The International Cessna^® 170 Association

While on the subject of stuck valves, I feel this is the time to tell my valve story. The day was July 5th of this year, I was flying back from Rochester New Hampshire after a weekend of visiting with a friend. The weather called for hot hazy and chance of T storms in the afternoon, Typical. I left about 10:30 am figuring I'll be back at Aeroflex by 1:30 in the afternoon, well before any convective build up. I climbed to 8,500 feet to get above the haze and into some nice cool air, called for flight following everything was going as planned. A hour and a half into my flight my attention was caught by the chatter on the frequency about several corporate types going missed at Albany saying that they need to go to there alternate. In response center advised that the system is moving a lot faster than planned for and was rerouting aircraft as they spoke. No sooner I noticed that ahead and below was a definite frontal line forming, and not being instrument it would be bad to get stuck on top. But those clouds were forming real fast. I called center as told them I was going to descend to 4500 feet, there response was of course "maintain VFR" .

Well, this is where it gets interesting. The clouds building faster I couldn't see the ground ahead of me but I could see down so I started a slow spiral descent, after dropping down to 6500 my "HOLE" was getting smaller, OK carb heat on engine Idle I was descending quite rapidly and apparently fast enough to have center kinda worried but aviate navigate communicate. I'm now down to about 2500 and still not below the clouds and now some rain is hitting the windscreen, well one thing I now is that its still VFR back toward new Hampshire so I just head back. Not so, as I throttled up everything shook, carb ice? nope, mags? nope. Being that the engine was still running it's not a intake so it must be a exhaust valve. So much for heading back let alone climbing or flying for long. At this point I'm thinking of a possible forced landing, I can still see the ground right below me and see some fields and houses, my main concern was flying into terrain for the charts showed 2300 ft and I was at 1500 and still descending. I dropped below the clouds finally at 800ft agl engine and airplane shaking, I was able to get about 2300 rpm so level flight was obtainable. I could see dutchess county to my right so there must be sky acres close by, now at 800 feet I couldn't see skyacres but the gps (never leave home without it) showed it 5 miles dead ahead. At this point I guess as the adrenaline started to wear off I started hearing the radio again along with center still calling my aircraft. I guess when you see a radar target drop 2000 feet per sweep and then lose contact due to terrain well I apologized and said that I was diverting to sky acres, there response was "maintain VFR".

I landed at skyacres, down wind I think, sorry no pattern, taxied to the ramp and shut down. I got out of the airplane to walk the ordeal off, past a gentleman that was preflighting when he asked me a favor, he wanted to borrow if possible some approach plates for he left his home. I said I don't have any, he then looked at me, then the airplane and then the sky and said " say no more, I don't want to know".

Sure enough #2 cylinder exhaust stucker than stuck, why? I figured I must of shock cooled the engine to make probably a already tight valve stick. I tried to borrow tools but got no help from the local shop, so much for the brotherhood of A&P's, so got a rental car drove the 150 miles home, borrowed a reamer, a spring compressor, a fellow Mech, got some rope, lacing cord, a brass drift and some other tools for the trick went back to the airport later that week. the job took about 45 Min's, I usually take longer because I used to drop the exhaust to work the valve back into the guide, but my fellow mechanic friend showed me his way that saved me hours. My anual is due next month so I'm going to check the guides on rest of the cylinders

mrpibb wrote: I tried to borrow tools but got no help from the local shop, so much for the brotherhood of A&P's, so got a rental car drove the 150 miles home, borrowed a reamer, a spring compressor, a fellow Mech, got some rope, lacing cord, a brass drift and some other tools for the trick went back to the airport later that week. the job took about 45 Min's, I usually take longer because I used to drop the exhaust to work the valve back into the guide, but my fellow mechanic friend showed me his way that saved me hours. My anual is due next month so I'm going to check the guides on rest of the cylinders

Vic, now that you have our attention we are all anxious to know what is your fellow mechanic friend's way of reinstalling the exhaust valve?
Johneb

Vic, I identified with you on that story.
Back during the middle ages (1972) I was flying pipeline patrol near Cleburne, TX in a 140A with a fresh overhauled O-200 in it. (Same cyls/valves as our O-300's). I was about 300' AGL when a rain squall appeared ahead of me directly on the right of way (ROW). No problem. Just stay on the ROW because all I needed was downward visibility to stay on course and keep away from obtacles that might be just off the ROW.
As I entered the heaviest rain, the airplane started shaking so hard I couldn't read the instruments. The panel held a manifold pressure gauge but the needle was wildly a blur. Stuck valve. No viz beyond the wingtips in the heavy rain.
On only 3 cylinders, I was sinking and going to strike the earth with no viz and had to get out of that rain so I could see before I hit. Any direction was better than straight ahead deeper into the rain squall, so I turned 90 degrees left. Next thing I noticed was a barn under my left wing. Nothing but bldgs farther left, nothing but barnyard under my nose, and couldn't see to the right at all, but I made a snap-decision that most barns had to be near a pasture and there was no pasture behind me, to the left of me, or ahead of me that I could see,...so I turned right and flared just as I ran out of altitude and touched down. Stood on the brakes and slid to a stop.
The rain came down even harder and I couldn't see past the nose or the wingtips for the next 10 minutes. I shut it down and just sat there kinda shaken and exhausted. (pardon the puns.)
When the rain finally dissipated....I could see I'd stopped only about 40 feet from hitting an big oak tree square on the spinner, and there was a fence between me and the oak.
I walked down the road about a mile and couldn't find any kind of house to borrow a phone or anything, and when I returned to the airplane, just for drill I started it up and it ran perfectly. The field was terraced to the left, and the weather had cleared, so I simply took off downhill dropping down onto the next terrace as I came to each,...until it finally flew and I got it all the way home to Houston. When the mechanics looked into it, ALL the valve guides were undersized and had to be reamed.
It was decided that the valves were just waiting for something to cool them off suddenly (like rain) to cause them to seize.
My adrenal glands have never quite recovered since that day.

