Point vs Electronic ignition and switching between the two

[hkusp9]

So I should be acquiring a Mcculloch Super Pro 125c at the beginning of the month and plan to clean it up a little and rebuild it.

Im still trying to decide between soda blasting and sand blasting it but yall can save that bit of education for another thread.

I saw a video on youtube of a guy that rebuilt a super pro and put an electronic deal in it, kind of looked like a big fuse with two copper terminals, and he said that it resolve alot of the electrical issues that can occur with the old saws like running in the rain, high humidity, ect.

Can anyone educate me on the mechanics and operation of point ignition and how this swap occurs.

I get most of how a gas 2 cycle engine works, but the point system and how it generates a spark escapes me at the moment. Hopefully it becomes a little more clear when i have hands on the saw.

 

[Ifishsum]

The simple explanation is that points work by breaking the power connection to the coil when they open - which triggers the coil to discharge its stored energy through the spark plug wire. There is also a condenser which acts to diminish the current coming backwards and prevent arcing/burning of the points.

Personally I don't mind point iginition systems at all and would not switch to an electronic trigger system unless the points or condenser were bad, and either unavailable or expensive to replace. They produce a nice strong spark at slower starting speed, and on a small engine like a saw they really don't seem to need messed with much.

 

[hkusp9]

The simple explanation is that points work by breaking the power connection to the coil when they open - which triggers the coil to discharge its stored energy through the spark plug wire. There is also a condenser which acts to diminish the current coming backwards and prevent arcing/burning of the points.

Personally I don't mind point iginition systems at all and would not switch to an electronic trigger system unless the points or condenser were bad, and either unavailable or expensive to replace. They produce a nice strong spark at slower starting speed, and on a small engine like a saw they really don't seem to need messed with much.

Thank you! You explanation was much more simple than the other ones and helped me get the concept a little better.

I did find this thread here:

http://www.arboristsite.com/chainsaw/199641.htm

Which went into a little more detail and was helpful as well. I think im going to stay away from the chips for my new saw as it seems like they dont set the timing quite as precisely as the the stock system.

Lets keep this discussion alive though, as im still not quite understanding how the position of the flywheel relates to "air gap" and timing.

Im guessing that the flywheel has a magnet built into it somewhere that i cant find on the pictures of saws online, and since the magnet causes the field to collapse away from the points and the spark plug to fire, you have to time/position the flywheel correctly to the crank so the spark occurs when the piston is at it highest position and the fuel air mixture is the most compressed, so the explosion can force the piston down with the maxium force?

 

[hkusp9]

Are there any operators or repair manuals that discuss the process of setting the points and timing the magnet that affixed to the flywheel so the spark goes off at the right time?

Also, does setting the gap on the points just make sure that the arc cant reach them when they're opened and prevent premature arcing from buring them up?

 

[Ifishsum]

The flywheel magnets create the current that charges the coil (magneto generator). It's the opening of the points that cause the field to collapse and fire the plug. The points are controlled by a lobe, usually part of the flywheel base with a high spot that pushes the points open as it rotates. Your ignition timing is where the points start to open during that rotation of the flywheel.

It's the condenser that prevents arcing and burning of the contacts by keeping the voltage discharge on the primary side low - when the coil fires through the secondary and plug wire, there is also a discharge back through the primary side. The condenser is supposed to reduce/bleed off that primary discharge voltage low enough to keep the contacts from burning. As I understand it, the points gap (dwell) has more to do with controlling how long the points stay open. Ignition timing on a chain saw is pretty much set by an index key on the shaft and flywheel - adjusting the timing is not something the average saw user can easily do. It involves changing/widening the keyway in the flywheel by grinding, or removing the key so the flywheel position can be changed. But the flywheel could then slip on the shaft while running and ruin your timing.

On some saws, updating to electronic trigger modules also may require changing the flywheel; I believe because the magnet location can be different between the point and electronic versions of those saws which would of course affect the timing. I don't know how many models that applies to, I imagine it depends on the trigger unit itself and the saw model.

 

[heimannm]

In addition to reducing arcing at the points, when the condenser discharges back through the coil it speeds the collapsing magnetic field and thus increases the voltage induced in the secondary windings (connected to the spark plug lead).

Ignition timing in a points ignition saw is easily adjusted by increasing or decreasing the point gap. How far the points open (or not) have nothing to do with the arcing as there is not enough power in the primary side to sustain much of an arc once they open.

Increasing the point gap means they open earlier in the rotation, advancing the ignition and vice versa.

I find points ignition systems to be very easy to work on, diagnose, and maintain. As long as saws are not stored for long periods in damp locations I find the points ignition to be extremely reliable.

Mark