Custom Cox 049 with spark ignition

When I first saw it I also thought it was a Tornado case.
After another look I realized it is a Cox cast case that has been smooth out and polished.
The cylinder threw me at first because of the two short fins between the exhaust ports.
I definitely need to run it.

So, how does that work, is there a cam lifting a push-pin to contact the points? And the curved extension coming out of the cam housing(if that's what it is)? A timing adjustment, maybe?

RknRusty wrote:So, how does that work, is there a cam lifting a push-pin to contact the points? And the curved extension coming out of the cam housing(if that's what it is)? A timing adjustment, maybe?

Exactly right Rusty, there is a flat spot ground on the crank shaft that the push pin
runs over. When the pin hits the flat spot the points close causing the spark plug
to fire. The pin is located under the arched part of the moving points.
The curved extension is called the timer arm and you are right again, that
is how the timing is adjusted. Just needs a coil, condensor, battery pack,
and fuel to run.

Very interesting, did I understand right that you can change the timing of the ignition while running or is it static?

coxaddicted wrote:Very interesting, did I understand right that you can change the timing of the ignition while running or is it static?

You can (and have to) adjust the timing on all spark ignition engines, you normally have to retard the spark for starting, then advance it as the engine picks up speed, too far advanced on starting can result in a very nasty kick-back and a VERY sore finger!

I know what you mean. On 4 cycle engines it is standard with a variable ignition but for 2 cycle engines you can use a static-ignition position I think (of course a variable ignition is better for starting and peak performance).

From my understanding:
Starting - early ignition (high torque and hot combustion)
peak - late ignition ( combustion gets colder, torque is low)

Tell me if i am wrong. I also know that it is not easy to compare 4 and 2 cycle engines.

The cox motor is something between 2 cycle and diesel engine I would say .

coxaddicted wrote:From my understanding:
Starting - early ignition (high torque and hot combustion)
peak - late ignition ( combustion gets colder, torque is low)

Tell me if i am wrong...

Yeah, actually the other way around. For spark igntion engines, ignition is/should be retarded for starting/slow running, so you don't have combustion/max pressure before TDC ('kick back' when starting a m/c for example). Then ignition needs to be advanced at higher rpm as the burn rate (and time to reach maximum pressure in combustion chamber) stays more or less constant, so you don't have maximum pressure way after TDC, which is inefficient (less power) and leads to other bad things. In a nutshell.

Historically, two strokes could get away with fixed timing, because it made the ignition system cheaper/more reliable (no advancer needed), and at low rpm the two stroke has less energy per revolution (but twice as often) as an equivalent (whatever that means) four stroke. So kick/pull starting was less of a problem.

ahrma_581 wrote:

coxaddicted wrote:From my understanding:
Starting - early ignition (high torque and hot combustion)
peak - late ignition ( combustion gets colder, torque is low)

Tell me if i am wrong...

Yeah, actually the other way around. For spark igntion engines, ignition is/should be retarded for starting/slow running, so you don't have combustion/max pressure before TDC ('kick back' when starting a m/c for example). Then ignition needs to be advanced at higher rpm as the burn rate (and time to reach maximum pressure in combustion chamber) stays more or less constant, so you don't have maximum pressure way after TDC, which is inefficient (less power) and leads to other bad things. In a nutshell.

Historically, two strokes could get away with fixed timing, because it made the ignition system cheaper/more reliable (no advancer needed), and at low rpm the two stroke has less energy per revolution (but twice as often) as an equivalent (whatever that means) four stroke. So kick/pull starting was less of a problem.

Yes, as I said, but I must admit that I had a momentary doubt as to if I'D got it backwards, despite always starting model spark ignitions with the ignition retarded after the first time I got a sharp rap on the finger!

Wilf