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View Full Version : I've got a good ignition problem for you guys....



LarsonAero
07-07-2009, 07:14 PM
Some of you recip guys may get this right off...I'm still a bit baffled.

Engine: O-360 A1A that's been converted to an IO-360.

Symptoms, rough right mag, occasional rough left mag. For quite some time...both mags got better by leaning for ground ops using the "best RPM" method...or pegging the Peak EGT needle, during run-up and taxi.

Even when the mags are rough, there is an rpm drop. That is to say...in both, the rpm is 100-150 higher.

Progress ~20 flight hours, to the engine dying on the right mag....and left still being very occasional failure (once every 5-10 flights, always corrects on the ground.). The left still drops 150rpm on a mag check.....but when right is selected the engine won't run.

This is how it came to me.

I de-cowled the engine, and checked P-leads and grounding shroud connections. Then I started pulling off the ignition harness....as #3top ignition spring shot out of the spark plug. I started thinking....easy $$ :D, fixed the lead...put the harness back on and pulled it out of the hangar for a test run. Rough mag still. Ok, I thought...make sure the fixed lead is indeed fixed. I shot the harness wires, and ALL leads checked good. Next?

Pulled the plugs, and looked for an obvious foul, none found. A little lead, but otherwise normal looking plugs. Fine wire plugs also. Just to be sure it wasn't still a plug problem I couldn't see....I went ahead and ran them all through the plug tester. All checked good, a little dull....so I went ahead and blasted them anyway so they all sparked really well.

Now I was starting to think perhaps a switch problem.....so I switched the P-leads...and the problem followed (or rather stayed...depending how you look at it). I was obviously suspecting a mag issue now....this engine has 2 slick 4373's installed, both with ~690 hours on them. The engine log book indicates a 500 hour inspection completed IAW the Unison/Slick overhaul manual, but I didn't do it....so I wasn't banking on it. I didn't recognize the shop in the logbook.

Just because its easy to do....I checked the timing, and found the right mag to be a hair out...but not anything to be concerned with. Nothing that would cause a dead mag. So I pulled the right mag.

I found the distributor block & rotor were pretty worn, and had evidence of arcing. Problem solved right? These mags aren't usually worth re-building.....so I got a new mag and installed it. Timed it...to right on, closer than before. The impulse couplings both break at the exact same instant.

Test run time. Engine starts up, perfectly. Better than ever even....rough right mag still. Grrrr. The engine will run on the right mag, but it has an excessive RPM drop, 300-400 rpm...hard to tell the engine runs so rough the whole plane shakes. I bet its only running on 2 cylinders. It shook so bad...that one of the shielding wires that was grounded to the case broke. The one on the right mag. So....I spliced in a new jumper (there wasn't enough shielding wire to reach), and repaired that break. I pulled all the plugs again...looking for a fouled one to help with troubleshooting. Nothing. I decided to pull the mag again...just in case I got it off a tooth, or timed to the wrong hole somehow...:roll:). Ran it again...just to see if it was the broken wire. Still excessive RPM drop...and really rough on the right mag.

Well....at that point I called it a day. It was already an hour past dinner time.

I re-used the same harness...which I shot all of the leads already. The harness is good. I tested each spark plug individually, and inspected for fouling after the test runs. I've rotated the plugs....all the R's to the L, and vise versa. Problem stayed on the right.

Next I'm going to swap P-leads again....but I'm thinking the the P-lead wire itself now. I can't narrow down a certain cylinder that doesn't work as of yet....when on the right mag, so perhaps its the whole mag itself which is cutting out, though only intermittently. That could be a break in the P-lead wire from the switch. I'm not a magneto expert. 90% of my experience comes from turbo props and fans.

I'm also not an electrician. I understand the basics...can explain/regurgitate concepts....but in depth application of electrical theory is beyond my current abilities. Could this be the capacitor? Might the mag have come with a bad capacitor? I've tried testing capacitors before...and honestly, I have a hard time picking out good ones from bad ones. I could pull the mag, send it back and get another one....but if there isn't anything wrong with the mag...I'm gonna look really stupid.

I'm a bit perplexed here. Any recommendations? I double checked the engine dataplate with the engine logs...and build paperwork...it is supposed to be timed at 26 BTDC. I've right on the marks, both on the starter and the case. I'm sure the mag was pinned properly and placed properly....again, I checked the timing with the beeper box., and the impulse couplings both fire at the exact same time....

Ideas?

Captainkirk
07-07-2009, 09:14 PM
Were Slick SB8-02A and SB8-03A complied with? Both exhibit symptoms of roughness. I would check.....

http://www.lycoming.textron.com/support/publications/service-bulletins/index.html

http://www.lycoming.textron.com/support/publications/service-bulletins/pdfs/SB584B.pdf

http://www.lycoming.textron.com/support/publications/service-bulletins/pdfs/SB583A.pdf


What does your mag drop do when the engine is leaned? Get better or worse? You could be flooding due to a heavy float.....

http://www.lycoming.textron.com/support/publications/service-bulletins/pdfs/SB582A.pdf

Do a mag check, running the engine on the bad mag for several minutes, then pull the mixture without switching back to "Both". Quickly, before the engine has time to cool, shoot the cylinder heads and exhaust stacks with adigital thermometer (or lacking one, use the old fashioned "boil test" by squirting water on the exhaust stack just below the flange; a cold cylinder will allow the water to simply run off the stack while the others will hiss and evaporate in front of your eyes).
A cold cylinder is indicative of a bad plug, wire, or ignition tower. You already know which plug or lead because you're running on only one mag, right?
Evenly temp'd cylinders running rough is indicative of a mag problem.
Try this and let me know what you find.

