Rough Right Mag, any thought?

Magman said:
I doubt if the plugs are the issue and would test Leads.
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Oh, if they're the old Champions (no slot in the lead contact at the bottom of the plug well) I'd certainly suspect them. They're terrible and caused all sorts of headaches. Probably caused a lot of mag replacements, too, and maybe even carbs, since so many mechanics (and owners) automatically blame the fuel stuff when the engine misbehaves. Electrical problems are actually responsible for 90% of performance problems.
 
I did not mean to imply that plugs could not an issue in most cases.

However; he has already gone through existing and replacement plugs ( and God

knows what else).

I see no mention of actually using a Harness Tester though.

OTOH- Maybe a 4 cyl. Top Overhaul, another new mag, new p-leads , new ignition

switch might narrow it down too.
 
Doug Reid said:
Post #5 maybe ?
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The resistance check doesn't find the lead that is arcing from the core out to the shield. This tool does:

upload_2023-3-3_15-27-6.jpeg

One of the leads goes to ground, the other goes to the spring on the plug end of the lead. Push the button. If a spark appears in the window, the lead isn't arcing internally. I did the test with the leads still connected to the mags, and if it doesn't spark it might be arcing inside the mag, from the distributor terminal for that wire across to the rotor finger, so turn the prop some to rotate the rotor away from that terminal and test again. It should spark.
 
I haven’t used an ohmmeter for the test as it seems it would not indicate the quality of the insulation. Using the device Dan has will check the Distribution section of the system. If you are familiar with the device you may want to observe the Quality of the spark in the window. A leaking garden hose will still have some water come out the end. A leaking Lead will provide a weak spark in service and in the tester window. Sometimes you can actually see or hear where the arcing/ leaking is taking place. It will identify a cracked Distributor Block in the mag as well.
 
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Dan Thomas said:
Oh, if they're the old Champions (no slot in the lead contact at the bottom of the plug well) I'd certainly suspect them. They're terrible and caused all sorts of headaches. Probably caused a lot of mag replacements, too, and maybe even carbs, since so many mechanics (and owners) automatically blame the fuel stuff when the engine misbehaves. Electrical problems are actually responsible for 90% of performance problems.
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If you are referring to the old Champions with the so-called "replaceable" resistor, there IS a slotted screw head at the bottom of the plug well. And they are crap. Even if everything seems well, replace them and toss them.
Champion.Resistor.Screw.jpg Champion.Resistor.Screw.Spring.jpg
 
The reason there is a Mag “ Drop” in the first place may not have anything to do
with the Magneto. “ Quality of Combustion” is the major player here.
The “ Quality “ will decrease when the engine is operated on single ignition vs dual. This is normal.

Any factor that reduces the “ Quality of Combustion “ will cause a decline in efficiency. This can be one or all cylinders and is reflected in the RPM.
Ignition issues would be the most common culprit and have been discussed here.
An Induction Leak on one cylinder may result in a Mixture that will not burn properly with single ignition. This can also result in a Mag Drop either on one Mag or on Both.

A 200- 300 ROUGH drop is indicative of dropping one cylinder. My thought is it is best to determine which cylinder is the issue and then diagnose what action is needed.
 
I don't see anywhere in the thread where you've looked upstream of the mag. Did your guy check for any worn components there, worn or missing drive bumpers, or maybe a defective mag drive bearing?
 
Chip Sylverne said:
I don't see anywhere in the thread where you've looked upstream of the mag. Did your guy check for any worn components there, worn or missing drive bumpers, or maybe a defective mag drive bearing?
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The O-200 mags are gear-driven directly off the camshaft. The right mag has a gear mounted on the rotor shaft. The left mag has a gear with an impulse coupling on it. No separate mag drives in the accessory case as we see in some other engines.

upload_2023-3-4_12-57-8.png
 
Dan Thomas said:
The O-200 mags are gear-driven directly off the camshaft. The right mag has a gear mounted on the rotor shaft. The left mag has a gear with an impulse coupling on it. No separate mag drives in the accessory case as we see in some other engines.

View attachment 115484
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Oh, sorry. For some reason I had it in my mind this was a PA-28 with a Lyc O-320
 
Post #30 brought a Cessna 150 into the conversation as well.
 
Nothing is 100% .

Some Skyhawks and Cardinals have O-320s and O-360’s that have the infamous

Dual Mag.

SM—“ Exercise care when removing and installing the magneto as the cushions
may fall into the engine”.

