182 lacking performance
 

The 182 at the school I instruct at just got back after a gear up landing repair. The engine was completely redone but now it feels like it lacks power. The takeoff role is almost twice as long as published in the poh. It's a Lycoming o-540 making good rpm and normal manifold pressure. Maintainence says It's fine. Any ideas what could be causing poor performance on a rebuilt engine?

Even though you may have max rated MP & RPM and engine power, a different propeller could have been installed, causing issues. Also check wheel alignment; Does it seem to take more power to taxi? Does it seem to perform satisfactorily once in the air?

Our club 172 had an engine rebuild - with the valve springs installed up-side down. Could not get over 6,000 ft and would climb like a brick. Probably a long shot.

If you know you are right, you need to demand that it be corrected. Compression values? There's always a reason and with modern maintenance requirements the aircraft performance not should be that far off, that's the whole point of engine rebuilds and maintenance. If you are still concerned something is up with it and nothing gets done, call FAA airworthiness. Otherwise, it could kill someone. I've been through similar situations, where an engine would constantly overheat that never gave an ounce of trouble in the years past. Something changed rather drastically and it would constantly go to redline. Forget what the issue was, but there was an actual issue, despite the initial "there's nothing wrong with it".

Though the OP's problem could have many more possibilities, which I'm too tired to list, I wouldn't necessarily say valve train problems would be that much of a long shot, at least something to consider. I had an O-540 (Fresh Factory Reman, direct from Lycoming) that would not
achieve required oil pressure. I did not fly the airplane. I sent the engine back to Lycoming and they actually admitted they discovered an oil galley plug that was left out... I do need to at least give them credit for the admission rather than trying to BS me. Also tell maintenance you want to see the engine uncowled. Look for anything loose or out of place, especially on the induction side ( I believe it is normally aspirated?) Also look for rags/shop towels potentially left in the engine... (seen that happen more than once)

It could be a number of issues. How long was it down for the engine swap? I would imagine if you last flew it in the winter the performance would have naturally degraded due to density altitude.

What if one cylinder was completely dead? It wouldn't show a difference during the magneto check. Can you check EGT individually at each cylinder?

In light aircraft with constant-speed props, you can get rated RPM and manifold pressure, even if the engine is weak. The blade angle will adjust to make the parameters fit. But it doesn't mean you are getting the expected thrust.

In a turboprop, you check torque. Not a 100% guarantee, but pretty certain you are getting the thrust you expect. (The exception I can think of is a bad blade). Obviously, not available in a C-182RG.

Double the takeoff roll? Even winter to summer shouldn't cause that much difference. I say have a different mechanic look at it before someone dies. Unless they did a lot of structural repair that significantly increased the weight of the airplane, I think something is wrong.

In my OV-10 Bronco Squadron, we had an airplane that took three times the normal roll to get airborne, and had half the climb rate of all the other airplanes. If it was in a 4-ship when we went to the bomb range, we would have to take extra passes around the pattern so he could get up to pattern altitude.

They sent it back to Rockwell twice and weighed it and checked it for straightness. They swapped the engines, and checked the torque on the ones they took out.

They never found anything. When the Air Force Museum said they wanted an airplane, it was the first one to go.

(If you've seen it at Wright-Patt, I've flown it, and it is this clunker!!)

If you have a dead cylinder, the vibrations would be terrible.

Had a car worked on once, and as I drove away, it was obvious something was wrong. It was smooth, just gutless. (V-6).

One cylinder dead---plug wire.

With a flat-four, probably true about vibration....but maybe not. Partially-dead; ie, burned valve, broken valve?

What other repairs were done to the airframe? The rigging could be way out. If something is misaligned it can rob performance and be dangerous. If the engine appears to be developing full power this is the next thing to check.

This^ You could have a cylinder down on compression and not know it until it gets checked. In the past I've seen a write up for a failed mag check that ended up with having two cylinders replaced.

Don't forget to check the airspeed indicator. It could be reading low too.

