Norton Atlas Barrels (Head Bolt Threads)

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Jul 16, 2020
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HI Guys.
I am new to the group and this is my first rebuild (1966 Norton Atlas)
The original Barrels had been bored to the maximum and there was evidence of the sleeve breaking away causing internal damage. I had sourced some new / second hand barrels in great condition , i bored them out +20 and have the oversized pistons and rings.
Just doing a dry fit of the barrels and head before assembly and noticed the threads for the head bolts to the barrels are a larger size ?
Is there a difference in the threads on various models?

any advice would be greatly appreciated .
Thanks
Dave
 

L.A.B.

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Just doing a dry fit of the barrels and head before assembly and noticed the threads for the head bolts to the barrels are a larger size ?
Is there a difference in the threads on various models?
If 3/8" diameter (3/8 x 26) then they are Commando barrels.
 
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The 3/8 head bolt was introduced in late '66 or 67, I have a '66 Atlas & 650SS which are within 100 numbers of each other 119XXX the Atlas has 5/16 bolts where as the 650SS has 3/8, I have previously owned a P11 with 3/8 head bolts [ by this I mean the 2 bolts closest to the spark plugs on each side]
 
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The 3/8 head bolt was introduced in late '66 or 67, I have a '66 Atlas & 650SS which are within 100 numbers of each other 119XXX the Atlas has 5/16 bolts where as the 650SS has 3/8, I have previously owned a P11 with 3/8 head bolts [ by this I mean the 2 bolts closest to the spark plugs on each side]
Aha ... that explains it then .. looking on the Andover Norton site for a new Bolt kit and they don’t specify sizes ( just bolt kits up to engine number xxxxxx and From engine number xxxxxx i would assume then the 3/8” engine bolt kit would be the later numbers.
Thanks for the advice :)
 

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