Featherbed frame design went against all engineering princip

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Re: Featherbed frame design went against all engineering pri

I'll still preach to my old point (look back two pages or so)

- Even with dynamically balanced, rigid mounted parallel twin with somewhere around a 3.5" stroke, you're looking at vibration in places you don't want, and an overall embarrassing design for a mainstream production bike in the 70's. Keep in mind that just because we find things acceptable and neat now, doesn't mean they were that way back then. Think ammeter vs. WLA. The mechanical WLA is just excessive, poorly engineered , and not as good as an ammeter (which has the neat feature of "finding the right starting point" used by nearly every big single maker to start a bike easily). The reason for the swap mainly was the negative stigma associated with a gauge that tells you what your charging system is doing, as it indicates there could have been a need for such a thing (implications of unreliability). We know now this is not true...but back in the day different story. Keep in mind the japanese by then were offering bikes with an electric start so reliable, they kept the kickstarter hidden "just in case", only 2 or 3 warning lights, brakes that didn't rust or wear funny and "worked", and had motors that were nearly fully oil-tight. The last thing you wanted was for people to see your current product line as a "old fashioned". Cool when your product is 30 years old, or your customer base is older, but a tough sell for a new product being sold to young people.

- The bigger the reciprocating mass of the engine for a reasonable frame design, the more vibes you will see on a balance factor optimized 360 twin, that's a fact. The key is in reasonable frame design... a featherbed relies a LOT of the engine stiffness (as pointed out before) including the use of the head steady for a large portion of the steering neck stiffness. Put in a vibrational monster in there, and you'll find all kinds of problems quick. Compare that to something like a Seeley, Egli, Foale, etc.. frame and you'll find a very different story usually. The balance factor also plays a big role. Note that most makers at the time were not dynamically balancing cranks and a lot weren't even really balancing them much at all, just due to cost (balance marks were cast in, maybe lightly touched up on many bikes). If you spend the time on an atlas and weight match the pistons, weight match the rods, dynamically balance the crank, and tune the balance factor to the chassis and play around with weights, I'm sure you can get the vibes down a LOT from a factory setup. Doesn't mean that's feasible for a production bike.

- As mentioned before, keeping afloat for the next quarter decade was the main goal for Norton, not creating the next racing machine. In that regards the isolastic made perfect sense...and it actually made more sense than what most British makers were doing at the time. The problem with the commando is just that at the time, it was too much and not enough in a lot of ways, and coupled with poor management that's what ended up killing Norton.
 
Re: Featherbed frame design went against all engineering pri

Combat blow ups were mainly d/t bad manufacture of ignition system stability and cases bores alignment. Capt. Norton Notes has scattered gems on how early 70's drag racers got by w/o SuperDuperblends which is my spoof on the unique Norton only advertising sales pitch survival name. Old school path was using better ball bearings in thin wall 750 cases to allow crank to flex a good bit before hitting much resistance from cases till lightened cast iron flywheels and cases could take it but bearing still fine. New age path is beef everything up to resist crank flex till crank bends and cases fracture then make cases thicker heavier some more.

We know Cdo frames fracture w/o the rubber isolation, would Combat in Featerbed frame break w/o isolation too?
 
Re: Featherbed frame design went against all engineering pri

Rohan said:
Jose Refit said:
I agree, Ashman's comments don't make sense. Prepare a 750 engine to the same standard as an 850 (828?) and there will be less vibration due to the reduction in reciprocating weight.

This statement is written ambiguously then.....

If 'a 750 was prepared to the same standard as an 850',
then you'd have to fit heavier pistons to a 750 ??
The problem with the 850 is that when you balance it to suit high revs, it becomes extremely smooth and very easy to over-rev. Balancing the crank does not change the piston weight or it's effect on the aluminium con-rods when they hold them back from hitting the head. The loads on the rods are a squared relationship as the accelerations increase when you rev the bike. If the vibration is there at high revs, it must be balanced out, however the absence of vibration doesn't mean the engine is internally safe.
 
