Mag trouble

[zero.one.victor]

Re: Mag trouble

When I discovered the burnt points in my Slick mag, a local shop told me the cause was that the condensor wasn't up to snuff. And that if I replaced just the points I'd be doing it again before too long. So I replaced both.
BTW, the way we discovered the faulty points (they looked OK on initial inspection) was to check impedance thru the points when they were closed. Unless you held them closed with your fingers, the slightly pitted point surfaces didn't allow the spring pressure alone to close them tight enough to make a good contact. Probably could have dressed them out, but I just bought new, since I was already buying a new condensor anyway.

Eric

[Mark Julicher]

Re: Mag trouble

For what it is worth, a quote from Sacrament Sky Ranch "The Magneto Ignition System".

If the engine is rough on one magneto but smooth on both magnetos then check for a cold cylinder. Allow the enigne to cool down and then start and idle teh engine for a minute or two on the magneot that gives you roughness. Shut down the engine and feel each cylinder for the cold one. Most likely you will find a cylinder that has a fouled spark plug or a bad ignition lead. If the engine is rough regardless of the magneto setting then the problem is not ignition. Suspect an induction leak or a valve train problem.

Magneto problems are characterized by irregular roughness that cannot be isolated to a particular cylinder. Breaker point and capacitor problems fall within this category.


Not my words, just good advice from top engine folks.

[selje]

Re: Mag trouble

I once went to inspect a Taylorcraft for possible buy. The owner said that he had one mag that he had overhauled and he and his mechanic had done everthing but could not get it to work correctly on this mag.

My mechanic told me to go ahead and buy the aircraft at the requested discounted price due to the "mag" problem. After we concluded the deal. My mechanic went to the aircraft and switched two spark plug leads and we flew the Taylorcraft back home without a problem.

Make sure the wiring order for this mag is correct.

[FunkyMonkey]

Re: Mag trouble

thanks for the advice. my a&p now suspects the points after taking a closer look. i plan to replace the condensor as well just in case its an accessory to the crime.

[gilligansae]

Re: Mag trouble

I had a bad left mag once. Diagnosed it to be the mag via the same plug/ wire swap route. Sure enough, upon removal from the engine the bendix mag had an out of adjustment point. I then re-gapped it, put it back together, timed it and it has been perfect since. Check the gap on the points, they are adjustable and could save you some serious $$

Jeff LaChausse
N43294

[zero.one.victor]

Re: Mag trouble

Beside the point gap in the mag, there is a thing called the "e-gap". No, it's not a clothing store for E's-- it is adjusting the mag's internal timing so that the points open and it fires just as the coil is producing the highest voltage. I don't know about other mags, but with a late-model Slick the e-gap is automatically set correctly when the points gap is correct.
Some people will debate the actual existence of the e-gap, kinda like they do "the deadly downwind turn" or Sasquatch.

Eric

[Len Petterson]

Re: Mag trouble

Testing mag Ah!!!!
I did the following then testing my old Case mags:
They crossfired. meaning the spark was not timed propperly as the spark jumped across the rotor to the wrong or all pluggs on the same time.
I set up an electric motor to run the mag with a belt and 4 new CAR plugs.
Cleaned and reassembled the mags.
low and behold the cross fire was gone ! Great back to the plane: Idle was Ok but not realy good any more then 1200 rpm. Back fire!
Why? tried agin at home, no misfireing! The new carpluggs has resistors in them and the old C 25 unshieldled plugs does not and the resitior cleard up the low powered crossfireing > the law of least resitance!
In this case new mags solved the problem so now the" Case's" is HISTORY.
Anyone for tractor mags I have 4 pc 4 (for) sale?
Len Petterson

[Karl Rigdon]

Re: Mag trouble

If the engine is missing or rough on the ground on one mag this this will put you in the right area. From a cold start switch to the rough mag after start and run the engine for a few minuets and shut down. Then check the exhaust stacks at the cylinder outlet. Temp stick or a small candle may work. If a cylinder is missing that stack will be cold.
On large radial engine 9 , 14, 18 or 28 cylinder air cooled engines this can be used to find bad spark plugs or bad wires. Doing this we used a contact tempature probe. On opposed engines the temp probe may or may not work as well as radial engines due to the more rearward cylinder being heated from the front cylinders. Of course this only checks for a bad plug or wire. I am assuming you do not have fuel injection!!! In that case all bets are off.

[Karl Rigdon]

Re: Mag trouble

Mag "E" gap is the point of max flux reversal and current in the primary winding. This is a position between the the rotor and the stator where there is max magnetic flux reversal. This is the position you want the points to break. The point gap is not a factor as long as they break clean at "E" gap. At max flux reversal you will have max current in the coil primary.
A point gap setting will approx. the points breaking at "E" gap. The proper method is to use a mag timer and set the points to break at the mechinical "E" gap. In some cases this may require the use of a degree wheel.

[FunkyMonkey]

Re: Mag trouble

replaced points and condensor today. Engine ran well, problem solved.