T120 engines in Norton Featherbed frames

Hi ,the two very early tritons featured in the magazine were owned by a friend , I got a good look around them. Built in the early 50's they were both tatty unrestored race bikes with GP carbs,manx stuff etc, one a close fin alloy barrel 500 trophy motor, the other a 650 poss a 110. They were runners and found to be very fast . Thank God not restored.

Back in the day I had a Tribsa, consisting of a twin cared T110 engine in a BSA goldstar frame with a BSA gearbox, other than the impossibility of properly sealing the primary chain case, it was Avery fast and reliable bike.

Unfortunately it ended its life flying over the front of a car, which kind off buggered up the frame!

I had a Tribsa with a full race 650 Triumph motor and gearbox. It was fitted with unit construction Triumph fork yokes, was fast and handled beautifully. A friend had a similar bike with 650 Gold Flash fork yokes and it scared him silly, however because the yokes were chromed continued to use them. - Different priorities ?
I've often wondered about t he steering geometry on the BSA Gold Flash. The Super Rocket BSA seemed to be a really good bike.

I had an BSA golden flash A10, before the Tribsa, it had a great engine, relatively smooth and would pull to an indicated 105mm. Very stable with good handling, relatively reliable when being ridden by an 18 year old without much mechanical skills or sensitivity!

Having read through all this several times, I understand that if one had a Atlas 750 engine within a featherbed frame it would be absolutely pointless to swap it in favour of a T120 engine, given the Atlas engine can be made and setup to run very well with crank balancing etc. and produces more power than the T120 unit 650?

I have lots of queries regarding the Atlas 750 engine, not sure whether to put this into another thread, but hypothetically if the vibration issue is alleviated somewhat by the methods described in this thread, can the engine be described as reliable and what are other things to watch out for etc. etc.?

Acebars,
I would 100% agree that you are correct. I cannot see any reason why one would need / want to swap an Atlas motor out of a frame, in order to drop in the T120. The Atlas motor can most definitely be made to be extremely reliable, very well behaved and put out plenty of power. It's weight would sit much lower in the frame, and it wouldn't cause any issues with aligning the rear sprocket. Personal opinion of mine, is that the Norton motor looks miles better than the T120 as well. So unless someone was absolutely dead seat on building a Triton, the Atlas motor is the far superior choice for all reasons.

Music to my ears/eyes wilkey113, I too prefer the look of the Atlas engine.

After my next project build which has turned out to be using an XS650 powerplant I'd like to finally get the OHV brit bike I've been hunting for a few years now, I've been searching around different forums for varied options but I think I'd like to go for something with the Atlas powerplant, I'm fascinated by the G15CSR and N15CS bikes (the AMC/Norton hybrids). I just wonder how they handle on roads as mine would be for road use and I understand they were initially designed as off-road bikes.

Acebars,
Glad to hear that you're into the idea of keeping the Atlas motor option. The hybrids you're talking about, are virtually the same powerplant as the Atlas, but for road use, the hybrid wouldn't hold a candle to the featherbed framed Atlas.
I certainly understand the origin of the Triton, and their initial benefit back in the 1950's. The pre unit 500 Triumph motor was easier to tune and get power from, than the 500 Dominator. Personally, I think that once the 650 Dominator came onto the market in 1961, there would have been no reason to build a Triton, other than for vanity or simply matching up discarded motor with discarded frames.
The Atlas is known for it's vibration, which is true, depending on the individual bike. Obviously the castings had reached there limit once bored out to 750cc. But, with modern lightweight pistons etc, even the Atlas can be quite smooth.
I also think that it's all relative perception. It's a bike form the 1960's, so you're going to get a 1960's riding experience. It'll never be a modern bike, and it'll never be as free of vibrations as the isolastically mounted Commando, but with the handling you get, along with the classic styling, I personally think it's hard to beat.
I've owned an Atlas for a very long time, and ride it nearly everyday (weather permitting). Even with clip ons and rearsets, I've never found it to be uncomfortable. And that includes longer rides. If I was 70 years old, and trying to tour 300 miles at a stretch, perhaps it would be a different story. I owned a Commando for a long time as well, and I can tell you that there's no comparison to the handling of the featherbed.
Anyway, that's my personal opinion, but based on lots of experience with the bike. This is generally a "Commando" forum, and guys here also tend to like the Triton, so my opinion may be in the minority.

wilkey113, from what you have described I'm completely sold on the Atlas engine, and it's relief to finally find the Brit motor that checks all the boxes I'm after, looks, power, reliability, some vibration (call me mad I like it), the fact it's a Norton powerplant (I'm not a Triumph guy, I have a real eye for AMC and Norton bikes).

