Vibration

Alterfede · Post by **Alterfede** » Fri Oct 31, 2003 7:40 pm

Last thursday, i was going to go to lincoln for the annual, did carb heat, mag check, and max static rpm, just before take off, oil press and temp ok, only max rpm showed 2200 rpm, but as i dont know the acuracy of my tach i asumed it was ok. Whe i took off, the plane has a little but very noticeable vibration (Mean not a crazy shake), and the rpm in the take off run were in the 2200 rpm, not the 2350 it usually gives, as i was taking off from a 1000 feet runway decided to continue, it didnt have a good climbing performance, dont ask numbers i was too worried about the vibration, inmediately, i did a pattern and landed in the same runway becuase main one had too much xwind. Back in earth, did the checks again, everythig the same, What could it be, stuck valve, ignition problem?. It has done this 3 times before, on the first three the problem disapeared on the next flight without doing anything, the last was in april, and the plane didnt fly until the last flight im talking about. In the meanwhile i cleaned and regapped spark plugs, and changed oil. Any advice, today im calling the mech who is going to do annual for advice, on what can i do before he cames here. Saludos

N73087 · Post by **N73087** » Sat Nov 01, 2003 1:13 am

Sounds like a valve. When it happens again, feel for the cold cylinder.

Post by **Bruce Fenstermacher** » Sat Nov 01, 2003 2:08 am

What N73087 means is you may have a valve stuck open or sticking. Since the cylinder won't be firing it will be colder than the rest. So when it happens again shut down and feel for the cold cylinder. You can also pull your prop through compression and you probably won't have any in one cylinder. What probably happened before is the cylinder finally warmed up and expanded, freeing the valve. If you determine it is in fact a stuck or sticking valve thens see all the "rope trick" posts to learn how to fix it.

Alterfede · Post by **Alterfede** » Sat Nov 01, 2003 1:14 pm

I rotated the prop by hand, i and felt one that passes, what do you think of taking out the plugs and looking inside with a light and rotating the prop? IÂ´ve read about the rope trick, be sure ill do that if i have a stuck valve. Hope this stops soon, Thanx guys

Post by **GAHorn** » Sat Nov 01, 2003 3:31 pm

What kind of gas have you been using, Fede?

Alterfede · Post by **Alterfede** » Sat Nov 01, 2003 3:58 pm

Car gas, but for just 50 hs

Post by **Bruce Fenstermacher** » Sat Nov 01, 2003 6:53 pm

I think you've comfirmed a stuck valve. Pull the plugs and holding your fingers over each cylinder will rotating the prop. Find which one has no compression. Doing the rope tricK is not a big deal. I've done all six cylinders, pulling the valves and cleaning then in an afternoon, but I'd done it before. Read all the posts here about it especially the warnings. If you have one valve stuck I'll bet the rest are getting ready and should probably be cleaned. Email me privately if you need more detailed info on this process.

Alterfede · Post by **Alterfede** » Sat Nov 01, 2003 11:02 pm

Bruce, ill do the rope trick as soon as possible and coment the results. Thanx a lot, this was starting to worry me a lot. Saludos

Alterfede · Post by **Alterfede** » Thu Nov 06, 2003 3:41 pm

Hey boys, flew yesterday, first checked compresion on cyls with my finger, all had almost the same, then started the engine, stayed a few minutes, about 4, warming up, then checked megs, carb heat, and mex static rpm, on last one, 1150 rpm and the dam vibration. Cristian, a cessna 310 owner, who was with me, told me to continue checking in the runway, we went there, about 1 minute, then re checked some times the max static, everything went fine, 2330 rpm and no vibration, so we took off, went up to 3400 ft, checked cruise settings, everything went smooth and fineMaybe is a stuck valve fixing itself, i know it can happen again, this stuff hapened 3 times before and fixed itself by the enxt flight. Hope this doesnt happen again next wednesday when i ll take the plane to lincoln fro annual (Hope no anal). Any sugestion saludos

Post by **GAHorn** » Thu Nov 06, 2003 6:05 pm

Alterfede wrote:Hey boys, flew yesterday, first checked compresion on cyls with my finger, all had almost the same, then started the engine, stayed a few minutes, about 4, warming up, then checked megs, carb heat, and mex static rpm, on last one, 1150 rpm and the dam vibration. Cristian, a cessna 310 owner, who was with me, told me to continue checking in the runway, we went there, about 1 minute, then re checked some times the max static, everything went fine, 2330 rpm and no vibration, so we took off, went up to 3400 ft, checked cruise settings, everything went smooth and fineMaybe is a stuck valve fixing itself, i know it can happen again, this stuff hapened 3 times before and fixed itself by the enxt flight. Hope this doesnt happen again next wednesday when i ll take the plane to lincoln fro annual (Hope no anal). Any sugestion saludos

Fede,...the problem you are having is intermittent, and therefore difficult to diagnose. So when you finally were able to duplicate it, (when you saw the max static rpm at 1150

(is that correct?) then WHY....WHY did you continue to operate until it disappeared? THAT was the time to identify the cause....while it was broken. It is impossible to fix things that are working correctly.