LarsonAero
07-08-2009, 12:32 AM
I've got an IR thermometer, I've shot cylinders using that method before. I'll do it tomorrow on this one and see what shows up. I checked the old mags for these SB at the condition inspection, but didn't think to check the new one. I bet both of these apply to this one....and the breaker point cam one...kind of makes sense. I'll definitely check these tomorrow as well. Thanks!

I should have started with ADs/SBs before even considering installation of the part.

As far as mag drop when leaned.....no difference today/yesterday with the right mag. The left mag ran perfectly for me every time. I let the cylinders and oil come to temperature, leaned for smoothness...which resulted in about 75 cool of peak on the egt. Didn't make any difference at all.

I'll troubleshoot more tomorrow on it.

Bubba1090
07-08-2009, 04:49 AM
Were Slick SB8-02A and SB8-03A complied with? Both exhibit symptoms of roughness. I would check.....

What does your mag drop do when the engine is leaned? Get better or worse? You could be flooding due to a heavy float.....

Do a mag check, running the engine on the bad mag for several minutes, then pull the mixture without switching back to "Both". Quickly, before the engine has time to cool, shoot the cylinder heads and exhaust stacks with adigital thermometer (or lacking one, use the old fashioned "boil test" by squirting water on the exhaust stack just below the flange; a cold cylinder will allow the water to simply run off the stack while the others will hiss and evaporate in front of your eyes).
A cold cylinder is indicative of a bad plug, wire, or ignition tower. You already know which plug or lead because you're running on only one mag, right?

Evenly temp'd cylinders running rough is indicative of a mag problem.
Try this and let me know what you find.

...in an IO-360! Engine: O-360 A1A that's been converted to an IO-360. :oops:

KISS principle, throw a new set of plugs in it & see what happens. (I read you tested them but the bomb test isn't a fail-proof test)

I'd rule out your SBs at least on the RH mag, being new, the LH is worth checking. Have you done a low RPM mag check? You may have a distributor cap cracked/faulty.

Does the engine make full static RPM? Who converted the engine? When? ETT SMOH? If it's recent, you may have an internal gear alignment problem. If there's 100s of hours on it, disregard that.

B 8)

Captainkirk
07-08-2009, 07:25 AM
[FONT="Comic Sans MS"]...in an IO-360! Engine: O-360 A1A that's been converted to an IO-360. :oops:
My bad. You got me Bubba, I was in such a hurry to help him out I overlooked the IO thingie.

Bubba1090
07-08-2009, 08:03 AM
KISS principle, throw a new set of plugs in it & see what happens. (I read you tested them but the bomb test isn't a fail-proof test)

I'd rule out your SBs at least on the RH mag, being new, the LH is worth checking. Have you done a low RPM mag check? You may have a distributor cap cracked/faulty.

Does the engine make full static RPM? Who converted the engine? When? ETT SMOH? If it's recent, you may have an internal gear alignment problem. If there's 100s of hours on it, disregard that.

B 8)

I'm assuming this O-360-A1A is a Lycoming. Is the converted model a -A1A as well? Have you checked the application chart for the correct plugs? http://www.lycoming.com/support/publications/service-instructions/pdfs/SI1042Z.pdf Have you inspected/cleaned the lower plug ports? Lead deposits commonly build up in the lower ports that can repeatedly melt @ operating temperatures & foul an engine. I regularly clean them with a dental pick.

I don't understand "Even when the mags are rough, there is an rpm drop. (I would hope so!) That is to say... in both, the rpm is 100-150 higher." :banghead: What does that mean? At what RPM are you doing the mag check? What is your RPM drop? Differential RPM drop?

B 8)

Bubba1090
07-08-2009, 08:53 AM
Do a mag check, running the engine on the bad mag for several minutes, then pull the mixture without switching back to "Both". Quickly, before the engine has time to cool, shoot the cylinder heads and exhaust stacks with a digital thermometer (or lacking one, use the old fashioned "boil test" by squirting water on the exhaust stack just below the flange; a cold cylinder will allow the water to simply run off the stack while the others will hiss and evaporate in front of your eyes).

A cold cylinder is indicative of a bad plug, wire, or ignition tower. You already know which plug or lead because you're running on only one mag, right?

Evenly temp'd cylinders running rough is indicative of a mag problem.
Try this and let me know what you find.

I should have asked this first so I will now ass/u/me this aircraft does NOT have any kind of engine monitoring system where you could isolate it to one cylinder or download performance data? This is an excellent example of why they should have one! (Sales pitch) It's a great tool for both them & us! Sell them one from your on-line store! :mrgreen:

Also, I agree with the Captain but I wouldn't necessarily limit this to ignition. Have you flowed the nozzles? A dirty or clogged nozzle can cause one cylinder to differ! Depending on the installation, you may be able to notice that on the F/F gauge.

BTW, what aircraft is this beast in? A comanche? B, D or E model Mooney? Travelair? Or experimental?

B 8)

LarsonAero
07-08-2009, 03:59 PM
OK...a lot to address. The aircraft is an RV-6A, the engine is experiemental as well. It was built by Hatch Racing, before Hatch Sr. Died. To my knowledge...this motor is one of the only Lycomings they built while exploring the possibility of getting into aviation applications. The motor has 690 hours on it, about 200 since a teardown due to a prop strike (nose gear collapse). I used a mag given by the customer, which is supposed to only have 120 hours on it. Again...this is experimental.

I did the condition inspection a few months ago, and have done it several other times as well. 4 out of the last 5 years. The plane has flown about 25 hours since the condition inspection. The runup then did not reveal any mag problems, though there is a history of them as described in my first post. I just hadn't encountered them.

