T120 engines in Norton Featherbed frames

Joined
Aug 26, 2010
Messages
8,216
acotrel said:
I raced a very nasty 500cc Triton for 12 years against a friend who has a well-developed 650cc Triton. I've ridden his bike which is extremely fast. I've also ridden a very original 1961 500cc Manx. Forget Tritons. Even a featherbed frame fitted with a two valve Jawa speedway engine is better for classic racing . Tritons are good road bikes, if you enjoy riding beautiful camels.
If they are eligible in their class, a good triton was the mainstay and in the forefront of classic racing for many a year.
And possibly the least expensive way of getting a competitive bike...

Your 'nasty' 500cc obviously needed some good engine development work. ?
Dough Hele etc won Daytona races with highly developed 500cc engines.
 
Joined
Jun 30, 2012
Messages
9,540
Country flag
Every fast pre-unit Triumph which ever raced in our historic racing has blown up and they are very rare these days. My friend still has his 650cc Triton which is extremely quick, however only gets run at the Broadford Bonanza these days. It has never been run at more than the factory prescribed 6,300 RPM, and is built for torque. I raced against it for years with my 500 short stroker and could never convincingly beat it. I rode it once at Calder and out accelerated a good H2 which was fitted with chambers. The other guy chucked the kawasaki down the road trying to keep up with me as I outbraked him.
Rohan, you need to ride a bike with a nasty top end motor and find out what I am talking about. If the motor is short stroke with long rods, and fitted with long duration cams and megaphones, it can be a real bastard. If it ever dropped off the cam, you had a real problem. You could never slip the clutch to get it going again. You need to find out what it is like to be cranked over in a corner at 60 MPH, and find the bike suddenly snapping around sideways. I sold it when I built the Seeley, and I was glad to see it go. I rode it about six years ago when it had been fitted with a 5 speed box, straight pipes, and decent tyres. I still ended up with it sideways in a fast corner, however with the good tyres, simply rode through the problem. The problem was the motor was over-developed, originally built by Baldo Meli, an old Irish TT rider who used to work for the Triumph factory. I read somewhere he got a 12th at the IOMTT in about 1948. The bike was great to ride on a really big circuit, however then the drum brakes would scare the shit out of you. My Seeley 850 is a really lovely fast bike to ride with none of that bullshit. I have nightmares even writing here about my early racing and I believe I should be dead because of it. I had a lot of very nasty crashes, however these days I go nowhere near that stuff with the Seeley. It is fast and safe.

My friend's 650cc Triton is #62 in this video with Jeff Curley in blue leathers on board:

https://www.youtube.com/watch?v=UbnGGl3m4KY
 
Joined
Apr 20, 2011
Messages
4,388
Country flag
Acrotrel’s comments on the 500 Triumphs pre unit engines could be put down to experience.
Rohan’s comment show what a good professional engine tuner could do with the 500 unit engine. A factory 500 Triumph also finished 2nd in the Spa Belgium GP behind an MV ridden by Percy Tailt. Dave Dregens raced for many years on a 500 Triumph in his own frame winning the Classic Racing Club championship again and again it became boring.

He’s still knocking them out;
http://www.bing.com/images/search?q=dav ... M=IQFRBA#a
http://www.bing.com/videos/search?q=dav ... E2B1C10048
 
Joined
Jan 22, 2008
Messages
944
Bernhard said:
Acrotrel’s comments on the 500 Triumphs pre unit engines could be put down to experience.
Rohan’s comment show what a good professional engine tuner could do with the 500 unit engine. A factory 500 Triumph also finished 2nd in the Spa Belgium GP behind an MV ridden by Percy Tailt. Dave Dregens raced for many years on a 500 Triumph in his own frame winning the Classic Racing Club championship again and again it became boring.