Bill

So that would cause it to use 2x the normal takeoff distance?

I have seen a c182 with the incorrect carburetor installed that sounds kind of similar. Took awhile to figure out because no one though to look there.

I flew a Seneca once with an obviously weak engine. It was written up several times but nothing could be found wrong with the engine. Eventually mechanics found that the muffler had come apart internally restricting airflow.

Thanks for all the info the airplane is grounded until maintenance can find the problem.

Was originally a gear up landing and repaired?
Could have dragging brakes? you stated it takes twice the normal distance for takeoff, but what about climb and cruise performance?

Does it land in the 'normal' distance? Does it require unusual trim for straight and level, i.e. rudder trim? also was it carbureted or turbo before?
Curious.

If it was dragging brakes its unlikely the dragging would be symmetric, pulling left or right and once airborne it would feel like it lept off the ground.

Cylinder Break-In:
How many hours does the engine have on it and what is the oil consumption? Has the engine had oil fouled spark plugs? Higher than normal oil temperature? Since the engine has been recently overhauled, the cylinders may have not broke in correctly, which would cause the above as well as low power (because of the excessive blow-by past the rings).

When an engine is breaking in after an overhaul, the rings are setting up a wear pattern with the cylinder wall. In fact, that's why Mineral oil is used during the break in period for an engine, which increases wear to assist the ring and cylinder wall break in. After break in is achieved, normal Ashless Dispersent oil is used. Contrary to popular belief, cylinder walls are not perfectly smooth, they have very small ridges, which hold oil and this oil help lubricate the rings. Durning break in the top of these ridges are worn off and the bottom is left to hold engine oil.

If the engine does not break in correctly, too much oil stays in these small ridges, and over time the oil is baked in the small ridges and ring is now riding on a perfectly smooth surface, which is NOT a good thing. When this happen the oil control ring removes all oil (none is left behind because there are no ridges to hold the oil). This is called glazing. This can cause low compression, low power and high oil consumption. The only way to rectify this is pull all of the cylinders, hone them, and reattempt the break in.

Ignition:
Do the mags check good? What's the drop? If there is a large smooth drop, the mag is probably internally mis-timed. If you have a rough drop then a cylinder is dead (ignition wise), which would be a dead plug or bad harness.

If the mag drop seems good, this still doesnt rule out ignition until the tech checks the mag to engine timing. A grossly mistimed mag can reduce engine power (and if the timing is retarded would not cause a rough running engine, unless it's waaaay off).

Fuel and Induction:
Does the engine run rough at low power settings? If so, there could be an induction leak, or the primer system could leaking.

Camshaft/Wrong Pushrods/Lifters:
A extemely worn camshaft or lifters would cause and engine to not make power, however, this is extremely rare with a new regularly used engine (usually corrosion begins the high wear).

However , if the wrong length pushrods were used during the build up, the valve will not open as far as it should, causing the engine to make less power. Have the tech conduct a tappet clearance.

Burned valves are unlikely unless the engine has been REALLY abused, but its easy to check, while doing the compression check, listen for air hissing out of the exhaust. If there is a lot, a burnt valve is the culprit.

Obviously all of the above items should've been checked/replaced/addressed in the overhaul (OH) but you'd be surprised what you DON'T have to do according to the FARs to call and enigne an overhaul.

Hope this helps!!!

One hot summer day 2 FAA inspectors were renting our 172RG. After the one hour preflight, thay taxied out for takeoff. I hear over the radio "Cessna is aborting takeoff" and they pull off the runway. They taxi back and do the same thing. So they taxi back again, wait a long time then take off. A few hours later they came back and I asked why the two rejects. They said the takeoff roll seemed long so they rejected and tried again. Still seemed long so they rejected and then looked up the numbers in the POH and it turned our to be about right. So the third time they took off. They said they would have grounded the plane if it hadn't roughly met the POH numbers. I guess they weren't familiar with the 172RG's nickname of "Guttless".