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Magneto Maintenance?

Ironflight

VAF Moderator / Line Boy
Mentor
OK all you Electronic Ignition folks can stop reading now - this is all about those of us stone-age people using old-fashioned Mags, sitting around campfires to keep warm, and tossing old spark plugs at noises in the night....:rolleyes:

Are they gone?

OK folks, some really basic questions. Here I sit with 600 hours on my engine, and I flew right past the 500 hour recommended maintenance point on my Slick mags. My old Grumman went about 1100 hours on a set of mags before I finally realized that the hard hot starts (just didn't want to fire!) were due to the mags being way beyond the conventional-wisdom life, and my mechanics said "hey, they're Slicks - throw them away and order new ones!", which is what we did, and the engine started up better than ever.

However....I have been re-educated by Mahlon who said that I should just due the routine maintenance, and they should last to TBO. Hey, I like that idea! The question is...how do I do the routine maintenance without a lot of downtime. Never having worked on the inside of a mag before, I am hesitant to buy an overhaul kit and try it myself - sounds like a good way to end up with a broken mag that was working beforehand. (I've read through the manual - looks like I'd need some special tools, and there might be a few tricks to learn by experience) I don't really think I want the local shade-tree types opening them up - does anyone send them to a mag shop that can turn them around quickly? And, if so, what does it generally cost? I mean...new mags are about $600 - if the maintenance cots is half that, I have to wonder if I shouldn't just order some.

I can't really say I am having any problems, except for an occasionally longer cranking period when hot starting - it might even be my imagination, but I'd just as soon keep to the scheduled plan.

OK, the floor is open - what are folks generally doing for their Slick maintenance?

Paul
 
Ironflight,

FWIW I do "simplified" 500-hour inspections on my Slick 4371 mag. First of all, get the Unison manual and it's a breeze.

When I say "simplified" I mean I tear it down as best I can for inspection without having any pullers or expensive tools.

I set internal timing, visually inspect everything...particularly the coil & condenser & impulse coupling...clean & adjust the points, make sure internal timing is right on, and reassemble. Pretty straightforward.

I did a couple of 500-hour inspections, and then around 1300 hours I was getting a lean misfire on one cylinder. Turns out it was just worn/arc'd/pitted contacts on the distributor block. Well, that little plastic gear & rotor costs over $200!!! I went 'round and 'round on this one, because all I needed was that little plastic rotor. In principle, I didn't want to throw away a whole mag just because I needed one little part. But the "Slick economy" ended up winning me over. Ok, so I would spend $200+ on the distributor block "now," and then maybe a few hundred hours from now have to blow another few hundred on more parts. Screw it. I broke down and exchanged the mag for new. $550. They make it hard to rationalize any other way. It bugs me that they over-price these parts, but that's reality.

Anyway, adjusting internal timing and cleaning up & adjusting the points & contacts can make a pretty big difference in smoothness. Highly recommend you do AT LEAST that before even considering replacing. If you find anything suspect during the tear-down (i.e. cracks in the coil), well that's another story.

Again, snag the maintenance manual and go from there. We shoulda done this while you were at Big Bear...I could have helped. I'm sure you must have folks around in TX who know how to tear down & set up a Slick mag... :D
 
Thanks Dan - I did download the Slick manual (well, it was an appendix to the Superior engine manual that Gil Alexander posted the link to - great info!), and maybe I'll read it a little more closely - I only skimmed it, but your experience working them without special tools is encouraging. I am pretty much convinced that the E-gap probably drifts a little as points wear, and that is what needs a little adjusting.