There is not an engine analyzer installed, it is in the long range plans along with making the aircraft IFR legal.

If it is a fuel issue, why does it really only affect the engine when the left mag is turned off? If it was fuel related...wouldn't the same problem present itself when the right mag was turned off? I mentioned the RPM drop....because if there was no drop when turning off a mag...then it would indicate that the mag was not working at all in the both position. Swapping P-leads from left mag to right mag can narrow down if it is a switch or wiring issue.

I've been doing low RPM mag checks and high/medium RPM mag checks each time. The low RPM, is at around 800 RPM, the high at 1800 RPM. The results are the same, high or low. Other than....the engine wants to die more at low RPM when on the right mag.

I'm unclear as to why I would look to the left mag for problems....when it is the one that is performing good 99% of the time? Currently, when starting, then going to both....the engine runs great. When switched to Left (turning off the right mag), there is a good RPM drop....and the engine runs fine. No backfiring, no sputtering..and no vibrations. The RPMs smoothly return when switching back to both. When switching to right....the RPM drop is excessive, the engine sputters, coughs & vibrates like its running on 2 cylinders....but doesn't die altogether (as it did with the old mag). The old mag...when selected the engine would die altogether and not even try to run. What is baffling me is that so far....I can't find or narrow down the cylinders which aren't firing when the right mag is selected.....as if the cylinder that doesn't fire floats around. Which is making me think coil/capacitor.

I think that shutting the engine down while it is running on the right mag only.....should help. We'll see if the evidence stays on the plugs then. Or if it truly is a floating problem....which definitely points back towards the mag.

The other thing it could be still....is a chaffed P-lead wire. If it occasionally grounds out, you probably wouldn't notice in both. but on the mag that has the chaffed wire, it would be noticeable...and would explain why no particular cylinder fails consistently.

So those are the directions I'm going in now.

Replacing all plugs cold be an option....but honestly, these fine wire plugs don't have a ton of time on them. I believe they were added when the aircraft was bought by the current owner....which would have been about 300 hours ago.

Also...if it was a plug problem....wouldn't that plug always not fire well? So...wouldn't it indicate a problem visually? Also, when I swapped plugs from mag to mag (rotated the top to bottom on each cylinder)...shouldn't the problem have switched mags? It stayed the same.

Keep the ideas coming....I'll let you know what I find out later today.

Captainkirk
07-08-2009, 08:20 PM
Something else I didn't think of; since it is experimental, is it possible they've got one mag firing all the tops and the other, the bottoms? They used to do this in certain applications back in the sixties, before they realized that lower plugs will foul at higher rate than uppers. Virtually every application I've seen today (with the exception of homebuilts) split them up now, for that exact reason.
And, since we are dealing with fuel injection (duh! sorry, Bubba) Big Bee is correct in the fact that it could be an injector problem. Top plugs will ignite a charge in a different manner than a bottom plug. Sounds goofy, but I've experienced it both by sound, RPM and via multiprobe EGT readings.
I have a few other ideas, but eliminate these, first.

LarsonAero
07-08-2009, 09:03 PM
OK...at the hangar now. I decided to check the P-lead wire for a short. While I was there....I checked for continuity between the P-lead input & the Ground on the mag. I get zero resistance. Bad capacitor? I'm still no mag expert...but that isn't correct, right? Now a number of things internally could cause a short, but at least this narrows my problem to the mag...right?

LarsonAero
07-08-2009, 09:11 PM
ok....obviously that isn't it.....as the left mag does the same thing. Now I feel like an idiot.

LarsonAero
07-08-2009, 09:12 PM
Something else I didn't think of; since it is experimental, is it possible they've got one mag firing all the tops and the other, the bottoms?

nope. Traced the harness...isn't built that way. Good thought though.....because that is exactly how its behaving. Like its firing at the wrong time. Which points to the service bulletin....or incorrect internal timing.

Captainkirk
07-08-2009, 10:02 PM
[QUOTE=LarsonAero;12936]nope. Traced the harness...isn't built that way. Good thought though.....because that is exactly how its behaving. Like its firing at the wrong time. Which points to the service bulletin....or incorrect internal timing.QUOTE]

Which could be a symptom of a melted breaker cam, per the SB......

Or, a symptom of a bad carbon brush, no?

ppolstra
07-08-2009, 10:05 PM
OK...at the hangar now. I decided to check the P-lead wire for a short. While I was there....I checked for continuity between the P-lead input & the Ground on the mag. I get zero resistance. Bad capacitor? I'm still no mag expert...but that isn't correct, right? Now a number of things internally could cause a short, but at least this narrows my problem to the mag...right?

My first thought is that it sounds like an intermittent wiring problem. One of the p-leads or ignition wires is probably flakey. Try testing the wires while wiggling them vigorously.

When the mag switch is in the off position the p-leads are pulled down to ground. Essentially, the mag is sending its sparks to ground instead of the plugs. It isn't completely clear to me what your connecting to for your continuity test, but your indication could be normal. Also, be careful about measuring continuity on mags and other items with coils. Such things can have low DC resistance. It is better to consult your maintenance documentation and see if a correct DC resistance is listed and check for that.

LarsonAero
07-08-2009, 10:17 PM
Didn't foul any plugs.....but with the IR laser, I found a bad plug. Swapped it with the top....and the problem followed. Old standby.....you may not just have one problem. THis time it was the mag...and a plug. I'm ordering replacement plugs now.

Bubba1090
07-09-2009, 07:39 AM
...that I'll address in your post.


