Topic: Continuity on coils indicates open circuit...advice please

[HS]

OK...I posted a somewhat scattered thread yesterday so I'll be more specific asking for a bit of guidance.

New battery and RH control installed.  All lights, starter, horn working good but no spark...very weak when I do see one.  So I tested the spark plug caps and they clearly were starting to go and measured 10.5K resistance so new NGK ones ordered. 

I have a replacement Daiichi breaker assembly that came with bike, but I've yet to install it.  Stock one currently in the bike looks pretty good, but I have to test it.

The coils look to be bad...continuity test indicates an open circuit.  Is this a conclusive test???

So my question is, if coils are indeed bad, do I just go replace the coils with two of these or is there a smarter approach? 

https://www.davidsilverspares.com/CB500K1-FOUR-1972-USA/part_219304/


Thanks.

Sam

[HS]

The coils for reference

[goldarrow]

Many will tell you Daiichi points are inferior and not recommended. 

[TwoTired]

...but no spark...very weak when I do see one.  So I tested the spark plug caps and they clearly were starting to go and measured 10.5K resistance so new NGK ones ordered.

You are not guaranteed exact value for the resistors.  The Cb550 came with a nominal 10K ohm resistance.  But, that value can be 10-20%  off from what is labeled.  Anyway 500 ohms is mouse nuts to the coil secondary voltage and only comes into to play DURING the spark event actual when current is flowing.

Perhaps you can send me your old plug caps, as I'm having difficulty locating new ones in that value?  I'd happily use 10.5KΩ plug caps on my bikes.

The coils look to be bad...continuity test indicates an open circuit.  Is this a conclusive test???

Given what you report, I'd say your test was faulty, and therefore not conclusive.  If the primaries were open circuit, you would never get spark, or any current draw at the coils.  Both coils bad at the same time?  Very unusual.
Was it the secondaries that measured open? ... from which test points?

Is the secondary lead insulation damaged?

[HS]

Many will tell you Daiichi points are inferior and not recommended.

I've read that hear, GA.  I'm going to leave my stockers in until I get the coil issue worked out and go from there.  If I need to swap them, I'll try them since they're already in my hands.

Thanks.

Sam

[HS]

...but no spark...very weak when I do see one.  So I tested the spark plug caps and they clearly were starting to go and measured 10.5K resistance so new NGK ones ordered.

You are not guaranteed exact value for the resistors.  The Cb550 came with a nominal 10K ohm resistance.  But, that value can be 10-20%  off from what is labeled.  Anyway 500 ohms is mouse nuts to the coil secondary voltage and only comes into to play DURING the spark event actual when current is flowing.

Perhaps you can send me your old plug caps, as I'm having difficulty locating new ones in that value?  I'd happily use 10.5KΩ plug caps on my bikes.

The coils look to be bad...continuity test indicates an open circuit.  Is this a conclusive test???

Given what you report, I'd say your test was faulty, and therefore not conclusive.  If the primaries were open circuit, you would never get spark, or any current draw at the coils.  Both coils bad at the same time?  Very unusual.
Was it the secondaries that measured open? ... from which test points?

Is the secondary lead insulation damaged?

I was following this shop manual and it shows to test for continuity as the step one in the test.  So that's what I did and it indicated it was an open circuit.  I put one of my voltmeter leads in the plug caps and the other in the connector (after the coils had been removed from the bike).  The manual indicates that if your voltmeter shows an open circuit then they're trash.

I'm no expert...just following the manual.  I saw very little to no spark on cyclinder 1 and then it disappeared altogether.  The bike has 6800 miles on it and sat for a very long time.  That's why I'm going through everything.

The wires look good...nothing cut or exposed. 

Only other thing I can add is I was testing it this morning with only one plug in the plug caps and it was up against the heads for contact.  I used the starter to turn the engine looking for spark...nothing.  When I removed the coils shortly thereafter, one was warm and one was cold.  Don't know if that's telling me anything.

As for the plug resistance, I read here that on pre-1976 bikes it should be 5K and once it hits 9.5K (I believe that was the figure hondaman quoted), they're trashed.

