Loss of power on IO-360; spark plugs

Bubblehead · #1 09-20-2008, 09:01 AM

Last Tuesday one of my sons and I flew from DeKalb, Illinois, to Lansing, Illinois and then took the Chicago lakefront tour and landed at Janesville, Wisconsin for lunch and fuel. So far so good!

As we departed Janesville the plane seemed a little sluggish, and at about 500 ft AGL the engine rumbled a little and the climb rate slowed. I checked boost pump on (it was), fuel pressure correct (it was, and there was no fluctuation), RPM (2500), manifold pressure (25") and a quick glance at 1 cylinder's EGT and CHT (normal). Since it was still delivering enough power to climb slowly I did not change any settings until reaching 3500 ft. During this time I turned toward DeKalb but kept Janesville and Rockford in sight and watched for alternatives.

I called Rockford Approach and told them I had a rough engine and would like to transit their airspace on a track that would allow a quick entry and landing. The guy at Approach was really great, and it felt somewhat reassuring that I was in communication. I then switched tanks, wit no increase in power. By this time I'm level at 3500 ft and power settings are 2500 rpm and 25" mp but I'm only seeing about 120 kts TAS! The engine would rumble every few minutes and run rough and then smooth out. I don't remember checking EGTs and CHTs. I was mostly concerned with aviating my way home and keeping good landing locations close at hand.

Once close to DeKalb I told Rockford I was changing freqs and would get back to them by phone or radio to let them know what happened. I went to CTAF, announce location and rough engine and several pilots in the pattern communicated they were leaving east to get out of my way! Again, my faith in human nature was confirmed!

After an uneventful landing I asked one of the guys in the pattern to contact Rockford Approach and tell them I was ok. I taxied to the hanger and took the cowling off. I could not see anything out of the ordinary except more oil than usual on the lower cowling. I knew the front seal of the engine was leaking a little but not to this extent. I pulled all the spark plugs, and they all were intact, undamaged, with normal gaps. They showed signs of running rich, which I was not surprised about since I typically err ont he side of caution because I don't have a EMS to help spot peak temps while leaning. Two showed a little oil film.

Next I drained the fuel sumps and the gascolator. I did not find any evidence of water or dirt in either place, although I'm going to pull the gascolator tomorrow. I pulled the fuel inlet screen on the fuel injection system, but it was clean. I replaced the two o-rings and reinstalled and lockwired it.

Just for grins I took of the air intake scat tube where it goes into the horizontal intake. The inside of the tube had some visible oil in it and when I looked into the throat there was an oily film on the butterfly valve. I reached in with a screw driver and scrapped a little off so I could look at it more closely. It was oily and fuzzy, like some paper had discolved in the oil! So I pulled the air cleaner and gave it a thorough inspection, but it looked very clean. No evidence of oil going through the filter or of the filter being carried away was visible.

A couple of local A&P/AI types stpopped by; one a fellow RVer. They looked everything over and the only thing they noticed was they thought I had the wrong plugs. The engine had Champion REM37BY plugs when I bought the plane and I did not question it. I'll check the Champion and Lyc literature later to see if they were right, but we all concluded that the wrong plugs were working correctly for a long time and they would not cause an intermitten problem like I had experienced.

Three other tidbits of info:
1) I recently installed an AWI 4-into-1 exhaust and positioned the breather tube to drop any oil on the exhaust collector. I cut the tubing at the end at a slight angle so air flowing through the cowling would not pressurize the engine and blow oil. Several people here and at other sites have mentioned doing that with good results. There is an oily film on the top of the collector where the breather would discharge oil.

2) the compresion on #3 cylinder was low at the November condition inspection 60/80. We have not checked the compression yet. We'll do that after the plug situation is resolved.

3) The engine uses the two in one magneto and there is no information in the log books signifying that it has been rebuilt. The engine has almost 500 hrs on it so perhaps it's rebuild time for the mags

Some of the things we found are issues but don't seem to add up to a rumbling engine. The engine ran fine on the plugs for the 100 hours I've flown the plane, but it's not one of the faster -8's around it cruised at 8500 ft 150 kts TAS and 9 gph. The oil leak needs to be fixed. In fact I'll start taking the propellor apart this week too, but it would not cause a sudden loss of power.

Any ideas? Oh, and yes, I am very glad the engine did not loose power while at 2400 ft and a mile off the Lake Michigan Shoreline. It would have been much more stressfull!

