Magneto nuts

seattle##gs · Oct 30, 2022

I do not have the pieces in front of me...I would like to replace the top two magneto nuts with a longer nut to make it easier to put a wrench on them. I think the Atlas had a cylinder stud up front that takes the same diameter nut and is a british thread. Is it possible to use those nuts for the top two magneto nuts?

kernel65 · Oct 30, 2022

Both are 5/16 BSC.

robs ss · Oct 30, 2022

There is another type of Magneto Nut - @ashman, but I think he's lost his thread! (boom boom!)

texasSlick · Oct 30, 2022

It is the bottom nut that is the bitch, at least prior to 1965.

It has been suggested by someone on this site, to rethread 1/4
BSC nuts to 5/16, or rethread 1/4-20 to 5/16 BSC . The spanner for the smaller nut will be easier to negotiate in the limited space behind the magneto. The reduced strength of the rethreaded nut is of no concern ...... the nut does not require much strength to hold the magneto flange.

Slick

robs ss · Oct 30, 2022

texasSlick said:
It is the bottom nut that is the bitch, at least prior to 1965.

Slick

I bought this somewhere (may remember soon?) but it still wasn't waisted enough to clear the crankcase flange, hence a bit of fettlin' in the middle.
Works very well with the spanner hex under the LHS of the magneto.
Probably not too hard to copy.
Cheers

EDIT: for those who may want to go this route it is 150mm long, the middle 20mm is waisted down to 5.7mm (trial & error until it cleared the flange.

seattle##gs · Oct 30, 2022

for the bottom bolt and nut I plan to use a 5/16 american allen button head and an ARP 12 point nut...I believe it takes a 3/8 wrench. I hope I can make a 3/8 obstruction wrench do the job. I've already done similar to that on an Atlas special, the allen is much easier to tighten but I used a standard nut on the backside which is a real bear. It takes a 1/2 wrench...doable if you have an hour or two and infinite patience. My theory is that the ARP nut will solve that problem.
Thanks for the info, I will order four of the brit nuts.

texasSlick · Oct 30, 2022

@robs ss

That nut is usually referred to as the BSA Long Nut. Upon looking over my Atlas, it sure does not look like it will clear the cases, but kernal65 assures me that it does .... at least on an Atlas.

I plan to go with the rethreaded smaller nuts should I find it necessary to pull my mag again.

Slick

texasSlick · Oct 30, 2022

@seattle##gs

I am not sure I follow your plan. I may be wrong, but from what I gather, you plan to do a mod similar to what Norton did in the 65 and later models. They replaced the lower stud with a thru bolt fitted from the timing case side.

I looked over my Atlas with the intent to do the same, but concluded some machine work would be necessary, the very minimum would be to spotface the area under the bolt head. Your plan to use a cap screw might alleviate the spotface, but some machining will still be in order. You must also provide clearance for the mag drive chain to pass over the head of the cap screw.

Keep us informed how it works out.

Slick

seattle##gs · Oct 30, 2022

The cases are of unknown vintage, belonging to someone else. If I remember correctly I just lightly drilled out the threads so I could use an american bolt. No spot facing, no washer. The head of the bolt sits flush to the case. I gooped the bolt with Yamabond and there were no leaks. However, I did not have a thinwall nut so the current nut requires a 1/2 wrench. There is just barely enough room for the chain. Access to the head is best done with a ball driver.

kernel65 · Oct 31, 2022

texasSlick said:
@robs ss

That nut is usually referred to as the BSA Long Nut. Upon looking over my Atlas, it sure does not look like it will clear the cases, but kernal65 assures me that it does .... at least on an Atlas.

I plan to go with the rethreaded smaller nuts should I find it necessary to pull my mag again.

Slick

I used a BSA extended nut (67-1259) on my 99 Domi magneto without issues. My Atlas is a 65 with the improved design.

Might be a tighter fit on the larger Atlas cases?

texasSlick · Oct 31, 2022

kernel65 said:
I used a BSA extended nut (67-1259) on my 99 Domi magneto without issues. My Atlas is a 65 with the improved design.

Might be a tighter fit on the larger Atlas cases?

Begging your pardon, Scott, when we discussed this I was on an Atlas wavelength!

Slick

texasSlick · Oct 31, 2022

I feel that I have contributed to confusion regarding the BSA Long Nut.
To clarify:

robs ss has put one on his 650SS by turning down the center section
Kernal65 has put one on his Dommie 99 with no problems
The Long Nut MAY NOT clear Atlas cases.

Slick

Magneto nuts

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