Low rpm

[very easy]

Hi all,

I am repeating a post I put in the varieze section. My varieze has the usual 0-200 engine which I just bought from the USA. I can't get more than 2400rpm on cruise, and 2300 static rpm. I just phoned the previous owner and he said it would occationally drop on cruise from 2800 to 2400 and would bring the throttle to idle and then back to cruise to correct it. He tried another carby on it but did not solve the problem. The engine runs very smoothly from idle to 2400, but has never gone higher for me in 10 hrs flying. Any fault finding guys out there with ideas.

 

Thanks,

Norm

[Kent Ashton]

Start with the basics: check the timing, change plugs & read the old plugs, do a compression check, check the carb linkage, confirm that the plugs are getting a spark.

[very easy]

Thanks Kent,

By the time I fault find this engine, I'll know it inside out. Thats how I learned to fix cars decades ago. Just ordered a Continental manual from Aircraft Spruce.

[Drew Swenson]

Try also "Tony Bingelis on Engines" and "Firewall Forward" by Tony Bingelis.

[Waiter]

I would think 2300 static is about right. And the 2800 cruise is about right

 

The drop from 2800 to 2400 tells me something serious is going on that is reducing the power out.

 

Have you experienced this drop yourself?

 

 

 

If this drop is accompanied with a vibration, I would expect something that is effecting one cylinder, i.e. sticking valve.

 

If the drop is smooth with no vibration, I would expect something thats effecting All cylinders. Fuel delivery, air delivery, Ignition source.

 

I don't think dropping a mag would have this significant of a rpm drop! (100 - 150 rpm)

 

If you have CHT / EGT guages, what do they read when you get this drop?

 

Just re-read your original post and see that you never seen anything above 2400.

 

Floating (or broken) valve spring - Use a stethescope or hose and listen to each cylinder as the engine is running.

 

Use an automotive timing light and see if anything wierd is going on with the ignition timing. Check both mags, #1 cylinder.

 

 

 

 

Waiter

[Drew Swenson]

Did the previous owner actually hear the RPM drop--or was it just on the indicator?

[very easy]

Drew, he knew it dropped on the sound of the engine, performance. I had my asi checked and it is accurate. Not getting expected performance. Going now to look.

[very easy]

Just had a look at the plane. If I pull a knob which empties the gasculator [thats also a lowest point drain] only about a teaspoon of fuel runs out . Have to wait a couple of hours to get the same again. Thought gravity filled the gasculator constantly and kept the carby supplied with fuel on demand. Plane was half full, on three wheels, not running and got the same result on reserve and wing tanks. Could that be a blockage?

[Bob Setzer]

Norm

#1- Did you get a set of aircraft build plans and engine install plans with the airplane.

Its sounds like you have bought an airplane with a preexisting problem.

With that being said you have to start at the beginning.

#2- Did the builder deviate from the plans in the fuel delivery layout (vent lines, fuel valve and gasculator install). When was the last time the fuel lines were replaced (and for that mater the vent lines, you need to check for obstructions in these lines, don’t just look at the lines remove and check them for obstructions). What material are the fuel lines made of (not part of your problem but need to be replace if they are the vinyl style from the tanks to gascalator).

#3- Do a fuel flow check as pur the engine install manual.

After this you can move on to an engine-related problem (which would include how the engine control cables were installed to the “carby”, check the plans).

 

Bob Setzer

[very easy]

Norm

#1- Did you get a set of aircraft build plans and engine install plans with the airplane.

Its sounds like you have bought an airplane with a preexisting problem.

With that being said you have to start at the beginning.

#2- Did the builder deviate from the plans in the fuel delivery layout (vent lines, fuel valve and gasculator install). When was the last time the fuel lines were replaced (and for that mater the vent lines, you need to check for obstructions in these lines, don’t just look at the lines remove and check them for obstructions). What material are the fuel lines made of (not part of your problem but need to be replace if they are the vinyl style from the tanks to gascalator).

