Britbike forum

Commando Mk lll lower head nuts

Posted By: Samsmc1

Commando Mk lll lower head nuts - 09/10/19 5:52 pm

I just ran into a situation that I don't understand. I hope someone can shed some light on this. I'm building a Mk lll engine from a pile of parts, therefore I didn't take it apart myself.
On installing the lower head nuts ( retrieved from a pile of 750 hardware), I'm finding that the box end Snap On and king Dick wrenches are not fitting the nuts as they screw further up the threads toward the head (OD of box end is interfering with the fins).
From what I can see, Norton used the same part numbers (old number to new number the same as listed in Mk lll book) for all their engines.
That said. I saw that Baxter shows a round nut with a smaller hex on it using the same parts number.
Did Norton change this nut at the end and maintain the same number or is Baxter selling an aftermarket part?
I'm not about to grind down good wrenches to make this work.
Did I miss something here?
Thanks
Sam
Posted By: L.A.B.

Re: Commando Mk lll lower head nuts - 09/10/19 6:33 pm

Originally Posted by Samsmc1
On installing the lower head nuts ( retrieved from a pile of 750 hardware), I'm finding that the box end Snap On and king Dick wrenches are not fitting the nuts as they screw further up the threads toward the head (OD of box end is interfering with the fins).


From what I can see, Norton used the same part numbers (old number to new number the same as listed in Mk lll book) for all their engines.
That said. I saw that Baxter shows a round nut with a smaller hex on it using the same parts number.
Did Norton change this nut at the end and maintain the same number or is Baxter selling an aftermarket part?


Yes, the factory did reduce the hexagon size and change the design prior to the 850 Mk3 (which is probably why there's no superseded part number listed in the Mk3 parts book as it happened earlier) so the earlier large hexagon sleeve nuts probably do cause clearance problems if used with later '850' barrels as you have found.

https://andover-norton.co.uk/en/shop-details/16029/cylinder-head-sleeve-nut-nm24260-nmt2034-
© 2020 Britbike forum