Very true. Insert favorite “ Special Words” here! _______________________
 
Dan Thomas said:
The resistance check doesn't find the lead that is arcing from the core out to the shield. This tool does:

View attachment 115461

One of the leads goes to ground, the other goes to the spring on the plug end of the lead. Push the button. If a spark appears in the window, the lead isn't arcing internally. I did the test with the leads still connected to the mags, and if it doesn't spark it might be arcing inside the mag, from the distributor terminal for that wire across to the rotor finger, so turn the prop some to rotate the rotor away from that terminal and test again. It should spark.
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I have found several bad wires using my ohm meter set to megohms. Sometimes the arcing forms a carbon trail that will show up as a high resistance short. Nothing wrong with using a high voltage tester, but I prefer to test with my meter first....then follow up with whatever is necessary. Most aircraft owners have an ohm meter.

I agree if you find an issue, move the prop slightly to see if it changes..will possibly eliminate the issue coming from inside the mag.
 
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BB687074-EBEE-4B48-B0DA-B736318A1A0B.jpeg
Magman said:
Nothing is 100% .

Some Skyhawks and Cardinals have O-320s and O-360’s that have the infamous

Dual Mag.

SM—“ Exercise care when removing and installing the magneto as the cushions
may fall into the engine”.

Very true. Insert favorite “ Special Words” here! _______________________
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My old 0-320 H2AD motor had 2 loose bumpers and one did fall down when I removed the mag. I was able pick it out but I think it could have fallen farther down and would have been a problem?

This “new” H2AD engine has a steel retainer holding them to the gear or shaft, I can’t really tell? I was real concerned when I saw they weren’t on the end of the impulse coupler. Then took a look there they were. I thought they were stuck in with oil and was real careful reaching up to get them out. No go they are not going to fall off. I guess lycoming fixed that?

The dual mag is out for its 500 hour inspection. Remember when I put the engine in Magman? The whole engine has been great. Being it is a dual mag it is getting inspected at 500.
BTW WIW means what’s it worth.
 
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The IO-360 had bumpers with” ears” that retained them.

I have dropped a few. Sometimes pulling Oil Drain plug worked.

Other time I pulled the Sump. Found others in there}

I DO recall your engine change on 172 Forum.

Wish I could fly 1/2 of what you do.

btw- Regardless of WHO does the 500 I would INSIST on a new Impulse Spring.

Note there are 2 types that must be matched to the Coupling.

The “ improved” version is the only Spring I could not install with my meager

facilities. Aircraft Magneto Service was good enough to do it for me.


WIW = thanks

The “ H” had a bad start but I’ve seen some start but some were remarkable

after the early pains. I’m guessing they increased the oil flow to the valves.
 
Dana said:
Nowadays I doubt that. Perhaps (I hope) most owners who work on their own planes have one. I think I have six, but I'm the lunatic fringe...
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Me too. I tend to collect stuff like that.
 
I also own 4-5 cheap DVM. Too many times I needed one and did not have one on hand and went to buy one at the closest outlet. So now I have one for each shop, one in the hangar and one in my truck. Sadly I have never bought a good one...But did use flukes at my job provided by my employer.
 
Looky what I found. Picture of my last mag drive bumpers. Loose as can be.
IMG_6013.JPG

Professional Aircraft Accessories does the magneto 500hr. They are on the other side of town. I drive over there to pickup/drop off.
 
Harbor Freight Aircraft Supply just about gives their meters away.

Cheap enough to have many. Accurate enough for things I get into.

Harness Testers are are little more expensive and tend to be more of a Tech item

rather than the Owner. It would be a good items for several folks to go in on as an

“ Airport Tool “ for use by all.

Challenger

Not sure what you mean by “ loose”? wear?

In your configuration there is a gear that can be removed from the engine.

The gear has a wide “groove” to accept a “ Retainer Cup” that is about

2. 1/2 in Long x 1 1/2 in Wide and 1/2 in High . There is a radius at the bottom

so the bumpers can only go one way. Each of the bumpers has one squared edge

and one rounded.

As we know; nothing keeps the bumpers from departing the Retainer Cup

and hiding in the engine. With the IO-360 configuration the bumpers have

protrusions ( ears ) that keep them from “ migrating”. I’ve often wondered

if the complete gear , cup and bumpers could be used on “ O “ engines.

Probably costly for an Owner to do but cost little at manufacturer .
 
Gary Ward said:
Looky what I found. Picture of my last mag drive bumpers. Loose as can be.
IMG_6013.JPG

Professional Aircraft Accessories does the magneto 500hr. They are on the other side of town. I drive over there to pickup/drop off.
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I've found a little dab of fuel lube works great as paste to hold those suckers in place when installing a mag.
 
