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Author Topic: Lister RS1 Magneto short circuit to casing  (Read 661 times)

Big G

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Lister RS1 Magneto short circuit to casing
« on: March 14, 2024, 01:55:05 PM »
I hope that someone can help me.
I have just commenced the restoration of my 1950 Lister D 1.5 HP (after a 15 year wait!) and am now on the magneto. I have stripped everything down, cleaned all parts and replaced points and condenser. There is no spark or any sort of output so I suspected the coil. Before replacing this, however, I thought that I do a simple continuity test to check that the moving points were insulated from the magneto body via the insulated fixing post to the condenser and coil.  Well, wherever I put the tester probes it indicated continuity. I checked all the insulating washers etc and all ok. This brought me to the large bakelite insulating block on the inside of the body and the corresponding screw on the outside front at the top. I have looked through all the information I can find on these magnetos but no mention of these parts.
Mine had a large blob of solder which covered the back of the fixing post for the oval plate that holds the moving contact in place and also the back of wherever the screw on the front goes. I thought this looked wrong and removed the solder. I then discovered that I could not tighten the nut securing the oval plate because the post just revolved round - the solder had been holding it in place. I replaced the solder as it was and now total short circuit. I am fairly certain that the problem lies in the bakelite block but I can find out how it's put together or how it's meant to look.
My apologies for the long ramble but any advice would br greatly appreciated.

Big G

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Re: Lister RS1 Magneto short circuit to casing
« Reply #1 on: March 17, 2024, 02:22:45 PM »
The problem is now resolved! As suggested, I managed to completely dismantle the bakelite block and it's various components. It's not that straightforward as the end of the fixing that protrudes on the outside of the front, is piened outward to hold the felt washer in place. The other end of this is a hex head, held in place with a tab washer. I had to remove all of the felt washer and any of the remaining bent over bits. I also had to cut a slot in the hex head to get more purchase. The part is smooth on the outside and threaded internally to take the screw at the front. The hole in the casing has an insulating tube, which together with the felt washer stops any short circuit from the brass tab through the body....... well in theory anyway! I had to remove the remnants of the end that had held the felt washer and in doing so, lost most of the protrusion beyond the front of the casing. I also had to straighten the end and re-tap the internal thread. With all the parts out, it was easy to re-solder the fixing post for the points to the brass plate. I used a sticky felt pad (used for furniture legs) with a hole punched in it and an insulating washer, brass washer and spring washer, so I could tighten the whole thing and still keep it insulated from the body. I re-tested for short circuits and all now ok. The cherry on the cake was putting the whole mag back together with the original coil and getting a spark from casing to coil via a bit of brass wire when I spun the rotor.

cobbadog

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Re: Lister RS1 Magneto short circuit to casing
« Reply #2 on: March 19, 2024, 10:23:36 AM »
Well done to you for resolving the problem. Im not sure what it is you did so if you have a pic or two that may help my small mind put it together.
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cobbadog

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Re: Lister RS1 Magneto short circuit to casing
« Reply #3 on: March 20, 2024, 10:10:34 AM »
Well done to you for resolving the problem. Im not sure what it is you did so if you have a pic or two that may help my small mind put it together.
Coopernook - the centre of our Universe.