OK... a lot to address. The aircraft is an RV-6A, the engine is experiemental as well. It was built by Hatch Racing, before Hatch Sr. Died. To my knowledge...this motor is one of the only Lycomings they built while exploring the possibility of getting into aviation applications. You say "they built" but actually "they" just O/H it, correct? To Lycoming spec's or their own? Who did the teardown? The motor has 690 hours on it, about 200 since a teardown due to a prop strike (nose gear collapse). I used a mag given by the customer, which is supposed to only have 120 hours on it. Again... this is experimental. You said you put a "new" mag on when in fact you put a "new to this aircraft" mag on it. Was it yellow tagged or just one the owner had on hand? If so, what, if any, internal inspection/testing did you do before you installed it? You're letting this guy give you all sorts of chit to install, you do know that it's the installers responsibility for the airworthiness & applicability of the parts he/she installs? (I HOPE!)

I did the condition inspection a few months ago, and have done it several other times as well. 4 out of the last 5 years. The plane has flown about 25 hours since the condition inspection. The runup then did not reveal any mag problems, though there is a history of them as described in my first post. I just hadn't encountered them. When they encountered these other mag problems, who did they have address them? Was it not you? If not, was that person qualified? What did they do to rectify those problems?

There is not an engine analyzer installed, it is in the long range plans along with making the aircraft IFR legal.

If it is a fuel issue, why does it really only affect the engine when the left mag is turned off? If it was fuel related... wouldn't the same problem present itself when the right mag was turned off? In your original post you said "Symptoms, rough right mag, occasional rough left mag." Does it or doesn't it appear on both mags? If it doesn't then you might rule out fuel, note the word MIGHT! I mentioned the RPM drop... because if there was no drop when turning off a mag... then it would indicate that the mag was not working at all in the both position. Or that the mag was always operating, i.e. bad switch or P-lead Swapping P-leads from left mag to right mag can narrow down if it is a switch or wiring issue.

I've been doing low RPM mag checks and high/medium RPM mag checks each time. The low RPM, is at around 800 RPM, the high at 1800 RPM. The results are the same, high or low. The results can't be the same at both settings! At 800, what is your RPM drop? At 1800? Other than... the engine wants to die more at low RPM when on the right mag. Do you have the Lycoming Operator's Manual for an O-360/IO-360 engine? The little purple book (now a full page book)

I'm unclear as to why I would look to the left mag for problems... when it is the one that is performing good 99% of the time? How about because YOU said it ran rough? Currently, when starting, then going to both... the engine runs great. When switched to Left (turning off the right mag), there is a good RPM drop... Qualify "good" and the engine runs fine. No backfiring, no sputtering... and no vibrations. The RPMs smoothly return when switching back to both. When switching to right... the RPM drop is excessive Qualify "excessive". The more specific you are, the better equipped we are to help you!, the engine sputters, coughs & vibrates like its running on 2 cylinders... but doesn't die altogether (as it did with the old mag). The old mag... when selected the engine would die altogether and not even try to run. What is baffling me is that so far... I can't find or narrow down the cylinders which aren't firing when the right mag is selected... as if the cylinder that doesn't fire floats around. Which is making me think coil/capacitor. You never answered what dash IO-360 this was modified to. If it was done to Lycoming spec's, the TCDS sez timing is 20* BTDC, your original post indicated you timed it to 26*. You might want to look at that!

I think that shutting the engine down while it is running on the right mag only... should help. We'll see if the evidence stays on the plugs then. Or if it truly is a floating problem... which definitely points back towards the mag.

The other thing it could be still... is a chaffed P-lead wire. If it occasionally grounds out, you probably wouldn't notice in both. but on the mag that has the chaffed wire, it would be noticeable... and would explain why no particular cylinder fails consistently.

So those are the directions I'm going in now.

Replacing all plugs cold be an option... but honestly, these fine wire plugs don't have a ton of time on them. I believe they were added when the aircraft was bought by the current owner... which would have been about 300 hours ago. KISS man KISS. You believe there's 300 hours? How many times have you had them out? How hard would it be to change them? Don't you have a log entry for their installation?

Also... if it was a plug problem... wouldn't that plug always not fire well? Absolutely NOT! So... wouldn't it indicate a problem visually?Again, absolutely NOT! Also, when I swapped plugs from mag to mag (rotated the top to bottom on each cylinder)... shouldn't the problem have switched mags? Maybe, maybe not... Did you rotate in an X pattern (recommended)? Or just top to bottom? It stayed the same.

Keep the ideas coming... I'll let you know what I find out later today. Before I went too much further, I would KISS! I'd verify the timing issue first then change the plugs THEN I'd get into the sublime. But that's just me...

LarsonAero
07-09-2009, 10:47 AM
OK, I'm going to try and answer all of those points....as this may help others in the future when they search for problems on this board.

They, meaning Hatch, built this motor essentially to zero time. Following Lycoming's instructions...then added their own touches, like custom intake & exhaust (built in house), and a few other things....which I can't remember. It's all laid out in the engine log, which I don't have in front of me.

The teardown.....I think was done by superior, though that I'm guessing at right now, as I can't remember for sure. I seem to recall that nothing was changed/found to need repair with the engine.

I believe the prop was replaced....again I don't have the logs here, and I'm going off of memory (I can update the post when I'm at the hangar).

You are right, I put a "new to this aircraft" mag in. I did check out the mag before installing it....and figured that if I couldn't get it to work on the engine I'd pull it and address things at that point. I'm not signing the aircraft off as airworthy until it runs perfectly. IF the timing checks and the motor passes run tests, and then runs well in flight....I've got no qualms with signing it off. I indicated the history of the mag as relayed to me...as I didn't see any reason not to believe that information. Now....as problems ensued, I was starting to doubt.....