Paul
 
Mag maintenace

Paul: Make a stand out of scrap wood to set the mag on while you work on it. I have a piece of 1/4 plywood with about a three inch hole in the center, large enough for the gear and shaft to fit through. The plywood sits on two pieces of 1x4 pine that hold the plywood above the work table. You drop the mag through the hole, drive gear down, and go to work. Keeps everything clean and provides stability to work on the breaker points, et al. Mags are easy to work on if you have the manuals. At about 500 hours I replaced the points and condensers on both Slick mags after one mag suddenly died. (Bad points) I then realized that my engine ran much better and I should have done it sooner. Same deal after I replaced my 500 hour plugs, which really could have been kept in service. Much smoother, better mag checks. BTW, use only a tiny smidgen of grease on the felt wiper, as per the directions, or grease will get flung everywhere and ruin the points. Points and condensers are relatively cheap for airplane parts. I always replace both together. A bad condenser will ruin a set of points in no time. On the Slicks, everything else is priced too high to warrant replacing individual parts, which I am sure is Slick's intent. Oh yeah, check for carbon tracking around the distributor block, which can cause misfiring. I am sure that some of the working A&Ps on the list can give you more and better advice. The only special tool I have is the pin that comes with a set of points. The pin locks the mag so that the internal timing can be set. Every mechanic has a dozen or so extra laying around.
 
Flew his mags to 1800 hours w/o major maintenance.

A friend with a certified plane decided to leave well enough alone so he flew his mags to 1800 hours w/o major maintenance. You guessed it, one broke apart in flight spraying chunks of metal into the engine. Although he made it safely to the ground, what should have been an easy repair is now a major overhaul. Gee, think of all the money he saved on mag maint (sic).

Point gap makes a helluva difference. On our 150, we get almost 500fpm (whoopee) after the points were set properly and the mags were timed perfectly. Duration = saturation.

If you've worked on old car distributors, Slicks are a piece of cake. Not to investigate and check frequently is sheer madness.

Barry
RV9A - flying soon
 
Thanks Tad! I'd seen that before, but lost it....I definitely learn better with pictures...

Paul
 
OK, I'm convinced - DIY!

OK, I spent my lunchtime going over the manual and that excellent on line model in detail - looks pretty straightforward! I think I'll do the 500 hour myself - but I think I'll wait until after LOE - hate to end up in a bind if I screw something up!

So two more questions -

1) Do I need the T-150 "E" Gap tool, or is there a trick to doing without - ACS has them for $11, so that's nothing to get one, except waiting...

2) How often do you find that you need to replace the points - in other words, do I want to have new ones on hand before tearing down, or should I expect to just clean and re-time the things (based on average use, experience, etc...)

Paul
 
1) Do I need the T-150 "E" Gap tool, or is there a trick to doing without - ACS has them for $11, so that's nothing to get one, except waiting...
I do it without that tool. Best with the tool, but you can definitely eyeball it without. Now the PIN on the other hand...you can use a drill bit or hinge pin for that, but that T-118 (I think that's the p/n) timing pin really makes live easy. And it's dirt cheap. Don't get me wrong...snag the timing tool if you're ordering the pin or other stuff anyway...but you can do it by eye.

2) How often do you find that you need to replace the points - in other words, do I want to have new ones on hand before tearing down, or should I expect to just clean and re-time the things (based on average use, experience, etc...)
Imho it wouldn't hurt to carry a spare set of points in your tool bag. I replaced my points at the 2nd 500-hour inspection when I saw a fair amount of pitting & wear. Technically I could have just cleaned 'em up and reused 'em, but instead the old set got cleaned and became the spare that I carry. YMMV
 
T118 pin

The pins (one per mag) were included with my mag kit purchased from AERO / ECI. Someone local must've bought an engine w/accessories lately.

Steve
 
Paul,

I have several of the pins if you need one. I should be at the airport tomorrow.

Karl
 
I'm so glad to see all of those responses on maintaining the mags every 500 hrs. Too many people seem to think that as long as the engine is running, the mags are ok! I'll bet those same people are the ones who religiousy changed plugs, points, condenser, cap and rotor on their cars every 20,000 miles, and spent many minutes getting the dwell exactly to spec! Pitting of the points and wear on the cam can cause lots of timing variation cylinder-to-cylinder. Thanks so much for detailing your experiences!
 
If you have the Mechanics Toolbox CD from Vans (but created by Sacramento SkyRanch)

gil A


You know, I htink I down'oaded somethign like that a few years back from Sac Sky Ranch....gotta go lookign through all my archived bits and see what I can find....

