Spark between coil casing and coil bracket

[Tim]

I just got my rebuilt A-4 running in the garage. It starts easily and seems to run ok. I am temporarily using the points and condenser I got with the used engine (I will eventually switch to EI). The coil is a new coil I bought from Moyer as spare about 10 years ago. I noticed some arching between the coil casing and the coil bracket. Any ideas on what may cause this?

[redtim]

Have you checked the spark plug wires? I had a similar issue, traced it to a loose wire on the distributor.

[Mo]

I did a little read on the internet and found this link. I was thinking plugs, wires, points, condenser and cap to be checked. Retarded timing and fuel mixture????..In a few minutes I read a few things I wasn't aware of.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=544723&page=all

[hanleyclifford]

I did a little read on the internet and found this link. I was thinking plugs, wires, points, condenser and cap to be checked. Retarded timing and fuel mixture????..In a few minutes I read a few things I wasn't aware of.
http://www.bobistheoilguy.com/forums...44723&page=all

After reading that thread I'm more confused than ever. But my hunch is "too much voltage" at coil + or too much resistance between coil secondary and the block.

[Mo]

[QUOTE=hanleyclifford;90667]After reading that thread I'm more confused than ever. But my hunch is "too much voltage" at coil + or too much resistance between coil secondary and the block.[/QUOTE


Hanley, out of all of that, there was one entry that might have made sense. The one where the guy talks about secondary resistance, and mentions retarded timing as well. I remember seeing that type of thing years ago on chevy's (we are going back to Nova's etc) and if I remember correctly it was always something after the coil...not the coil itself.

Here's his post: his handle was LM
"Otherwise, what you're describing sounds like excessive secondary ignition resistance. The resistance is less between the coil and bracket, vs the spark plug gap(s) and high cylinder pressure, hence the arc. Some possible causes include: open or high resistance wires, lean fuel mixture, retarded timing, worn or improperly gapped spark plugs, corrosion build up on plug wire terminals (the latter you've already got covered). I'm not up on later ignition systems - probably no longer used or is integrated into the module - but if your system uses a ballast resistor, ck that it is okay/within specs

A scientific analog oscilloscope, an automotive scope, a modern day digital storage oscilloscope (DSO) or hand-held scope unit (first two are relatively inexpensive, last two aren't - all require some experience), with the proper pick-up clamps (probes), should be able to pinpoint the problem. Good diagnostic shops/garages will have them. Can usually discern between an electrical or fuel mixture problem, by the slope of the spark line, essentially displaying the ignition process as it occurs (do a google search for "secondary ignition waveform"). Some specific tests to perform would be a "Snap-throttle" and a "Cranking KV", to stress the secondary ignition system (yours would fail or be abnormal in it's present state)

Plug wire resistance generally shouldn't exceed ~20K ohms, depending on length, and more specifically so much resistance per foot (there should be min & max specs for your wires somewhere). But doesn't seem to be the root cause, as you've been thru several wire sets (am assuming you've been also replacing the coil wire, if present). Well-regarded aftermarket wires would include Magnecor, Holley, Accel, Crane, and others (but again, may not fix the fundamental problem). There are price/quality/ model steps within some lines

Suggest using only a light amount of dielectric grease, as is a weak conductor. Also make sure that the spark plug seating areas are clean".

[hanleyclifford]

Mo - I agree that was the best post. This is one reason why I do not like resistance wires, or plugs for that matter. I prefer to keep voltage as low as possible at coil+ and fire with minimum resistance down to the spark plug. Keeps all components working at the low end of their capacities, especially the coil.

[JOHN COOKSON]

Are the towers in the distributor cap clean and bright? Especially the center one that the wire from the coil plugs into? Also the center HV tower of the coil.
I assume you have solid core spark plug wires not graphite core?
Pull the spark plug wires and the wire from the coil and lay them on the bench and test each of them with an ohm meter to see where the resistance is. Also check the area where the spark plugs contact the head as mentioned in the link to the other forum.

TRUE GRIT

Edit: If nothing appears to amiss outside the coil there may be something going on inside the coil.

[Tim]

Mystery Solved

I replaced the cap and rotor, no change. Then I replaced the points and condenser, problem solved.
However, I'm not certain the old points and condenser were bad. I never set the gap on old points. Anyway, no more arching, the engine runs much smoother and now idles nicely at around 700 rpm.

[hanleyclifford]

I replaced the cap and rotor, no change. Then I replaced the points and condenser, problem solved.
However, I'm not certain the old points and condenser were bad. I never set the gap on old points. Anyway, no more arching, the engine runs much smoother and now idles nicely at around 700 rpm.

Interesting discussion: http://www.mopedarmy.com/wiki/Condenser