Sam

[HS]

OK...I suck at electrical.  I was looking at the picture in my bootleg shop manual and I noticed that the intention was to test the continuity between the two leads on each of the coils....FAIL on my part.  I was testing it between the leads on the plug wires on each coil.

The good news is I get continuity between the two leads on each coil.  What I don't understand is that the manual indicates to also test continuity between the two plug wires on each coil.  I get nothing on both the coils.

Any thoughts?

Sam

[TwoTired]

Dual output coils have each spark lead connected to the opposite end of a single coil.  The secondary is thus measured from one spark lead to the other.

The coil primary is measured from Black/white lead to the Blue (or yellow).  There should never be any continuity between the primary and secondary of the SOHC4 coils.

I don't know which manual to which you refer.  But, coils that operate on other than SOHC4s, particularly single output coils, can have a very different internal connection scheme.

The bike in your avatar is a CB550, which (all years) came from the factory with 10K plug caps.  CB750s often (usually, I think) came with 5K plug caps.  If those read 9K or above, they are certainly bad.

Coils can produce "weak spark" if the supply voltage is low, the condensers are too "leaky", and/or if the point contacts don't close with minimum resistance.

Feel free to buy any parts that ease your mind.  I'm just trying to save you some money.

The good news is I get continuity between the two leads on each coil.  What I don't understand is that the manual indicates to also test continuity between the two plug wires on each coil.  I get nothing on both the coils.

The primary winding inside the coil should measure ~5 Ω.
The secondary of the coil should measure ~15000Ω
You usually have to select a different meter scale for the two tests.  Some meters are auto ranging.  I don't know which meter you are using for the test/

[HS]

Dual output coils have each spark lead connected to the opposite end of a single coil.  The secondary is thus measured from one spark lead to the other.

The coil primary is measured from Black/white lead to the Blue (or yellow).  There should never be any continuity between the primary and secondary of the SOHC4 coils.

I don't know which manual to which you refer.  But, coils that operate on other than SOHC4s, particularly single output coils, can have a very different internal connection scheme.

The bike in your avatar is a CB550, which (all years) came from the factory with 10K plug caps.  CB750s often (usually, I think) came with 5K plug caps.  If those read 9K or above, they are certainly bad.

Coils can produce "weak spark" if the supply voltage is low, the condensers are too "leaky", and/or if the point contacts don't close with minimum resistance.

Feel free to buy any parts that ease your mind.  I'm just trying to save you some money.

The good news is I get continuity between the two leads on each coil.  What I don't understand is that the manual indicates to also test continuity between the two plug wires on each coil.  I get nothing on both the coils.

The primary winding inside the coil should measure ~5 Ω.
The secondary of the coil should measure ~15000Ω
You usually have to select a different meter scale for the two tests.  Some meters are auto ranging.  I don't know which meter you are using for the test/

To be clear, I'm all ears here and I'm a rookie so take that in the spirit it's intended...I appreciate the insight.

I have to clear something up though.  Despite my having my head up my arse at times, the bike in my avatar is a 1972 CB500 Four...I've been breaking it down for a while now and it was bone stock...I mean, practically untouched.  Purchased from a retiree that let it sit too long.  Block and frame confirm that.

The Service Manual for the 500 I found here

http://www.sohc4.net/cb500-manuals/

Section 6 ELECTRICAL, IGNITION COIL, B. Inspection on page 89

It states to test continuity so I did with a CEN-TECH digital multimeter.  I'm reading ohms.

Thanks.

Sam

[TwoTired]

I have to clear something up though.  Despite my having my head up my arse at times, the bike in my avatar is a 1972 CB500 Four...

Good to know.  However, I believe they share the same ignition components as the CB550, regardless of year.
Will it still "work" with 5K plug caps?  Yes.  Plug life will be slightly shorter, there will be some increase in power consumption and coil heating.

