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Spark plug analysis

  • Denis Ranque
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1 week 5 days ago - 1 week 5 days ago #16148 by Denis Ranque
Denis Ranque created the topic: Spark plug analysis
Hi everyone!

I just changed my spark plugs after 200h on my Rotax 912ULS. I would like to know what you guys think of their appearance.
The plugs from cyl. #3 have a different colour than the rest, they appeared yellowish.

PICTURE

Blue skies

Denis Ranque
Last Edit: 1 week 5 days ago by Denis Ranque.
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1 week 4 days ago #16155 by James Ott
James Ott replied the topic: Spark plug analysis
In my opinion, the #3 plugs are the only ones that look to be the right color; the others are too black (sooty). Did you run the engine at about 3500-4000 rpm for a while before you shut down to remove the plugs? Otherwise idling will soot them up.

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1 week 4 days ago - 1 week 4 days ago #16156 by Roger Lee
Roger Lee replied the topic: Spark plug analysis
Hi Denis,

I can tell by looking at the pictures that your gaps are too wide. They should be between .023 -.027. A nice place to be is in the middle at .025. If you live or are flying in cold country a narrower gap is better. If you start out at .027 then the gap will only get wider and work its way out of spec.
I know the manual says up to 200 hours, but most of us use 75 hours and I personally don't know of anyone that goes past 100 hours. For a couple bucks a piece these are cheap to keep in top condition. They are the heartbeat of your engine.
Idling will cause dry black sooty plugs at times. If you want to do a more accurate plug color check go fly and as soon as you land pull over and check the plugs or while on the ground run the engine for approximately 5 minutes at 4K rpm then back to idle with an immediate shut down with no idling.

As far as right now just replace your plugs with a better gap and go fly. :)

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
Last Edit: 1 week 4 days ago by Roger Lee.
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1 week 2 days ago #16167 by Denis Ranque
Denis Ranque replied the topic: Spark plug analysis
Thanks for the information guys!!!
I was not aware that running at idle turns the plugs sooty. Next time I will make sure to have the engine at high RPM prior checking. However, I do remember being advised against removing spark plugs from a hot engine to prevent thread fretting. I guess I will have to wait for it to cool down :)

Blue skies

Denis

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6 days 19 hours ago #16182 by Roger Lee
Roger Lee replied the topic: Spark plug analysis
Hi Denis,
You can remove plugs hot or cold. They should have thermal paste on them which helps with thread lubrication.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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6 days 10 hours ago - 6 days 10 hours ago #16185 by Jim Flock
Jim Flock replied the topic: Spark plug analysis

Roger Lee wrote: I know the manual says up to 200 hours, but most of us use 75 hours and I personally don't know of anyone that goes past 100 hours.


Is this assuming exclusive use of 100LL?
Last Edit: 6 days 10 hours ago by Jim Flock.

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5 days 19 hours ago - 5 days 18 hours ago #16188 by Roger Lee
Roger Lee replied the topic: Spark plug analysis
For all the people I know and classes I've been to it's with either fuel. I personally don't see a reason to go over 100 hrs. It's up to you.
I look at plugs as the heart beat of the engine, the oil is the blood. Neglect either and they may become deseased like a persons body and go downhill.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
Last Edit: 5 days 18 hours ago by Roger Lee.

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5 days 18 hours ago #16192 by Jim Flock
Jim Flock replied the topic: Spark plug analysis

Roger Lee wrote: For all the people I know and classes I've been to it's with either fuel. I personally don't see a reason to go over 100 hrs. It's up to you.
I look at plugs as the heart beat of the engine, the oil is the blood. Neglect either and they may become deseased like a persons body and go downhill.


Good point. Do you have the same philosophy on oil changes? i.e. 25 hours regardless of fuel type.

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5 days 12 hours ago #16201 by Roger Lee
Roger Lee replied the topic: Spark plug analysis
Hi Jim,
25 hrs. for 100LL and 50 for auto fuel.
The manual says up to 100 for auto, but again I don't know a single person who does that.
My whole philosophy is to get to 2000 or more TTSN hours with no more than the prescribed general maint.

Neglect part of the system and it may be felt in the wallet later or over some really tall inhospitable mountains. ?

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
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5 days 12 hours ago #16203 by Jim Flock
Jim Flock replied the topic: Spark plug analysis

Roger Lee wrote: 25 hrs. for 100LL and 50 for auto fuel.


We're on the same page. Thanks!

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3 days 19 hours ago #16232 by Genival Pacheco
Genival Pacheco replied the topic: Spark plug analysis
Hi Roger,

I use AVGAS so I change oil every 25hours.
Question is:
It is necessary to change the oil filter every 25 hour or it could be changed every 50 hours.

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3 days 15 hours ago #16235 by James Ott
James Ott replied the topic: Spark plug analysis
I would go 50 hrs on the filter. I have never heard of the lead fuel additive clogging a filter; also the Rotax maintenance manual is OK with 50 hours I believe.

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3 days 11 hours ago #16239 by Roger Lee
Roger Lee replied the topic: Spark plug analysis
Hi Genival,
This may be a good debate. Usually the filter gets changed with the oil. Does lead help block up some of the filter medium? I don't know for sure. This would be the reason to change it since many of us go to 50 hrs. with no debris and Rotax is willing to go up to 100 hrs with auto fuel.
I guess this may be a personal preference item. I'm believe people will chime in here so let's see what the consensus says.

Rob what do you have to say?

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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2 days 18 hours ago #16245 by Jim Flock
Jim Flock replied the topic: Spark plug analysis
From Section 12.2 (Oil Change) of the Maintenance Manual:

Step 3: Replace oil filter at each oil change and inspect the filter insert.

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