I want to address this part specifically, since this is a public forum:

you do know that it's the installers responsibility for the airworthiness & applicability of the parts he/she installs?
Yes. I understand that any maintenance I do, I am held liable for on many levels. In this case, since the aircraft is experimental there are some slightly different rules that apply to the parts that can be installed. Every bit of this repair could have been performed by the owner of the aircraft also. In the case of experimental aircraft, when an A&P works on them as a non-owner, they are simply required to (correct me if I'm wrong, I'm just stating my understanding of the rules here) ensure that they (the A&P) are personally satisfied that the existing (at time of sign off) aircraft with all of its alterations repairs is currently airworthy. Certificated parts don't apply....they just make life a lot easier. Some things I insist on certificated parts for, others don't matter as much. There is a fine line when it comes to experimentals. As a mechanic, I need the aircraft to truly be airworthy, something I'd fly in with my daughter...if I'm going to sign it off. As a businessman, I need work. As a Man I choose work that can meet both of those criteria. Work that is productive, and work I'm not ashamed of. I don't know if that clears up what your asking or not.....but some A&P students may read this and not quite understand the experimental thing. We might need a whole thread for that....hmmmm

Moving on....

The other mag problems were not addressed to me. The owner leaned the mixture on the ground....which solved the problem, then flew. At the condition inspection, when the mag problems were mentioned....I checked for them at the runup prior to dropping oil and pulling plugs. I did not encounter any mag problems, and the plugs did not show any evidence of fouling...and all tested well after cleaning. I attributed/wrote off the reported mag problems (which were mentioned nonchalantly, sort of...."A couple of times I noticed that the mags would check rough on the ground, but after leaning for a bit...they would run fine". I didn't take it too serious...as I didn't see any evidence of mag problems during the inspection.

I appreciate the fuel input, it wasn't something which I had considered.

I understand that RPM drops can't be the exact same at different RPM settings. The biggest problem is that I have been mostly posting these from home....where I'm not doing the maintenance. Also, I've looked back at my troubleshooting procedures in this situation...and decided that the lack of a coherently written series of steps on paper has hampered my ability to look at the data objectively. What I've been doing is....noticing a problem, then trying to think of all the causes that could result in that problem...checking what I can think of....perhaps making a change, then running again...then going back to looking somewhere else, then perhaps research online, then run.....this disorganized troubleshooting is actually a bit embarrassing to admit online. I'm mentioning it now....so others can learn.

Traditionally, I'm a heavy aircraft maintenance technician. I specialize in the C-130 series aircraft (except J models...I haven't touched those motors), and C-17's. I've got a bunch of experience with C-5's...but I won't pretend to be any sort of expert on those. With experience comes a slightly different mode of troubleshooting. Generally you check the easy stuff first, even if it isn't real plausible. From there....often experience on airframe leads me to go directly to a certain place...as I've seen it happen before. After that....the FI comes out (or I've got an OJT troop already running it). In the case of light aircraft....there's an engine manual, a magneto manual, perhaps an aircraft manual (though not usually when it comes to experimental, the operators handbook, which the builder created, isn't a maintenance manual beyond basic preventative maintenance). Some of these manuals have troubleshooting sections, some don't. In this case, I have the 76 series overhaul manual for the engine, and the 4300 series overhaul manual for the magneto. (Not the operating manual specifically for the 0-360/IO-360, sounds like I need to source one). My point is...(since I seem to be getting away from it) when in unfamiliar territory, or when your first hunches start to go wrong....its time to break out a checklist. If you don't have one, you need to draft one. I'm going to draft one, including everything I've learned from this experience. I chased my tail a few times, and lost sight of the fact that often....when things don't make sense, there's more than one problem. Things don't always fail singularly like in the books. Often times when one part goes....another goes as well, or it uncovers the failure of another part. Also....owners/operators often won't come to you for help until multiple parts have failed and they can't figure it out (especially experimental owners...which is why many A&P's avoid them). I think that's enough on troubleshooting technique...you guys get the point.

I used 26 for the timing, because it was in the engine builders paperwork. The timing was not on the dataplate, which was a custom dataplate because this is an experimental motor. One of the things done to this motor was the addition of high compression pistons, which would be why the timing was changed from standard. If timing at 26 didn't work....the mag could be reset to 20. When checking timing though, the left mag was set to 26. The owner does not claim to have messed with the timing, and the condition inspection was performed as an owner assist. We had a conversation about timing procedure.... I'm reasonably confident that he has not changed the timing, if he had....it would have been slight...by rotating the mag. Again, checked with the light/beeper box, the timing checks. BUT good point. Definitely an area to be checked, and that'll go on my checklist for next time.

The plugs have always been rotated in the X-pattern. For this problem, I rotated slightly differently, writing down where each plug went each time. Somehow....despite trying to eliminate plugs early on, I've still found a plug to be bad. I was trying to not shotgun parts....as these plugs are $75 a piece. They all tested good on the spark plug tester....and were all good a few months ago at the condition inspection....and none looked bad visually, so I was inclined to not believe that was the problem. It may not have been at first, but it certainly was in the end. No owner likes to pay for parts that didn't need to be changed. I didn't have any other plugs in my shop that could have been installed for troubleshooting. I'm learning all kinds of lessons in this one. Again....good points bubba.



Which could be a symptom of a melted breaker cam, per the SB......

Or, a symptom of a bad carbon brush, no?

