Tom Martin
Well Known Member
During August, on a couple of occasions, I noted a slight shudder in the engine. Both occurrences were following power reductions. A passenger would not have noticed the slight change in the engine but I did. It reminded me of what had happened to a friend, Terry Jantzi, in his RV6 a few years ago, which was a stuck valve. In his case the valve fully stuck open for a while and was alarming. In my case it was just a subtle hint and at that point I really did not know what it could be. Many things come to mind, a drop of water in the fuel, ignition issues, etc.
Last winter I installed an Advanced Flight Systems 3500 complete with engine monitor. This system records engine data so I downloaded the data to a card and checked it out on my computer using X-cell. I looked at the last 12 hours of test data, over 8500 entries, and immediately noted that the #6 EGT was always lower then the other cylinders before the first flight of the day. This clearly pointed to “morning sickness” which is indicative of a stuck valve. However in my case the engine still ran well because the valve was not fully stuck open.
I now knew which cylinder to check so my mechanic and I went to work. Off came the cowlings and the tappet cover on #6. Both spark plugs are removed and the piston is positioned in the down side of the stroke. A long rope, about 8 feet, 3/8” is shoved into the cylinder, leaving a bit hanging out. The prop is then rotated, pushing the piston up against the rope. This keeps the valves from opening and reduces the tension on the valve springs. The pin that the tappets rotates on is simply pushed away from the exhaust valve allowing that tappet to be removed. My mechanic had a tool that allowed the last bit of tension in the springs to be removed and the “valve keepers” were removed. This allowed the springs to be taken away from the valve. Prop is turned, the rope removed and this allows the valve to be pushed into the cylinder where it drops to the bottom. He had a tool that he mounted into his drill that was inserted into the guide and cleaned away some “dark” areas on the guide. The tool is not really a reamer, just some wires mounted around a spindle. The object is not to remove metal, just to clean the by products of combustion off the guide.
The stem of the valve is pulled/pushed out the bottom spark plug hole and the dark areas are cleaned using solvent and a scotch brite pad. The valve is then pushed back in the cylinder and using a curved wire inserted into the top plug hole the valve is carefully raised and directed into the guide. Gently nudging the valve forward with the piston helped to move the valve into place. The rope is now pushed into the cylinder and the whole process is reversed. From start to finish the whole job took less then an hour and a half, including the removal of cowlings.
I would not have been able to diagnose this issue without the Advanced Flight System data and it would likely have continued until the point where I experienced a fully stuck valve. Before this incident I never looked at start up EGTs but now I have added that to my check list as a noted difference could indicate a potential problem.
Last winter I installed an Advanced Flight Systems 3500 complete with engine monitor. This system records engine data so I downloaded the data to a card and checked it out on my computer using X-cell. I looked at the last 12 hours of test data, over 8500 entries, and immediately noted that the #6 EGT was always lower then the other cylinders before the first flight of the day. This clearly pointed to “morning sickness” which is indicative of a stuck valve. However in my case the engine still ran well because the valve was not fully stuck open.
I now knew which cylinder to check so my mechanic and I went to work. Off came the cowlings and the tappet cover on #6. Both spark plugs are removed and the piston is positioned in the down side of the stroke. A long rope, about 8 feet, 3/8” is shoved into the cylinder, leaving a bit hanging out. The prop is then rotated, pushing the piston up against the rope. This keeps the valves from opening and reduces the tension on the valve springs. The pin that the tappets rotates on is simply pushed away from the exhaust valve allowing that tappet to be removed. My mechanic had a tool that allowed the last bit of tension in the springs to be removed and the “valve keepers” were removed. This allowed the springs to be taken away from the valve. Prop is turned, the rope removed and this allows the valve to be pushed into the cylinder where it drops to the bottom. He had a tool that he mounted into his drill that was inserted into the guide and cleaned away some “dark” areas on the guide. The tool is not really a reamer, just some wires mounted around a spindle. The object is not to remove metal, just to clean the by products of combustion off the guide.
The stem of the valve is pulled/pushed out the bottom spark plug hole and the dark areas are cleaned using solvent and a scotch brite pad. The valve is then pushed back in the cylinder and using a curved wire inserted into the top plug hole the valve is carefully raised and directed into the guide. Gently nudging the valve forward with the piston helped to move the valve into place. The rope is now pushed into the cylinder and the whole process is reversed. From start to finish the whole job took less then an hour and a half, including the removal of cowlings.
I would not have been able to diagnose this issue without the Advanced Flight System data and it would likely have continued until the point where I experienced a fully stuck valve. Before this incident I never looked at start up EGTs but now I have added that to my check list as a noted difference could indicate a potential problem.
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