Re: Featherbed frame design went against all engineering pri

hobot said:
Combat blow ups were mainly d/t bad manufacture of ignition system stability and cases bores alignment. Capt. Norton Notes has scattered gems on how early 70's drag racers got by w/o SuperDuperblends which is my spoof on the unique Norton only advertising sales pitch survival name. Old school path was using better ball bearings in thin wall 750 cases to allow crank to flex a good bit before hitting much resistance from cases till lightened cast iron flywheels and cases could take it but bearing still fine. New age path is beef everything up to resist crank flex till crank bends and cases fracture then make cases thicker heavier some more.

We know Cdo frames fracture w/o the rubber isolation, would Combat in Featerbed frame break w/o isolation too?

Regardless of the isolastics, if motor vibration is due to crank balance and not primarily piston weight, the crankcases must cop a beating. The isolastics provide a little give so the forces don't meet a completely immovable object. If vibration is due to piston weight, the first thing to fail would probably be a rod. The limitations of 650cc Triumph motors come down to this factor - to get high comp. in order to use methanol fuel, you must use heavy high crown pistons. A balanced Triumph one-piece crank will easily cop 8000 RPM all day, the piston weight makes that a no-go. I don't know about carillo rods - never done a weight comparison, however I think I would live with a bit of vibration if I had those. Jim Schmidt obviously has the right combination with the long rods and light pistons.
My motor has near standard internals, doesn't get used much however it hasn't blown up yet. I try very hard to never rev it past 7000 RPM. I still believe it will hand-grenade.
 
Re: Featherbed frame design went against all engineering pri

Alan you are one the few to consider that iso's besides protecting frame and pilot also act like gun firing recoil cushions taking some the spike shock off the bearings by allowing some engine recoil. Fun frustrating stuff to get most of of engines with least amount of moving materials. I lived on Peel till 2000 miles after her stuck throttle let down but so spoiled only ride my others now and then on special occassions half of them d/t car out of action. Completely oppositie of any thing else to me, always working hard riding fast to avoid crashing vs always trying to get fast enough to control crash Peel but missing the ground. Better than sex and drugs I wish for others to share the rushes.
 
Re: Featherbed frame design went against all engineering pri

Triton Thrasher said:
84ok said:
The tests were done on bare frames (no engine/transmission or Isolastics installed)

Why? Featherbed steering head is braced to the cylinder head and the engine plates are bolted to the same frame gussets as the swing arm is.

I'm not sure what this thread is about. if you're worried about handling differences between Dominators and Commandos, ride the bikes and make a judgement.

Nothing can go against all engineering principles!

i'm not worried about it, just a noob reading up (most of it for the first time) on what went down at the time, then combined with folks who have gone there inside out hands on prob for decades or more,

looking into it, i then ran across a few threads that clearly reflected the commando as a superior platform period, it seemed a bit strange that those comments weren't challenged,

dunno if there is any merit in measuring 2 bare frames, where one shows far superior stiffness that way and how that may relate to overall stiffness with engines installed, and that may be the true measure of a frames measured stiffness....

but this comment was made
featherbed-frame-design-went-against-all-engineering-princip-t20512-180.html#p267372
Additionally, the Commando structural design gave about a 10-fold increase in torsional stiffness, keeping the front and rear wheels more accurately in line. Vertical stiffness increased by about a factor of 3x.

Provided the lateral clearances in the polyurethane discs that control side-to-side rocking motion are kept within specs, the Commando should out-handle a Featherbed by a facotr of at least three.

can't find it now but there was the comment that commando handling ultimately came down to the cyl head arrangement to the frame, and that it was very problematic, end of story

EDIT - ahh, here it is
featherbed-frame-design-went-against-all-engineering-princip-t20512-195.html#p267547
acotrel wrote: When a bike relies on it's head steady for it's handling - that is dangerous bullshit.

then the counter
Triton Thrasher wrote: Maybe not the most elegant ever engineering, but used by the one-time World top racing bike and also by tens of thousands of road bikes.