He’s still knocking them out;
http://www.bing.com/images/search?q=dav ... M=IQFRBA#a
http://www.bing.com/videos/search?q=dav ... E2B1C10048
+1, Bernhard. Reading Acotrei's comments (which we've heard so many times before), one could get the idea they were all like that. I lined up with Dave Degens at a CRMC meet in Cadwell Park in 1985. A fast, tidy rider on his neat and quick 500 Triumph. He showed how it could be done.
 
Joined
Jun 30, 2012
Messages
9,540
Country flag
The Percy Tait motor was the 65.5 mm stroke T100 unit construction type with the short rods. I believe it was the long rods in my motor which were most of my problem about getting some vestige of torque. Tait would also have had a close box which was different to the pre-unit box, so copying his efforts would not be so easy. Also the comp. ratio would not be so much of a problem as the combustion chamber would have been smaller than the one in the 650 head, so the piston weight would have been lower. I'm certain that Triumph would never have used the radical type cams which my 500 had. The motor which Percy Tait used did not appear in road bikes until about 1973 when the T100 had the proper timing side bearing, instead of the BSA type plain bearing. So using one for historic racing would not be a goer in the strictest sense. I looked at a bike with that motor years ago, however the immediate problem would be the gearbox - $5000 up front.
My 500cc (converted 650) Triumph was actually very fast, however the 73 model T100 motor would be much better - is there a race class to suit it ? I believe that Monty & Ward built a Tricati using one of those motors.
 
Joined
Aug 12, 2013
Messages
55
All this race talk and technicalities about v rare race engines is beyond me I'm afraid :( (like you are talking another language :D )

Is there anything inherently wrong with an Atlas engine in a featherbed frame that would mean somebody should swap it over and Triton it?

Anyone tell me more about the Dommie 650 and Atlas 750? The only thing I know is it was Bert Hopwoods baby, he considered his 500 to be better than Turner's, in reality it may have not been so.
 
Joined
May 6, 2010
Messages
431
Country flag
The Atlas motor was known to vibrate, and that's what everyone refers to. This was caused because the smaller displacement Dominator motors were simply bored out to accommodate the displacement of the 750cc Atlas. This was mostly due to demand from the North American market.
Bear in mind that the Atlas bore was large enough that the head bolts needed to be moved further out, and the bolts themselves were a smaller diameter. Basically the bore had gotten too big for the actual casting, and therefore vibrated. Less meat in the cylinder walls and heavier / bigger pistons. An obvious and foreseeable problem.

These days, there are lightweight pistons, balanced cranks etc etc, that really help tame the vibration problems. Even belt drive primary's that take stress off the motor. Jim Schimdt makes rods and pistons that greatly reduce the vibration.

All that being said, most Atlas owners will attest that their machines are just fine. Mine included. I've built it properly and I ride it regularly. I don't find it to be much in the vibration department. Even with clip ons, I find the ride to be plenty comfortable. Some say their are good ones and bad ones, and I feel it's a matter of how they're set up.

Lastly, the 500, 600 and 650 Dominators are certainly smoother motors that vibrate much less than the Atlas. In my opinion, there was really no need for anyone to build a Triton once the 650ss Dominator came out. These days, the Triton is seen as some sort of legendary cafe racer. Unless someone was to find an orphan frame and orphan motor, it would be senseless to take a Norton motor out of it's featherbed frame in order to build a Triton. But it's in vogue etc. I just think that most people forget that it's not really a plug and play type affair. If someone is going to build a Triton, they'll need to be prepared to deal with all sorts of fitment issues in order to get everything just right.
 
Joined
May 1, 2013
Messages
420
Country flag
I had a 650SS, personally I think a good 650SS would be nicer as a street bike than an Atlas. I've only ever ridden one Atlas, it was a very nicely set up bike used mainly for long distance touring, but he also rode it to work. It was reasonably smooth mainly because the owner/builder had spent a lot of time on the motor. However my 650SS was smoother, faster, and more economical. Not by much in any category, but the difference was there.
What this would lead me to suggest is that get what you can, be it an Atlas or a 650SS and then spend time getting it sorted out to suit you, and how you want to ride it.
Because I had one and loved it, I would love another 650SS, but if I was offered an Atlas at a sensible (i.e. affordable) I would jump at it.
cheers
wakeup
 
Joined
Jun 30, 2012
Messages
9,540
Country flag
I suggest that as the motor gets bigger piston weight becomes more important towards vibration. You choose the balance factor to suit the application.
 
