Checking Spark Plugs

[FlyingMonkey]

How often should spark plugs be pulled and checked? I have about 20 hours on my plane since its annual and Rotax 100hr service. Should I check plugs every annual? Every oil change? Every pre-flight (joking)? Or only if I note some type of roughness or performance change?

 

Is there a detailed online walk through of how to properly check plugs and gap them for a Rotax 912?

 

Also, can somebody shoot me a link to the correct plugs to get? IIRC there are two very similar plugs with different heat ranges, one correct and one not correct...

[Jim]

Just replace them every annual works for me.

[Doug G.]

Annual seems to be fine. I will be re-gapping mine this fall because of our temperature extremes, I have them on the wide end of the range now.

I ordered mine from CPS. I don't have the number handy but I am certain it is in at least one thread on the forum. I know you need them with the removable caps (evidently you can get them non- removable).

[Jim Meade]

You have an $18K engine that should go way past TBO don't do anything by act or omission to cause it a shortened life.

I agree. And one act is unnecessary maintenance. If it ain't broke, don't fix it.

[Jim Meade]

Oh, Roger, good grief. There are standards for most things and sensible people can understand and apply them. Oil has a life that most of us could agree on. As do spark plugs. Rubber hoses can be inspected as can nearly any part on the airplane.

 

Your problem on this forum is you insist on putting forward your own interpretations and preferences as the best practice or the preferred way even when it is in contravention of Rotax and Flight Design publications.

 

The airline industry and the military are two area that use the approach of periodic inspection as opposed to time based maintenance. Only part 91 still does things the old way. People like you don't help any because you confuse your personal comfort level and operating practices with good, sound condition inspections and appropriate maintenance and actually make the old way even more restrictive.

 

You make a continued practice of talking down to the members of this forum as if you have special knowledge and they don't, so they should trust you and do it your way. This practice serves your purposes because it gives the person who is not sure the same feeling as they get when they talk to their doctor or priest. The sad thing is, it becomes a matter of faith and trust rather than a matter of knowledge and science.

 

Your job as a mechanic is to apply good, legal maintenance practices to your work, not to convince someone to replace their plugs at 75 or 100 hours when the book calls for 200 UNLESS THERE IS A REASON. Rotax, in all it's experience and wisdom, doesn't know better. Roger does. I'll stipulate that more and more you will put in the book numbers before you go off on your own tangent, which is better than you used to. So, there may be hope for you yet.

 

 

 

 

[Jim Meade]

Annual seems to be fine. I will be re-gapping mine this fall because of our temperature extremes, I have them on the wide end of the range now.

Doug,

A question for you and everyone. If you are going to pull the plugs every spring and fall based on temperature, what are the considerations of setting up a spring and fall set of plugs? They are cheap, after all. Then you don't have to regap them. Set them once. I'm not a great fan of regapping plugs although it is not a big deal.

The disadvantages of having two sets of plugs might include keeping track of how many hours are on them. If you are going to go on time based maintenance, you could us them each for two seasons if you fly less than 200 hours/year. Or you could date them. Or, of course, you could write the engine hours down on the storage box. It may be it's not worth the trouble. But, I have to confess, I might toy with the idea of having a summer and winter set of plugs.

What do you all think, pro and con?

[FastEddieB]

I made a little spark plug holder from an old battery box I had lying around (click for larger image):

 

 

Originally had 12 larger holes for my Cirrus plugs, which I sleeved down for the smaller ROTAX plugs.

 

Anyway, plug condition can be an indicator of problems with a given cylinder and overall mixture and potential lead issues - good thing to take a look at and monitor any time you have them out.

 

You can see where I applied the conductive paste.

[Dan Kent]

When I was getting my 100 hr service the mechanic sent me to O'Reily's to get the plugs. I think the total cost including tax was less than $22 for a dozen (may have been 10) plugs. Very inexpensive.

[FastEddieB]

Less than $2.50 each at both Advance and O'Reilly's, IIRC.

 

Make sure they have the removable "barrels" before leaving the store - some do, some don't.

[Tom Baker]

Roger already gave the plug number, but the stock number for the one with removable top is 4339. One thing that no one has mentioned is in reality the gasket on the plug is intended to be a one time use gasket. It is designed to crush and make the seal and after it has been torqued down it doesn't crush again. I buy 40 at a time boxes 4x10 to make 5 sets of plugs. I change them any time I pull the complete set from the engine.

[sandpiper]

 

You make a continued practice of talking down to the members of this forum as if you have special knowledge and they don't, so they should trust you and do it your way. This practice serves your purposes because it gives the person who is not sure the same feeling as they get when they talk to their doctor or priest. The sad thing is, it becomes a matter of faith and trust rather than a matter of knowledge and science.

