Cylinder Head ID ?

I received this cylinder head in a bunch of Norton parts a while back. I’m not sure what it is for. It appears to have at least the intake ports heavily modified and the exhaust ports opened up as well. It has a casting number 25316 on the bottom and the number 7 cast into the top, there is also a small “V” stamped into the top.
Some dimensions:
Intake ports 35mm, Exhaust ports 36mm,
Intake valves 1 1/2 inches, Exhaust valves 1 3/8 inches, carb/manifold stud spacing is 2 1/4” and the stud holes are tapped to 8mm x 1.0.
The rocker arms appear to be unmodified.
I believe the head is for an 650SS or Atlas by the casting number but am not sure.
Any ideas? Beginnings of a race head with splayed Japanese carburetors?
Thanks,
JVigs

I'm no expert but have that same head by the Part #, mine is mated to an ex-spigoted (but now milled flat) barrels. It's 25319 not 25316 right? That's what the pic shows.

http://atlanticgreen.com/nhth.htm says:

"This is the late Atlas head 25319. It has the same combustion chamber and squish band as the 750 commando (no provision for a spigot)" Has top oil feed and looks like mine anyway.

Yes 25319. I shouldn’t read numbers upside down…
Are the Atlas ports splayed or straight like a Commando?

More than likely was modified for the purpose you are thinking of. Rubber spigot mount for Mikuni carburetors. Back in the olden days nobody was making Atlas manifolds for Mikuni carburetion. MAP now makes a single Mikuni manifold for straight up motors.

My original P11 head is a 25319 with flat intake mounts for Amals with 1/2 inch aluminum intake manifolds. Talk about carburetors getting hot. Lock up the slides in Amals in no time. I made my own spigot intakes for Mikuni carburetion from MAP Commando intakes for Mikuni's. Then later made manifolds for Keihin FCRs from standard Commando MKII spigot intake manifolds. Tedious stuff, but well worth it in my opinion. Depends on what one likes.

Thank you for the info. I found there are rubber spigot mounts available with 57mm mount spacing which is close to 2 1/4”. I’m still wondering about the size of the ports. They seem huge for stock valve sizes. Are they standard for an Atlas head?
JVigs

JVigs said:

Thank you for the info. I found there are rubber spigot mounts available with 57mm mount spacing which is close to 2 1/4”. I’m still wondering about the size of the ports. They seem huge for stock valve sizes. Are they standard for an Atlas head?

Click to expand...

No, of course not. Standard inlet ports for 25319 heads are 28mm.

JVigs said:

Are the Atlas ports splayed or straight like a Commando?

Click to expand...

Ports are straight (parallel).

- Knut

Schwany said:

My original P11 head is a 25319 with flat intake mounts for Amals with 1/2 inch aluminum intake manifolds. Talk about carburetors getting hot. Lock up the slides in Amals in no time.

Click to expand...

Thanks to the inventive work of member Vecu, we have an option which will work better than the OEM set-up. I grabbed the idea immediately for my N15CS restoration project.


- Knut

mdt-son said:

Thanks to the inventive work of member Vecu, we have an option which will work better than the OEM set-up. I grabbed the idea immediately for my N15CS restoration project.

P11 basket case

Those heat guards look good, especially with the finned rocker spindle covers. Now you need to get the finned rocker box covers. ;-) Vinyl in the garage. Nice. I used to have a TT in the garage when I lived in Seattle. I had a few nice records sprout legs...

www.accessnorton.com

- Knut

Click to expand...

What Vecu did for Amal carburetion installation on an upright motor is delightful for many a Norton owner I'm sure, but not anything I would or will ever be interested in. I don't like Amals.

JVigs said:

Thank you for the info. I found there are rubber spigot mounts available with 57mm mount spacing which is close to 2 1/4”. I’m still wondering about the size of the ports. They seem huge for stock valve sizes. Are they standard for an Atlas head?
JVigs

Click to expand...

My intake ports are 31mm and I use stock size valves. My head was ported by Fred Barlow who was good at preparing engines. He's long gone, and not that popular a name mentioned in reference to Norton head work these days on this site. I'm real happy with it and what I have done with the carburetion. Then again I'm one of those horrible guys that don't think Norton did everything right.

Your head could possibly work with the right combination of other parts. I would put it in a box and forget about it though. It's definitely not something ideal for a street bike. If you are going to race with it, plan on spending a lot of money to put a package together that works.

If any of the racers are looking at this thread maybe they could give you an idea about what it would take to make a big port head work. Mine is a mild port job with nice bowl work. It responded well to 34mm Mikuni carburetion, a 2S cam, and some unique exhaust work. I don't have a clue what it would take to make a head like yours work. Hench the box it up comment.

I left my rose-colored glasses in the 90's.

Thanks again, all, for the info and advice. I was wondering if it would be worth it to rebuild the head but now I agree it’s better to put it back on the shelf.
JVigs

Schwany said:

More than likely was modified for the purpose you are thinking of. Rubber spigot mount for Mikuni carburetors. Back in the olden days nobody was making Atlas manifolds for Mikuni carburetion. MAP now makes a single Mikuni manifold for straight up motors.

My original P11 head is a 25319 with flat intake mounts for Amals with 1/2 inch aluminum intake manifolds. Talk about carburetors getting hot. Lock up the slides in Amals in no time. I made my own spigot intakes for Mikuni carburetion from MAP Commando intakes for Mikuni's. Then later made manifolds for Keihin FCRs from standard Commando MKII spigot intake manifolds. Tedious stuff, but well worth it in my opinion. Depends on what one likes.

Click to expand...

The manifold costs more than the Mikuni carb.