?Sticking Valve or Carb Ice?

[n3833v]

Why after reducing power to idle and then back to power, it disappeared. That doesn't sound like springs. Springs don't change tension that quickly.

John

[Bruce Fenstermacher]

Why after reducing power to idle and then back to power, it disappeared. That doesn't sound like springs. Springs don't change tension that quickly.

John

John we don't think the springs change during the time frame of a flight except however springs can change strength from cold to hot to cold.

What we are talking about is a spring or springs that are marginal that may or may not change strength throughout the flight but at certain harmonics allow the valve, intake or exhaust, to float open. Changing or reducing RPM allows the valve to seat and the situation corrects itself.

Makes perfect sense to me and after checking the basics and exhausting those avenues. We do not know the condition of the springs and largely based on the experience of another who had the exact same symptoms cured with new springs, that is the route I'd take. And I don't through money willy nilly at a problem.

[fangzz]

This thread has a happy ending.

Short version. All along, it was a sticking valve, and getting stickier. Just what many of you posited.

While waiting for the analyzer, I kept working on things that might be a contributor to the issue. Things I could see. One of those things was a welded intake elbow on #2. The weld didn’t look that great, so I bought a replacement. The day the analyzer arrived and we began prep to install same, I began to replace the elbow. I discovered the flange nuts were only finger tight. Once off, I saw that there was nothing wrong with the weld, visually, but that the gasket had visible tracks of fluid; it had been leaking. Equals xtra lean mixture. You see where this is going.

It was overheating the cylinder and had created a 'coking' cover of oil residue on the exhaust valve and in the valve guide. Heat buildup was causing the valve to periodically stick open. The repeatedly over-heated valve springs probably had lost some of their strength, and could not overcome the sticking valve, leaving the valve open until the cylinder cooled as a result of there being no combustion in that cylinder with the valve stuck open.

My IA and I proceeded to do the 'rope trick.’ With the exhaust valve off we found the valve stuck. We could have driven it into the barrel, but decided to pull the cylinder completely off and clean the goo off the valve stem and out of the guide. Which we did. I felt I was assisting an old midwife with my first-borne. He just pulled that jug off like it was no big deal. Scared me half to death. It took all day. I got to look inside the cylinder barrel and actually inside the crankcase through the cylinder opening. An extremely awe-inspiring experience for me. IA took a cursory glance, like it was an every-day experience, and casually mentioned, "sure is clean in there!" I puffed up like my son had just hit a homer. A proud dad. On your advice, I had bought a set of valve springs, so we replaced them on the workbench, me nervous as a cat about every little thing, every piece of dirt, and the IA just keeping on, getting the job done. The cylinder cleaned up and reassembled, we set about sticking it back on the engine. Hey, I'm thinking, I gotta fly this thing back home TONIGHT, before sunset. And, right now I'm holding Danielle's open heart in my hands. Absolutely sobering experience. IA just keeps moving. Getting the cylinder off was the easy part. Getting the muffler, the baffling and all the rest off, and keeping track of all the nuts, springs, etc, etc, was the hard part. Then getting that stuff back on. Cylinder was the easy part. About 5pm, we got her cowling back on, weather turning cold, we were done. I was tired. IA was exhausted. He left for home and I cranked Danielle, relieved by her familiar healthy roar. She sounded fine. I'm in disbelief. I take extra time. A lot of extra time. I'm looking at the engine instruments like I never had. Finally, no excuse to delay, and the sun about to sink out of view, Danielle and I launch over the cliff that is the airport’s approach, into the space 1000' above the valley below. My eyes were glued to the analyzer. #2's temps perfectly normal. Power better than ever. And faster than ever. 2 days to go until the weather window opens for the long trip home. Just in time, as they say.

She flew straight, true, and fast all the way home. 30 knot tailwinds all the way. The third day we landed after a 475nm final leg, with, I would determine after gassing up, 6 useable gallons remaining.

Along the way, not only did the analyzer help with leaning, it was most useful keeping me aware of CHT’s that became borderline a couple of times. My belief is this instrument, though a little pricey, will enable us to enjoy flying Danielle longer before her next TBO. And that will pay for the instrument. So, we don’t feel it was in any way a waste of time and money, even though, ultimately, it wasn’t the analyzer that focused us on #2 as the culprit.

Thanks for all your help along the way on this thing. Especially yours, Bruce.

[Bruce Fenstermacher]

Well how about that. After all this I'm glad you found the trouble and able to take care of it.

[fangzz]

BTW, Bruce, during the 'cleanup,' of the guide, we used your soft copper tube that I had prepared ahead of time, just in case, and the .30 cal bore brush that blueldr threw at the discussion. We got the valve so that it would pass the wiggle test without reaming. Thot you'd be tickled by that. Gotta get me one of those valve spring compression tools. They're pretty cool. Without one, I was as stuck as the valve.

[Bruce Fenstermacher]

Drew, there is nothing like the satisfaction of using a (inexpensive) home made tool. So long as it works of course. That soft tube has worked for me and would be my first tool of choice, and I have the correct reamer.

The first several valves I did I used nothing but 3 large screw drivers. Removed the rocker arm and shaft and placed a protected screw driver in the rocker shaft bosses and then used the other two screw drivers under the first to pry down on each side of the valve spring cap to remove the keepers. A bit tricky and a three handed job.

So I made this valve spring compressor out of some flat stock. It is a bit tight getting the keepers out but does work.

