Atlas, P11, N15 and G15 question

I am wanting to build an Atlas powered late 60s style long bike over the next couple of 5 to 10 years. I will be building the frame myself and piecing together what I want it to be. I have built several panheads and ironheads in the past piecing projects together. But for what will most likely be my retirement bike I want to do something a little different and so am thinking 750 Norton and the Atlas has caught my eye.
My first question is this: are Atlas , P11, G15 and N15 essentially designations of what is basically the same engine? From what I can tell about parts fitment from various websites it seems to be the case. If that is incorrect could some one please school me on where my error is?
Second question is this: How much interchangeability is there of these motors from 63-68? There is a good chance I will be piecing together a motor(I kind of enjoy doing that) and if 63-68, Atlas, P11, G15 and N15 are all interchangeable that project becomes much easier but if not I will need to know what goes with what.
I thank you all for any help you might lend.

For all intents and purposes, the 750cc motor ye speek is is broadly the same for those years.
Nortons and then AMC turned them out for quite a range of Nortons and Matchlesses and Ajays.

Note that there were quite a few changes and upgrades along the way though - so spiggotted heads and cylinders together gave way to plain jointing faces, low pressure oil feed to the rockers gave way to high pressure feed, magneto ignition gave way to points ignition, thin wall cylinders gave way to thicker, slender rods gave way to stronger rods, single carbs to twin carbs, and so forth. But broadly, they are all about the same, and can (mostly) work together.

Why do you want to do your own frame ? What style will this take.
Norton and Matchys made a good reputation for the whole package, and obviously the frame is a big part of that.
Plenty of home done choppers and cafes around, but not so many good ones ?!

We look to hearing more of this, hopethishelps.

The Atlas motor was used in the Atlas (1962-1968), the G15/N15/33 series of bikes (1963-1969) and the Norton/Matchless P11 series (1967-1969)

The early Atlas had spigoted barrels (pre-1966). Early G15/N15/33 bikes would have the same engine.

Engines prior to 121007 (mid-year 1967) had Amal monoblocs and Lucas Magnetos. Again, the Atlas and G15/N15/33 shared the same engine.

All P11s, and any Atlas, G15/N15/33 built from engine 121007 would have Amal concentrics and Lucas distributor/coil ignition.

Except for a handful of special-order machines, the last of the regular production Atlases and G15/N15/33 bikes were before engine 126146.

Norton built 496 or 497 Ranger 750s in September-October 1968, running from P11/128646 to P11/129145.

Atlases used the Norton stamped primary. N15/G15/33 and P11 used the AMC alloy primary, but the P11 also had a hole drilled through the primary case for the footpeg support.

Hey, Zonker.

I've got a G15 chassis that just needs the headstock de-raked from it's previous chopper days. It would save you some headache. It's got the swingarm and the main engine/tranny mounts.

Thank you guys for the info, sounds like I had pretty much gotten close with my interpretations of things. I appreciate it. As for frames I am wanting to go hard tail and fairly well raked and I am 6'4, it is easy for me to look like an ape on a roller skate so I am going to go with most of the dimensions I used on my last chopper it actually fit me quite well. Since I am planning on a chop with this I want to piece together the motor since it would seem wrong to take a good one from a restorable bike. Besides this is going to be a long term project. I might even plan for a second one for my daughter since nobody in the rest of the family will ride with me.

If this works here is the last chop I built about 15 years ago. I want to go with pretty much the same stance and profile.

There is a full on thread on choppers in the Commando section.
(the Commando 750 engine not being that different to the earlier Atlas 750,
apart from being slanted forward a bit).

Those frame tubes look somewhat slender, the roads must be quite flat in your area ?

Rohan, actually that frame is 1 inch dom just like the original panhead frames were. Just a few inches added here and there (actually everywhere) to size it up for me

Featherbed frame tubes are all 1 & 1/4" in the areas that matter.
AND the front down tubes are braced inside.

Going back to inch tubing would be a serious downsizing....

Rohan I am not trying to argue with you but I really don't think that what the Featherbed frame has matters at all to what I am wanting to build. The frame in that picture is 1 inch 1020 dom with 1/8 inch wall and tigged up nicely. The original harley frames from the 30s to 60s were 1 inch tubing and I know of at least 20(personally) that are still on the road. I have also chopped XS650s and CB750s and those started with frames that were predominately stamped sheet metal. One of the main uses for the featherbed was for desert racing and if I were restoring a classic desert racer the featherbed would be at the top of my list, if I wanted to build me a cafe racer i would also count it as the top of my list. my interest is not in that direction. I am planning to build a late 60's style long chopper which will be used almost entirely for leisurely paced rides through the hill country of Texas and maybe some Ozarks trips. But I have no interest in the wheels ever leaving the ground nor any interest in getting past about 70 mph. There is a possibility that I might use 1 1/4 simply for looks, it wouldnt make but about $20 difference in the cost of building the frame and tigging a slightly bigger diameter would be more comfortable but for the needs of what I am building 1 inch with 1/8 wall has lasted a lot longer and in tougher situations than what I am going to ask of it. And besides to me building as much as possible myself is what matters(to me).

here is a chopper I built in 2005. the owner is in the 6foot 4 range so with me @ 5 foot 9 it was hard for me to test ride it
commando-choppers-please-t6850-75.html#p110148

ZonkerA said:

If this works here is the last chop I built about 15 years ago. I want to go with pretty much the same stance and profile.

Click to expand...

[quote="ZonkerA" One of the main uses for the featherbed was for desert racing and if I were restoring a classic desert racer the featherbed would be at the top of my list,.[/quote]

I've never actually heard of anyone desert racing a featherbed, they mostly used
the Matchless compy type frames (with Norton engines factory fitted at some stages),
featherbeds were more a road racing type of bike,
so we are little concerned of your history on this !

It is your frame though, so you can do what you like.
Skinny frame tubes generally dont' produce good handling bikes though,
for anything but lightweight bikes (250cc etc) in the british world,
so getting engineering approval for it must be interesting ??

Bill i like that one alot.
Rohan,
I dont think you get it. I am perfectly aware my history on Nortons is not complete. I dont claim that it is, if it were complete i wouldnt have asked about motors would I.So what if I was mistaken on the featherbed. My point is two fold: 1. I didnt ask anything about the featherbed I asked about the engines and got very good answers, and 2. The frame of the bike in the picture is the same size tubing as used by Harley Davidson for at least 30 years for the same engine that is in it i am pretty certain it will do the job. Due to the fact that that is the size tubing they came from the factory with it wouldnt be a problem getting past engineering if we had such an issue in Texas. Now to try to explain what I thought I had explained the tubing on the bike in the picture is the same as the factory tubing used from at least 1936 to 1966 and perhaps earlier and later. The panhead did not come in a 250cc. Here you will find a picture of the bike this was was inspired by and if you look closely you will notice the tubing is the same diameter and the bike in this picture has a chopped factory harley frame.

Fair enough, I am just commenting for the benefit of other readers here.
Nortons had a proud racing heritage, so that tells you something.
Or tells us something anyway....

I just picked up a 1964 atlas chopper. I will sell .rolling chassis gear box and engine . I cant figure out how to post a pic. I am a idiot!!

bthor I had to post a picture somewhere else and then post the url here. i am really not ready to spend the money but I would like to see it and get an idea how much you will be wanting.