"Dangerous bullshit" it was not.

this also has come up
featherbed-frame-design-went-against-all-engineering-princip-t20512-195.html#p267611
Tony Foale, another advocate of the spine frame, reckons the featherbed is an inefficient design i.e not much stiffness for the weight, http://www.tonyfoale.com/ Click on 'Articles' and scroll down to 'Practical' and click on 'Frame Stiffening',

So, after throwing away all those unnecessary bits, it seems that the best place to start any handling improvements is with the frame and swing-arm to ensure that you have a rigid base from which to work. The main objective is to keep the wheels in line with one another, both torsionally and laterally. To do this the main frame loop must maintain the steering head and swing-arm pivot in their correct relationship to each another. Probably, most frames are still of the double loop type, pioneered on the 1950 Manx Norton, designed by an Irishman with the name of McCandless, this machine was renown for it's good handling, but we must remember that it had only 50 bhp. to con- tain, it weighed only 300 lbs. and the tyres of the day were only capable of feeding in much lower forces than those with which we are now accustomed. Despite it's past successes this type of frame is not very structurally efficient, that means for it's weight it does not provide much stiffness. Fortunately, it is often possible to improve on this quite substantially with the minimum addition of weight and with only a small amount of work.

The Real World

From the forgoing we can see that from the structural view point the fully triangulated frame such as that on the Krauser BMW is potentially the best, but a cost conscious volume manufacturer runs a mile from the concept because of the labour intensive nature of the construction, after all there are a lot more joints to weld up. Easier from the production angle is the spine frame in all it's variations. this uses the stiffness that can be obtained in both bending and torsion from the use of one main large section member, and this concept has found volume application on some moped type machines in the form of welded up pressing. The Yamaha FS1E. is a good example of this technique. However, apart from small volume chassis makers, such as Egli and Moko in Switzerland and yours truly in the U.K. there have not been many attempts at using this type for larger machines. The Norton Commando is a notable exception, but that was spoilt in two ways, one;-- the backbone could have been larger, and two;-- the potential stiffness from this frame was thrown away by the method used for rubber mounting the engine AND swing-arm. Probably the main reason for its lack of use in production, is that on a large bike the space needed for the engine, airbox, battery, etc., is not compatible with the concept in most cases
 
Re: Featherbed frame design went against all engineering pri

84ok said:
EDIT - ahh, here it is
featherbed-frame-design-went-against-all-engineering-princip-t20512-195.html#p267547
acotrel wrote: When a bike relies on it's head steady for it's handling - that is dangerous bullshit.

In case you missed it, Allan was referring to the featherbed head steady.

And also in case you missed it,
if Allan hasn't taken his morning meds ?,
some of us think that everything that follows for a while is likely to be 'bullshit'.
!!!!

There is also the minor matter that he confesses that he has never ridden a Commando....
 
Re: Featherbed frame design went against all engineering pri

acotrel said:
The problem with the 850 is that when you balance it to suit high revs, it becomes extremely smooth and very easy to over-rev. Balancing the crank does not change the piston weight or it's effect on the aluminium con-rods when they hold them back from hitting the head. The loads on the rods are a squared relationship as the accelerations increase when you rev the bike. If the vibration is there at high revs, it must be balanced out, however the absence of vibration doesn't mean the engine is internally safe.

Have we reverted to stating the bleedin obvious ?

As we keep saying, the balance factor is to give the rider a comfortable ride.
The rev limit from the forces on piston accelerations, bearing loadings etc are numbers that are calculated
from piston and rod weights, etc and rpms - and not really related to BF selected...
 
Re: Featherbed frame design went against all engineering pri

hobot said:
Combat blow ups were mainly d/t bad manufacture of ignition system stability and cases bores alignment. Capt. Norton Notes has scattered gems on how early 70's drag racers got by w/o SuperDuperblends which is my spoof on the unique Norton only advertising sales pitch survival name. Old school path was using better ball bearings in thin wall 750 cases to allow crank to flex a good bit before hitting much resistance from cases till lightened cast iron flywheels and cases could take it but bearing still fine. New age path is beef everything up to resist crank flex till crank bends and cases fracture then make cases thicker heavier some more.

While Combat blow ups may have resulted from a myriad of quality control issues,
you'd have to conclude that if fitting heavier duty bearings fixed the engine bearing failure problems,
then the bearings simply were marginal, and not initially man enough for the job ??

Steve Maney etc has demonstrated that thicker cases can solve other issues.
As someone said a long time back - on a road test of a Laverda I believe -
if Nortons had added 20 lbs of weight dedicated to improved reliability, who knows where they would be today....
 
