rear suspension

gnolan · Dec 19, 2013

I've been looking into Ikon suspension. Correct, the recommended part number is 7610-1653 SP9. Looking at the ikon USA web site, this is a black bodied damper, with a chrome spring, appearance similar to stock. Length is 12.99". Since I have replaced my rear 19" wheel with an 18", I inquired about slightly longer dampers. Ikon replied "No Problem, just need to assemble them." 340mm (13.385") looks like what I need. These specials were the same price as the standards.

The manufacturing plant is closed until mid January, but they would produce them shortly after they open.

Talked to David Gardner at ikon USA, very helpful.

http://www.ikonsuspensionusa.com/

Wishing all of the Access Norton community a Merry Christmas.

George Nolan
Indianapolis, IN

baz · Dec 20, 2013

acotrel said:
The rear wheel is not coupled almost directly to the headstock yet isolated from the rider's bum and feet on a manx Norton. The head steady is a turnbuckle used to strain the motor in the frame. The swing arm is supported at both sides by plates welded to the frame so the rider has direct feel of the rear contact patch through his hands and backside. Anybody who has ever ridden a pre-unit triumph fast knows what flex feels like. It cannot be tolerated if you want to be safe - It destroys confidence with good reason. Have a ride on a manx sometime, Baz - they inspire a lot of confidence - stable and fairly neutral, wherever you want to send them you set your mind, and wind on the power. If the handling depends on the head steady, you are asking for trouble. I've raced Tritons with the head steady broken and there is no difference in handling , however the frame is likely to crack somewhere due to vibes when the motor can move. The head steady only has to be very flimsy to stop that happening. My Mk3 Seeley has a bit of spring built into the front down tube in one direction to stop cracking, and the head steady has rose joints to allow it to jump slightly without breaking the bolts.
I apologise for having this discussion, I know you guys love and believe in your commandos, and they are probably OK if you keep at them. I just get a bit concerned, it is very unpleasant if a bike suddenly goes out of control for no apparent reason. I've had it happen and escaped only because of my previous experience at crashing. It can end someone's career almost before it has started. When I started racing in 1967, I crashed at the first 5 meetings, and once four times in one day. Knowing what I know now, I'm amazed that I'm still alive - so bloody dangerous. Those drum brakes - JAM THEM ! They are a good way to get dead.

whether you felt any difference or not when a headsteady broke on a triton is irrelevant l!! its just your opinion another rider may have a different view (peter williams springs to mind),the question i asked you was whether you would want to ride a norton featherbed framed bike as that also depends on the headsteady to support the headstock and hence the handling it is designed that way! and thanks for explaining to me that a featherbed frame has the swingarm support plates welded to the frame i never would have known!!!! regards baz

acotrel · Dec 21, 2013

Baz, the featherbed frame is an entirely different concept to the commando frame. The commando frame was developed so a British bike could be as smooth as a 4 cylinder Japanese bike. It was successful in doing that, in spite of the parallel twin motor. Ducatis get away with the rigid frame due to the angularity of their motors. How many modern bikes use floating engine/gearbox/swing arm assemblies ? A while back there was a magazine article which explained why the cardboard Suzuki of Team Heron was so successful. It had to do with rigidity. There are two considerations - comfort and handling, a balance between the two is difficult with a big parallel twin. I know that Doug Macrae somehow locks up the frame on his commando racer, and he says it is as good as Kenny Cummins Seeley. I think that fanging a standard commando on public roads might be a career limiting strategy. Rohan is right, on the road just ride the bike sensibly and enjoy it - standard commandos are what they are.
Many of the Norton Atlases in pre '62 Australian historic race classes have commando engines in featherbed frames. I think they would have made very bad road bikes.

Rohan · Dec 21, 2013

acotrel said:
Many of the Norton Atlases in pre '62 Australian historic race classes have commando engines in featherbed frames. I think they would have made very bad road bikes.

Ashman here may disagree with you. !
He's had his Commando-in-featherbed on the road now for how many decades now ?

There seems to be some secret in finding the perfect balance factor for this combo. ??

