Norton 650 Unified Twin

74ok

74ok

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https://walridgemike.wordpress.com/2016 ... fied-twin/
Here’s something you don’t see every day. Norton’s 650 unit construction twin, a bike which never went into production. My good friend Anthony Curzon owns two of these, the one pictured above having just been assembled, utilizing the Matchless frame. Anthony’s other machine uses a Norton slimline featherbed frame and I had the pleasure of taking it for a spin around the South London suburb of Croydon a few years ago. The motor revs very freely and is remarkably smooth. The head resembles that of an A10 and, as with BSA twins, the camshaft is to the rear of the crankcases.
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Thanks for posting the link.

One of the many projects that came to nought !
No mention of how the supposed overheating was solved ?
Nor that it took many decades to get it together and running,
better than never we suppose.
All that work for no gain ?
 
Anthony Curzon had the remains of 2 engines, for the past oooo 4 or 5 (?) decades now.
At last he has them up and running....
Supposedly he has also written a book on them and the hybrids (and 650 ?), last heard of he was looking for a publisher.

When BSA and Triumph came out with unit twins, Nortons probably figured they better follow suit,
and started developing their version of a unit 650 twin. Late 1950s, apparently.
It had a few teething troubles (overheating ?) and wasn't proceeded with.

Instead, they developed stronger cranks for the Norton 650, and the downdraft heads that became the 650SS.
Before coming out with the 750cc Atlas not that many months later.
So they must have all been on the drawing board together, not to mention being tooled up for production.
 
from what i've stumbled on, i didn't get the impression that there was any particular interest/value in these engine/bikes?
 
Its pretty neat that the prototype engines have survived, and been built into bikes.

But at the time they were pretty secret I think, and very little info has come out about them until quite recently.
I sort of thought they'd found the engines problematic, and didn't even proceed with them once finding that.

It would be good too if Anthony's book on them is ever published, but this has been bandied about for years/decades,
and nothing seems to happen. He is expecting to make money ?, authors do it for love !
The inside story could be good to see, if he had access to it......
 
There was an article and pictures of this deveplopment motor and bike in Classic Bike September 2004. Never seen anything on the 250 horizontally laid 5 speed box lump AMC were developing....so a friend working at AMC once told me about. One part of the tale was that the development model was clocked at just over 90mph by the plod and the rider booked for speeding.....another was that after spending over £100,000 on development the Directors cancelled the project saying no one would want a 5 speed 250 single....and what did Royal Enfield produce not long after, with its exploding 5 speed box!!
The picture of the motor shown on page 33 is interesting in that it shows how the hole up the inside of the drive side crank was SUPPOSSED to be so the drill used to clean it out left NO stress raiser directly beneath the big ends outer 90 thou stress reducing radius. Unfortunately the people doing the job did NOT often do the job as per the drawings and the consequence is that cranks break at this point....with expensive consequences.
Of course as one friend said to me several decades ago as I told him about the stress raiser I thought only I had found.........'" Oh did you not know about it??? I thought you did. I have been removing it from my and customers road and race cranks for decades ...the cranks break if you dont".
If EVER you have your crank in bits CHECK it and if the stress raiser is in the wrong place get the drive side half checked because it could be well on the way to complete failure. A friend and I had all our second hand cranks checked and I ended up with two more timing side halves than drive side halves having lobbed two drive sides into the scrap bin as they were already on their way to failure ...NOt that you could see it with the naked eye. If the crank is still OK get the streess raiser moved and polished out BEFORE shoving the motor together. And IF the person you ask to do the job does not know what a stress raiser is GO ELSEWHERE very fast and NEVER use that person or company again.
No spell or grammer checks done.
 
The Unified twin that AC built from a couple of bits was well before the unit triumph as the same designer went on to Triumph to do it. This Engine was supposed to be the successor of the Dommy and so would have become the 650SS,Atlas, Commando etc. It certainly would not have had the Mains issues of the Commando as the bearings were huge .It was not given any time for development and was only dumped because of AMC sour grapes politics . Its main issues were easily solved by a back street mechanic. It starts and runs well and had room to stretch much bigger. Like any prototype that never reached production it still needs some development to make it a properly servicable bike . I will do my best help to make it a pleasure to ride.
 