Joined
Aug 26, 2010
Messages
8,216
acotrel said:
I suggest that as the motor gets bigger piston weight becomes more important towards vibration.
No surprises there ?!!
This has been known since steam engines went beyond toy sizes...
 
Joined
Jul 25, 2010
Messages
4,942
Country flag
" I've only ever ridden one Atlas, it was a very nicely set up bike used mainly for long distance touring " ( wakeup )

indeedski , the ATLAS would be the better two up + baggage tourer , the 650SS the better scratcher & maybe the Mercury the better commuter / alrounder . Maybe .

Then theres 99SSes , etc et al . A unbuggered with original of any type could be appreciated for what it was / is . An undoubed pleasure . The problem was thrasing & neglecting
well used ( read old and not quite idealy maintained ) things owned by young brats with no mechanical sympathy or empathy . Though pre 70 ( or later , some might say ) Brit
vehicals in general are often far from foolproof . As a ' learning exercise ' in this context , you can see why a few met their demise . Nortons letting go & triumphs visiting the sceneary .

So the Road Going Triton was a Child of its Times .

Any carefully / well put together Norton is going to be pretty good , if it isnt a collection of disparet worn out odds & sods . When a thing gets past it its often better to pare it to the bones ,
trash the trash , & do a ' Coustom ' . Where butchering a essentially complete & original machine is a diferant story alltogether .

And for someone where Only a NORTON will do , theres the opertunity to build a updated uprated version of any of the elderly machines , whilst maintaining somewhat of the original appearance .

Horses for Courses , and depends from where youre starting and where you wish to end up , as far as the machineary goes , and the budget :oops: . :cry: :)
 
Joined
Jun 30, 2012
Messages
9,540
Country flag
I've only ever heard of one real problem with the Atlas - the barrel flanges on the first model apparently broke off sometimes. As far as vibration is concerned, in nearly every high speed bike which doesn't have balancing shafts, you must balance the crankshaft to suit the application. (Ducati twins are a bit different). With a vertical twin, you can choose whether you want to have the bike vibrate at low revs, or at high revs. If it vibrates at high revs you do more damage to the cases, bearings, and the crankshaft itself. Fitting isolastics only hides up the problem of having an incorrectly balanced crankshaft. My choice is always to let the motor vibrate at low revs so that when you spin it hard it doesn't shag itself. I believe the 650ss used a 72 % balance factor and that is where the Atlas and all commandos should have been. The difference was due to the need for Norton to compete with the CB750 in a market place full of commuters. The combination of isolastics and 58% balance factor is bullshit. It works - sort of ? Spin your 750 commando engine to 8,000 RPM and find out.
There are more Atlases in our Pre '62 class of historic racing than were ever imported into Australia - most use 750 commando engines. I've seen one with an 850 commando engine.
 
Joined
Sep 15, 2013
Messages
246
bill said:
IMHO IF you just have to build a triton than a pre unit lump is the better route. the unit turnip lump is to short for a PROPER fit. either the countershaft is to far forward, the crankshaft is to far back or both are to far from where they should be.
I had a wonderful Triton with a 750 unit single carb engine 5 speed. She handled great,was fast,and got terrific gas mileage. Regretted sell her. I'll build another one one day.
 
Joined
Jul 25, 2010
Messages
4,942
Country flag
Any Tritons better than NO Triton . :)

though a unit 500 or worse 350 may be debateable . Nothing wrong with a unit 500 in itself though .
 
Joined
Aug 12, 2013
Messages
55
Amazing, I would love a V4 rather than a V6, probably costs an arm and a leg or a Vincent
 
Top