But we diverge, as usual...

trident sam · Dec 22, 2013

acotrel said:
Baz, the featherbed frame is an entirely different concept to the commando frame. The commando frame was developed so a British bike could be as smooth as a 4 cylinder Japanese bike. It was successful in doing that, in spite of the parallel twin motor. Ducatis get away with the rigid frame due to the angularity of their motors. How many modern bikes use floating engine/gearbox/swing arm assemblies ? A while back there was a magazine article which explained why the cardboard Suzuki of Team Heron was so successful. It had to do with rigidity. There are two considerations - comfort and handling, a balance between the two is difficult with a big parallel twin. I know that Doug Macrae somehow locks up the frame on his commando racer, and he says it is as good as Kenny Cummins Seeley. I think that fanging a standard commando on public roads might be a career limiting strategy. Rohan is right, on the road just ride the bike sensibly and enjoy it - standard commandos are what they are.
Many of the Norton Atlases in pre '62 Australian historic race classes have commando engines in featherbed frames. I think they would have made very bad road bikes.

The Commando frame wasn't developed to be as smooth as a 4 cylinder Jap bike, as the Commando preceded the pig ugly 750 honda . It was developed because vibration was deemed unacceptable.
sam

PeterJoe · Dec 22, 2013

kickstart said:
it sounds odd, but I don't have any shocks at the moment and am rebuilding the frame, does anyone know the travel of the standard shock on the 850?

I took a measurement of my original Girling shock absorber travel that I removed from my Norton 850 Commando. The travel measures just under 2 3/4 inches. Of course the rubber stop will crucnch a little bit at full compression.

Progressive Suspension makes travel limiters for their shock absorbers in various lengths. They would probably would work fine on any other brand of shocks as well. They fit between the top of the shock and the rubber bump stop and are held on with a snap ring.

Rear Shock travel measurement

acotrel · Dec 22, 2013

This is probably irrelevant to most of you. I use Koni shocks on my Seeley with the springs set very soft. I recently noticed that the head of a bolt has been touching the rear tyre when the bike is under full rear compression, so I set the spring adjusters up a notch. I rely on a fair bit of self-steering coming out of corners to allow me to get on the gas really early. So now I will have to concentrate the next time I take the bike out, and see how much it self-steers after the change. It alters the amount steering head angle changes under acceleration and affects the trail. If the line in the corner doesn't tighten enough I could end up on the grass and going too quickly when it happens.

kommando · Dec 22, 2013

The greater pre load will only reduce the frequency of tyre hitting the bolt not eliminate it, you need to put a spacer to limit the movement of the shock as per the progressive picture, Koni's use the same type of spacer so they can use one main body to fit several bikes by varying the thickness of the spacer. The same body was used on both the Triumph 650 pre oif, the tridents and the commando but the fittings varied. Once the thicker spacer is in place the pre load can be put back to the softest setting.

ashman · Dec 22, 2013

I have had my 850 Commando motor in my Wideline Featherbed for over 33 years now, one thing that I was made aware off when I first built my Feathebed was to make a very strong head stay as well as getting the balance factor right, I run Koni shocks on the rear and I have had no reason to change as they have worked so well on this bike, I do get a little vibration in the foot pegs but not much it feels good and the same in the handle bars, the slight vibrations I get feels like the bike is talking to me throught the handle bars and foot pegs, but the higher the revs the better the bike feels, its hard to explain but the vibrations I feel is all smooth, I can ride this bike all day long and come home still feeling as good as when I left and I ride this bike very hard all the time.

Ashley

baz · Dec 22, 2013

i appologise to kickstart for hijacking his post but i have been trying to get an answer out of acotel regarding the statement he made that he would not ride a bike that relied on its headsteady for good handling i have tried to point out to him that a featherbed frame also depends on a decent headsteady but he just goes on to tell me the difference between a commando frame and a featherbed frame! i have been involved in the manufacture of motorcycle frames for 37 years this year!! i darent tell acotel that i have run my commando without the headsteady fitted (albeit with an extra isolastic under the gearbox and oval braced swingarm etc) and noticed no difference in handling but then i am not a racer so i cant really comment also for my sins back in the eighties i used to have a wideline featherbed cafe racer fitted with a re balanced 750 commando engine i really miss that bike cheers baz

ashman · Dec 22, 2013

I am willing to start a new thread in another section just on Cammando motors in Featherbed frames or any other frame if there is intrest.

Ashley

Rohan · Dec 22, 2013

That Girling photo is missing the plastic bumpstop spacer that limits the travel to ~ 2".

I'll see if i can get a pic of the girlings that came with my Commando when acquired.
Looks like someone has removed something from yours - or did Nortons limit the shocks more on the 850 ??

PeterJoe said:
I took a measurement of my original Girling shock absorber travel that I removed from my Norton 850 Commando. The travel measures just under 2 3/4 inches.