 

I went to LSRM school with Roger. Time together was not only class but also after hours as we had our recreational vehicles parked next to each other on the ramp. Since then, 2008 I think, I have communicated with him on this forum, phone, face time and face to face. He has never talked down to me even though he easily could since his maintenance knowledge and skills far exceed mine. He has always gone out of his way to help, me and others, making sure I knew what was required and never once made me feel "talked down to" in the process.

[Doug G.]

Although I do not always agree with Rodger, I do find the info he provides helpful, and he has always been more than willing to assist me in any way he can over the phone. As he said, it is up to me to decide to accept his advice or not - most times I do. I find him exceptional in that we can argue here on the forum, but if I call him he is more than willing to help me out. A lot of people don't seem to deal with life that way.

 

Jim and Eddie, as far as using two sets of plugs - that makes a lot of sense. On Roger's advice, I gapped to .27 for the summer and will be going to .23 before the weather starts getting cold. Using two sets (and a good plug stand) would make that an easier task. Thanks

[Tom Baker]

Although I do not always agree with Rodger, I do find the info he provides helpful, and he has always been more than willing to assist me in any way he can over the phone. As he said, it is up to me to decide to accept his advice or not - most times I do. I find him exceptional in that we can argue here on the forum, but if I call him he is more than willing to help me out. A lot of people don't seem to deal with life that way.

 

Jim and Eddie, as far as using two sets of plugs - that makes a lot of sense. On Roger's advice, I gapped to .27 for the summer and will be going to .23 before the weather starts getting cold. Using two sets (and a good plug stand) would make that an easier task. Thanks

 

Those are rather large gaps. You might want to try .027 and .023. It might work a little better.

[sandpiper]

Good catch Tom!

[Doug G.]

:blush: Good thing my feeler guages don't go that large or I might have been in trouble. lol

[Doug G.]

On the other hand, maybe I was using a different number base - I love a challenge.

[Jim Meade]

Is the plug gap difference between winter and summer only for starting purposes? If so, does it matter if one always uses an engine heater so that even in winter it starts warm? If it is for operation purposes, please explain what internal temperatures or other factors require the gap difference.

 

And, since I don't have my book at hand, does ROTAX say to do this or is this some more field wisdom?

[Jim Meade]

I fully agree that Roger often provides useful information. I read and respect his suggestions on tips and procedures that make maintenance easier.

 

Where I disagree with Roger is when he sets himself up as knowing more than Rotax or Flight Design and does not show the science to support his difference.

 

Who else besides Eric teaches Heavy Maintenance? As of two years ago, no one else was permitted to, I was told by Ronnie Smith.

 

I'd like Roger to give me some examples of any time that he feels that Rotax requirements are too stringent and that he suggests we don't have to follow them. I don't recall any. He frequently tells us that ROTAX is wrong and maintenance should be done more often (plugs, e.g.) but I don't recall him saying that ROTAX is wrong and we should extend or skip the interval.

 

Even if he believes that an SLSA should stay with a published interval (so long as it's not longer than Roger's own standard) I hope that he would share with us ELSA owners any information he has where he knows that ROTAX is being overly conservative. If they're wrong one way one would assume they are also sometimes wrong in the other direction.

[Doug G.]

As far as the gaps are concerned I do use an engine heater, but I am not always home, so my hope is that it makes a difference. My engine has run fine this summer with the the wide gap.

I can offer no scientific proof that it makes a difference and am willing to listen to other reasoning.

I deal with temps from the upper 90s to - teens. ( although I usually don't fly below -10).

[Jim Meade]

Go ahead and post the examples, Roger, and we'll work it out.

 

As for you being John The Baptist foretelling the coming good news - I'm not buying it. It is simply inconceivable that ROTAX would use that way to disseminate information.

 

BTW, does Eric work for Rotax? Directly, as an employee? Do you know of any of the instructors who are Rotax employees?

[FlyingMonkey]

It was just a simple spark plug question...

[Jim Meade]

The current Rotax Line Maintenance manual says to set plugs for 0.6mm-0.7mm (0.23-0.27 thousandths) for new installation and the wear limit is 0.9mm (0.35).

 

There is one entry that discusses plug gap as an issue in winter operations. It does not specify a value.

 

From what I can find out, a wider gap will increase the voltage needed to fire the spark. It increases tip temperature. A wider gap will give a better spark that will result in better fuel burn.

 

One can see that if battery performance in winter is marginal that a wider gap requireing more voltage may make starting more difficult.

 

My immediate impression is that if your airplane starts OK, a wider or "summer" gap setting is preferable. There is some very interesting reading in spark plug technology. The following is for cars but much of the information is generic and should be useful for airplane engines.

 

http://www.ngksparkplugs.ca/tech-info-spark-plugs.cfm

http://www.ngksparkplugs.com/techinfo/spark_plugs/installation.asp

http://www.globaldenso.com/en/products/aftermarket/plug/basic_knowledge/spark/conditions.html

http://vdlfuelsystems.com/?p=273

http://www.carcraft.com/howto/116_0703_spark_plug_guide/viewall.html