One wrong spark plug

jd21476

jd21476

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jd21476
I had a seat of the pants vibration in my plane and what I perceived to be a bit of a rough running engine. My mag checks were all good and my engine monitor did not show anything wrong.
I decided to pull and clean my plugs and I noticed that the bottom plug on cyl 4 is different than all the others. I have a O-360 engine and all my plugs were 40E except for that one which was a 38YB. I called my mechanic and he hd no clue. Ive been flying with the plane like this for at least the last 50 hours and only noticed the issue in the last 10 hours or so.

Any ideas?
 
I dont know. Thats kind of the answers I expected from my mechanic but instead I got, “thats odd, go get the correct one.”

Here is a picture of the two. The one on the top is correct, the bottom is not
 

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jd21476 said:
I dont know.
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Well I can tell you its not the first time this has happened. The usual suspects of a rogue plug are you're stuck somewhere and the oddball P/N was the only one available to get home then not changed out. Or too many plugs laying around the spark plug test machine. Or you're related to ol' Mr Benny who perfected dumpster diving years before it became the craze. I dont think he had more than one plug of the same type in any of his aircraft.:rolleyes:

As to a 38 plug not playing well with a 40 plug, sure.
 
I tend to think that my mechanic probably just grabbed the wrong plug off the bench.
I also noticed that the old plugs I have which are 40E said 3k19 on them and the new plugs say 2k20 but they are also 40E. Do these numbers matter?
 
jd21476 said:
I tend to think that my mechanic probably just grabbed the wrong plug off the bench.
I also noticed that the old plugs I have which are 40E said 3k19 on them and the new plugs say 2k20 but they are also 40E. Do these numbers matter?
Click to expand...
They look like manufacturing dates...
 
REM37BY plugs are approved for O360 engines according to SB1042.

I run these in my Jacobs and E225 Continental. They are very good plugs and are less prone to oil fowling which might be a clue to why you have one on a bottom cylinder. Double check the plug to see if is not a 37BY.
 
You’re right it is a 37BY not a 38, but can you mix plugs like that without any issues?
 
The big question: Did changing the plug fix the vibration? If not, it wasn't the plug. Not that one, anyway. When were the mags last off for internal inspection?
 
Dan Thomas said:
The big question: Did changing the plug fix the vibration? If not, it wasn't the plug. Not that one, anyway. When were the mags last off for internal inspection?
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That was going to be my question as well ..... my guess is the vibration will still be there ... a wrong plug should still fire and besides there is also a second plug in the cylinder which presumably was the right one.

.
 
If you have full engine monitoring a bad plug will show up on the mag check. If not on the ground a inflight mag check will find the bad plug. The 37 verses 40 plug deals with heat range. To cold a plug will tend to foul but not a catastrophic problem. To hot a plug could cause preignition which can quickly destroy the engine.
 
A Martin said:
You nailed it ..... and the pilot reported his mag checks were OK

.
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I flew a 320 that would have a good mag check on the ground but then would have a slight vibration under power in cruise. I would clean the plugs and it would run smooth again.
 
You pulled the plugs and cleaned them. How did they look?
I suspect someone at sometime decided one cylinder was fouling a bit and needed a projected core plug to keep it clean.
However, at this time, with plug rotation and other maintenance, there is no guarantee the 38BY is in the original location.
 
Were these your spark plugs or were the plugs installed from another engine.
 
Dan Thomas said:
The big question: Did changing the plug fix the vibration? If not, it wasn't the plug. Not that one, anyway. When were the mags last off for internal inspection?
Click to expand...

I had planned on flying it to check it out but I did not get a chance to. I will try it this week and give an update.
 
I finally got to take her flying today and she seems to fly great. The slight vibration that I felt seems to be gone so it probably was a fouled plug.
 
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