MTFCA Forum

Hello everyone, in checking the circuits to prepare to fire the engine,i thought id confirm spark at all plugs and on the right cylinder at the right time (to make sure someone hadnt mixed up the commutator wires ).

What i found was everything was firing correctly,but i have continuity between all positions in the cup and also with ground.
Ground id expect at the point of firing because the rotor touches the pad and is connected to ground through the cam.

But why would all terminals have continuity to each other ,other than the chance that they are all missing isolating washers.

thanks Vince

Remove all coils from the coil box then repeat the timer continuity measurements. There should be no connectivity between timer terminals then.

With the coils installed in the coil box and sharing a common power connection, there will be continuity between each timer segment via respective coil primary winding, closed coil points to common power connection.

MKossor wrote: ↑

Tue Oct 10, 2023 2:29 pm

Remove all coils from the coil box then repeat the timer continuity measurements. There should be no connectivity between timer terminals then.

With the coils installed in the coil box and sharing a common power connection, there will be continuity between each timer segment via respective coil primary winding, closed coil points to common power connection.

That makes sense , or that there is continuity through the box if the primary coil contacts are shorted through the box.

Is there continuity through the key switch when the key is off ? otherwise im wondering how there would be a connection through one coil primary circuit to another .

Or ,, i assume then that all + contacts are ganged with a pigtail from the box to the key.
The schematic doesnt show this,,just that there is Connection from the + to the tumbler.

Thanks Vince

Hello ,
Pulled the coils , yep exactly as mkossor said .
Continuity back through the primary windings .
Thanks for the answer

What did really intrigue me is how far retarded spark is when you adjust to full retard .
The piston is Almost half way down the Cyl and ready for the ex valve to open !

I run hit miss engines with a slight push to the crank on retarded timing but never that far ,, I don’t think I’d even get them to fire and they are the same compression ratio as a T engine.

Interesting

How did you adjust the timer for retard? The pin through the front crankshaft pulley should be about the 10:20 position as viewed from the front looking like a analog clock dial. That position would be the same for each cylinder. only it takes half a rotation of the crankshaft between the cylinders in the following order 1,2,4,3. The old method of measuring between the bolt and the timing rod only works with the original timer. Each type timer is a bit different, but the retard should be fine when using the method unless you have an unusual crankshaft with the pin in a different position. You will also notice there is a different position of the spark lever when cranking on magneto VS cranking on battery.
Norm

bagotcorner wrote: ↑

Tue Oct 10, 2023 9:34 pm

The piston is Almost half way down the Cyl and ready for the ex valve to open !

The stroke is 4". Full retard should be 15 degrees after TDC. At that point the piston should have gone down .087". Here is a good method for setting timing.

https://dauntlessgeezer.com/DG97.html

Here is how it was done back in day. Here is manual