#3- Do a fuel flow check as pur the engine install manual.

After this you can move on to an engine-related problem (which would include how the engine control cables were installed to the “carby”, check the plans).

 

Bob Setzer

Sorry Bob,

Don't have any plans. Can see the fuel line goes from the tanks to the gascalator then to the carby. There is no fuel pump other than gravity. No fuel comes out of the gascalator. Will disassemble and clean fuel system.

[Waiter]

There is no fuel pump other than gravity. No fuel comes out of the gascalator. Will disassemble and clean fuel system.

 

Sounds like you may be on to somethng.

 

The gravity feed must supply at least 2x the required fuel.

 

If the O-200 maxes fuel burn is 5GPH, then the fuel system must gravity feed 10 GPH.

 

Check the lines, filters, valves (is the valve opening fully) (sometimes, the carb imlet connection is also a metalic filter), etc

 

ALSO, don't forget to chek the vents to see if they are plugged.

 

Waiter

[Drew Swenson]

You need to do what you can to get hold of the plans. You are at a severe disadvantage without it. The terf cd is one source

[very easy]

Found the source of my rpm drop-two exhaust valves leaking. Can't believe the engine idled so smoothly in that condition and so left the compression test for the last. Does anyone have cyl head torques for the Continental 0-200 engine and bolt tightening sequence. Also, what should the compression be by the book? Two other cyl. are 90 psi hand propping. Bought an overhaul video but they don't list any specs.

[Lynn Erickson]

Found the source of my rpm drop-two exhaust valves leaking. Can't believe the engine idled so smoothly in that condition and so left the compression test for the last. Does anyone have cyl head torques for the Continental 0-200 engine and bolt tightening sequence. Also, what should the compression be by the book? Two other cyl. are 90 psi hand propping. Bought an overhaul video but they don't list any specs.

when all else fails red the dam manual. seriously you should have the book before you attempt this. also you need to check compression with a leak down tester, not an automotive type and the readings you should have will be in the book. did I mention that you should have the book.

[very easy]

when all else fails red the dam manual. seriously you should have the book before you attempt this. also you need to check compression with a leak down tester, not an automotive type and the readings you should have will be in the book. did I mention that you should have the book.

I was looking for a comparitive test of compression. The leakage was as ovious as dog b---- It went into the exhaust pipe and all done under the guidance of a LAME who confirmed my inital test.

[youngmic]

Norm,

 

all done under the guidance of a LAME who confirmed my inital test

So why did you not ask him/her these questions.

 

It may have escaped your notice, presumably you've been to busy researching thoroughly what your doing, but the O-200 cylinder heads are screwed on.

 

If the leakage is so severe that it is the cause of 400 RPM loss at the top of the RPM range and top of the horsepower curve, I would be most suprised it could be hand started, let alone idle properly.

[Lynn Erickson]

Norm,

 

 

 

So why did you not ask him/her these questions.

 

It may have escaped your notice, presumably you've been to busy researching thoroughly what your doing, but the O-200 cylinder heads are screwed on.

 

If the leakage is so severe that it is the cause of 400 RPM loss at the top of the RPM range and top of the horsepower curve, I would be most suprised it could be hand started, let alone idle properly.

why would say it won't start? I have seen them not only start on two cylinders but run on two. not much power but they will run all day that way. I have seen many bad valves on flying aircraft. thats how they got to us for the annual, they flew in but did not leave until the valves were redone.

[very easy]

Unbolted the two pots and they are already in the cylinder head reconditioning shop. Valve guides for both exhaust valves extremely worn-about one sixteenth inch wobble of the valve. Should be around 4 thou. Suspect the valve stems are not getting lubricated from the rocker. Push rods and rocker holes clear. Might be blockage toward the valve lifters. Intake valves like new, but they can go on less lubrication. Surprised they dont have valve stem seals.