Sign in to follow this  
Followers 0
FlyingMonkey

Checking Spark Plugs

31 posts in this topic

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...

0

Share this post


Link to post
Share on other sites

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).

0

Share this post


Link to post
Share on other sites

This question has a couple of variables and can even have more than one answer.

 

First the book answer. It says to check them at 100 hrs. and re-gap and you can use them to 200 hrs. I wouldn't even think of doing this and I have never been in a school that advocated it.

 

The next part is how many hours a year do you fly. So for some the annual may be too soon and for some the annual may be too late. The annual may work well for some. If it flies more than a 100 hrs. a year then it may be too long.

 

Then we have 100LL adding its wonderful lead coating and 91 Oct. unleaded to add to the equation.

 

So what the majority of us do (you will get different opinions) is change ours at 75 hrs., but you could go to 100 if you wanted, but I would never go past that. I'm sure someone will chime in and say they haven't changed theirs for the last 10 years and the engine runs. :huh:

 

Gaps are to be between .023 - .027. The wider gap for the hot summer months and the narrower gaps for the colder winter months. If you live in a real winter state then I would use .023 this winter. Do not forget the thermal conducting paste. That alone can make a 40+F difference between the plug and head temp sync. Do not put thermal paste on the last 1/3 of the plug. More or less the top 1/2 - 2/3 (closest to the gasket). If you get it on the tip it will not burn off as it is silicone based and will cause a misfire so clean it off well if you get the tip in the paste. Absolutely no anti seize.

 

The plugs are NGK DCPR8E with the removable insulator tip. There is only one heat range for this specific plug. You can buy them any where so shop around and try to find a good price. I would bet you can get them local at an automotive store or a motorcycle shop.

 

Even with older plugs you may not as a human feel the difference, but the engine can tell internally. Don't be a penny pincher and skimp on plugs and oil. Do we change oil and plugs a little early, sure, but you can't tell as a human by looking at either when it's gone too long. 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 had a guy ONCE that bragged he hadn't changed his oil in his tractor for 20 years and it still ran. No one in southern Arizona would work on his plane so he sold it.

0

Share this post


Link to post
Share on other sites
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.

0

Share this post


Link to post
Share on other sites

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

 

I'm all for not doing un-necessary maint, but who gets to decide?

 

With that train of thought why do any maintenance at all until it breaks.

 

We have always disagreed on what is necessary and what is not, but I try to put the other peoples or my wife's safety in front of all my decisions as a mechanic and a pilot and money or time involved should never be a consideration against safety. Don't fix it if it ain't broke doesn't work when you crash because you didn't want to fix it until it broke. Lots of dead bodies in the cemeteries since 1912 when the Wright Brothers flew and of course things break even when good maintenance practices are followed so why add to the failures. Poor education and poor maintenance practices from mechanics and owners cause many a crash then you dump poor pilot decisions on top of that and we kill way too many people a year un-necessarily.

 

Don't fix it if it ain't broke is a 20 year oil change.

That's why we have rules because people don't do what's necessary or right. They make poor decisions based on money and John Doe's neighbor's comment from next door. So rules get made to protect the 20 year oil change people and keeps the 20 year oil change mechanic from using their own rules of maintenance being used on the the under or uninformed. Most owners make maint. decisions without enough knowledge because they aren't in the business or don't keep up on a continuing education program.

I hate rules as much as the next guy so blame the guy who doesn't do the right maintenance and so the government steps in to protect the rest of us. It's certainly the shotgun approach, but we all get to see the ones that need protecting from themselves and need to protect the others those same people will injure. You can't say it only affects me and I'll only kill myself because that same guy takes passengers or kills the people on the ground when he goes into the house or shopping center. If he makes it through his ownership then he sells his mess to the next guy.

Money should never be a deciding factor when aircraft safety and good maintenance is at stake. We bought into an expensive elite sport. If someone can't afford the maint. then it was a poor choice of a money based activity.

 

It has always been and always will be the acts of the few that dictate the rules to the masses.

 

My job as a mechanic or a pilot is to make sure everyone gets to go home at the end of the day and even then there is no guarantee.

 

Safety first and continuing education for the life of the owner and mechanic while they are flying.

0

Share this post


Link to post
Share on other sites

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.

 

 

 

 

0

Share this post


Link to post
Share on other sites

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?

0

Share this post


Link to post
Share on other sites

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

 

9741785566_d619644b50_c.jpg

 

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.

0

Share this post


Link to post
Share on other sites

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.

0

Share this post


Link to post
Share on other sites

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.

0

Share this post


Link to post
Share on other sites

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.

0

Share this post


Link to post
Share on other sites

"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."

 

"If it ain't broke, don't fix it."

 

But that's not what you said and unfortunately too many take this to heart. You don't see it because you don't maintenance those 20-30 LSA a year

 

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

 

"There are standards for most things and sensible people can understand and apply them."

 

But they don't or we wouldn't have as many issues with some of the products. This fully bears out with all the request and problems that Rotax and aircraft Mfg's deal with on a daily basis. I talk directly to the MFG's quite often so I get to hear first hand.

