Recessed nuts on crankshaft 71 750

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Akl52

Akl52

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Can anyone tell me the point of the two recessed nuts on my crankshaft, I’ve had the crank reground and the chap said he thought the crank had been assembled incorrectly previously, hadn’t had a previous grind but had been apart .
Thanks
Allan
 
He was right then as the two recessed nuts were on opposite sides of the crank.
 
That diagram has all studs , 4 short , 2 long, my 71 crank has 4 short bolts with 4 nuts, 2 long studs with 2 short nuts & 2 long nuts
 
Akl52 said:
any idea why they are recessed ?
Click to expand...

I don't know if there was an actual engineering reason behind it or not.

Akl52 said:
He was right then as the two recessed nuts were on opposite sides of the crank.
Click to expand...

There was a drawing in early manuals that showed the long nuts in the wrong positions so whoever rebuilt the crank perhaps used that drawing.

Akl52 said:
That diagram has all studs , 4 short , 2 long, my 71 crank has 4 short bolts with 4 nuts, 2 long studs with 2 short nuts & 2 long nuts
Click to expand...

Yes, that particular drawing shows the later (UNF) 'all studs and nuts' assembly.
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Your '71 crank would have had the (BSC or Whit form?) bolts and studs that you mention although either fastener set can be used.
andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Factory Spare Parts for Norton motorcycles built before 2002.
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With the recessed nut do I fit with recess to crank or to stud end ?
 
Ok thanks for that,
The Conrad’s on my engine have 2 nuts on each bolt , it seems only 1 locknuts is fitted now ?
 
Akl52 said:
Thanks , any idea why they are recessed ?
Click to expand...
The bolt circle is not concentric with the journal and so two of the studs/ nuts land more deeply in the large filet on the crank .
The spot face on the crank which provides the necessary flat for the nuts to bear on leaves a shoulder which the wrench must clear and so the need for longer nuts . These nuts originally were turned down some on one end in order that the nut fit in the spot face . The distance across the points is greater than the diameter of the spot face . When I reassembled my crank a few years back the new nuts from AN were not turned down enough and so the points fouled on the spot face before the nut could bear against the flat . Easy fix with a few minutes on the lathe but shouldn’t be needed. I informed AN about this . I wonder if some cranks had a larger diameter spot face . Anyone know ?
 
A check on a bolt or stud is to take a non locking nut of the same thread and run it up and down the threaded section on the bolt or stud. It should run up and down freely with no binding or notchiness, if not that indicates the bolt/stud has been stretched by over torquing or stresses in the engine and its gone into the plastic deformation zone of the steel. So its into the bin and order new ones.
 
Ok , the 2 nuts are on the new old stock replacement rods , normal nut to hold them together so the lock nut is just on by a few threads , obviously have to remove the “ extra spacer nut “ and fit the rods with the lock nut,
Thanks for all you replies
 
Richard Tool said:
The bolt circle is not concentric with the journal and so two of the studs/ nuts land more deeply in the large filet on the crank .
The spot face on the crank which provides the necessary flat for the nuts to bear on leaves a shoulder which the wrench must clear and so the need for longer nuts.
Click to expand...

That explains the reason for the additional length but not for the "recess" (unthreaded section) inside the nut which I believe was the question. It could make it slightly easier to centre punch I suppose?
andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk
 
L.A.B. said:
That explains the reason for the additional length but not for the "recess" (unthreaded section) inside the nut which I believe was the question. It could make it slightly easier to centre punch I suppose?
andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk
Click to expand...
Never realized that about the nuts . Once again thanks for the info Les . Perhaps it it is to prevent the nut from being installed backwards ?
I don’t know if it is an illusion but the photo from AN of the nut in question appears to have the flats convergent - i.e. not parallel in order to fit the spotface . I hope this is just an illusion because if not it is a terrible solution from an engineering standpoint as it minimizes the contact surfaces of the wrench ( spanner) .
 
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