Q: I recently bought a 1984 Maule M7 with a Lycoming IO-540 engine. I have about 50 hours on it and it has been running quite well. I have a six-place EGT/CHT.
Recently I flew for a couple hours and after a few hours stop went to fly again and saw that the #5 EGT/CHT were both very low and the engine was running rougher. It got better as things warmed and I flew back. The next morning it was the same.
Compression and plugs are both good. I suspected a sticking valve. I pulled the rocker cover on 5 and found the outer exhaust spring broken into three pieces. I pulled the other covers and found another exhaust and an intake outer spring broken low, but in only two pieces.
The top has 1,400 hours on it, 500 on the bottom. I am replacing all of the exhaust and intake springs and reaming all of the exhaust guides. Halfway through and not a hint of drag on the valves yet. Is there something other than sticking valves that would have caused the breaks? Fatigue maybe?
JOHN DAILY
A: Now here’s an interesting subject that I haven’t heard about in probably 50 years. However, I’m going to guess that it may still be caused by the same condition today that caused it to happen so many years ago.
The common report back then was that at just about lift-off the engine would lose maybe a couple hundred RPM, but continue to operate somewhat normally with maybe a little roughness. As you experienced, the next flight of the day would be perfectly normal with no indication of the symptoms observed on the first flight. At the time, those of us at Lycoming gave it a name called “morning sickness” since it usually occurred on the first flight of the day.
Even though the total time on the engine is 1,400 hours, if you do the math, that means it’s at least 36 years old.
What concerns me the most is where it spent its time. I think I’d be safe in saying that there had to be some extended periods of inactivity over that time period and exactly where that took place may be the answer to the problem.
If the aircraft had been located in a hot, humid climate and failed to be flown on a regular basis, this could be a contributing factor.
Another factor that could contribute to valve spring breakage, coupled with a hot humid environment, would be infrequent oil and filter changes.
If you’re confused as to where I am headed here, just think corrosion and you’ll be in the ballpark.
As you can imagine, there is a tremendous load on the valve springs and if for some reason corrosion begins, at some point the spring is going to fail. Corrosion is probably the biggest contributing factor when it comes to fatigue failures on valve springs.
I commend you for your troubleshooting skills and agree 100% with your decision to replace all of the valve springs. As you probably know, this project can be accomplished without removing the cylinders, which will not only be a time savings, but a financial savings as well.
By the way, I don’t think your valve sticking theory holds any water, especially after you found no problems when reaming the exhaust guides. I’m glad you decided to do that work as well and I believe you should be good to go.
I have no compression in #4,
I found a leek from the intake valve,
Removed both valves, everything looks good, no cracks, seats look good,
Springs look good, going to lap the valve seats, but need to clean the carbon
Out of the inside end of the cylinder, not sure what the best way to do it?
Don’t won’t to damage the walls?
Have repairman certification.
What puzzles me is how can you ream the valve guides
without removing the pots.
unlessthats what he did.
The valve is pushed into the cylinder,with a string tied to the valve stem. The guide is then reamed. The string is then grabbed through the guide and the valve pulled back into place. It is common to fill the cylinder with small rope to keep the valve close to the head aiding in the installation of the valve back into the guide. The reamer is packed with grease to contain the material that the reamer is removing. The reamer is removing primarily lead deposits,the same stuff that collects in the spark plugs.