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lightweight rotor size

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Working on an Electra that was pulled apart by a Norton dealer in Kansas many years ago so things could be a bit mixed up. With the engine mainly finished I am now looking at the primary drive. With the sprocket and rotor on the engine shaft I find they overhang the end of the shaft by about 1/4 in, this prevents the dogs in the starter engaging. I think the sprocket is the correct one but not sure on the rotor. The rotor is 1  1/4 in wide the part no on it is 06720 which is different than the one in the Norton book. If this is the wrong rotor what are the options. The stator is also very rough. Does Lucas make any replacement.  Bryon   

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There was a thinner rotor made for the Triumph Tiger Cub, this may be another application for that rotor. On my search for one there were no new replacements around so I bought an NOS one with keepers in place so good magnetism. I will measure it and give you the part number later.

 

The one I have is Lucas number 54212284

28mm wide at steel core, 25.4mm wide on rest of alloy/magnet body

3/4" bore which is the issue for you using it.

74mm OD (very close to 2 15/16")

So your issue is the bore if it is 1" and the width of the steel core would need trimming.

A O Services in the UK can re-magnetise a rotor if you can get hold of one with the right dimensions 

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Good morning Byron,

The Electra was fitted with a Wipac alternator. The dimensions of my Electra rotor are:-

2 15/16'' overall diameter

1'' bore

1 3/8''central boss width  (the rotor width is 1 1/4'' )

 

 The Norton part no is S0374. My rotor has part no 06720 cast onto the body which I assume to be the Wipac part no.As far as I am aware there isn't a Lucas equivalent.

Frank Anderton

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Hi Byron,

The Electra engine sprocket width is 15/16'',if your sprocket is the same then perhaps the woodruff key has rotated a bit when you fitted it onto the crankshaft taper and it is preventinf the sprocket seating far enough onto the taper.

Frank Anderton

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Byron,

I agree with Frank. It is almost certainly the woodruff key for the engine sprocket being pushed backward in it's slot and rotating up the back of the engine sprocket.

You need a nimble finger behind the engine sprocket as you push it on. Feel the back end of the key and it should not be pushed upward. I am assuming you have the keyway at 12.00 o'clock while pushing on the sprocket.

Have a practice assembly without keys to prove the case.

Peter

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On behalf of the OP I feel obliged to point out to contributors that his name is BRYON, not Byron. I have no doubt that Bryon is too polite to make an issue of it himself but, nonetheless, he must be a little fed up by now!

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Hi Bryon,

If you are fitting a new woodruff key,perhaps the new key is a bit too wide and is preventing the engine sprocket going fully home on the taper,try assembling the sprocket and rotor without the key and then carefully file the top of the key to suit.

Frank Andertton

Thanks every one for the help. I now know the rotor is correct.  The sprocket appears to be the problem. I have a spare crankshaft which makes it easy to work on. I used a hammer to send the sprocket fully on, there was about 20th gap between sprocket and shaft on the nearside on the back you could still see the key way. Wrong taper being the problem. That is why the Woodruff key from NOC was no good and the new chain was very tight. I believe NOC might have one Bryon

 

 

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Good news about the rotor Bryon, just a thought about the woodruff key - I bought one from NOC last year when I replaced my Navigator primary chain and although it fitted in the crankshaft and sprocket slot it was too big and I couldn't get the sprocket fully on with similar problems to you.  I was lucky enough to have the old key which I compared to the new one and rrealised the small difference in dimensions.   In the end rather than try to file down the new one to fit I decided to clean up the old woodruff key and used it again and it fitted perfectly and has been fine ever since.   I hope that helps!   Nick       

 

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