Cylinder base nut inquiry

BERT · Jun 5, 2021

I am renewing the base nuts on this 72. All part numbers came from the parts catalogue. The front center nut (different part no.) requires a different wrench size than the other 3/8" nuts. Can it be replaced with one of the others? The only difference I can see is it is a wee bit shorter. Also, why is there no washer required with this one? I am asking because I made a crowsfoot wrench to torque the nuts, and have discovered this front center one to be an oddball. Thanks guys in advance.

gforce · Jun 5, 2021

That front center nut is 1/4" Whit on pre-72 bikes.

Post-72 it was changed to 9/16" AF

I have also wondered about that washer - rightly or wrongly I always add one

grandpaul · Jun 5, 2021

BERT said:
The front center nut (different part no.) ...The only difference I can see is it is a wee bit shorter. Also, why is there no washer required with this one?

Because the book says so!

Onder · Jun 5, 2021

...keep in mind the thread form is different not just the hex size.

BERT · Jun 5, 2021

Onder said:
...keep in mind the thread form is different not just the hex size.

Yeah,its a mystery how a UNF thread pattern takes a Whitworth wrench on 6 of them, and the oddball at the front center takes a 9/16 wrench. Another unanswered question and further wonder about these great machines.

BERT · Jun 5, 2021

I was thinking maybe there could have been a reason, or maybe not...

texasSlick · Jun 5, 2021

BERT said:
I was thinking maybe there could have been a reason, or maybe not...

Sometimes there is a very good scientific engineering reason for something like this, that only the most esoteric investigators are aware of ..... sometimes they just wanted to use what they had.

Slick

BERT · Jun 5, 2021

texasSlick said:
Sometimes there is a very good scientific engineering reason for something like this, that only the most esoteric investigators are aware of ..... sometimes they just wanted to use what they had.

Slick

Maybe that was a time necessary to count nuts and bolts for survival.

BERT · Jun 5, 2021

Yeah, and it would be nice to attach one cylinder to one crankcase with one torque wrench with only two different size wrenches instead of three. But even so, this machine is putting a big smile on my face.

seattle##gs · Jun 6, 2021

similarly, I wish Norton had used the same size nuts on the crankshaft and the clutch. One wrench instead of two.

Onder · Jun 6, 2021

Later, and that can be a pretty broad limit, British bikes were hardly a clean sheet of paper design. If the oriental imports had been delayed another ten years the fasteners likely would have all been changed to Unified not metric. USA market was the big
thing at the time.

Carl H · Jun 7, 2021

BERT said:
I am renewing the base nuts on this 72. All part numbers came from the parts catalogue. The front center nut (different part no.) requires a different wrench size than the other 3/8" nuts. Can it be replaced with one of the others? The only difference I can see is it is a wee bit shorter. Also, why is there no washer required with this one? I am asking because I made a crowsfoot wrench to torque the nuts, and have discovered this front center one to be an oddball. Thanks guys in advance.

The front base odd ball nut can be torked as is with a socket and an extension that is long enough to clear the cylinder. But I think all the nuts and bolts used on the cylinder base and head were just wrench tightened at the factory and the same way by most all dealers and owners after that.

L.A.B. · Jun 7, 2021

BERT said:
Yeah,its a mystery how a UNF thread pattern takes a Whitworth wrench on 6 of them, and the oddball at the front center takes a 9/16 wrench. Another unanswered question and further wonder about these great machines.

Do 9/16AF nuts actually fit without clearance problems?
I'd guess that as the 1/4 Whitworth hexagon size (0.525") is smaller than 9/16AF (0.563") the Whitworth hexagon size was retained where nut to barrel clearance is possibly tight but which didn't include the front nut.
A UNF threaded nut with a Whitworth hexagon (and taller than standard) would almost certainly have been a special (therefore probably more expensive?) so wouldn't have been used unless they thought there was a good reason for doing so.

texasSlick · Jun 7, 2021

L.A.B. said:
Do 9/16AF nuts actually fit without clearance problems?
I'd guess that as the 1/4 Whitworth hexagon size (0.525") is smaller than 9/16AF (0.563") the Whitworth hexagon size was retained where nut to barrel clearance is possibly tight but which didn't include the front nut.
A UNF threaded nut with a Whitworth hexagon (and taller than standard) would almost certainly have been a special (therefore probably more expensive?) so wouldn't have been used unless they thought there was a good reason for doing so.

Yeah! Just as I said above ...... there are usually sound scientific engineering reasons for something like this, but ONLY an esoterically astute investigator can reason it out.

Slick

BERT · Jun 7, 2021

texasSlick said:
Yeah! Just as I said above ...... there are usually sound scientific engineering reasons for something like this, but ONLY an esoterically astute investigator can reason it out.

Slick

I don't really care why it is different. Just trying to get away with not welding up another crowsfoot adapter if one of the other nuts would work. Either way, not a problem.

Cylinder base nut inquiry

BERT

gforce

grandpaul

Onder

BERT

BERT

texasSlick

BERT

BERT

seattle##gs

Onder

Carl H

L.A.B.

Moderator

texasSlick

BERT

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