probably the wrong way (having done years of flight reviews to members as a club CFI). Recently more new pilots with the bare minimum required by the club (100 hours total time) have been flying it quite a bit. Besides needing a bigger plane, this was a BIG motivator in getting my own aircraft where I am the only person flying it! I believe that it is totally possible that this engine has had cylinders cooked repeatedly.

2) This engine has had nothing but problems since we had it overhauled by Precision Power in Bountiful, UT. And it's the second engine that we had done by this place. On both of them it took over 6 months to get it done and, with this one specifically, we had issues from the get go. I don't have anything good to say about this operation. No customer service, no communication, and multiple problems with this last engine. I believe that this is the third or fourth cylinder that has had to be replaced or had something addressed on an engine that is mid time or less I believe.



Just as an FYI type of thing, Arnold's over in Cascade did the work. It took two months to get the plane fixed and we went up and picked it up at the beginning of September. So far it is running well. I flew it a few weeks ago and am actually going to fly it today. I would be lying if I said flying that engine sometimes doesn't give me mixed feelings. Especially knowing the variety of people that fly it. I guess having flown in the club for so many years without incident tempers that feeling a bit, but I sure do like flying my plane better!

I'll let Carey correct or add as needed. But with so many variables with how this plane is ran, I don't know if they will ever know the cause. I pushed for years for engine analyzers to be put in them, but we never had the money for them. I think they are starting to get more serious about making it happen, which would be a good thing to monitor how all the club planes are ran, in addition to the other obvious benefits.

In reading back through this, I think I have had a small epiphany about Snake's complaint. My students and I have had little problem getting down in one try. But with crop dusting and patrol students I used a four hundred feet pattern altitude. I wonder if Snake makes low patterns. When we are high, like in a 1,000' pattern, we don't really pick up any change in the apparent rate of closure until we get down to 500' on final. Like most things, it is easier to judge when close to the target.

The go around is the safe solution to misjudgment. The fact that those who stay low all day have an advantage doesn't change that.

Thanks GSP. I suspect it probly had something to do with being a club plane. I was thinking about the possibility of him forgetting to adjust mixture as he descended to JC. The detonation margin gets smaller as the plane descends then enough deto occurs to cause a hot spot and when full power is applied then violent pre-ignition blows the cylinder. I've forgotten to adjust mixture on decent before and didn't think much of it. I think this scenario could really happen which is making me rethink how I'll manage the engine in my next plane.

Grassstrippilot wrote:
In my opinion, here are the real issues.

1) It's a flying club plane being flown by numerous people, none of them flying the plane the same way. And in my opinion, most of them probably the wrong way (having done years of flight reviews to members as a club CFI). Recently more new pilots with the bare minimum required by the club (100 hours total time) have been flying it quite a bit. Besides needing a bigger plane, this was a BIG motivator in getting my own aircraft where I am the only person flying it! I believe that it is totally possible that this engine has had cylinders cooked repeatedly.

That right there is the very reason I quit flying club airplanes and bought my own as well, and I've never flown a club plane again.

Flying government planes was bad enough, but in my case, I did most of the flying of the planes that I flew regularly. It was always interesting to me, how fast an airplane went downhill in condition when it no longer had a "primary pilot" who took care of it. Fleet airplanes got beat to shit, and I never liked flying them if I could avoid it.

The good thing about engine monitors is it allows maintenance to know what parameters may have been exceeded, and how the engine was run. That alone MIGHT make the pilots a little more careful.

Maybe

MTV

That's also the reason I won't lease my airplane to anyone. Back years ago, my pard in the TR182 and I allowed it to be rented to commercial applicants, because the FARs had just been changed to require a complex airplane to be used for the commercial checkride. Initially I checked out all of the pilots who were going to use it, and I was pretty picky about power control. But I was tied up when a particular pilot, Andy, wanted to be checked out in it, so he was checked out by one of the other instructors at the FBO, who wasn't nearly as persnickety as I was.

Pretty soon we started having plug fouling problems among other things, and then one day when I flew it, I couldn't get the gear to lock. After several attempts at retracting it and extending it, it still wouldn't lock--the green light wouldn't. So I tried to pump it down, and I couldn't get the telescoping handle to extend--it was jammed.

Long story short, I landed, and when I lowered the nose gear to the ground, the green light came on. I checked the flight records, and Andy had been the last pilot to fly it. So I called him, and after a little cross examination, I learned that he'd had some trouble getting the handle to go in after a mock gear problem, so he'd just hit it in with his hand. In reality, the pump handle was not down all the way, which is why it jammed, and because it wasn't down all the way, there was some bleed-by which was not allowing the electro-hydraulic pump to develop full pressure, sufficient to push the nose gear down enough to lock. But somehow, when I lowered the nose gear to the ground, it locked anyway.

In that conversation, Andy also said that he had been flying the airplane at much reduced power settings, and he was bragging about the low gph reading he was getting on the fuel flow meter, but even so he was still flying around 120 knots!!! He was flying an airplane that trues at over 165 knots at only 120 knots, less than 172 speeds!!! My pard and I discussed it, and we banned Andy from further flying our airplane. We had no problems with the other half dozen pilots who flew it.

But it's sure a fact that in general, non-owners just don't care for things the way owners do. Rental cars, rental airplanes, rental houses, all get mistreated. The difference is that mistreated airplanes can fail as a result of being mistreated, and people can die.

Cary

whee wrote:Thanks GSP. I suspect it probly had something to do with being a club plane. I was thinking about the possibility of him forgetting to adjust mixture as he descended to JC. The detonation margin gets smaller as the plane descends then enough deto occurs to cause a hot spot and when full power is applied then violent pre-ignition blows the cylinder. I've forgotten to adjust mixture on decent before and didn't think much of it. I think this scenario could really happen which is making me rethink how I'll manage the engine in my next plane.

That all being said, the club has routinely taken engines 1,000 hours past TBO with no issues. The fact that they fly regularly I'm sure contributes to their longevity.

Regarding descents, here is a good article by John Deakin. I use his cruise descent advice and it works well.

http://www.avweb.com/news/pelican/183094-1.html?redirected=1