I don't want you to get hurt or to hurt your airplane. Here's what I suggest. Let your engine cool overnight. Remove your upper cowl, and remove all your valve rocker covers. With your ignition OFF and the fuel OFF and the Mixture LEAN, turn your prop by hand and watch all valves that they fully close (keep themselves against the rocker arms) when they are supposed to do so. IF any of them stick, even momentarily, you should remove the rocker arm shaft, rocker arm, spark plugs, and remove the valve keeper keys and valve springs. Push that valve down into the cylinder. Ream the valve guide to the proper size. (Or if you don't have a reamer, use a rifle bore brush and solvent to scrub the valve guide clean---not an officially blessed method.) If you can use a wire and hook the valve stem out the spark plug hole, you can also use crocus cloth or emery to clean the valve stem. You can relocate the valve with wire or relocate the valve stem with a slender magnet. (Hint: you can hold the valves closed by pressurizing the cylinder with air while you reassemble the valve springs and keepers onto the valve.)
While the engine is being disassembled be alert for broken valve springs and broken valve guides. A broken/cracked valve guide can allow a valve to seat most times, but occasionally close only partially at other times causing vibration and a loss of power that will continue until the valve accidentally seats completely once again. Test for broken valve guides by "wiggling" or attempting to move the valve stem sideways while it is in it's guide. Motion more than 1/16" is excessive.
Lubricate the guide and valve stem before reassembly with engine oil or Lubriplate white grease. Reassemble the rest and run the engine around the pattern for a test.
You should also examine the lower vent plugs on your magnetos for internal oil contamination. If your magneto drive seals are leaking oil into your mags, it can give erratic results.
Also if your mechanic has a "high tension lead tester". This will check your spark plug leads for shorts and/or leaks to ground, which can give intermittent vibration and loss of power.
Don't just operate hoping for "suerte".

Post by **Bruce Fenstermacher** » Fri Nov 07, 2003 2:47 pm

Fede I agree with George. When your engine was not working correctly would have been the time to shut down and check for acold cylinder. I think I said that if you have a sticking valve as the engine warms up and the cylinder expands the valve may work fine. Eventually when the engine or cylinder cools the valve will stick and your running on 5 cylinders. Hopefully this won't happen when you need the power! I had this happen on final with my C65 powered Cub. A C65 running on 3 cylinders doesn't make much power. Good thing I didn't need to go around.

For a reamer I have used a piece of ordinary soft copper water pipe which is small enough to fit inside the valve guide. This is the kind of pipe that you can bend with your hands. I use a knife to gouge out the inside of the tube making the edge sharper. By running this tube at an angle with some pressure back and forth in the guide I have scraped out the carbon build up that is helping to stick the valve. the soft copper water pipe will not gouge the valve guide. In every case of a sticking valve that I have had, I have also had to clean the valve of the deposits.

Alterfede · Post by **Alterfede** » Fri Nov 07, 2003 3:37 pm

George and Bruce, thanx for the advice, i was talking with a friend who was a car mechanic, he has many tools, so we are going next week to do the job, hope to find the valve and fix the problem. This Froum is so good.....

wa4jr · Post by **wa4jr** » Thu Nov 13, 2003 2:14 pm

And here we have the argument for a good 6 cylinder EGT panel instrument. Not so much for leaning as for a quick and accurate diagnosis of what is happening with the engine. How much time was spent wondering what was happening? What cylinder or cylinders are producing the problem? With even the non-scanning EGT instruments, one could quickly cycle through all six cylinders and immediately find the problem child, remove the cowls and go right to the source of the problem. Well worth the $500-$600 for the instrument.

In this case, I seem to remember George saying there was some way to diagnose a stuck valve with the panel MP gage, but don't have the hint with me here. With the combination of MP gage and EGT, one could trace the problem accurately to a stuck valve in a certain cylinder before the expensive mechanic ever arrives at your plane.

dacker · Post by **dacker** » Fri Nov 14, 2003 12:51 am

Wouldn't a stuck valve make your MP guage fluctuate?
David

Dave Clark · Post by **Dave Clark** » Fri Nov 14, 2003 1:51 am

John

Yes indeed! I had some plug fouling a couple of times this Summer. The first time I didn't think of finding it with the UBG as I got it cleared very quickly. I thought of it later though and the next time it happened I tracked down the cylinder and mag but it cleared up fast then also. I wanted to know if it was the same plug but it didn't foul a third time because I got used to leaning it on the ground. Anyway it is indeed a great diagnosis tool.