Yes. Both are definitely a symptom of what was present. I did go back and check for the SB.....and didn't find them applicable. I looked at the carbon brush anyway...and didn't see any signs of the arcing or wear indicated in the SB. Again....another thing to add to my troubleshooting checklist for mag problems. Check SB/AD. That should be standard practice....it is during my condition inspections (though not required for experimentals). What I failed to do....was check the replacement part. I had looked at all the SB's & AD's at the condition inspection....but new parts weren't installed back then, and can't be assumed to be in compliance. That was a NOOB mistake. One I won't make again.

LarsonAero
07-09-2009, 10:48 AM
**had to break this into two posts...it was too long for the forum settings**



My first thought is that it sounds like an intermittent wiring problem. One of the p-leads or ignition wires is probably flakey. Try testing the wires while wiggling them vigorously.

When the mag switch is in the off position the p-leads are pulled down to ground. Essentially, the mag is sending its sparks to ground instead of the plugs. It isn't completely clear to me what your connecting to for your continuity test, but your indication could be normal. Also, be careful about measuring continuity on mags and other items with coils. Such things can have low DC resistance. It is better to consult your maintenance documentation and see if a correct DC resistance is listed and check for that.

Initially, I was checking for continuity from the shielding of the P-lead wire to the P-lead wire itself....and yes, while moving the wire both in front of and behind the firewall. This is with the mag off. Had continuity been found, it would have indicated a break or chaff in the wire. Then I got the bright idea of checking the mag from p-lead to ground with the mag turned on....don't ask why I thought that was a good idea. :banghead::oops: It became immediately evident.....after I posted stupidly, that I was not discovering anything by doing that....OTHER than my multimeter works properly. There is a more detailed inspection method that can be done using those two points, as pointed out....but I wasn't turned to that page or trying to do that test. I went ahead and left my stupidity for the world to see.....we've got students who browse this forum, and perhaps they can learn from my mistake. I've made a few in this case...and I'm laying them out for others to learn from. Though....it is a bit embarrassing...some of these.:oops:


OK. That's where we're at. I'm ordering some spark plugs, and we'll go from there. I do expect this to fix the problem. I located a dead spark plug...or non-firing/weak firing, during the runup last night. I swapped that plug to the top of the cylinder and the problem followed the plug. The right mag ran perfectly. Again...there isn't anything wrong with the plug visually....I also shot the ignition lead from end to end on that plug, and couldn't find anything wrong with it. (continuity, while twisting, bending, and manipulating the lead) Besides, the problem followed the plug on the next runup, by shooting each plug with the Laser temp.

I recommended replacing all of the plugs, but was shot down. I insisted on replacing at least 2, which visually appear a bit rough. I can't realistically call every plug necessary for airworthiness. I'll update you guys when I get the plugs.

Also....anyone heard anything about Unison stopping the production of fine wire plugs?

Bubba1090
07-09-2009, 11:28 AM
I want to address this part specifically, since this is a public forum:

Yes. I understand that any maintenance I do, I am held liable for on many levels. In this case, since the aircraft is experimental there are some slightly different rules that apply to the parts that can be installed. Every bit of this repair could have been performed by the owner of the aircraft also. In the case of experimental aircraft, when an A&P works on them as a non-owner, they are simply required to (correct me if I'm wrong, I'm just stating my understanding of the rules here) ensure that they (the A&P) are personally satisfied that the existing (at time of sign off) aircraft with all of its alterations repairs is currently airworthy. Certificated parts don't apply... they just make life a lot easier. Some things I insist on certificated parts for, others don't matter as much. There is a fine line when it comes to experimentals. As a mechanic, I need the aircraft to truly be airworthy, something I'd fly in with my daughter... if I'm going to sign it off. As a businessman, I need work. As a Man I choose work that can meet both of those criteria. Work that is productive, and work I'm not ashamed of. I don't know if that clears up what your asking or not... but some A&P students may read this and not quite understand the experimental thing. We might need a whole thread for that....hmmmm

If you have an experimental aircraft with a Type Certificated engine, you must maintain that type certificated product I/A/W the manufactures's instructions including AD's! Absolutely, without a doubt, no arguments from the peanut gallery... And NO, the owner cannot do repairs to a certificated product (the engine) unless he holds a "P" license or they're one of 32 items specifically listed in 43 Appendix A Preventative Maintenance & I don't recall seeing Overhaul Engine in there recently, do you?

Now, if you remove the Data Plate, which is perfectly legal to do, you can put R-980 cylinders, a pressure carburetor & Eiserman mags on it if you wanted to & the owner can piddle to his heart's content. That's why I'm delving into the O/H & teardown portions of this squawk. You don't have the logs so how do you know: 1-How it was O/H'D? 2-What parts were used? 3-What spec's were used? 4-What was done on the teardown? Your putting a lot of trust in an owner when you sign your name to that! You're treading close here, be very, very careful what you sign your name to!

B 8)

Bubba1090
07-09-2009, 11:51 AM
I recommended replacing all of the plugs, but was shot down. I insisted on replacing at least 2, which visually appear a bit rough. I can't realistically call every plug necessary for airworthiness. I'll update you guys when I get the plugs.

You're signing this off! Install the # of plugs you want & tell the owner what it's gonna cost him. I disagree with you, I would think every plug is necessary for airworthiness! When in doubt, get out the ol' CT482 & stick 'em in or you could just accidentally drop 'em...

BTW, I still have the old 2X4 I used to give my old boss when he needed to simulate a backbone in cases like this. It still has the original instructions & you can still see the arrow indicating direction of insertion! There's a few more splinters now but I'd be glad to send it to you... :mrgreen:

B 8)

LarsonAero
07-09-2009, 12:35 PM
You're signing this off! Install the # of plugs you want & tell the owner what it's gonna cost him. I disagree with you, I would think every plug is necessary for airworthiness! When in doubt, get out the ol' CT482 & stick 'em in or you could just accidentally drop 'em...