It's a prototype engine/bike conceived end of the 50's. One reason the development for production was halted may be that technology had advanced too much by the time the go-ahead had to be given.
Layoutwise, the engine looks like an early 50's BSA twin. It lacks a selling point over the Dominator engine. Mixing old and new is not a recipe for success. AMC and Norton had many interesting projects in their design trays. If they had worked together better, we could have seen an OHC unit twin engine production ready by 1962.

- Knut
 
But no where near as ugly as the AMC OHC offering that resides in the SM museum. The undeveloped unified now gives a similar performance to the 650 SS that had much more time spent on it. Its short stroke motor and one piece crank with much improved mains is a much better bet for expanding .
 
norton bob said:
But no where near as ugly as the AMC OHC offering that resides in the SM museum. The undeveloped unified now gives a similar performance to the 650 SS that had much more time spent on it. Its short stroke motor and one piece crank with much improved mains is a much better bet for expanding .
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What are bore x stroke of the engine? What are ID and OD of the mains?
Do you have an idea why the one-piece crank with bigger main bearings wasn't adopted for the Dominator engine? Is there a similarity between this crankshaft and that of the Domiracer, which (if my memory serves me) was a one-piece design also?

- Knut
 
Personally, although a one piece crank is obviously superior in principle, I’d argue that the 3 piece Norton crank is not a problem / weak point in the design, as proven by Steve Maney who kept with the design on his high revving and very powerful race bikes and even on the 1007 engine format.
 
norton bob said:
But no where near as ugly as the AMC OHC offering that resides in the SM museum. The undeveloped unified now gives a similar performance to the 650 SS that had much more time spent on it. Its short stroke motor and one piece crank with much improved mains is a much better bet for expanding .
Click to expand...
I haven't found photos of the Featherbed framed Unified twin.
I did find some photos of the Matchless framed bike.It's a very good looking machine.
Yes the timing side cases are in a different shape than the standard y shape for most other old British twins. I don't see that as a negative in any way.
That, and other differences make it an interesting bike for me.
I'll be interested to hear how things progress with the bike.

Screenshot_20240523_093531_Google.jpg
Screenshot_20240523_093544_Google.jpg
 
From memory the motor is 77.5x68.5 stroke, so oversquare . The mains are around double the size of the Atlas . So the bottom end is very strong . The crank is a one off that Anthony had made by Nourish .The featherbed version looks a bit less tidy . I dont think Norton would have used the Bed frame , They would have probably shortened it and changed it in other ways . Its a pretty heavy lump so a lighter frame would help. It was road tested at 120 mph as a prototype that needed a fair bit more work.Very hard to kick over now its bedding in . The old Atlas feels like a Navigator in comparison the longer stroke helping to get it over compression . It would really have needed an electric start and a big battery . A sort of brit Harley further down the line after boring and stroking out to 9oo cc or there abouts .
 
Norton Bob, the layout and dimensions look like a Navigator times two (bore/bore square = ca. stroke/stroke). The small Norton twins had one piece crankshafts as well. Location of points equals that of the Navigator. Mains are around double the size of the Atlas? 60mm ID is unlikely. I'd be interested in the original accurate sizes.

- Knut
 
Cant remember the mains dimensions ,just remember thinking never ever seen anything that big ,and they must be double size . No wonder its a heavy lump. Anyone less than 14 stone would struggle to kick over at all, A prime candidate for a fully synthetic 5/30 oil although at the time its seals were designed the norm would have been 30 winter 40 summer. If mine i would invest in a roller starter. And a time machine to take 30 years off me. In the meantime its a fun thing to work on and good exercise for the brain trying to work out the best set up to make it a pleasant rider . There is no owners manual !. But i am sure its a real rocket waiting to be lit. The valve timings are based on the 650SS but being a very short stroke that is surely a compromise .
 
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