magneto installation help

[Dick]

Please, need some advice.

The plane is an experimental homebuilt with a
C-85 engine and 2 new factory overhauled Bendix S4LN-21 mags, each with
impulse couplings and to be timed at 30 & 28 degrees BTC.

Have been trying to install and time mags in acordance with TCM MSB94-8A.
Basically: Ignition wires disconnected and top plugs out of engine; then to
TDC on compression stroke, prop mounted degree wheel to 30 btc for left mag
after unloading the impulse coupling, red tooth of plastic gear positioned
in center of mag access hole (temporarily restrained so as not to move while
installing mag); same for right mag at 28 degrees; remove temp restrainer
plug; hook up "Inductor" (dual mag synchronizer with four phase audio
signal and two LED's); upon hookup, find LED's off and continuous tone which
means the points are open; then try to rotate mag to a position where
points are closed and LED's on........tried many, many times to get points
to open at specified timing BTC!

my problems are:
1. Can't turn prop slow enough to get anything other than a very quick LEDs
blip-blip (on-off). I would have thought the points would be closed for a
longer duration..?
2. Can't get enough "travel" on rotating the mags.
3. Have never done a mag installation
before <G>.

Any help would be appreciated, Dick

PS-I have the Continental engine manual and read and reread the mag
installation section.

[Orval Fairbairn]

In article >,
"Dick" > wrote:

> Please, need some advice.
>
> The plane is an experimental homebuilt with a
> C-85 engine and 2 new factory overhauled Bendix S4LN-21 mags, each with
> impulse couplings and to be timed at 30 & 28 degrees BTC.
>
> Have been trying to install and time mags in acordance with TCM MSB94-8A.
> Basically: Ignition wires disconnected and top plugs out of engine; then to
> TDC on compression stroke, prop mounted degree wheel to 30 btc for left mag
> after unloading the impulse coupling, red tooth of plastic gear positioned
> in center of mag access hole (temporarily restrained so as not to move while
> installing mag); same for right mag at 28 degrees; remove temp restrainer
> plug; hook up "Inductor" (dual mag synchronizer with four phase audio
> signal and two LED's); upon hookup, find LED's off and continuous tone which
> means the points are open; then try to rotate mag to a position where
> points are closed and LED's on........tried many, many times to get points
> to open at specified timing BTC!
>
> my problems are:
> 1. Can't turn prop slow enough to get anything other than a very quick LEDs
> blip-blip (on-off). I would have thought the points would be closed for a
> longer duration..?
> 2. Can't get enough "travel" on rotating the mags.
> 3. Have never done a mag installation
> before <G>.
>
> Any help would be appreciated, Dick
>
> PS-I have the Continental engine manual and read and reread the mag
> installation section.


It sounds as if you have too much point gap. Recheck the mag internal
timing with your Time-Rite. The points should open just as the red tooth
passes the pointer.

[Dick]

> It sounds as if you have too much point gap. Recheck the mag internal
> timing with your Time-Rite. The points should open just as the red tooth
> passes the pointer.

My manual also references a "pointer" but I can't see one in the hole where
the red tooth is visible. I can see an aluminum straight slot screw. One
fellow hereabouts thought the "pointer" might be inside the points area but
I'm reluctant to open up a freshly overhauled unit. Thoughts?

Thanks, Dick

[[email protected]]

The pointer is a special tool that refers to a protractor,
also a special tool. Neither are present on your mags. If they're
factory overhauled thay should be properly set inside.
Are you turning the mags past the impulse click and then
backing up to the mark on the gear? If not, that might be your problem.
Check to see you have a good ground for the timing box, too. The short
blip might be the points overlap between mags if the tester isn't
grounded.

Dan

[J. Severyn]

"Dick" > wrote in message
m...
> Please, need some advice.
>
> The plane is an experimental homebuilt with a
> C-85 engine and 2 new factory overhauled Bendix S4LN-21 mags, each with
> impulse couplings and to be timed at 30 & 28 degrees BTC.
>
> Have been trying to install and time mags in acordance with TCM MSB94-8A.
> Basically: Ignition wires disconnected and top plugs out of engine; then
> to TDC on compression stroke, prop mounted degree wheel to 30 btc for left
> mag after unloading the impulse coupling, red tooth of plastic gear
> positioned in center of mag access hole (temporarily restrained so as not
> to move while installing mag); same for right mag at 28 degrees; remove
> temp restrainer plug; hook up "Inductor" (dual mag synchronizer with
> four phase audio signal and two LED's); upon hookup, find LED's off and
> continuous tone which means the points are open; then try to rotate mag
> to a position where points are closed and LED's on........tried many, many
> times to get points to open at specified timing BTC!
>
> my problems are:
> 1. Can't turn prop slow enough to get anything other than a very quick
> LEDs blip-blip (on-off). I would have thought the points would be closed
> for a longer duration..?
> 2. Can't get enough "travel" on rotating the mags.
> 3. Have never done a mag installation
> before <G>.
>
> Any help would be appreciated, Dick
>
> PS-I have the Continental engine manual and read and reread the mag
> installation section.
>
>
>
Also make sure that the mag switches are "hot" (not grounded) or the P leads
are disconnected.

J. Severyn

[[email protected]]

Should also have mentioned: If you can't get enough travel in the
rotation of the mag case, you have to remove it and reinstall it in a
more favorable position, keeping the timing mark lined up in the
window. It's a matter of meshing the right gear teeth.

Dan