Now I'm all excited to do my Mags, but I've got a couple weeks of flying to do before I'll have a free couple days to take anything apart!

Now it's off to do a tech visit, then go get some BBQ at Hilltop Lakes!
 
2) How often do you find that you need to replace the points - in other words, do I want to have new ones on hand before tearing down, or should I expect to just clean and re-time the things (based on average use, experience, etc...)

Paul

I replaced my points at 1,858 hobbs hours or 1,805 tach hours on my Bendix mags. Only one set was pitted more than I liked. I was having digital tach fluctions so I replaced both sets of points. I always have at least one overhaul kit in stock in case I need parts. My 500 hour inspections are typically I.R.A.N. (Inspect Repair As Necessary) At engine overhaul time, I replace anything that looks like it will not last 2,000 hours. I did overhaul both of my mags right before first flight.

In the past 10-years, I only replaced aircraft spark plugs once at 783 hobbs or 682 tach hours. The plugs in the airplane now have 1,272.3 hobbs hours on them. They still PASS the Champion erosion gauge test as being good.

I never bead blast my plugs. I only use the vibrator pencil spark plug cleaning tool on them. I lean aggressively and only need to clean them between 100-200 hours. Now flying formation as wing, I will need to clean them as often as 50 hours. I have found out that when I return to my hangar after formation flying, (I am now single ship by myself) that doing a run up to mag check RPM and then slowly leaning, the engine will drop 300-400 rpm then run rough and shut off. This appears to help clean the plugs and they do not need pulled as often.
 
Mag Gear question

I have a slick mag gear off an old 4251 that is now on a 4317 (I think) the gear seems to have alittle "play" on the shaft. Is this normal for a mag gear? It seems to be together completely correctly, but just seems alittle odd in my "General" experience. I used a new washer and the nut is solid against the washer and washer against the shaft, but the gear has just a bit of play on shaft and can slide on the keyways at the rear of the gear just slightly.

Bryan
 
Hey! I'm an EI kind-of-guy, but please don't knock the mags! Sure, they don't give as much starting voltage as the electronics, and they won't give the better timing advance with load that some of the EIs do, and they need to have maintenance performed on them periodically, but they've flown lots of people around for a lot of years and done so very well. On cars, the old coil-cap-condenser worked pretty **** well for years, too, before the EIs came along. EIs are great, but mags are good, too!
 
Doh!!

OK, SO I decided to go out this evening, and with all my newfound knowledge and an E-Gap tool, do the 500 hour maintenance check on my Mags. Got the top cowl off, pulled the top plugs and found #1 TDC, just as the Unison book said. Pulled the mags (why in heck did Unison change to Torx screws? Hey, I know they're nice, but I don't keep those drivers with my aircraft tools! Fortunately, they also have slots in the screw heads....), took them apart one at a time, and sure enough, setting the gap was a piece of cake. Man, these things are simple inside!

Ready to go back on the plane and it is only 8:00 pm - hey, I can get the job done! Put the pin in the hole, lined things up, hooked up the timing light, pulled the pins, timed them until they were PERFECT - no noticeable difference between them, and the lights went out simultaneously when my laser pointer (on the flywheel) was on the timing mark. Sweet! Put the cowl back on, and pulled th airplane out for a run-up. Mags on Left, hit the starter and....cough, spit, pop!! Oh nuts - I must be an idiot....how could I screw this up?! Just for grins, I selected the right mag only, and it started right up - but wouldn't idle, and I wasn't going to risk the engine after more than five seconds.

Rolled it back in to the hangar, and pulled the cowl. Man, this bugged me! OK, so maybe I didn't get the impulse coupler set up right - yeah, that's it! Put it back at TDC (have you caught my mistake yet?), pulled the left mag, started over with the timing procedure, set it up perfect....long story short - the same thing, although this time, it didn't want to start - just popped a few times. OK, now it's almost 10:00 pm, I haven't had supper, I am tied an frustrated....I decided to pull the mags and bring them home, start over from scratch with a new day....

