N15CS head education

Think its due to the changes made as the bore increased and the engine became desaxis in order  to use existing crankcases . or something like that!.

Hello Richard - you don't say whether or not your donk has a spigot on the cylinder barrel.  I presume that you have top feeds to the rockers and 5/16 inch outer bolts to the barrel.  I say this because that casting you have is normally a Commando head with side feeds to the rockers and 3/8 inch outer bolts to the barrel.  You probably had a substitute head fitted when Norton machined up some of those early Commando heads as spares for existing models.  Also the Mercurys from 1968 used the same casting machined for 650cc.  As Bob said the engines, bigger than 650, were De-Saxe cofiguration - with the centre line of the head behind the centre line of the small-end/big-end alignment.  Have you considered a decompression plate between the cases and the barrel ?  Cheers, Howard

Yes, it is a squish band. And removing it will reduce the compression ratio, however one or more compression plates under the barrel would be a better choice:
https://andover-norton.co.uk/en/shop-details-2/20527/compression-plate-028-750-commando-atlas

2S cam does move the power up the rev range and works best with higher compression. A standard camshaft might be more suitable for your application.

Richard - I am inclined to agree with Stan. A standard SS  camshaft preferably with X1 stamped on it will give your engine the power it needs.  The X2 cam has the same profile but they do wear out quicker.  A later SS cam as fitted to the Mercury and fitted in the first Commandos will also be OK.  They usually have a overlapping RR cast into the cam and no hardness stampings.  Good luck.   Howard

Richard........your photograph shows a picture of a late AMC (Norton) 750 Hybrid or early Commando cylinder head. The casting number being 06 0380.  These were generally fitted on post-1967 models.
The Commando head had a side rocker spindle feed whereas the Atlas/Hyrid 750 heads used a top rocker feed.
I had JP pistons in my Commando 750 engine and the flat top versions were rated at 8.9 to 1 compression ratio. That is not to say you can't get high CR pistons but these are generally domed.

If you wish to lower the Compression the easy way just fit standard Atlas 7.5 to 1 pistons.  Hang a big 34mm single carb off the head and enjoy the bottom end poke when the throttle is opened wide.

As pointed out above......the shelf inside the back of the head arrived when the original 650 cylinder head was extended back by roughly 3 mm to allow for an increase in cylinder bore from 68mm up to 73mm.
R-shaping the combustion chamber, moving the valve guides and changing rocker arms, pushrods  and other chunks would have been expensive. So it did not happen.

Be careful, the 06.1084 cam is none other than the earlier SS cam which the grind had been around since around 1960. The 2S Commando cam is different. What is called the standard cams these days are the SS profile and it is a very good cam to use. We have the drawings and the grind data for most of the cams and a couple of EXP cams which show the history.