 

 

The LSA mechanics that do 20-30 CT's and or other LSA a year and take continuing and on going classes and talk among themselves to share other technical info may vary well have a better insight or handle on issues, new ways of thinking, new technical data before it goes public from the Mfg's (both plane and engine MFG) and those mechanics tend to talk to the Mfgs on a regular basis and all that info may not make it down to an individuals level. So some of us on different sites try to help disseminate that info. I'll will be the first to tell you that not all info is shared down to the individual level from MFG's and some Mfg's call us so we will post the info without them being directly involved.

 

You always said there must be some inner loop. Well you were right and it works that way so info can get out to all without any one MFG trying to write a book and every item and it can stay ahead of waiting for it to be a once a year manual change.

 

I don't pull numbers or items out of a hat, they come from the Mfg's and the many ongoing classes and some of this info is new and a head of what is in the manuals. So I was taught what I talk about or given the info from the MFG. You always want documentation, well it isn't there so we rely on each other and help each other where we can.

 

People have helped me my whole life and I have realized how good those people were to me. So now I want to give back and this is my way.

 

It isn't written in stone from me, nor do I ever profess to know everything, but if you happen on an issue I can help on and ask a question I'll try and do my best to give back and you can choose to use the info or not. I don't talk down to anyone I just give as truthful and straight forward answer as possible. Everyone on this forum has areas of expertise and areas that they would like more info. I'm no different I learn from many here and help where I can.

 

 

I take from your statements of me you have never benefited or I have never helped you with your LSA (CT or Rotax).

 

"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."

"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. "

 

 

If I have led you astray and caused you to fail at knowing a little more about your Rotax and CT or it's maintenance I'm sorry.

0

Share this post


Link to post
Share on other sites

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.

 

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.

 

-------------------------------------------------------------------------------------------------------------------------------------------------------------

 

Good info guys,

 

Tom,

 

Sometimes I use my bore scope to look inside the cylinders to see how the burn, carbon build up and leading are inside. Because of our water cooled heads and thermal paste our plug burn is fairly good and consistent.

0

Share this post


Link to post
Share on other sites

 

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.

0

Share this post


Link to post
Share on other sites

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

0

Share this post


Link to post
Share on other sites

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. :)

0

Share this post


Link to post
Share on other sites

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?

0

Share this post


Link to post
Share on other sites

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.

0

Share this post


Link to post
Share on other sites

Manuals don't keep up with current teachings and these items get passed along in classes and are not in any writings. Not my doing and I only report what Rotax or any aircraft MFG tells me. I don't make these things up someone up high had to tell me so I pass it along and no documentation is included. I also get calls from MFG's so I can help pass the info out since many aren't in a position to get it and these Mfg's know there are people like me on several forums. People don't always take classes, instructors have different teaching ideas or forget and owners rarely keep up continuing education by going to classes. this last comment is a biggy because no matter what you think the answers are there and it cost money to get it. Not my decision. I just spent $5K to get classes on the 912is and it will be an uphill battle to get people to a 912is class until they figure out you can't do anything to this engine unless you do and buy a BUD. I rarely do documents on forums after I read them. I figure those are up to the people that want the information and that would add more time than I have in a day to do that since I help on several forums (under different names). I work out at the hangar all day then come home and spend another 4-6 hours on the computer helping people. Being a secretary and slave to everyone else documentation wouldn't ever let me sleep. A Mfg won't come on line and discuss all the things going on because of the verbal accusations and abuse that a few would dish out which is a no win situation for any Mfg. These last few post are perfect examples of how an MFG can be put under attack by some. I will say that Dynon is one of the few exceptions that have done well in this field and respected for it, but they also have a limited product exposure. There are many things that are discussed behind the scenes and new ideas worked on constantly and problems being worked on.

The Mfg's talk all the time , but manuals may not be changed , but once a year and sometimes much later. Then Mfg's make product changes 1-2 times in one year and the public never knows. An example of the info loop: (I predict , documentation not included ;) ) there is a big SB coming out soon and probably only 1-2 people in the US even know about it. You have to be deep in the system and work everyday with these folks to be included in this mix and show them they can trust you and without that you're out of the loop until it becomes public. I work hard and every day to stay in that loop.

 

Again it isn't of my making just the way it is and all I do is try hard at my job to be trusted in those information circles.

 

Documentation not included. ;)

 

As far as a MFG's too stringent intervals, do I believe there are some, yes, but I'll follow the rules to protect the company, myself and the owner from liability.

 

The system is what it is from all our sources. I don't fight it because it takes too much time and effort. I learned to work in it because to do anything else puts you on the outside.

0

Share this post


Link to post
Share on other sites

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).

0

Share this post


Link to post
Share on other sites

Hi Doug,

 

Wider gaps tend to help run a tad cooler for the warmer weather and the fuel ignites just fine with the warmer OAT temps that have the engine already at a warmer start temp than the winter engine temps. If you run them too wide then you get poor burn and the plugs tend to start getting black and sooty. I have had some come into my shop over .038 and they are sooty, but it still ran. They had 140 hours on them and had never been checked. The narrower gap tends to let the engine run a little warmer and makes it easier to start with the colder air in the combustion chamber. The old Rotax gaps used to be .020 to .028. That was changed a few years back. Gap also affects the mag drop rpm. Can the engine run on a .020 gap yes, but Rotax eventually thought it too narrow and changed it after many years.

 

Your engine would run winter or summer with any gap within range and all we're doing is trying to help it out a little bit.

0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0