FlipSideFlyer

My Feedback: (58)

Okay, so here was a first for me and I’ve been flying gas engines for over 20 years.

After 5 years of trouble-free flying a Zenoah G-62 powered Edge 540T, the plane started encountering problems with intermittent engine failures. During anywhere from one to three flights, the electronic ignition equipped engine would die mid-flight offering lots of practice with dead-stick landings. It was if someone reached over and turned off the ignition switch.

During the course of the next six weeks along with a handful of additional dead-stick landings, I worked through the following replacements: changed out the ignition battery, changed out the ignition switch, changed the spark plug, changed out the complete ignition system including the timing sensor and replaced wiring leads with new ones.

On the bench, everything worked fine. After a short time in the air, however, not so fine! Also, not so fine was the last dead-stick landing. You know how it goes when you’re low, slow and upwind.

Back on the bench, everything worked fine. THEN (a tad bit late) I noticed something unusual. My post-mortem Xacto blade would hardly stick to the small timing magnet located in the after-market flywheel. Hummm…when I rotated the flywheel by hand, with the ignition on, it fired every time. However, when I warmed the flywheel with my heat gun, the magnetic force went to zero and the ignition quit! I was able to repeat this test several times before the magnet gave up completely.

Bottom line: next time I’m experiencing ignition problems, I’m going to START by checking the magnet!

All Day Dan

My Feedback: (5)

Flip, Thanks for the post. That's a new one to look out for. Dan.

av8tor1977

My Feedback: (6)

Very interesting and a good catch. Thanks for the info.

AV8TOR

skip1320

Where did conversion magnet come from? Radio shack 2.99 for two.

BadAzzMaxx

Had the same thing happen with a ZDZ 60, Customer thought the ignition was bad, I installed a new one and still no spark.

If I pushed the sensor bracket all the way down to where it was rubbing the prop hub it would fire. installed new magnet in a different with opposite pole and engine ran fine.

I think it is coming from over heating the engines and killing the magnets over time.

clivemc

very interesting - thanks for the post

jedijody

My Feedback: (1)

Heat does kill the magnets.

bgw45

My Feedback: (1)

Flip, Thanks. I would have never checked the magnet. I would have been on the phone telling somebody it on it's way. Good work!

Antique

My Feedback: (4)

Magnets cost $.04 when bought 500 at a time....
The older molded ceramic magnets lose magnetism sooner than the new nickel plated neodynium(SP) magnets....Not likely the heat from normal operation could get a magnet hot enough to kill it...
I have used many different sizes of magnets, some as small as 1/8 diameter..Can 't tell any difference between the small ones and larger ones...
They alll trigger the ignition when the magnet leaves the edge of the sensor...
If there's a timing difference I haven't found it....
Stronger magnets will trigger as far away as 1/8 of an inch, weak ones have to be close...

FlipSideFlyer

My Feedback: (58)

Fixed!

Bought a handful of 5mm x 3mm Neo magnets for $3.33 (shipped!), replaced the failed one in the flywheel and tested the engine with various sensor gap settings. Here is how it went:

1. Drilled a series of very small “test” holes in the back of the flywheel to locate the bottom edge of the original magnet. In this particular case, the original magnet was approximately ½” long.
2. Once the base of the original magnet was located, the hole was enlarged (and deepened) to accommodate a ~2mm pin.
3. A 2.5mm slot was cut from the hole to the outer edge of the flywheel gobbling up all the “test” holes in the process. In other words, the slot runs in a radial direction along the full length of the original magnet.
4. A steel pin was inserted in the hole and used to drive the old magnet out of the flywheel.
5. The new/replacement magnets were checked for polarity and MARKED. I used the actual ignition for determining which polarity to choose – the end of the magnet that triggered the spark got marked with a red marker!
6. Because the original magnet (and associated hole) was about 4 times longer than the replacement, I decided to fill the hole with TWO of the new magnets. The two magnets were stacked and once again (important!) the polarity checked and marked.
7. The new magnets were then pressed, one at a time, into the flywheel. I used a ~4.5mm steel pin mounted in my drill press to do the job. Because it took considerable force, I decided simply stake the outer magnet no bonding materials needed.
8. I test-fired the ignition using various settings between the ignition sensor and the flywheel and found that it would fire at the maximum air gap (~3/8”) – that’s all the bracket would allow.
9. I set the air gap at 0.1mm, checked the timing and test ran the engine for several hours in cycles of anywhere from 5 minutes to 20 minutes. Started first flip and ran from idle to max power every single time without a hitch.

Bottom line: If you like tinkering, this fix may just be up your ally, however, should someone offer you a replacement flywheel for a reasonable price, TAKE IT!

Tired Old Man

My Feedback: (1)

Good catch. Only the most experienced would even look at the magnet, and since heat damages a magnet, and heat damage is accumulative, it probably happens more often than is recognized.

Never hurts to get information out about how our ignition triggers work and their caveats. Strength, distance, and alignment are important indeed.

Jezmo

OK I'll bite, how hot does the magnet have to get to "kill" it? I've run my gassers as hot as 360 to 370 degs F and never had one fail. (These days I have an alarm set at 330F so if I hover too long it'll sound on the DX8 telemetry) Seems like the amount of heat it would take to kill a magnet would be more than enough to kill the motor. Just sayin.

Tired Old Man

My Feedback: (1)

The engineers will tell you above 300C. Experience has shown it to occur >200C.

