Points and Condenser Advice

[Vintage Engine Repairs]

Hi guys,
I’m racking my brain trying to figure out how the current flows through this points and condenser setup. It’s on a Briggs engine not chainsaw but the principles are the same, however on a chainsaw the points are constantly closed until it hits a cam and opens breaking the circuit. This makes sense in my head, however this setup, the points are open until a pin drops onto a slot on the crank allowing the points to close. Have a watch of this video and any advice would be really appreciated.

 

[Mad Professor]

Hi guys,
I’m racking my brain trying to figure out how the current flows through this points and condenser setup. It’s on a Briggs engine not chainsaw but the principles are the same, however on a chainsaw the points are constantly closed until it hits a cam and opens breaking the circuit. This makes sense in my head, however this setup, the points are open until a pin drops onto a slot on the crank allowing the points to close. Have a watch of this video and any advice would be really appreciated.

When points are closed coil is charging, time closed is refered to dwell sometimes measured in degrees. When points opens , the coil fires.

I think you have your thinking backwards weather coil fires when points close (no) or open (yes).

I've set timing on many engines using a rolling paper in the points. Turn flywheel until rolling paper just pulls free of points , that is when coil fires. That should happen when flywheel crosses the timing mark. This works on old cars, motorcycles etc......

If you have a distributor/timing plate which rotates, you can turn that instead of flywheel which should be set to the timing mark

On old cars/trucks here is how to static time with a rolling paper. Need clean points properly gapped (gap determines dwell amount of time coil can charge). Put engine on proper timing mark. Insert rolling paper between point contacts. Rotate distributor until paper just pulls loose of points, lock down distributor. This method always gets me within 1-2 degrees of proper timing when checked with a timing light (will get you home or out of the woods). If dwell/point gap is off a little it won't make a big difference, coil just won't charge proper amount of time but will still fire. If you don't have a dwell meter or feeler gauges to set points, use a match book cover, ~ 0.020" close to gap spec for most engines.

 

[RED-85-Z51]

Briggs 394970....it slips next to the windings and essentially makes it a breakerless magnetron coil. Briggs points always gave me problems when they got older and the crank bushing seeped oil at the plunger

Sent from my SM-G996U using Tapatalk

 

[Canyon Angler]

That is kind of confusing and unexpected. On most engines, doesn't the coil fire when the points close?
Reminds me of my motorcycle engine, which fires twice as often as it needs to (at end of compression AND exhaust strokes), which I never would have expected, either.

 

[grizz55chev]

That is kind of confusing and unexpected. On most engines, doesn't the coil fire when the points close?
Reminds me of my motorcycle engine, which fires twice as often as it needs to (at end of compression AND exhaust strokes), which I never would have expected, either.

Just the opposite, they're called breaker points, they fire when they open.

 

[frank_]

Just the opposite, they're called breaker points, they fire when they open.

yes the back emf when the field collapses

 

[Mad Professor]

That is kind of confusing and unexpected. On most engines, doesn't the coil fire when the points close?
Reminds me of my motorcycle engine, which fires twice as often as it needs to (at end of compression AND exhaust strokes), which I never would have expected, either.

two or four cylinder bikes have the points that fire two sets of cylinders, 180 degrees apart. I set of points for 2-cyl, two sets of points for 4-cyl.

I worked at a Honda/Suzuki dealership in the 1970s when lots of bikes still had points.............

 

[Canyon Angler]

Just the opposite, they're called breaker points, they fire when they open.

Thanks for the info. Just to clarify -- on most engines, does the coil fire when the points close -- or when they open? A long time ago, I had a 71 Pinto that ATE condensers like Doritos and I was always having to replace condensers and mess with the points getting burned and dressing/regapping them and having to adjust the timing with a timing light, etc...and it seems like on that motor, the spark plugs fired when the points closed.
But my memory might be foggy.

 

[Canyon Angler]

two or four cylinder bikes have the points that fire two sets of cylinders, 180 degrees apart. I set of points for 2-cyl, two sets of points for 4-cyl.