BTW, I still have the old 2X4 I used to give my old boss when he needed to simulate a backbone in cases like this. It still has the original instructions & you can still see the arrow indicating direction of insertion! There's a few more splinters now but I'd be glad to send it to you... :mrgreen:

B 8)

I appreciate the 2x4 reference....but honestly, I do have enough backbone for this. These are finewire plugs(REM-38S)...so the CT482 go nogo gauge doesn't apply. You can visually see the wire & electrode....and see that these are not worn. Likely....the failed plug is
likely an insulator crack that I can't detect visually. I've looked with a 4x magnifier and a surefire light....and can't see any cracks...but that doesn't mean they aren't there. The plug is firing intermittently, its noticeably cooler than other plugs (about 100 degrees F less).

This aircraft is not signed off yet. If I replace plugs, and it still runs rough.....more plugs may get replaced. It is a hard argument that a plug that looks good, fires good, and tests good should be replaced. The difference between 1 or 2 plugs @ $72 (my cost) and 8 plugs is $430 bucks. Now if I have any markup at all for parts....retail on these plugs is $129.64 a piece. Now that comes to $777.84 more than what is immediately needed. Replacing plugs without good cause is a good way to lose a customer. IF anyone could source some Autolite plugs(unison), I could make a bit of a valid argument for replacing more (they're $35 a piece cheaper). Currently the plan is to replace 2 with champions, and plan on sourcing some Autolites (UREM38S) when they get in stock again....for replacement as needed.

Now...if there is any indication of roughness or excessive RPM drop after replacing those two plugs, then more plugs may become necessary. I respectfully disagree that replacing all the plugs is necessary for airworthiness right now.

Back to the dataplate issue....this engine has had the Lycoming dataplate removed, and a hatch dataplate installed. Engine paperwork lists the exact work done by Hatch, with part numbers of upgraded parts...and an explanation that the Lycoming Manual was followed for a zero time overhaul. Superior...who did the prop strike check, listed what they did. That was not a zero time overhaul. This is an experimental motor.

I understand that certificated motors have to be maintained as such, regardless of what they are installed in. EXCEPT when the owner is wishing to make it an experimental engine....at which point the dataplate has to be removed and maintenance log documented as such. The person signing off the motor as airworthy still has to believe and articulate (with their "P" license on the line) that the experimental engine is airworthy.

Again....this is why a lot of A&P's won't touch experimental. I keep notes (which are getting more and more detailed) on every maintenance operation I conduct. If I think an experimental anything is airworthy, I explain why I think that. That includes for an engine...an AD/SB search. While not necessary for the experimental engine...I figure that if the FAA thinks its necessary enough, or the manufacturer thinks it necessary enough to put out paperwork on it....then who am I to think otherwise? I always include an ops check, and if possible an overhaul manual/operator manual figure & index/task number listing...or at least page numbers. It was required for the military, and I have carried it over to my civilian work.

As for this....

or you could just accidentally drop 'em...

I know you are joking. BUT just in case anyone else thinks this is an ok practice......don't. Damaging some else's property...to sell them more products, even if you think they need to be replaced...is dishonest and illegal. Bubba...I know you weren't serious. :) I just thought that should be addressed.

LarsonAero
07-09-2009, 12:51 PM
I think I didn't address this:

You don't have the logs so how do you know: 1-How it was O/H'D? 2-What parts were used? 3-What spec's were used? 4-What was done on the teardown? Your putting a lot of trust in an owner when you sign your name to that! You're treading close here, be very, very careful what you sign your name to!

I do have the logs....they just aren't here with me. They are at the hangar with the airplane...I operate out of my house during the day, because this is the shipping and receiving center. I do Maintenance in the evenings/nights a the hangar when it is needed (I'm selling products primarily right now....as there isn't a ton of maintenance work to go around lately).

I'm not signing that the initial build or overhaul/teardown inspection was done properly...they have their own sign offs in the logbooks. Detailed, and professional. This motor has been running quite well for the last 690 hours. The occasional mag problem...was traced to a burned up distributor block in the old mag. Further compounded..or perhaps because of the mag, by a (singular) bad plug. When I'm done with my maintenance....I'll sign off the engine as airworthy. At that point I will have performed a thorough run-up without any hiccups. I'm going to test fly it with the owner as well. He isn't getting the logbook back with my signature in it until it has passed every inspection/ops check I can come up with or feel necessary. He can at any point take his aircraft back, without my signature in the logs if he doesn't like my solutions/recommendations. I just don't think at this time that replacing 8 fine wire plugs is necessary.

When I sign the log....I will be signing the maintenance that I performed, and the ops check I performed/witnessed. If I sign it, I will do so because I believe it airworthy with the manuals I used and ops checks I performed as justification for the airworthiness.

Even with certificated engines.....how can anyone know that the previous mechanic did everything right? When you perform an annual inspection...do you tear down the motor each time, just because YOU didn't overhaul it? No. You do the best inspection you can, given the recommended procedures. If something leads you to look deeper, you do, or you send it to someone who does.

In the case of this experimental motor...if the owner has done something to it that he didn't write in the logs, and you can't detect upon inspection....then you can't be responsible for it. As a mechanic, I log everything that I do, and look for evidence of something that isn't reported in the logbooks. I also take pictures of the motor and airplane....with as much detail as possible, so I can hopefully prove that an alteration isn't something I performed...or had chance to inspect should the need arise.

