The Old Rope Trick

[Tom Martin]

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.

[mahlon_r]

If one is sticking or close to sticking, the others are possibly not far behind. If it were me, I would have SB388 C done to check the others and repair as or if necessary.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."

[aeropunk]

Originally Posted by Tom Martin

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.

Wow, that's a great anecdote and a testament to the usefulness of digital data acquisition systems.

Out of curiosity, what does the "raw" data look like that you download from the AFS device? You mentioned using Excel to view it; is it just a .csv file or something? Does AFS provide any analysis software for use on a PC?

[frankh]

Nice write up on the procedure..Thanks

Frank

[Tom Martin]

There is no extra program required to read the data. You will have to excuse my ignorance regarding the file name. AFS gives some clear instructions for using X-cell and if I can make it work any one can!
As for the other cylinders needing the same work that is certainly on my list for this winters maintenance. I have 360 hours on the engine and apparantly this is not an unusual service item. Others with more engine experience can chip in on how often this occurs and what contributes to it.

[kentb]

Originally Posted by aeropunk

Wow, that's a great anecdote and a testament to the usefulness of digital data acquisition systems.

Out of curiosity, what does the "raw" data look like that you download from the AFS device? You mentioned using Excel to view it; is it just a .csv file or something? Does AFS provide any analysis software for use on a PC?

I have the AFS 2500 engine monitor and the data is .cvs and includes the column headers and date in the first 3 lines.
I am sure that the EFIS use the same output. Just load into Excel and tell it to use commas as delimiters.

Kent

[rv8ch]

Anyone know what the black stuff is? Is there an oil or fuel additive that might help either clean it or prevent it from building up?

Thanks,
Mickey

[RVbySDI]

Originally Posted by rv8ch

Anyone know what the black stuff is? Is there an oil or fuel additive that might help either clean it or prevent it from building up?

Thanks,
Mickey

That would be carbon build up. Most likely from incomplete combustion. Having said this please be aware I am not a mechanic, nor do I play one on TV. But I have seen that "black stuff" enough to know that what you are describing is most likely carbon build up.

As far as "clean or prevent it", try leaning your engine more often. Running rich can lead to excessive carbon build up.

[Janekom]

Very good idea
Just to clarify - did the data show a low EGT after start-up and then after full power for take-off it became the same as the others, or in other words when did it catch up with the others?

[Tom Martin]

On start up, until full power, the EGT was reading lower. After that and for the rest of the flight the readings were similiar to the other cylinders.