I started rebuilding and doing up 70s twin Jap bikes really to get mechanical experience because they are cheaper, have finished a Honda DOHC CB500t complete engine rebuild and restoration, now doing an XS650 OHC. Next I hope to do the Brit OHV I've been searching for for years now, I was also thinking an RE interceptor would be a good idea.

The hybrids you're talking about, are virtually the same powerplant as the Atlas, but for road use, the hybrid wouldn't hold a candle to the featherbed framed Atlas.

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Yes I understand the hybrids are geared differently much lower and the featherbed frame is obviously superior for handling as it has race pedigree. The Atlas bike is beautiful stock, but I personally would want to change the tank to something like a G9, G11 or G15, my only concern is these tanks would not work looks wise.

As I'm not after a racer just a good road handler if I slung an Atlas engine into a G15 CSR frame this bike would tick every box for me, looks, engine, the fact that it's badged an AMC bike and with a Norton engine! My only concern is I read somewhere the road handling of these hybrids is dire.

I actually rebuilt the CB500t starting from just a frame with a V5, all the other parts I bought in very cheaply from all over the world and rebuilt meticulously, that way I could choose and customize without waste parts i.e. CB450 from drum instead of CB500t disc.

It'd be my intention to do the same when I begin building my Atlas powered bike, rather than butchering an already existing Atlas which would be sacrilege!

" read somewhere the road handling of these hybrids is dire. ' You mean like an old Jap Bike ?? half of what you read is tripe . You get that with jurnos who donr know how to drive .

Familiarity with characteristics and a inteligent approach can do wonders . If not miricals .

theres a lower hump tank on some US F'bed Nortons , a bit sportier . AMC heavyweight chassis I regret not takeing up the offer of one , for 50 bucks . some time ago .
Young Brown used AMC forks on ' NERO ' no doubt slightly tricked up . 72 on engines are a little stronger , so dont pass on a 850 if offered , itll improve the Vibration .

:mrgreen:

Acebars said:

Yes I understand the hybrids are geared differently much lower and the featherbed frame is obviously superior for handling as it has race pedigree. The Atlas bike is beautiful stock, but I personally would want to change the tank to something like a G9, G11 or G15, my only concern is these tanks would not work looks wise.

As I'm not after a racer just a good road handler if I slung an Atlas engine into a G15 CSR frame this bike would tick every box for me, looks, engine, the fact that it's badged an AMC bike and with a Norton engine! My only concern is I read somewhere the road handling of these hybrids is dire.

It'd be my intention to do the same when I begin building my Atlas powered bike, rather than butchering an already existing Atlas which would be sacrilege!

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The G15/N15 and P11 series both used the Atlas engine without change from the Atlas spec. The G15/N15 use a unique oil junction, as the transmission is so close to the crank case, the oil pipes have to be routed under the transmission rather than over. The G15CSR/33CSR use a unique gearbox with a reversed cam plate and outer cover, to keep the standard AMC 1-up, 3-down shift pattern, and indicate the proper gear with the pointer.

The standard drive sprocket for my G15CS is a 17-tooth unit, compared to the 19-tooth of my Ranger. At idle in first gear, the G15 proceeds at a brisk walking pace - probably a good gearing for rough terrain.

I don't have many miles on the G15, so can't attest to its road handling characteristics, but the Ranger is a very good-handling street bike, except for the puny brakes. I tell people that one must plan all stops, even panic stops! I've not had the Ranger over 90MPH. It is rock stable at that speed, but the engine sounds like a banshee, and my hands start to go numb after about 20 miles.

I like all the 1960's pre Commando Nortons, but I certainly like the featherbed framed bikes the best. Obviously the frame type will limit the choice of tanks, but plenty of vendors make some nice options. I've not ridden any of the hybrid bikes, so I can't personally attest to their handling. Going off only what I've ever heard. Obviously the featherbed has its famed handling and has been quite well proven in race results, and my experience with it has confirmed that. I'd say that in most cases, there are very few of us that can out-ride any of these bikes, so often times, it comes down to personal preference. I always say that the best bike, is the one that you love the most. Hard to go wrong with any Norton.

chasbmw said:

I had an BSA golden flash A10, before the Tribsa, it had a great engine, relatively smooth and would pull to an indicated 105mm. Very stable with good handling, relatively reliable when being ridden by an 18 year old without much mechanical skills or sensitivity!

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I think that was the trouble with the Gold Flash - too much trail, so too stable and possibly dangerous at speed braking. It is possible for a bike to stand up and turn the wrong way under brakes if it has too much trail. I know my mate was scared of his tribsa which had the GF fork yokes.

The G15CSR/33CSR use a unique gearbox with a reversed cam plate and outer cover, to keep the standard AMC 1-up, 3-down shift pattern, and indicate the proper gear with the pointer.

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Just brilliant, is it not 1-up then down on the other atlas powered bikes?

