Engine stumble

[skylor]

Originally Posted by crabandy

...About minutes after setting 20-80 LOP the engine ran rough like it was ingesting water or had bad carb ice (too instantaneous for carb ice). It felt like a LONG time, data shows just over a minute of rough running. I swapped fuel tanks, turned on the boost pump with no change. When I went full rich with the mixture it bogged the engine more and I leaned it about where I thought it should be it eventually smoothed out.

After it smoothed out I tried ROP and LOP and both ran fine, after running LOP for about 30 minutes I started descending. I left the throttle full in and mixture at 20-80 degrees LOP. At about 13.2 the engine ran rough again for about a minute with the same drop in EGT's/CHT's/RPM/Airspeed. Small mixture adjustments as well as large mixture adjustments didn't seem to make a difference. After it smoothed out it ran flawlessly through several
level offs and different mixture/power settings for the last 40 minutes of the flight.

...After startup on the ramp for my last leg I had the same stumbling...
...after a cautious takeoff the hour flight back home was uneventful....

Originally Posted by crabandy

...I switched to the main engine page and it was obvious the #2 was not firing correctly with a 500* EGT, exactly as seen on the engine data on the ramp the other day. I aggressively leaned it and #2 started running normal, again about a 1 minute event.

I did another extended run-up and cautious takeoff and short flight but couldn't reproduce the problem ROP/LOP. Landed, fueled up and the re-start/taxi back to the hangar was all normal.

I'm sorry, but I just don't understand this. Why do people insist on continuing to fly their planes when experiencing engine issues? You clearly have an intermittent engine problem that you didn't previously have. Why do you continue to fly it? Find the problem on the ground and get fixed now BEFORE it gets worse in flight or worse, on takeoff!!!

Skylor
RV-8

[Russ McCutcheon]

Originally Posted by crabandy

Before I just put new plugs in it and fly it how do I rule out a sticky valve?

Get your "trusted" A&P or buddy (maybe someone from your EAA chapter) who know how and has the tools come and help you do a valve wobble test, It's Imperative you do this before you fly it, my money is on the exhaust valve on #2, for it to be ignition you would need to have two failures for #2 to stop running, if one plug or one wire failed your EGT would rise and #2 would keep running, for the EGT to fall and #2 to stop running you would need both plugs to fail or a plug and a wire or a combination of both.

[Bevan]

The NGK 5044 has a removable terminal nut that could come loose with vibration. It is recommended to use the "solid" style, part number 6747 if I'm not mistaken.

Bevan

[brooksrv6]

Originally Posted by crabandy

Mike S,
I put the socket on the sparkplug and both come out, it's consistently been that way when I remove them. I finger tighten the adapter on the sparkplug and then screw/tighten that assembly to 30 ft/lbs via the sparkplug. All the plugs looked similar when I removed them, but I didn't put the ohm meter on them.

I use this method from the Lightspeed manual and the adapters remain in the heads?
Install adaptors in cylinder head using the supplied copper washer.
Torque to 35 - 45 ft-lbs using anti-seize compound.
? Install automotive style spark plugs with their washer. Torque to 20 ft-lbs using
anti-seize compound.

Chris

[sailvi767]

Originally Posted by crabandy

Mike S,
I put the socket on the sparkplug and both come out, it's consistently been that way when I remove them. I finger tighten the adapter on the sparkplug and then screw/tighten that assembly to 30 ft/lbs via the sparkplug. All the plugs looked similar when I removed them, but I didn't put the ohm meter on them.

I would recheck your procedure on the plugs and inserts. I don't have access to the books at the moment but I believe lightspeed calls for the inserts to be torqued to 24 ftlbs and the plugs to 20. My inserts always stay in the heads.

George

[Skysailor]

Check your installation manual. I think the adapters are set to a higher torque than the plugs so they remain in the engine when plugs are removed as was mentioned before.

[crabandy]

Originally Posted by Russ McCutcheon

Get your "trusted" A&P or buddy (maybe someone from your EAA chapter) who know how and has the tools come and help you do a valve wobble test, It's Imperative you do this before you fly it, my money is on the exhaust valve on #2, for it to be ignition you would need to have two failures for #2 to stop running, if one plug or one wire failed your EGT would rise and #2 would keep running, for the EGT to fall and #2 to stop running you would need both plugs to fail or a plug and a wire or a combination of both.

Russ, Thanks for the advice. I'm going to schedule my trusted A&P buddy today.

[mannanj]

Be carefull! All adapters aren't created equal! I had one break off while torquing to 30 foot pounds without the plug being inserted.

[N941WR]

Originally Posted by crabandy

Mike S,
I put the socket on the sparkplug and both come out, it's consistently been that way when I remove them. I finger tighten the adapter on the sparkplug and then screw/tighten that assembly to 30 ft/lbs via the sparkplug. All the plugs looked similar when I removed them, but I didn't put the ohm meter on them.

Keep doing it this way. What is described below happened to me.

Originally Posted by mannanj

Be carefull! All adapters aren't created equal! I had one break off while torquing to 30 foot pounds without the plug being inserted.

[DanH]

I understand the focus on cylinder #2 given a 500 degree EGT during a runup, but returning to your original post, did you or did you not record a drop in all EGT and CHT indications, along with an increase in fuel flow?

Originally Posted by crabandy

I pulled the SD cards and looked at the data this morning, about 250 RPM and 10 knts IAS loss in the minute. Fuel flow went from 7.8 to 9.6. EGTS were all 1310-1330 before and dropped to 895-1070 with #2 being the lowest. It was long enough that CHT's even dropped around 30 degrees.