Two Saturdays ago I was on my first instrument rating lesson - something I have been putting off for some time now. The lesson was pretty straight forward - climb up to 6,500' heading 360, following by a series of ascending and descending climbs while under the hood. Next up was a VOR/ILS approach into Capital City airport near Harrisburg, PA. After figuring out how to get the Grand Rapids EFIS to properly display the CDI/HSI from the Garmin 430W, we were in business. Next up was a practice hold followed by a GPS approach into York, PA (KTHV).
As we were approaching the fix for the hold, the airplane developed a very noticeable shake. Clearly something was not right with the engine. Automatically without me even thinking, I pushed the mixture full rich and turned on the fuel pump. My CFII looked out the window to point me towards York airport. I didn't have it in sight, as my mind was going a million miles an hour. I was lucky to have him in the airplane to point me where I needed to be. We were still developing power, and we were within easy gliding distance of the airport just in case the engine had other ideas. A glance at the engine monitor showed what the root cause of the issue was - the EGT for the #2 cylinder was non-existent. The CHT was decreasing quickly. It was clear that the #2 cylinder was not producing power.
We were 2,000' over KTHV when the engine all of the sudden started performing normally again. The EGT immediately came back to normal, and the CHT was increasing. I glanced at my flight instructor and we both thought it would be better to put the airplane down back home at KDMW - a short 10 minutes away. We circled over KTHV gaining altitude and listening to the engine. Things seemed fine. All engine parameters looked to be back in the green. We headed to KDMW.
Roughly half way to KDMW, the engine stumbled very quickly. Not enough for the engine monitor to notice anything, but both of us definitely heard something. We stayed high and circled down to a non-event of a landing.
I was lucky to be in the presence of Captain John and his endless knowledge of everything airplane at KDMW. We decowled the RV and started digging around the #2 cylinder. Both spark plugs looked to be in fine condition (EMAG on the top plug with an auto plug, Slick mag on the bottom with a massive electrode plug). Next up was a compression test - 78/80, with the slight leakage coming through the rings (audible noise through the oil filler tube).
Naturally I would be lucky enough to have an intermittent issue. Now how to figure out how to fix it?!?! An engine needs three basic criteria to work - spark, compression and fuel. If the spark was lost, both the EMAG and Slick mag would of stopped firing in that cylinder. If the EMAG would of quit, the other cylinders would have symptons of elevated EGT's. This wasn't the case. The lack of fuel was a more likely symptom, especially if an injector was clogged. However, I found it to be unlikely that an injector would be clogged so immediate, and then unclogged immediately also. Typically when I have had a clogged injector, I get elevated EGT's, and it typically doesn't cure itself. The last issue is a lack of compression. What could of caused this is a stuck exhaust or intake valve being open. An open valve during the compression stroke of the engine would definitely cause the symptoms I saw.
The first step to investigating a stuck exhaust valve was removing the valve cover.
Next up was removing the rocker valves. To do this, you need to push out the rocker shaft. The rocker shaft is kept in place by the valve cover - the cover prevents the shaft from moving left or right. With the #2 piston at BDC, the shaft pushes out easily with just your fingers.
I removed the shaft and the two rocker arms and stored them with where they were originally on the engine.
This is the top of the cylinder with the rocker arms removed.
There is a cap over the top of the exhaust valve stem. This pulls off easily with a magnet or a dental pick.
Next up was compressing the exhaust valve spring and removing the keys which hold the valve stem to the top of the springs. There are a number of Lycoming valve spring compressors on the market for $60-$150, but from the looks of the pictures of them online, it looked like something I could easily fabricate. This would save me some money, but more importantly, buy me time as I could get the job done ASAP, instead of waiting for a tool to ship.
I ended up purchasing two pry-bars (Stanley 55-515 12-3/4-inch Wonderbar Pry Bar - p/n 1-55-515 - $12 @ Ace and a Kobalt 7-in Pry Bar - Item #: 117699 / Model #: 62897 - $6 @ Lowes). It took about an hour using the angle grinder to get the shape just right, but it worked flawlessly! I wrapped the tool in electrical tape in order to prevent any scratches on the engine pieces.
A poor picture of the took in action. I put a 3/8" socket extension through the holes of the rocker shaft for the valve compressor tool to attach to. Pushing down on the tool compressed the valves enough to get the locking keys out.
After using a dental pick with the spring compressed, the keys holding the top of the valve springs to the valve stem came out.