Chip Sylverne said:
I've found a little dab of fuel lube works great as paste to hold those suckers in place when installing a mag.
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That stuff is handy for a lot of things like that. I used to put a bit on a screwdriver blade to stick a nut on to reach it way into some horribley tight spot onto a stud, then turn the nut with another long screwdriver by pushing on the nut corners.
 
Dan Thomas said:
That stuff is handy for a lot of things like that. I used to put a bit on a screwdriver blade to stick a nut on to reach it way into some horribly tight spot onto a stud, then turn the nut with another long screwdriver by pushing on the nut corners.
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Like a nut that hold a carb or air box on some engines.
 
Dan Thomas said:
That stuff is handy for a lot of things like that. I used to put a bit on a screwdriver blade to stick a nut on to reach it way into some horribley tight spot onto a stud, then turn the nut with another long screwdriver by pushing on the nut corners.
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Or that bottom left nut and lockwasher on a Lycoming dry vacuum pump mount...yikes.
 
Gary Ward said:
Professional Aircraft Accessories does the magneto 500hr. They are on the other side of town. I drive over there to pickup/drop off.
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Mike has been servicing both of my dual mags for the last 20 years. Highly recommend him!
 
Lon Stratton said:
Mike has been servicing both of my dual mags for the last 20 years. Highly recommend him!
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I agree^^^^
I was over there yesterday talking with Mike picking up my mag. I agree I am lucky to have Mike so close. He did a overhaul for me a few years ago in record time. This time he only did a 500 hr. I learned some more good stuff by talking with him. Very nice guy. Here are the old parts out of my magneto. He said he does a lot of dual mags. The capacitors are new along with the hardware.
IMG_E2724.JPG
 
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My mechanic and I are reinstalling it tonight after work. Last night I checked all the plugs for high resistance even though they only have 43 hrs since cleaned and the leads were checked with a tester like Dan showed above. Ready to get back in the air except the weather sucks this weekend. So I will take my time putting it back together tonight. Friday!!! love Friday nights at the hangar!!
IMG_2728.JPG
 
I thought that was a automatic replacement, the impulse spring. BTW this was the first time I got to lay my eyes on one. I heard some much about them.
I was told years ago that if that spring broke in my dual mag, my plane would become a glider!! Engine may still run but with no power. Never forgot that.
So that is why I was Not going to stretch the hrs on the mag when it got to 500. Plus this is a good time of year to be down for a couple weeks. The whole mag looked good to me at 500 before the inspection, but what do I know. Other than hopefully it is good for another 500 hrs, fingers crossed.
 
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At one time Bendix published “ I am your Impulse Coupling” which contained pix and criteria for inspecting the Spring. I believe later it changed to “ if you disassemble the Coupling you should replace the Spring”. That is my practice.

RUST is the enemy of all Springs . A tiny pit leads to failure in your Mag or supporting your Car. Aircraft flown regularly seldom have an issue. Those that
seldom fly are the ones that fail.

One thing I do that is not included in mfg instructions is to immerse the assembled
Coupling in Engine Oil. A dry Spring in a non- flying humid Engine will often suffer premature failure.

Generally a broken Spring will render that mag essentially inoperative as Dan said.
However; I have encountered Slick Springs that fail and sort of jam up. This also retards the timing but to a lesser degree. This presents as hard starting along with
a 300-400 Drop that is relatively smooth as all cylinder are still firing.. Never saw this on a Bendix.
 
Challenger

My take is a little different as the 500 hrs is not as significant as the the other part of the the recommendation. FOUR Years.

Operating your engine will put your Spring in a bath of Hot Oil which is good.
Not flying allowed oil to run off and the dry Spring rusts , pits and fails.

Before removing a “D” ( darn ? ) mag I will assure there are 2 contacts and a Spring on

hand.
 
The mag was only in service for 31 months since it came from lycoming on a zero hour engine.
 
With 500 hrs in 31 months I would put your mag in the “ wear-out /adjust “ category.

A similar mag with 20 hrs in in 4 years is in the “ rust-out” category

Both valid reason to remove / inspect.

Particularly on a “ D “ mag.
 
For those contemplating the use of just any DVM to measure plug lead insulation - An ordinary DVM will not test leads unless the DVM is specifically designed to have a very high source voltage - and these are very rare - IOW making it a voltage breakdown test.

Testing a plug lead isn't an ordinary resistance test - it is a breakdown voltage test, which to be worth anything. Dan Thomas's rig looks like the correct method, but most common DVMs have only low voltage sources.
 
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