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#675200 - 11/22/16 12:36 pm coil checking  
Joined: May 2006
Posts: 148
TriVin Offline
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TriVin  Offline
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Joined: May 2006
Posts: 148
Warrington, Cheshire, UK
Hi

I've been experiencing intermittent ignition failure with my Comet. It's fitted with a Boyer. It can just die when warmed up. It will refuse to start again until it's cooled down and then we are off again.
I am in the process of checking all the connections etc but now I'm checking the coil with my meter. I'm getting 4 ohm on the primary and 7000 ohms on the secondary. Trouble is I don't know what it is supposed to be! Of course since it only happens when warm this may be a waste of time and swapping it for another may be the best option anyway. But I'd like to know anyway.
It could be the Boyer it self of course!


Dave
Tiger 100SS 1966
T120V 1972
Vincent Comet 1952
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#675207 - 11/22/16 2:12 pm Re: coil checking [Re: TriVin]  
Joined: Sep 2013
Posts: 1,583
quinten Online content
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quinten  Online Content
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Joined: Sep 2013
Posts: 1,583
Pacific northwest

Your cold coil figures are reasonable , but there is much more to a coil than simple ohms .

Try testing the coil when its hot and failing ,
against the baseline figure you have established for the 'cold' coil .

.

#675236 - 11/22/16 6:09 pm Re: coil checking [Re: quinten]  
Joined: May 2006
Posts: 148
TriVin Offline
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TriVin  Offline
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Posts: 148
Warrington, Cheshire, UK
OK. The next time I go out I'll take my meter with me. In it's failed state, if it is the coil, what should happen to the figures? Go up or down?

Last edited by TriVin; 11/22/16 6:10 pm.

Dave
Tiger 100SS 1966
T120V 1972
Vincent Comet 1952
#675318 - 11/23/16 10:11 am Re: coil checking [Re: TriVin]  
Joined: Dec 2004
Posts: 8,890
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,890
Scotland
Could go either way, a short to the outer casing or a break that opens up when hot. If the primary drops below 3 ohms the Boyer will overheat and stop sparking, I had that once, a new coil fixed the Boyer.

#675341 - 11/23/16 1:48 pm Re: coil checking [Re: kommando]  
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quinten Online content
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quinten  Online Content
BritBike Forum member

Joined: Sep 2013
Posts: 1,583
Pacific northwest
Originally Posted By TriVin
OK. The next time I go out I'll take my meter with me. In it's failed state, if it is the coil, what should happen to the figures? Go up or down?


The coil should read the same hot or cold .
Any change in value would be suspect .


As an example , (If the coils primary was 20ga.)
394 ft. of 20g 'mag' wire would have a resistance of 4 ohms , whether it was coiled or not .
But if it were tightly coiled and some part of the coil
shorted against itself , some effective lenght would be lost ... and resistance would go down in accordance with how much wire , (how many turns ) , are lost . There is still a circuit , but now of shorter length .
The 4 ohm coil might now read 3 or 2 , it would saturate more quickly , overheat and not deliver the inductive kick necessary for the secondary to
Reach its full capacity ... and while doing so , perhaps strain the output switching capacity of the Boyer box ( kommandos coil )

Or the coil could short to its metal housing ... there would be unwanted continuity to ground . ( this short can be metal on metal or may only be an inductive short , an internal spark path that worsens as small conductive carbon traces are layered in ) ... the coil may still work if the 'can' is insulated from ground ?


Or what ive seen a few times , as the coil heats up , this wire that was at one one time continuious , opens up , somewhere in its tighty wound 400 ft , enough to lose all continuity ... an open circuit . In this instance , the reading would go from the 4 to zero .
... and these same faults could happen on the secondary side ... or between the 2

While you're at it ;

The Boyer stator also has 2 small coils . There are a few , small handful ? ,
Of reported instances of one of these
Coming loose .
Their total ohms can be easily checked . There is no need to check them
Individually unless a problem is found ... off the top of my head , the reading is 137ohms ... thought there may be different readings for different production years .
And the stator 'good' if it is 'in the range'.

Sorry for being so long winded , as this appears to make the problem bigger than it is .
.

#675343 - 11/23/16 2:04 pm Re: coil checking [Re: quinten]  
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Posts: 148
TriVin Offline
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TriVin  Offline
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Posts: 148
Warrington, Cheshire, UK
OK. I'll keep you posted.

Thanks


Dave
Tiger 100SS 1966
T120V 1972
Vincent Comet 1952
#675422 - 11/24/16 8:04 am Re: coil checking [Re: TriVin]  
Joined: Nov 2007
Posts: 112
Twin Pot Phil Offline
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Twin Pot Phil  Offline
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Posts: 112
Birmingham, UK
Hello Dave,

Try getting the coil hot in the garage - aim a hair dryer at it until the (back of) casing is 'on a run' hot enough through. You can then test it more easily.

There also seems to be some discussion elsewhere (can't remember exactly where) about Boyers being sensitive to battery voltage and getting grumpy.

#675465 - 11/24/16 1:21 pm Re: coil checking [Re: Twin Pot Phil]  
Joined: May 2006
Posts: 148
TriVin Offline
BritBike Forum member
TriVin  Offline
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Joined: May 2006
Posts: 148
Warrington, Cheshire, UK
Hi Phil, it's been along time since we met. I retired from that Coventry job back in 2012 so have not been going to any of those car club meets.
I'll try that hairdryer trick and see what happens. As you suggest it could also be the battery/Boyer playing up as well. I'll try switching the battery to one off my other bikes and see if I get different outcome.
I suppose it could just be Boyer itself packing in through old age. It's been on the Comet since 1998. Not mounted in the coolest of positions either. But never given any trouble before.

cheers


Dave
Tiger 100SS 1966
T120V 1972
Vincent Comet 1952

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