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B31 - Hot coil problem
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MylesB
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June 30, 2020 - 9:39 am
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 As well as my Bantam's I have an Alternator 1959 B31 BSA which has developed a fault as follows:- it starts up ok and rides fine for about 2 miles then the engine splutters and loses power then stops. After a cool down period I can get it going again and limp home. The coil is getting really hot and I think that is the problem. I have replaced the coil with a new one but same problem. I have checked the earth from battery to frame which was high at 38 ohms and I have fixed the earth connection so that is now zero ohms. I have checked the wiring and removed the additional wire from coil to ignition switch so now the only connections to the coil is -12v from ignition switch and the output to the points. The points look good and there is no sparking on engine running. It has been previously been converted from 6v to 12v with a Wassell Rectifier/regulator. Does anyone have any ideas what else I could try??

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sunny
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June 30, 2020 - 10:23 am
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i  think   youv  a  problam    in  the  new  12Vt  system   so i  would refit  6 Vt  stuf   &  see  if  its  doing  the same  on that   ,.,. then  rewier  the  12 Vt system   

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dienelt1
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June 30, 2020 - 10:26 am
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  Is the coil 12 volts?

 

  Diene.

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cocorico
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June 30, 2020 - 10:39 am
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The coil would normally get warm in use, but if it's getting really hot, to me that implies a connection to earth or something like points not opening properly. If you can hot-wire it (ie isolate everything from the ignition system, connect the battery to one side of the coil, points to the other, preferably through a fuse), you should be able to see if it is a problem with points / condenser or not. If that cures it, look at the loom.

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MylesB
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June 30, 2020 - 4:02 pm
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Thanks for the replies chaps. It has been running on 12v for 18 months with no problems. The coil is 12v and so was the new one I just fitted. Having said that it went away for repair after a car driver knocked it over for 6 months and the garage did say that the coil had burnt out just before they were going to deliver it back to me last January and they had to fit a new one. I said that maybe someone had left the ignition switch on by accident and they agreed. I had 3 rides out without incident then on the 4th ride it broke down with this problem.  I will have a go with Cocorico's suggestion to hot wire it direct and see what happens.

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dienelt1
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June 30, 2020 - 4:26 pm
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could it be a coil that needs a ballast resistor, 1.5 ohms or 3 ohms or about ,non ballast type.

  Diene.

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mike p5xbx
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June 30, 2020 - 4:56 pm
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Have you tested the battery voltage after the engine has been running for a few minutes
I not a great lover of regulator/rectifiers, they seem to be related to Sheep rolleyes

D? - D10- D14 Bantams 350 AJS -500 Triumph http://bsanotru.....lfire.com/

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Peterg
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June 30, 2020 - 6:56 pm
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When mine burnt out it took the condenser too. Check the voltage when running. It could be the controller is allowing too much current through.

When not moving the coil will get hot. Very hot if the engine is not running. Otherwise it is a pretty fool proof system.

Might be a bit of bad wiring, it often frays around the steering neck causing a periodic short.

Being a 4 wire controller you might consider making it negative earth. Just needs the battery turning around and the red connected to brown and black to earth.

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cocorico
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June 30, 2020 - 8:59 pm
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Peterg said
...Very hot if the engine is not running....

Surely it will only overheat if you happen to stop with the points closed, if they are open there should be no circuit. But the stop point is not something to bet on!

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Lone Wolf
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July 1, 2020 - 1:24 am
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Wotcha.

I've got an ** Please log in to view ** - converted to 12 volt.

Is it actually an electrical fault ?   Double check your valve clearances - if anything have them a tad more than the book says just to eliminate them. 

Change things one at a time - start with the spark plug.  You'd be surprised how many times a plug can play up.

It seems odd that it will run once it has cooled down - electrical faults tend to be either "on or off" as a rule, especially with a coil ignition model.

 

I once left my ignition on and a battery charger connected - came back into the garage a few hours later and there was a pool of oil under the bike.  It had cooked the coil and forced the oil out of it.  Thinking I now have a dead coil, I tried to start the bike just for the hell of it . . . .and it started.  Ah, I thought, best change the coil first chance I get . . . . that was about eight or nine years ago and I still ain't done it.  A hot coil doesn't necessarily mean it's had it.

^..^

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mcafee
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July 1, 2020 - 10:28 am
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Morning I have had a similar problem with my Greeves,it start fine run ok until it got hot then started to miss and finally stop,but would start ok when cold.My problem was rectified by changing the condensor.

Good luck   David

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