Ht cable routing

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Ht cable routing

Postby Steve Harding » Thu Feb 27, 2020 6:57 am

Can anyone tell me the correct route for the HT lead. I'm going back to magneto ignition and taking the electronic ignition off.
The magneto as the shield with 2 holes in

Thanks

Steve

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Re: Ht cable routing

Postby Rob Harknett » Thu Feb 27, 2020 10:04 am

One hole may be for the A/R cable, the other the plug lead. If the holes look too big, I believe that's so a rubber grommet can be fitted, so metal does not cut in cables. Plug cap should fit with cable exit pointing to the left, not mid way towards the front, so a short cable cable touches the barrel, or long falls down on it. Mag end of lead should easily enter the mag. Plug lead route should avoid cylinder and pipe. The lead should not be too long or short to prevent this. If that all looks good you have found the best route.

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Re: Ht cable routing

Postby Steve Harding » Thu Feb 27, 2020 4:18 pm

Thanks Rob,
does it run up the front tube and come down under the tank?

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Re: Ht cable routing

Postby SPRIDDLER » Thu Feb 27, 2020 5:45 pm

Mine goes forward from the mag, tightly held through a grommeted hole in the mag splash plate and around the front of the frame tube. Looking now it seems a long route but it's been O.K. like that for 25,000 miles through a lot of torrential rain ….I've never given the routeing of it much thought.

HT lead route.JPG
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Re: Ht cable routing

Postby Rob Harknett » Thu Feb 27, 2020 7:11 pm

Sorry but I would not like the plug lead wrapped round the down tube. I use a rubber figure of 8 type tie to secure the speedo cable to the down tube. I don't think you could go that route with a splash guard fitted. I would not run it under a tank full of petrol tank either. If water get's in and the cable is wet. It will conduct the spark running through the water on the outside of the lead. I once had a BSA A10, mag behind the engine. Carb started to catch fire on starting??? One wet night I discovered why. I saw a blue spark like morse code - - - - - - - along the outside of the lead. It set a light petrol that had dripped when flooding the carb on the plug lead.
Having said that, look how the lead is drawn on this 1953 sales cat.
Ashampoo_Snap_27 February 2020_19h14m45s_001_.jpg
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Re: Ht cable routing

Postby Stan Palmer » Thu Feb 27, 2020 8:44 pm

Sorry to diverge a bit. That bare connection on the sales photo took me back to my 1st bike. A hand change fanny bee. The gear lever was like a car one, straight up out if the gearbox. when you changed to top your knuckles were right next to the HT connection. If it was raining you always got at least a few shocks before you could whip it away. Strangely I put up with that all the time I had it and so did the next two owners, both school friends. We still laugh about it.

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Re: Ht cable routing

Postby spookefoote1956 » Fri Feb 28, 2020 1:17 pm

How come you're ditching the lecky ignition; what type is it? :? :?
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Re: Ht cable routing

Postby Group Leader » Fri Feb 28, 2020 6:30 pm

Mine was routed incorrectly when I purchased it (i.e. not as originally intended by the manufacturer) I know. I have to say, it the route does seem entirely sensible to me; the magneto connector is facing aft not forward so water would have a hard job entering it irrespective of shield or no shield and the cable length is such that it doesn't touch anything other than the HT cap and the Magneto connector.

What's not to like?

Alan

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Re: Ht cable routing

Postby SPRIDDLER » Sat Feb 29, 2020 3:21 am

Group Leader wrote:….the magneto connector is facing aft not forward

Mine faces forward (1954).
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Re: Ht cable routing

Postby Steve Harding » Sun Mar 01, 2020 12:00 pm

Thanks for the suggestion. Going back to mag so not reliant on battery. It is a thorspark I am removing

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