Jezmo

OK Pat, help me out since you have much better equipment for measuring temps than I. In order to get a hub reading (at the magnet location) of +200C how hot is my cylinder head temp going to need to be? Just average, nothing specific, because as I said above, I've run some of my engines in the high 300F range without a single magnet issue. I am thinking the engine would have to get really really hot or the airflow would have to be very poor around the crankcase and the engine would have to be very lean in order to get that much temp out to the end of the crankshaft. If your restrictions won't let you answer I understand.

FlipSideFlyer

My Feedback: (58)

Interesting comments on the effects of heat on magnets and it’s definitely something to keep in mind. My experience tells me that Tired Old Man is probably correct in stating that the effects of heat are cumulative over time.

The operating cylinder head temperatures of the engine I mentioned in my original post were typically in the 250F - 275F (121C - 135C) range. I guess it’s possible that following a flight on a hot summer day, with the plane parked in the sun, flywheel temperature could reach temperatures of close to 300F (149C).

I’m assuming that after nearly five years of exposure to this type of treatment, the magnet simply weakened to the point where it no longer triggered the ignition. During my testing, only a slight amount of additional heat (less than 110F) is all that it took to completely kill the magnet.

Anyone experiencing ignition issues – this is such a simple test and I only wish I had started here first! Not doing so resulted in some not-so-much-fun flying and a few weeks rebuilding.

BTW, the ignition system and associated flywheel comes from a real peach of a guy here in the USA who has since retired. I’ve been flying his ignition systems on a number of engines and NEVER had one fail. I love it when all that’s needed is a new magnet!

loser

My Feedback: (37)

How are the magnets "glued" into the hub? How do you remove an existing one and "attach" a new one? I have an old 3W 140 that I overheated and "cooked" the cylinders on. The prop hub on this engine got very warm/hot before I finally did the cyl damage. I am thinking maybe I should replace the magnet before I put the engine back into service.

Steve

captinjohn

You could try to break the old magnet with asharp punch. They are sometimes brittle and will break up. Then just JB weld a new one in its place. Make sure the poles are right....to trip the pick-up. Capt,n

FlipSideFlyer

My Feedback: (58)

Recently experience the sensor magnets failing in my six year old 3W75US. The engine was running fine right up until it quit while airborne on a nice cool day. It was as though the kill switch had been activated! Back on the ground, there were no signs of a spark and a quick check of the ignition timing magnets (I’ve learned to go there first) showed very little sings of life.

Following the advice of Gerhard at Aircraft International the repair was quite simple.

1 DON’t remove the prop hub or disturb the sensor pick up.
2. Order the correct size magnets. The 3W75US uses 3mm magnets and were replaced using the same size neodymium.
3. Tape off the area around the old magnet(s) to prevent damaging the hub and keeping particles from migrating into bearings and/or the sensor.
4. Check the polarity of the old magnet(s). You’ll want to duplicate this with the replacement(s). Remember “Opposites attract – likes oppose.” Assuming you have two sensor magnets, mark the ends of the old magnet(s) with Green for one polarity and Red for the other, then transfer the same color to the “opposing” end of the new magnets – the ones that’ll go into the hole(s) with the color facing up.
5. Center punch the old magnet(s) and use a small sharp drill to further recess the mark (my drills wouldn’t penetrate the old magnets more than a fraction of a mm)
6. Using a Dremel Tool with a small (1 – 1.5mm) high-speed, ball-end cutting bit, punch carefully through the old magnet. Use caution not to punch into the hub itself.
7. Use the appropriate size drill bit to resize the hole to properly fit the new magnet. This removes any leftover pieces of the magnet, bonding compound, staking, etc.
8. Install the new magnet(s) flush with the hub surface using a small amount of JB Weld.
9. Once the JB Weld has cured, gently stake at one or more locations around the edge of the new magnet(s).

Gerhard also had this to say...

When you start up your engine the first time please make sure that you use a chicken stick!
No bare hands please for your own protection!!!
You should always start your engine with a chicken stick or heavy duty welding gloves!
Never with bare hands!
The prop is faster than your hand.

JRgraham

My Feedback: (1)

Good stuff, flip! Thanks for sharing that

JRgraham

My Feedback: (1)

By the way... Surely Im not alone when thinking the chance of a guy having one of these magnets fail before the engine has got to be seriously slim in itself.. but has been known to happen... But you happen to have two older, seemingly perfectly fine running engines that out lived the magnets after some years?!! wow
Not sure what that means, but its sure somthin !

Corsair2013

My Feedback: (2)

I just had my maiden and of course the ignition dies on my first flight. My ignition says it is CDI. I took the sensor off the prop hub but there is no magnet with this type of system so it must be a Hall effect or proximity system.

Is there anyone out there that knows how to test the sensor itself?

Thanks

keith

av8tor1977

My Feedback: (6)

RCEXL sells a neat sensor tester that is also very effective for timing engines. It's cheap, and I keep one in my flight box and one on my bench for setting timing.

Scroll down a bit and look for "sensor tester" here: http://www.rcextremepower.net/ignitions.html

Or, go to Post #36 here: http://www.rcuniverse.com/forum/gas-...rmation-2.html

Also triple check your battery, wiring, and switch.

AV8TOR

Corsair2013

My Feedback: (2)

I figured out how to test the switch - applied power then used a magnet and monitored the voltage on the connector. The switch seems fine. The magnet in the hub still "seems" to have pull so I think the Ignition just died. Tried different battery and same thing.

Ordered new ignition and all parts - just to be sure!!

Keith

av8tor1977

My Feedback: (6)

That post I referred you to will allow you to definitively check to see if the ignition module is really bad.

AV8TOR

Corsair2013

My Feedback: (2)

I read through it and am heading to test the ignition - again. I did order a new one so I hope it gets here this week.

Thanks

Keith