One day I had time to kill and decided to improve on my valve compressor tool and fashion one similar to another I saw and that which Arash showed. This one works better.

[fangzz]

EXTREMELY clever, Bruce. The one my IA had was a single piece, no hinges. Had the fingers that fit under the rocker shaft, like yours and Arash's. (That's a good looker, Arash) But this was VERY simple and very effective. Bruce, the image of you and three screwdrivers is scary. And I'm fearless. I was, once again, impressed by how simple, yet sophisticated, the design of the engine is. If you can remember back that far, maybe you can recall how intimidating it is when you first get your hands into the guts of one. That was me.

The thought of how hot that cylinder got through the 250 hours or so of that loose intake elbow makes me wonder how much life old #2 has left in it. On visual inspection, the valve and piston looked fine. Guess we'll just have to watch and see.

[Bruce Fenstermacher]

If you can remember back that far, maybe you can recall how intimidating it is when you first get your hands into the guts of one. That was me.

It is not that far back that I don't remember and to be perfectly honest I try not to forget. Lots of times, specially on a forum we talk about procedures like it is a piece of cake and nothing can or will go wrong. Many procedures are not hard but lots of stuff can go wrong and hopefully if it does it only cost a lot of money and not life or limb. Spending lots of money is intimidating enough, life or limb ups the ante considerably.

[hilltop170]

Glad you finally got the problems solved. Now might be a good time to review the link to optimize engine operation.

http://www.lycoming.com/support/publica ... SL185B.pdf

It's a Lycoming service letter but applies to most if not all carburated aircraft engines.

[blueldr]

I notice that the last sentence of the first paragraph of the Service Letter mentioned above says to NEVER use automobile fuel. As the howl goes on by the enviromentalists to get rid of the leaded aviation fuel, have any of you noticed that they are beginning to admit how a vast percentage of the existing general aviation aircraft engines could probably thrive on the existing premium grade automotive fuel?
I may even live long enough to see the day when the general aviation airplanes are falling out of the sky like snowflakes due to trying to force feed them a diet of mogas.
I'll bet that the author of that service letter didn't know about the US Army Air Force dash one Technical Order for the Stinson L-5 with a Lycoming O-435 engine. That T.O. specified that when working with the Ground Forces where avgas was not available, Mogas was a suitable subsistute.

[hilltop170]

I wonder when everybody decides mogas is ok after all if they will still try to mandate that it contain ethanol?

[GAHorn]

I notice that the last sentence of the first paragraph of the Service Letter mentioned above says to NEVER use automobile fuel. As the howl goes on by the enviromentalists to get rid of the leaded aviation fuel, have any of you noticed that they are beginning to admit how a vast percentage of the existing general aviation aircraft engines could probably thrive on the existing premium grade automotive fuel?
I may even live long enough to see the day when the general aviation airplanes are falling out of the sky like snowflakes due to trying to force feed them a diet of mogas.
I'll bet that the author of that service letter didn't know about the US Army Air Force dash one Technical Order for the Stinson L-5 with a Lycoming O-435 engine. That T.O. specified that when working with the Ground Forces where avgas was not available, Mogas was a suitable subsistute.

Yes...that was before leaded mogas had ethanol.

[Benwilson]

I recently had a bad case of sticky valves on my 170A and was able to fix it myself (with an IA looking over my shoulder of course...)

I used a valve spring compressor I bought from Oreilly's ($20) with a wrench to get the rocker off, and then depress the spring to pull the keepers out (you may need to stuff the cylinder with rope to keep the valve in place while compressing the spring). With the spring out you can move the valve in and out, it should be nice and smooth, capable of going in and out, and turning inside the guide.

Identify the sticky valves, and one by one push the valve out into the cylinder with the piston all the way back (with the valve in the cylinder be sure you do NOT move the prop as you could seriously damage the piston and valve)

WIth the valve out of the guide, you can then ream it out. The guide is between .430 and .440in in diameter, so a reamer of that size should do the trick. Also a 7/16 drill bit is .437in and works PERFECTLY! Be sure you file or dull the tip of the bit so it does not chew into the walls of the guide.

While the valve is out, fish it up through a spark plug hole and be sure the stem is free of any carbon or junk as well, then get it back into the valve guide with some mechanical fingers and a magnet, and things should be nice and smooth! Reassemble the valve assembly and you are good to go.

This is a cheap (and the proper way, look it up, its in the overhaul manual) way to fix sticky valve issues, and will take you the better part of an afternoon.

This was my experience and how I fixed it, so I hope it helps any others having the same issue.

[Bruce Fenstermacher]

Ben,

To be more precise a new valve guide should have a bore of .437 to .438. The clearance between the valve stem and guide new is .003- .0045 and service limit at .008. I haven't mic'd a valve stem lately but doing some math that meets the above criteria puts the new valve stem at .444.

If I used a 7/16 drill I'd run it in by carefully by hand which people not familiar with this operation might not realize. if your cylinders are fairly new and tight, which is the best time to get sticking valves, you could actually remove guide material with the 7/16 drill. Something you don't want to do, with a drill bit anyway. Using a reamer you should start at .437 then .438.

[Benwilson]

Bruce,

That is one thing I forgot to mention, that all the "reaming" was 100% done by hand, no power tools at all. The 7/16 bit in my experience took off only carbon and no metal. Agreed that a .437 reamer is the best tool, but was nowhere to be found in my town.