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Dolls head mainshaft bush.

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On the mainshaft, directly in front of the main drive sprocket securing nut , I have a bronze bush. It would butt up against the back of the clutch centre. It's about half an inch wide. I cannot see it only any parts diagrams. Wondering should it be there or has someone randomly added it? Many thanks .

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Hi Nick,

   Is this bush separate or is it fixed in the sprocket ? If it is fixed, what might have happened here is the bush has migrated out of the top gear/sprocket driveshaft, which is quite common. This should be level with this, so has moved out that much. This is caused by the side pull from the engine which gradually draws the bush out when under acceleration etc. As a quick fix and if the bush is not too worn, see if you can pull the bush out further but not right out using a rubber grip and then clean the out side of the bush with a brass brush, a suede shoe brush is good, and give it a good rinse with acetone or methylated spirit. Get the relevant grade of Loctite and a suitable close fitting tube and gently tap it back level. Make sure no Loctite gets on the mainshaft or inside the bush and check the shaft is free during the setting time, then leave over-night before reassembling. Ideally it will be good to fit a new bush using Loctite again, but you need to strip the gearbox completely to make sure of doing a good job.

Thank you Richard to your very useful response. The Bush is still in the sprocket and is flush. This bush I'm referring to, if it is indeed a bush , looks very much like an olive that you would use on Cooper pipe in central heating etc but with no chamfers on the edges. It's is bronze however. On the main shaft just beyond the spline , the mainshaft just in front of the sprocket, on mine at least, is just smooth for about qtr inch or so. This bush fits onto the smooth part of the mainshaft so is entirely separate rom the Bush you refer to. It literally would come into contact with the back of the spline on the back of the clutch centre. I'm just not sure if it should be there or should the clutch just go straight onto mainshaft. Also this bush thingy slides of the mainshaft easily so is not fixed in any way. Any more thoughts would be very helpful. Nick.

Hi again Nick,

   The clutch hub deliberately wedges into the lead-out of the groves in the mainshaft when tightened up, which is not ideal but has worked O.K. for decades. The clutch cannot be tightened up against this bush as this would make the clutch redundant, so I guess someone has fitted this for one of the following. #1 To stop the previously mentioned bush from coming out as per my earlier post. #2 To take up any end-float on the mainshaft, which is a bit misguided. #3 Simply to keep the exposed shaft clean from any road dirt. I guess by all of this you don't have the sliding round plates on the inner chaincase, which is not a big problem. Check the mainshaft end-float which shouldn't be much more than 25 thou. (.025")

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This sounds like the very similar feature found in a Rudge alloy chaincase to seal the case and also provide a way of keeping a gearbox seal in position.

That makes perfect sense Richard. End float is ok. I would say either I or 2 in your possible reasons would seem most likely,  I hope. Truely appreciate you taking the time to advise me. Fond regards. Nick. 

 

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