On the drive home, I finally realized what the heck I'd done. Did you catch it? TDC?! Gee, why was that impulse coupler snapping so late? Oh year, I was timing the engine to TDC instead of 25 degrees BTDC!!! Well, it was too late to turn around and go do it right, so I'll just sneak out there tomorrow sometime and put it back together. I guess one of the problems with a smooth running plane is that you get out of practice on some maintenance tasks....

Gee, I sure hope I have the right answer this time - if not, I wonder what I screwed up?!:eek:

Paul
 
Roll your own mag inspection?

I skimmed through this thread but didn't see the 500 inspection cost mentioned by anyone. I had my mags (Slick 4171 & 4173) 500 hour inspected. It was $250 per mag. The cost seems reasonable to me. The local technician I used only works on mags. He replaced two parts and showed me the old parts. No charge for the parts. He also told me to bring in the spark plug wires with the mags. He tested the wires on a special machine (large) at no cost also.

I felt like it was a good value for his expertise. I now have new yellow tags to go in my engine log and a good feeling about the units. I love to fix things so I'm with you on the "roll your own" inspection route. Once you train yourself, an emergency field repair on a mag will be less of an obstacle.

One data point
 
OK, Most of the discussion revolves around Slicks but what do I do if I have Bendix mags? I don't think I want to get involved puchasing necessary manuals / tools etc, but would like to send them to someone for a checkup and / or overhaul if necessary. They work fine, but don't know when they were checked last. Who has a quick turnaround for this service?
 
when to replace them

This last weekend, I had a problem with roughness when testing the RH mags on runup. I pulled the cowling last night and removed the plugs. The mechanic in the next hangar checked them and they are basically worn out. I think they are the original plugs (painted the same color as the engine). The time on the engine is just under 600 hours. I looked through the log book and don't see any maintenance on the mags. Other than the fouled plugs, I am not having any problems with the ignition. I don't think I feel comfortable overhauling the mags myself and thought about just buying new ones. Spruce has a kit with 2 mags, wires and fine wire plugs. This is on a 160 HP O-320

Should I go ahead and replace the mags at this time, or have someone overhaul them? I will replace the plugs either way.
 
Mags 101

Two things: It may prove cheaper to replace rather than rebuild. There have been some market shenanigans which preclude the sale of parts.

Second, a good friend of mine delayed rebuild/replacement until 1800 hours. At that point, one of the mags self destructed spraying parts all over the inside of his engine. Instead of rebuilding the mags, he now has the expense of replacing the engine.

If you decide to replace and wish to sell the old units, please send me the model and make and perhaps we will purchase the old ones from you.
 
Bryan,

My Mags looked great inside at 600 hours. I had been brought up as an "owner" beleiving that you were to throw away the Slicks at 500 hours, but that is not true of the newer ones - I'd suggest opening them up with someone that has a little experience and see how they look!

Paul
 
Thanks

Thanks for the information. I replaced the plugs this evening but ran out of time. I want to clean up a few things in the engine compartment before I put the cowling back on.

I know a few people who are A&P's, I'll check with one of them and see if they would help me inspect them.
 
Bryan,

My Mags looked great inside at 600 hours. I had been brought up as an "owner" beleiving that you were to throw away the Slicks at 500 hours, but that is not true of the newer ones - I'd suggest opening them up with someone that has a little experience and see how they look!

Paul

Paul:

Some of us that think we know what we are looking at do not always. Recently had friend with an engine miss in the RV-6 he purchased. Had over 500 hours on the Slick mags. They looked good inside as we (I) opened them up, cleaned, set points and reinstalled. Fine wire plugs looked good. Engine still missed. Buyer replaced mags. Still missing. Two of the less than 500 hour fine wire plugs were bad. Found after mags were replaced.

That was the first fine wire plugs that I have seen failed.

ALWAYS try the simple stuff first. The mags did need IRAN but that was not the problem in this case.

IRAN = Inspect, Repair, As Necessary
 
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