UPDATE according to the Champion website REM38E is the normal plug but REM37BY can be used if lead fouling is encountered.

asav8tor · #2 09-20-2008, 09:12 AM

Quote:

Originally Posted by Bubblehead

The engine would rumble every few minutes and run rough and then smooth out. I don't remember checking EGTs and CHTs.

I think doing that would have given you the answer. Sounds like you were running on 3 healthy out of 4.

az_gila · #3 09-20-2008, 09:23 AM

...checking the magneto timing... Is it set OK?

The approved spark plug list is here...

http://www.lycoming.textron.com/supp...fs/SI1042Y.pdf

Bubblehead · #4 09-20-2008, 09:33 AM

Quote:

Originally Posted by az_gila

...checking the magneto timing... Is it set OK?

The approved spark plug list is here...

http://www.lycoming.textron.com/supp...fs/SI1042Y.pdf

We did not check the timing yet. That could definitely cause the overall loss of power, but does it explain the occasional rumbling? The rumbling was a vibration and a slight shaking visually noticeable when I looked at the cowling.

Thanks for the link. It looks like the info in that pub matches what I found at Champion.

BTW, I did a mag check on the ground and the mag drops were normal.

asav8tor - I wish I would have checked them in flight. I checked them during the mag check and they looked normal but it would have been better to check them during the event!

Bubblehead · #5 10-11-2008, 07:25 AM

The timing checked out ok - 25 degrees BTDC.
#3 cyl was down to 45/80, it had been 60/80 for a long time so this is probably the root cause of the power loss. Other cylinders checked ok but I'm thinking about my options. Is it best to do a complete top o/h or should I just do the one bad cylinder?

Geico266 · #6 10-11-2008, 07:31 AM

Quote:

Originally Posted by Bubblehead

Is it best to do a complete top o/h or should I just do the one bad cylinder?

You can do just the offending cylinder. Rebuild the mag(s) while you are doing the cylinder.

I am concerned about the "stumbling" while you were flying. It could be this cylinder, but it would have been a steady problem. You may have been running too rich and caused carbon to get under the valve seat, but 60/80 is borderline anyway when the others are in the 70's.

Might be a good time to have an A&P look at the entire set up. Idle, mixture setting, idle speed, timing, mags, harnesses, ect.

rvbuilder2002 · #7 10-11-2008, 10:38 AM

I have seen this rumble symptom before from an intermittently sticking valve.
It is possible that you have a valve acting up in one of the cyl that is not low on compression.
I agree that it is time for some in depth engine condition evaluation.

az_gila · #8 10-11-2008, 11:48 AM

Quote:

Originally Posted by rvbuilder2002

I have seen this rumble symptom before from an intermittently sticking valve.
It is possible that you have a valve acting up in one of the cyl that is not low on compression.
I agree that it is time for some in depth engine condition evaluation.

...would help to evaluate this.

http://www.lycoming.com/support/publ...dfs/SB388C.pdf

Since the failure mode is usually a broken valve stem (often at TO power) an evalution would be a good idea.

See if a local A&P has the fixture... a lot of them don't even know about this SB....

asav8tor · #9 10-11-2008, 11:59 AM

How much time on those jugs,

-since O/H?
-since new?
-year of last O/H?

How much time on the bottom,

-since O/H?
-since new?
-year of last O/H?

Bubblehead · #10 10-11-2008, 04:03 PM

As always on VAF, there are lots of good ideas and suggestions. I appreciate you guys taking the time to post. Here are some answers and comments.

asav8tor - The engine has about 500 hrs SMOH in 2000. The plane was licensed in 2001. I put the last 100 hours on it in the last year, so the owners before me only flew it 400 hrs in 7 years. The 60/80 compression was found during the pre-buy inspection and the price was lowered $1,000 to cover a cylinder swap.

az_gila - thanks for the link. I'll bring it to the AIs attention before we pull the cylinder. Seems you always have a link to important information.

rvbuilder2002 - not sure how to check an intermitten sticking valve. Compressions on the other 3 cylinders are 72/80 or better.

Geico266 - the rumbling could have been the engine just running ruff because one cylinder was not developing power. During the incident I did lean (carefully) once at a safe altitude with no improvement. The previous flight was about 2 hours long and the engine was leaned and adjusted several times during it. Power was normal and the engine ran smoothly.

I think checking the valve condition per the Lyc SB is a great idea. I've printed the bulletin and will discuss it with the mechanic.

Perhaps I should pull all 4 and replace them with higher hp pistons and cylinders??? Tempting!