The Service Manual for the 500 I found here

http://www.sohc4.net/cb500-manuals/

Section 6 ELECTRICAL, IGNITION COIL, B. Inspection on page 89

Ok.  It says the same thing I am telling you, without the ohms values.  Measure primary leads and then measure secondary leads for continuity.

Continuity is the ability to conduct.   Resistance is what impedes conduction.  Both 5Ω and 15KΩ indicate continuity, infinite ohms, not so much.

It states to test continuity so I did with a CEN-TECH digital multimeter.  I'm reading ohms.

CEN-TECH makes several models of meters.  I can't tell from just the brand name, if yours is auto ranging.  But, if you have multiple ohms scales, then it isn't.

If you try to read 15000Ω on the 200Ω scale it will show an over range on the display (more than 200Ω), indicating the reading is higher than the meter can display on that scale.  You will have to switch to a higher scale setting, say 20000 (20K) to display a value that is within its range.  If you are on the highest scale and it still displays over range, then it probably has near infinity resistance which would include "open".

[HS]

I have to clear something up though.  Despite my having my head up my arse at times, the bike in my avatar is a 1972 CB500 Four...

Good to know.  However, I believe they share the same ignition components as the CB550, regardless of year.
Will it still "work" with 5K plug caps?  Yes.  Plug life will be slightly shorter, there will be some increase in power consumption and coil heating.

The Service Manual for the 500 I found here

http://www.sohc4.net/cb500-manuals/

Section 6 ELECTRICAL, IGNITION COIL, B. Inspection on page 89

Ok.  It says the same thing I am telling you, without the ohms values.  Measure primary leads and then measure secondary leads for continuity.

Continuity is the ability to conduct.   Resistance is what impedes conduction.  Both 5Ω and 15KΩ indicate continuity, infinite ohms, not so much.

It states to test continuity so I did with a CEN-TECH digital multimeter.  I'm reading ohms.

CEN-TECH makes several models of meters.  I can't tell from just the brand name, if yours is auto ranging.  But, if you have multiple ohms scales, then it isn't.

If you try to read 15000Ω on the 200Ω scale it will show an over range on the display (more than 200Ω), indicating the reading is higher than the meter can display on that scale.  You will have to switch to a higher scale setting, say 20000 (20K) to display a value that is within its range.  If you are on the highest scale and it still displays over range, then it probably has near infinity resistance which would include "open".

The multimeter was waaaaay more than I should have bought given my limited electrical abilities.  It was on sale...ugh.  I played around with the settings on the continuity setup and did get some different readings so you may very well be on to something.

The good news...and you helped motivate me not to just lay down on these coils...I've got SPARK!!!  I reset the gap on the breakers and cleaned them, then I took the coils apart, sanded all the contacts which were pretty crusty, used dielectric grease on everything....viola!  Big thanks for sticking with me.  I'm slow but I get there eventually....

Unrelated questions...I think.  When I turn the key to the on position, I get the Neutral light which is good.  I'm now getting an Oil Pressure light, though.  Is that normal without the bike running?  Oil level is fine and I'm wondering if I messed with something while I was unplugging the coils, etc...

Sam

[TwoTired]

Way to go sparky!   

The oil light relates to low oil pressure.  With about 7 lbs of oil pressure it should go off.  When the engine runs, it should go off, assuming a good pressure switch.

Proceed with resurrection!

[HS]

WINNING!!!!

I'll be looking to flush the tank and see if I can get her to run for a little while next week.  She's still got a lot of needs, but I'd love to see her purr if just for a bit. 


 

Sam

[goldarrow]

Oil pressure light might just need cleaning on the contacts, or may be bad bulb? The pressure switch is near front sprocket, and to get to that you need to remove the sprocket/clutch adjusting cover, and there lots of cleaning  down there.  Fun fun. 

[HS]

Oil pressure light might just need cleaning on the contacts, or may be bad bulb? The pressure switch is near front sprocket, and to get to that you need to remove the sprocket/clutch adjusting cover, and there lots of cleaning  down there.  Fun fun.

Thanks, GA. I'm hopeful it goes out once the bike is running, but if not I'll start peeling the onion...

Sam