Aren't the Ranger, P11, G15/N15 all the same or very similar frames? So similar handling characteristics?

I tell people that one must plan all stops, even panic stops! I've not had the Ranger over 90MPH. It is rock stable at that speed, but the engine sounds like a banshee, and my hands start to go numb after about 20 miles.

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Hahaha, yea I read this also about the braking, slapping a good 2ls/4ls on should fix that! Great to hear about the solid handling, indeed Jap handling is poor I'm always conscious of it when riding their 70s stuff, top heavy and wobbly on corners is the feeling! My next mod on my XS650 is to weld a bracket to stiffen the already pig heavy flexi-frame!!

I think that was the trouble with the Gold Flash - too much trail, so too stable and possibly dangerous at speed braking. It is possible for a bike to stand up and turn the wrong way under brakes if it has too much trail. I know my mate was scared of his tribsa which had the GF fork yokes.

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Wow you learn something everyday, always thought there was no such thing as too much trail!

half of what you read is tripe . You get that with jurnos who donr know how to drive .

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Yes some serious investigative work, that's why I've also been going around forums to talk to owners etc. and would like to get down to Kempton as well. What I really need now is some books on the Atlas engine and the hybrid bikes.

Obviously the frame type will limit the choice of tanks, but plenty of vendors make some nice options.

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The featherbed is a masterpiece and if I wanted a race bike no doubt, but I can't imagine a G9 fuel tank fitting or looking right on the featherbed frame (not to say the Atlas is bad looking). Whereas the hybrids are just perfect in that respect.

I've been really close to buying a 60s T120 several times in the last year, the year before that I was thinking a T110 or an old RE Bullet, but it never felt right as if I was just pushing it just to get a Brit bike I didn't know too much about. It's a wonderful intuitive feeling to have finally found the bike you know is right for you and I've been searching for a while now.

So now all I have to do is get back to the UK, finish the XS650 project (which I'll keep as winter hack etc.), gather some funds and find the Matchless G15CSR that is waiting out there somewhere for me!

Norton engine in a Matchless bike, just perfect! Really look forward to it. Thank you all for being so helpful!

These days, it's very trendy to have a Triumph engine in a Featherbed frame. So, to the original post's title, THAT'S why.

The G15CSR/33CSR use a unique gearbox with a reversed cam plate and outer cover, to keep the standard AMC 1-up, 3-down shift pattern, and indicate the proper gear with the pointer.

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Acebars said:

Just brilliant, is it not 1-up then down on the other atlas powered bikes?

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It is - but note that the G15CSR bike (pictured) has the gear lever REVERSED in that pic, and the shift pattern is still the same.
That takes a bit of jiggery pokery in the box to do that...

Acebars said:

Aren't the Ranger, P11, G15/N15 all the same or very similar frames?
So similar handling characteristics?

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No.
Note that the G15CSR (pictured there) uses Matchless's old lugged style frame.

The P11 and some of the others mentioned uses Matchless's all-welded competition dirt bike frames.
Chalk and cheese... ?

These days, it's very trendy to have a Triumph engine in a Featherbed frame. So, to the original post's title, THAT'S why.

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I pretty much came to that conclusion as well.. not a trend I wish to follow.

No.
Note that the G15CSR (pictured there) uses Matchless's old lugged style frame.

The P11 and some of the others mentioned uses Matchless's all-welded competition dirt bike frames.
Chalk and cheese... ?

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Ah thank you for enlightening me, that explains why the P11 is so much more expensive than a G15 CSR I was scratching my head over that, thought they were the same frame, well I think I'll be quite happy with the old G15 CSR frame.

It is - but note that the G15CSR bike (pictured) has the gear lever REVERSED in that pic, and the shift pattern is still the same.
That takes a bit of jiggery pokery in the box to do that...

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Ah I see now, I like it like it a lot, kind of a half way between rearsets! Hmmm but no rear pegs? So no pillion?

The G15/N15/33 machines used the frame that started with the Matchless G12

G15CS frame

The P11/P11A/Ranger frame is a very slightly modified G85 frame, built by Reynolds

Ranger frame

There are plenty of pictures to be found of the wideline and slimline featherbed frames.

Thanks for those photos Bill, simply beautiful bikes both of them.

Will let you know when I get mine in the garage, can't wait.

BillT said:

The P11/P11A/Ranger frame is a very slightly modified G85 frame, built by Reynolds

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Incorrect. All G85CS and P11 frames were built in-house, using Reynolds 531 tubing.
R531 is an alloy optimized for brazing (welding wil distroy the fine material properties) so all G85/P11 frame joints are brazed.

Actually, all heavyweight frames bade by Matchless right up to end of line (1968/69) were brazed. I can't comment on the lightweights.

-Knut