PeterJoe · Dec 22, 2013

Rohan said:
That Girling photo is missing the plastic bumpstop spacer that limits the travel to ~ 2".

My shocks do indeed have the limit travel spacers. I took another picture to show this more clearly. I believe these shocks are original to my motorcycle and I bought this bike from the original owner over 20 years ago. The bike only had 7000 original miles on it when I bought it. The shocks are both 12.9 inches between the hole centers. The number stamped on both shocks is 64052311B MG19. My Norton is a 1974 Mark IIA that was built in June of 1974.

With these shocks fully compressed on the motorcycle there is plenty of clearance between the tire and the rear fender.

I hope this is of some help and clarifies any confusion.

The limit spacer between the bumpstop and the top of the shock.

Rohan · Dec 22, 2013

The description of my 850 reads almost indentically.
And those components seem identical too.

I'll investigate why my shock only shows a possible 2" of travel (as the specs say, it must be said).
Maybe its partly seized (like my Konies were, before a rebuild).

kommando · Dec 23, 2013

Maybe Koni have a mistake in their specs and its 2" of vertical travel at the wheel not the shock travel, I have some NOS Koni's and will measure them later but just using my mk3 eyeballs they have the same travel as the Trident ones I have for my T120 which is nearer 3"

wakeup · Dec 23, 2013

PeterJoe said:
With these shocks fully compressed on the motorcycle there is plenty of clearance between the tire and the rear fender.

I don't want to throw another spanner in the works, but don't rely on the tyre missing any bolts, mudguards whatever in static mode. Tyres "fling", get bigger in diameter as speed increases. The last time I got excited about it was about 20 years ago, when tyre fling at high speed was (from memory) somewhere between 1/4" and 1/2" on diameter. Avon used to publish the data in their technical specs, but that was then. I'm sure that modern companies also publish stuff like that.
cheers
wakeup

acotrel · Dec 23, 2013

baz, the handling of a featherbed frame does not depend on the head steady to stop the swinging arm from sending the bike into a weave. It will handle just as good without the head steady. What can happen is that the motor is then able to move under torque reaction and vibration, and it can crack the frame. The effect of the head steady on a featherbed frame in stabilizing the pivot comes from the extra rigidity through the engine plates and crankcases, and these are bolted to the front mounts. The effect of the head steady on the swing arm is virtually nil compared with the commando isolastics setup. It does however stabilize the steering head by bracing it against the motor. - what does the commando have to do that ? Why did the Italian manufactured commando frames crack ?
My comment about isolastic is not to denigrate the design, only to point out the likelihood of a major and potentially lethal weave. I raced a featherbed Triumph regularly for 12 years, perhaps I might actually know why a bike mishandles ? I think a commando would be an excellent commuter bike, however I would never put myself in the position where my life depended on it's handling. If it depends on the head steady to keep behaving itself, something is wrong. I am fully aware that if the isolastics are properly adjusted, there is little problem. Tell that to some kid after he has been chucked up the road.
A bad mishandling problem can remain hidden for years then grab you at just the wrong time. I never expected it to happen with my Seeley. The bike had been raced several times with the Ducati fork yokes and a heavier motor. It grabbed both myself and a friend - both very experienced riders. We both got out of it, mainly by good luck.
Incidentally those beautiful 1000cc Vincents are also prone to the same thing if the forks are worn, and the seat dampers wrongly adjusted. I know a guy who got chucked onto his head at 70mph because the bike went berserk.

Baz, Have you read this topic ? :

commando-motors-featherbed-frames-other-frames-t18209.html#p228936

Matt Spencer · Dec 23, 2013

The ruber thingos are ' Bump stops ' https://www.google.com.au/#q=girling+bump+stops :shock: Theyre so the thing doesnt Jar steel to steel . Theres even ' progressive bump stops ' , which are hollow
3 ball rubber . on the back of a Mk 3 Cortina . :cry: hich progressively arrest the action . Suprised if theres not jap ones for M X shocks . :?

A C , a Commando will go round a bend , pipes dragging , in a drift , if you get the revs where the responce is instantaeneous - like a weber

.