Re: Featherbed frame design went against all engineering pri

The MK3 is a terrific bike for it's time(and still nice now), better than my CB 750 was in handling, acceleration, torque, smoothness and looks, but it did not matter. With all the debt being loaded onto Norton via forced mergers, one great bike could not support the financial weight being dumped upon it!

Glen
 
Re: Featherbed frame design went against all engineering pri

IIRC Combats Also needed & got better bearings at some point, roller on DS, balls on TS not superduper blends. Long run Combats still being found with these bearing still good to go. I love and depend on the strengths and weakness of isolastic Cdo so that's my tool of choice to upset the over tiffened cycle world by playing with go carts and rally cars. Will be scary fun. .
 
Re: Featherbed frame design went against all engineering pri

The comparison of frames was clouded by Norton selling new Commandos with a built-in exciting little tank-slapper as you passed 80 mph and other steering quirks, after years of selling Dominators that steered rather well.
 
Re: Featherbed frame design went against all engineering pri

All Commandos didn't do that though.

Was there any particular year or model that that was supposed to apply to. ?
I can't image road racing a Hi-Rider at a fair clip of knots !
 
Re: Featherbed frame design went against all engineering pri

acotrel said:
I rode the CB750 Honda when they first came to Australia. It was quiet, didn't leak oil or rattle, however it handled like a camel. I remember one race meeting when the CB750s first appeared and I rode my 500cc Triton weaving through them in a cloud of water, going miles an hour faster. It didn't last for long because the guys discovered the CB450 pistons would fit if they drilled bigger holes making the motor 830cc, then it was a different story.

Just for the record, CB450 pistons can't fit a CB750/4.
Thats a 7mm bore increase per cylinder !
Lot more than 830 cc
Memory again ??
CB450 pistons will fit the Kwaka 1000 though.
 
Re: Featherbed frame design went against all engineering pri

Rohan said:
All Commandos didn't do that though.

Was there any particular year or model that that was supposed to apply to. ?
I can't image road racing a Hi-Rider at a fair clip of knots !

They always say that properly adjusted Isolastics give good steering, don't they? So I guess that's what Norton and their agents should have done to the bikes they were selling and servicing.
 
Re: Featherbed frame design went against all engineering pri

Rohan said:
Just for the record, CB450 pistons can't fit a CB750/4.
Thats a 7mm bore increase per cylinder !
The pistons from the CB 350 twin were used to overbore a CB 750 Honda. That gave 830 cc.
 
Re: Featherbed frame design went against all engineering pri

Triton Thrasher said:
Rohan said:
All Commandos didn't do that though.

Was there any particular year or model that that was supposed to apply to. ?
I can't image road racing a Hi-Rider at a fair clip of knots !

They always say that properly adjusted Isolastics give good steering, don't they? So I guess that's what Norton and their agents should have done to the bikes they were selling and servicing.

True, isolastic clearance needs to be within limits for the bike to work at it's best but will not compensate for poor build quality. Norton should have invested more in production to ensure correct assembly of the Commando's rolling chassis. This done they work very well.
Featherbed frame design went against all engineering princip


The above was taken at Cadwell Park 1/8/14. Chassis went through the surface table/WSC treatment 2 years ago. Only addition to standard is an Isolastic head steady and the steering damper to compensate for front tyre after it's past half worn. Forks have the long top bush and modded damper tube.

You might be aware there's several Commando experts on this forum that neither own or ride a Commando, which model do you ride?

Jose.
 
Re: Featherbed frame design went against all engineering pri

Jose Refit said:
You might be aware there's several Commando experts on this forum that neither own or ride a Commando,

No, I don't know much about the people here.

which model do you ride?
.

I'm in the terrible position of being stuck with one of those bikes (that this thread is about), that go against all engineering something or other.
 
Re: Featherbed frame design went against all engineering pri

Same here...guess what, engineering principles or not, this thing is FUN. (It also outperforms most of my friends modern bikes...).

Featherbed frame design went against all engineering princip
 
Re: Featherbed frame design went against all engineering pri

Triton Thrasher said:
Jose Refit said:
You might be aware there's several Commando experts on this forum that neither own or ride a Commando,

No, I don't know much about the people here.

which model do you ride?
.

I'm in the terrible position of being stuck with one of those bikes (that this thread is about), that go against all engineering something or other.


You're also in the terrible position of not knowing what you're talking about,

Jose.
 
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