Topic: anyone know a lot about coils?

[honda_jason]

anyone know what kind these are? they came on my 71 CB500 when i got it and theyre definitely not stock. Also i tested them and one is giving no power. a friend has a set of 750 coils kicking around and im wondering if theyd work on my 500.

[JohnG]

Andrews coils, made in Chicago. Popular in the 70s and 80s for upgrading the ignition on Hondas and Kawis.  Probably .3 ohm resistance  (check yours).  Much better spark than stock.  Check all your wiring with a multimeter before you decide the coil itself is bad.

[HondaMan]

Those 750 coils will work fine on your 500.

Something you should know: if the Andrews coils you have measure 3 ohms on the primary side (like the Dyna grren coils or the Accel coils), you WILL have electrical troubles with the CB500/550 in the form of low battery charge. This is a too low primary ohms value: you will need to either change coils or add resistance in series with the coils' power feed (BLACK/WHITE wires on these bikes) to balance things back out. This is a common problem with the Mid Fours.

In addition, if the bike already has Dyna Ignition feeding those coils, you will have an even worse situation: the Dyna ignitions use even more current...
 

[honda_jason]

Andrews coils, made in Chicago. Popular in the 70s and 80s for upgrading the ignition on Hondas and Kawis.  Probably .3 ohm resistance  (check yours).  Much better spark than stock.  Check all your wiring with a multimeter before you decide the coil itself is bad.

the left side measured .4 and got nothing on the right side.
before i striped the bike down and started the rebuild everything worked and the bike itself somehow started. ill do a little more troubleshooting

[honda_jason]

Those 750 coils will work fine on your 500.

Something you should know: if the Andrews coils you have measure 3 ohms on the primary side (like the Dyna grren coils or the Accel coils), you WILL have electrical troubles with the CB500/550 in the form of low battery charge. This is a too low primary ohms value: you will need to either change coils or add resistance in series with the coils' power feed (BLACK/WHITE wires on these bikes) to balance things back out. This is a common problem with the Mid Fours.

In addition, if the bike already has Dyna Ignition feeding those coils, you will have an even worse situation: the Dyna ignitions use even more current...
 

i think i still have the stock ignition. honestly i have no idea what im doing in the electrical aspect of things. i just took the bike apart did some custom mods painted everything and put it all back together...almost anyway. still working on the back together part haah. thanks for the help guys!

[Alan F.]

We disconected the primary leads and measured a full 4 ohms on the left coil's primary, the other one measured something like 29K which really surprised me.  But I suppose without disassembling the coils from their brackets and cleaning every connection, that would be the next logical step before swapping them for the 750 coils.

The primary leads on these Andrews coils connect to screw terminals (like the antenna connections on the back of an old t.v.) and they each have a dab of clear silicone over them to prevent any corrosion, but maybe over the decades the bike was stored some corosion formed, or maybe there's even a break in one of the primary leads. Anything is possible at this point, it doesn't necessarily mean the coil is bad.
-Alan

[JohnG]

I would say you need to patiently take an hour or two and spend the time cleaning and polishing any and all connections related to the ignition system. Take nothing for granted.

Tools to have  (others will have opinions too): small brush, sandpaper, fine file, contact cleaner. 

Make sure and clean the leads to the points assembly  (blue, yellow leads)  and the points themselves.

If you still only have 2 cylinders, swap in one of your Honda coils.

You can also do the standard test of swapping the leads to the Andrews coils and see if the other two cylinders now run.

All the electrical connection cleaning is good for your bike in any event, regardless of coil problems.

[ev0lve]

You can also do the standard test of swapping the leads to the Andrews coils and see if the other two cylinders now run.

+1 as a positive test. Just had to do this recently. If the spark follows the lead then start chasing your points and condensers.

[Alan F.]

Very good news this afternoon about these coils, we removed them from the bike and cleaned up all of the contacts and connectors and both coils measured 6 ohms across the primaries and 14K across the secondaries.  Jason's gonna have a look at replacing the vintage accel 7mm wires with new.

Does he need to run resistor plugs with these coils?

[TwoTired]

Depends.  If its 6 ohms for both coils, each coils is 3 ohms and yes you should have a resistor.

If each coil is 6 ohms independently, they are more than the 4.7-5 ohm primaries that these bikes have stock and will draw less power.  Certainly no resistor is needed.  But, WTF, 6 ohms?
You sure there isn't some measurement error in that reading?

[Alan F.]

well I suppose I could try a different meter next time I'm over there, but I can't see a 20% error happening.

[w1sa]

I can't imagine any benefit from an aftermarket 6 ohm "performance" coil.

Could they have broken down internally to change the primary resistances?

[Alan F.]

I'll measure them with a higher quality meter next chance I get.
That should put the issue in a different light.
-Alan

[Alan F.]

I just ran a search of these forums (and the internet too) for info on Andrews coils, it seems everything to know about them is located here and here only...

The orange Andrews coils should be 3 ohms (as TT had stated)
They look like these, and are also p/n 6465  witha build date in 78 if I remember correctly.

[TwoTired]

well I suppose I could try a different meter next time I'm over there, but I can't see a 20% error happening.

When measuring low resistances, put the two probes together directly and note the reading.  That reading is test apparatus error and must be subtracted form any reading made on that meter's scale, with those probes.
Each scale selection can have a different measurement error.

[Alan F.]