Dogs , Small Children , water courses , oil slicks , gravle and other impediments should be taken into account . If you were in the right gear you might ride it through one , but storys of legends that take no account
of these things sometimes prove to be that they dont ride quite as maniacly as tales tell .

theres old pilots & theres bold pilots but theres no old bold pilots . http://www.youtube.com/watch?v=JqGpkWKCZiE

Hobot · Dec 23, 2013

I don't want to throw another spanner in the works, but don't rely on the tyre missing any bolts, mudguards whatever in static mode. Tyres "fling", get bigger in diameter as speed increases. The last time I got excited about it was about 20 years ago, when tyre fling at high speed was (from memory) somewhere between 1/4" and 1/2" on diameter. Avon used to publish the data in their technical specs, but that was then. I'm sure that modern companies also publish stuff like that.
cheerswakeup

Very interesting report here as I've seen some scooter and m/c tires spun up on center stand suddenly narrow and expand ~1/2" OD after 70-80 mph range and I believe this happened on Peel the only time I ever held on in an open till top out watching speed and tack to see speedo jump up 4-5 mph and tach needle go back to 6000 as the pull stopped with me face down out of wind buffet to make sure I was steamlined and really seeing needles clearly. Definitely gonna put some styrofoam blocks in swing arm V and custom mud shields to see how close it gets going fast as I dare.

Current Peel has ~4.5" rear and 6" front travel though can pull down each end 3" as needed to resist forces and match conditions. If you ain't explored handling into THE Hinged Wobble/Weavel then you can't say much about what limits Cdo handling in various combos of conditions, assembly alignments/slackness, tire pressure balance, wind gusts, lumpy roads and jacket-helmet-cargo wind eddie load cycles.

baz · Dec 23, 2013

acotrel said:
baz, the handling of a featherbed frame does not depend on the head steady to stop the swinging arm from sending the bike into a weave. It will handle just as good without the head steady. What can happen is that the motor is then able to move under torque reaction and vibration, and it can crack the frame. The effect of the head steady on a featherbed frame in stabilizing the pivot comes from the extra rigidity through the engine plates and crankcases, and these are bolted to the front mounts. The effect of the head steady on the swing arm is virtually nil compared with the commando isolastics setup. It does however stabilize the steering head by bracing it against the motor. - what does the commando have to do that ? Why did the Italian manufactured commando frames crack ?
My comment about isolastic is not to denigrate the design, only to point out the likelihood of a major and potentially lethal weave. I raced a featherbed Triumph regularly for 12 years, perhaps I might actually know why a bike mishandles ? I think a commando would be an excellent commuter bike, however I would never put myself in the position where my life depended on it's handling. If it depends on the head steady to keep behaving itself, something is wrong. I am fully aware that if the isolastics are properly adjusted, there is little problem. Tell that to some kid after he has been chucked up the road.
A bad mishandling problem can remain hidden for years then grab you at just the wrong time. I never expected it to happen with my Seeley. The bike had been raced several times with the Ducati fork yokes and a heavier motor. It grabbed both myself and a friend - both very experienced riders. We both got out of it, mainly by good luck.
Incidentally those beautiful 1000cc Vincents are also prone to the same thing if the forks are worn, and the seat dampers wrongly adjusted. I know a guy who got chucked onto his head at 70mph because the bike went berserk.

Baz, Have you read this topic ? :

commando-motors-featherbed-frames-other-frames-t18209.html#p228936

ok so you are saying that you would be happy to ride a featherbed framed norton with or without a headsteady fitted because it has no effect on the handling even though it could lead to the frame cracking through vibration (and they do) most of the featherbed replica frames that i have seen have an additional tube welded to the headstock someone should tell these frame makers not to fit these additional tubes and all the owners of these bikes should take a hacksaw to their frames and remove them imediately! ,i agree with you about pre unit triumph frames i have owned many of them but the very worst handling i have ever ridden must be either a plunger A10 beeza or a harley rubbermount which wouldnt even go in a straight line! everytime you change gear you have to shift your body weight when i gave it back to my mate i said there must be something wrong with it but he claimed there was not!!! i think harley went a bit mad pivoting the swingarm off the gearbox where on earth did they get that idea from!!!!,as for the kid chucking the commando up the road that was almost me as a green 19 year old i bought a well worn 850 mk 2a one day shortly after buying it and thrashing the hell out of it i was leaning right over on a left hand bend when the whole bike felt like it twisted and stepped out accross the road i could not work out what had happend ,i new nothing about isolastics but after looking over the bike i finally took the tank off and found both the triangular plates that form the headstaeady were bent outwards and the the threads were stripped on the rubber cotton reels and had been araldited into the frame i was lucky that day ,,,,,,,,,,,,,,,,,,,,, regards baz

rear suspension

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