Vic, someone else beside you also made a comment about "dropping the exhaust". I don't get it- are you working up thru the exhaust port somehow? I did everything thru the 2 sparkplug holes and it was no sweat. The dental floss tied to the tip of the valve stem helped too.
Along with John, I'm also curious about your friend's method. This stuck valve repair business is all new to me.

Eric

PMI, but when you ream the valve guide, where do the metal shavings go ? How do you keep the out of the engine ?
Rudy

Rudy if I was to ream out a valve guide and remove metal I'd blow out the cylinder with compressed air.

I haven't had to ream a guide in a long time (since I started using avgas exclusively ) so I don't remember the process. Is it done dry or with cutting fluid or light oil? If done dry, would having a small positive pressure (compression tester with the reg turned way down low) on the cylinder during reaming keep most of the chips out of the cylinder? How about a little grease in the flutes of the reamer to catch the chips? If you suspect some chips getting in the cylinder anyway, how about flushing with kerosene or a very light oil?

Miles

The way I used to do it was to hold the valve with mechanical fingers thru the exhaust port. The way we did it last month was to remove the upper and lower plug, again the rope trick to close the valve and hold it to remove the springs. Then we tied some Dacron rib stitch tread around the stem were the keeper would go. Then using a drift and some kroil tapped the valve into the cylinder ( bottom center ) then with safety wire fished the thread up thru the top spark plug boss grabbed the valve stem and held it with a spring clamp. then using a valve guide cleaner on a cordless drill ran it down the guide a few times, clean the crude of the tool and did it again until the guide looked clean. I then with scotch brite cleaned the valve stem, after that i let the valve drop back into the cylinder then thru the valve guide with safety wire and grabbed the thread and pulled until the tip of the stem touches the guide. I then with safety wire went thru the upper spark plug boss hooked the valve while holding tension on the thread and lifted the valve so it was parallel with the guide in which the valve slid in. I had to do this twice because after the first time the valve still wasn't sliding as smooth as I liked, the second time it was slick. Then of course the rope trick to hold the valve to reassembled the valve train. The whole procedure from cowl open to cowl close was no more than 50 Min's. The removal of the lower plug was to allow the crude a place to exit and to not foul the plug, and when I refered to I, I ment we for if it werent for the shortcuts my friend had it would of taken a lot longer.

Thanks Vic for the explanation.
Johneb

I too did it like Vic describes, working thru the sparkplug holes: Dental floss tied to the valve stem keeper groove,safety wire hooks helping the valve stem up thru the top plug hole & thyen again back out thru the guide. I used grease on the reamer to hold the cuttings, afterwards I sluiced the combustion chamber out with WD40 from the top plug hole while holding a small hose hooked to a shop-vac up in the bottom plug hole. Didn't appear to capture anything but WD40, so I guess all the cuttings stuck to the grease. Used MMO to pre-lube the guide & valve-stem.
Procedure worked great, plan on doing it just the same if or more like when I do the other five this winter. Great with the exception of the valve spring compressor, I borrowed a homemade tool that worked kinda OK- I mean it worked but not real handily. I see El Reno sells a valve spring compressor (p/n EL-25) for use on both Lycoming & Cont engines for about $30 (1997 or so price). What do you guys use?

Eric

Eric, I use 2 screw drivers.

We had 2 tools that where sold at the convention auction that looked interesting. They basically where a bar bent to hook under the rocker shaft with 2 tabs out the back at an angle to compress the valve spring evenly when pried down. Looked to me like they'd work well.

Bruce, did those tools appear to be homemade or were they store-bought items? A friend of mine uses screwdrivers too. This compressor I used worked well except for a protruding part that bottomed out on the cylinder head casting (in the pushrod area) before the valve spring was totally relaxed. Made it hard to get the valve spring ass'bly out and/or the tool removed. I could have removed or flattened the protruding part on the tool real easily but it was borrowed so I didn't.

Eric

The tools we had for the auction where not hand made but could have been. I think they where made by a company called Gibson or Gibbons I can't quite remember.

Having seen these I plan to make my own some time and probably should have bid more for one at the auction.

Here is a tool Aircraft Spruce sells that is similiar to the ones I saw at the convention. I think they sold for $20 at the convention. I should have bought one.

http://aircraftspruce.com/catalog/topag ... ressor.php

valve compressor tool - I used to have one from Gibson in El Reno, it's the one that uses a little bar (or screwdriver) in the rocker shaft holes

when in the boonies I have a little piece of angle steel with 2 holes, attach it to the cylinder with a rocker cover screw and stick your favorite big flat screwdriver through the other (bigger) hole to compress the spring

a little stick magnet works great for capturing the keepers while doing all this by yourself