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Undoing rotor nut/mainshaft

Hi

Checking norton commando 750 gearbox over, pulled mainshaft out completely. Mainshaft won't go back in through the clutch centre. Is there a way to do this?

Otherwise need to undo the rotor nut but no gearbox connected so no way to lock the primary chain to take the tension of the nut. It there a way to lock the crankshaft so the rotor nut can be undone?

Thanks

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Get piston or pistons to BDC. Remove spark plug or plugs and feed rope into combustion chamber that is due to fire next ie both valves shut at TDC, making sure a tail of rope for retrieval hangs out, you can then turn the engine over by the crank nut and you should be able to remove the nut.

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As long as the piston is coming up to the firing TDC both valves will be shut, no damage will be caused.

Previously andy_withers wrote:

Hi John

Thanks for this, it sounds as though it could work. Would the rope do any damage to the values?

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On the big twins the valves do not all fully close at TDC. There is always some overlap with one of the inlet valves coming open before TDC. Open up each of the tappet adjusters as far as possible. This will help close all of the valves earlier and help to get round this problem.

Also you will need more rope than you think due to it compressing.Probably about a skipping rope length and thickness for each pot. So about 2m x 8mm. Practise first on a bench or table top to see which way the rope curls round naturally. This will help to fill both sides evenly.

When dismantling my Atlas and desperate....I used a brass rod to wedge between the teeth of the sprocket and the alternator housing.

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A length of primary chain fitted round the sprocket and locked with a piece of round bar through the gap between links may do the trick. Good Luck

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Previously phil_hannam wrote:

On the big twins the valves do not all fully close at TDC. There is always some overlap with one of the inlet valves coming open before TDC. Open up each of the tappet adjusters as far as possible. This will help close all of the valves earlier and help to get round this problem.

Also you will need more rope than you think due to it compressing.Probably about a skipping rope length and thickness for each pot. So about 2m x 8mm. Practise first on a bench or table top to see which way the rope curls round naturally. This will help to fill both sides evenly.

When dismantling my Atlas and desperate....I used a brass rod to wedge between the teeth of the sprocket and the alternator housing.

Sorry, Phil. There is valve overlap at tdc on the exhaust stroke but they are fully closed at tdc on the compression stroke. Regards,

Dave

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I think the reason for Phils comment is he is filling both sides with rope.

I suppose it evens up the load.

Tony

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Quite right Tony......I rashly assumed that everyone else put rope inside both pots, as I have always done.....which of course you don't have to do.

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I first used it on a single, so when using it on a twin did not see the need to put the rope in 2 pots so stuck with the one.

The next logical step is to use the rope to keep the valves from dropping so you can pull the rocker shafts, compress the valve springs so you can pop the inlet valve seals back on or replace broken springs without the need to remove the head. It needs a specially designed tool but has been done on Twins.

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I shall need to inspect my rocker spindles, is there a previous thread on this? Bike is running nicely so I don't want to disturb the head unless essential, also I am lazy...

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What is the part number for the nut that holds the clutch on to the gear box (Laydown) shaft

 

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