I worked at a Honda/Suzuki dealership in the 1970s when lots of bikes still had points.............

Yeah, my DR650 (4-stroke, one-cylinder thumper) apparently fires once every revolution, can't remember why (simpler, maybe?)...mine has electronic CDI ignition.

 

[grizz55chev]

Thanks for the info. Just to clarify -- on most engines, does the coil fire when the points close -- or when they open? A long time ago, I had a 71 Pinto that ATE condensers like Doritos and I was always having to mess with the points getting burned and having to adjust the timing with a timing light, etc...and it seems like on that motor, the spark plugs fired when the points closed.

Nope, only when they open and " break " the circut.

 

[Canyon Angler]

Nope, only when they open and " break " the circut.

Huh. I'll be darned. I guess I never really understood how it worked. Thanks.

 

[Mad Professor]

two or four cylinder bikes have the points that fire two sets of cylinders, 180 degrees apart. I set of points for 2-cyl, two sets of points for 4-cyl.

I worked at a Honda/Suzuki dealership in the 1970s when lots of bikes still had points.............

An analogy to the above. Most old 8-cyl point cars had 1 set of points, and eight lobes on point cam.

Dual point had 2 sets of points and 4 lobes on the cam. Dual points were used to allow more coil saturation time (points closed longer) to get stronger sparks.

 

[Canyon Angler]

Dual points were used to allow more coil saturation time (points closed longer) to get stronger sparks.

Interesting how they steadily improved the design on the progression toward electronic ignition.

I have a 3-cylinder 2-stroke outboard (Yamaha) that (I believe) has a small coil for each cylinder (no points, though). I wonder whether the additional coils are mainly to improve ignition, or rather to give you a failsafe to at least "limp" home on 2 cylinders if one of them quits...If it just had one coil and that quit, I guess you could end up walking home.

 

[Mad Professor]

Interesting how they steadily improved the design on the progression toward electronic ignition.

I have a 3-cylinder 2-stroke outboard (Yamaha) that (I believe) has a small coil for each cylinder (no points, though). I wonder whether the additional coils are mainly to improve ignition, or rather to give you a failsafe to at least "limp" home on 2 cylinders if one of them quits...If it just had one coil and that quit, I guess you could end up walking home.

May have to do with design. Could be like new cars with coil each cyl. I hate those.

 

[cookies]

pretty sure you can swap a modern coil onto that engine and forget the points and gain ignition advance curve.

 

[Vintage Engine Repairs]

Ok, so these points are open 99% of the time and momentarily close. The points on cars and chainsaws are the opposite, then are closed 99% of the time. When the saw and car points are closed current flows through the complete circuit, but when they are open the whole time and momentarily close as in this rare instance on this Briggs, what is the rout of the current?

How does the points closing break the circuit to collapse the primary windings? I guess that’s what is confusing me right now.

 

[Vintage Engine Repairs]

pretty sure you can swap a modern coil onto that engine and forget the points and gain ignition advance curve.

Na I love keeping everything original!

 

[heimannm]

The spark occurs at the instant the point open. They only need to be closed long enough for the current to flow creating a magnetic field in the coil frequently called coil "saturation"...since electricity flows almost at the speed of light (just a slight exaggeration) it doesn't take long for the coil to reach saturation. Think about an older V-8 engine with points ignition and a single set of points that are firing 4 times per revolution...they are not closed for very long.

(I guess I should have read all the posts first...none the less we should be driving the point home by now)

Mark

 

[Canyon Angler]

How does the points closing break the circuit to collapse the primary windings? I guess that’s what is confusing me right now.

Same here ... good question. But I know just enough about electricity to be a menace to society...

 

[Old2stroke]

Heimannm is right. The primary of the coil, does not get "charged up", it only gets current induced into it as the FW magnets sweep past the coil, so the points only have to be closed briefly as the magnets approach the coil and then open slightly later to cause the spark when the coil current is at maximum saturation.