Bubba1090
07-09-2009, 01:22 PM
I appreciate the 2x4 reference... but honestly, I do have enough backbone for this. These are finewire plugs(REM-38S)... so the CT482 go nogo gauge doesn't apply. You can visually see the wire & electrode... and see that these are not worn. Likely... the failed plug is likely an insulator crack that I can't detect visually. I've looked with a 4x magnifier and a surefire light... and can't see any cracks... but that doesn't mean they aren't there. The plug is firing intermittently, its noticeably cooler than other plugs (about 100 degrees F less).

This aircraft is not signed off yet. If I replace plugs, and it still runs rough... more plugs may get replaced. It is a hard argument that a plug that looks good, fires good, and tests good should be replaced. The difference between 1 or 2 plugs @ $72 (my cost) and 8 plugs is $430 bucks. Now if I have any markup at all for parts... retail on these plugs is $129.64 a piece. Now that comes to $777.84 more than what is immediately needed. Replacing plugs without good cause is a good way to lose a customer. IF anyone could source some Autolite plugs(unison), I could make a bit of a valid argument for replacing more (they're $35 a piece cheaper). Currently the plan is to replace 2 with champions, and plan on sourcing some Autolites (UREM38S) when they get in stock again... for replacement as needed.

Now...if there is any indication of roughness or excessive RPM drop after replacing those two plugs, then more plugs may become necessary. I respectfully disagree that replacing all the plugs is necessary for airworthiness right now.

Back to the dataplate issue... this engine has had the Lycoming dataplate removed, and a Hatch dataplate installed. Engine paperwork lists the exact work done by Hatch, with part numbers of upgraded parts...and an explanation that the Lycoming Manual was followed for a zero time overhaul. Superior... who did the prop strike check, listed what they did. That was not a zero time overhaul. This is an experimental motor.

I understand that certificated motors have to be maintained as such, regardless of what they are installed in. EXCEPT when the owner is wishing to make it an experimental engine... at which point the dataplate has to be removed and maintenance log documented as such. The person signing off the motor as airworthy still has to believe and articulate (with their "P" license on the line) that the experimental engine is airworthy.

Again... this is why a lot of A&P's won't touch experimental. I keep notes (which are getting more and more detailed) on every maintenance operation I conduct. If I think an experimental anything is airworthy, I explain why I think that. That includes for an engine... an AD/SB search. While not necessary for the experimental engine... I figure that if the FAA thinks its necessary enough, or the manufacturer thinks it necessary enough to put out paperwork on it... then who am I to think otherwise? I always include an ops check, and if possible an overhaul manual/operator manual figure & index/task number listing... or at least page numbers. It was required for the military, and I have carried it over to my civilian work.

As for this...

I know you are joking. BUT just in case anyone else thinks this is an ok practice... don't. Damaging some else's property...to sell them more products, even if you think they need to be replaced...is dishonest and illegal. Bubba...I know you weren't serious. :) I just thought that should be addressed.

I still think the key to this issue lies in the Hatch modification. Have you looked into the timing difference yet? 6* is one helluva difference. And just for clarity, neither they nor Superior can zero-time that engine...

B 8)

LarsonAero
07-09-2009, 01:37 PM
Thanks for continuing to look at this bubba. I'm going to pour through all of the logs again this evening, or tomorrow after the parts arrive. IF the engine is supposed to be timed at 20* instead of 26*....what kind of symptoms would that produce? Would it even run smoothly at all?

I'm going to go over the original build paperwork thats in the logbook....and see about posting it here when I get a chance. So you guys can see what was done to this motor.

LarsonAero
07-15-2009, 07:14 PM
I'm here at the hangar reviewing the logs for this engine. The engine was major overhauled to tolerances within limits for a new, 0 time engine IAW SB240M. New cylinders were installed...pistons, valve guides, springs, retainers....everything. The following entry was then made,"This engine is no longer certified. The following modifications have been performed for experimental aircraft:....." Then all the custom parts and high compression pistons are listed. The dyno sheet is also present with 195hp @2700RPM highlighted.

The prop strike inspection was completed by premier. The crank & gear was removed and checked IAW SB475A, then re-installed with a new bolt & dowel pin.
Piston pin lugs were replaced, some repairs were made to the flange IAW SB201E. Several other SB's were checked as well. Both mags had the 500 hour inspection cw.

Ultimately....the timing was good, the SB's didn't apply.....there was a bad plug, which tested good on the testor...but didn't run in the motor very well. It ran occasionally, and didn't foul...but was noticeably cooler than the others. I replaced that plug and the engine runs perfect.

Bubba1090
07-16-2009, 05:39 AM
Oh how I detest hearing "I told you so..." so I will refrain from saying it myself...


Ultimately....the timing was good, the SB's didn't apply.....there was a bad plug, which tested good on the testor...but didn't run in the motor very well. It ran occasionally, and didn't foul...but was noticeably cooler than the others. I replaced that plug and the engine runs perfect.

When will y'all learn? :banghead:


...in an IO-360! Engine: O-360 A1A that's been converted to an IO-360. :oops:

KISS principle, throw a new set of plugs in it & see what happens. (I read you tested them but the bomb test isn't a fail-proof test)

I'd rule out your SBs at least on the RH mag, being new, the LH is worth checking. Have you done a low RPM mag check? You may have a distributor cap cracked/faulty.

Does the engine make full static RPM? Who converted the engine? When? ETT SMOH? If it's recent, you may have an internal gear alignment problem. If there's 100s of hours on it, disregard that.

B 8)

Now whose your daddy? :mrgreen:

B 8)

LarsonAero
07-16-2009, 10:01 AM
The plug was definitely good advice...the mag was still bad, what I failed to remember, as mentioned above, is that sometimes multiple problems are present.