Thanks TT I'm familliar with that one, I was just using a cheap meter.

[honda_jason]

i just spent a little over an hour taking them apart and cleaning them up and they are now all back together. next time alan comes over we'll measure them and see if were lookin good or not. thanks everyone for your help.

[Alan F.]

Depends.  If its 6 ohms for both coils, each coils is 3 ohms and yes you should have a resistor.

If each coil is 6 ohms independently, they are more than the 4.7-5 ohm primaries that these bikes have stock and will draw less power.  Certainly no resistor is needed.  But, WTF, 6 ohms?
You sure there isn't some measurement error in that reading?

OK so if we assume that Jason's set of orange Andrews 6465 coils are 3 ohms (because 6465's all are 3 ohms and I measured them with a cheap inacurate meter)
Does he need to run resistor plugs?

[w1sa]

Use either resistor plugs or resistor caps (not both), with copper core leads.

Also consider previously mentioned impact on battery/charging system, without a resistor between battery and coils.

[TwoTired]

If the primaries of coils are 3 ohms, they will suck more power from the bike's electrical and burn up points faster. To avoid this, you put a 1 ohm (50 Watt or higher rated) resistor in series with the primary circuit, usually inline with their power connection.  (assumption is, you are using points)

The secondary output of the coils should have a resistor associated with each spark plug, about 5K ohms.  This can be in the spark plug itself by using resistor plugs (they will have an R in the number marking).
Or, it can be in the spark plug cap, as the bike had when it came from the factory.
Or, it you can use resistance spark plug leads that have a rating of (about) 5K-10K ohm per foot of wire.

Only one resistor per spark plug is needed in the output, spark plug, cap, or wire itself.
The secondary output resistors still fire the plugs at the same voltage as without any resistance, but it makes the spark event duration longer, allowing a more complete burn during the power stroke of the engine.
(As a side benefit, the secondary resistance also reduces the radiated emission of the spark signal to reduce interference with electronic devices nearby, making you a less intrusive neighbor.)

[Alan F.]

Thanks TT, Yes points.  I was just reading some of your old posts and I understand just what you're recommending.  Since Jason presently has a set of non-resistor NGK plugs and a set of 7mm accel wires (the plug end contacts were corroded and fragile but the rest seem in nice shape) I'd almost think he'd be better off picking up a set of 5K NGK plug caps and screw them onto his wires (like the stock ones) and I'll have a look around for a pair of 50 watt 1 ohm resistors to wire in series with each coil's feed...black with white stripe wire?

On another note I wonder, his bike has astoundingly low mileage at 2399 miles (it's a 71 CB500) These Andrews #6465 coils have a build date in 78 (I forget the week) I'm wondering if this bike was likely to have a 'mysterious electrical issue' where it was constantly discharging the battery?

It makes sense now that I understand the need for at least  4 ohm coils.
Would it be better to install 2 ohm resistors to achieve 5 ohm primaries? or is 4 ohms good enough?  It's probably gonna be an 'around town' bike with not too much highway riding.

What are your thoughts?

[Alan F.]

http://forums.sohc4.net/index.php?topic=30938.0

Wow that's quite a bit to digest, lots of good info there.
-Alan

[TwoTired]

...and I'll have a look around for a pair of 50 watt 1 ohm resistors to wire in series with each coil's feed...black with white stripe wire?

I still think you only have to have one resistor, it's output will feed both coils.  But, if you decide on two, you can halve the wattage requirement for each one.

On another note I wonder, his bike has astoundingly low mileage at 2399 miles (it's a 71 CB500) These Andrews #6465 coils have a build date in 78 (I forget the week) I'm wondering if this bike was likely to have a 'mysterious electrical issue' where it was constantly discharging the battery?

Seems likely, particularly if the headlight was on at the same time.

It makes sense now that I understand the need for at least  4 ohm coils.
Would it be better to install 2 ohm resistors to achieve 5 ohm primaries? or is 4 ohms good enough?  It's probably gonna be an 'around town' bike with not too much highway riding.

Since you are using points, there is only a very short time that both coils are drawing power during each crankshaft rotation.
2 ohms series resistance will likely drop the voltage too much to make reliable spark.  1 ohm should be adequate.

Stock coils are just under 5 ohm, usually.  At a run voltage of 13.8V they draw about 2.76 amps each but are only on 54% of the time.  So the total draw is about 41 watts.
4 Ohm coils @ 13.8 V draw about 3.45 amps. Still on 54% of the time for a total power draw of 51.4 Watts.
It's still 10 watts more than stock, but as long as you don't spend a lot of time idling with the lights on and don't go to higher wattage bulbs for lighting, it should be live-able.

[Alan F.]

I picked up some 1 ohm 25 watt resistors today, and Jason is picking up some new plug caps tonight. He'll give the old accel 7mm wires a shot and with some luck everything will fire up happily.

Jason, here's a few threads with pics of the Honadman resistor pack mounted:
http://forums.sohc4.net/index.php?topic=29797.0
And here's THE thread that shows what a Hondaman resistor pack actually looks like.
http://forums.sohc4.net/index.php?topic=30938.75
-Alan

[honda_jason]

well i picked up some NGK plug caps today and alan grabbed some resistors for me so we should get this rigged up soon!

Alan, i checked out hondamans resistor set up and i think we can fab something up similar. ill talk to some guys at work in the metal shop and see if they can weld me up a lik bracket like that.