extra ISO under gearbox head steady delete

74ok

74ok

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baz

Post in thread '5sp triumph box, atlas head + lots more'

Brian Holzigal said:
This is of course a bitsa built over a few years from parts collected. The frame was pretty ordinary but staright with no loop and a few holes for chooper tanks I guess. Cheap. Very cheap, always a good starting point for a special. The gearbox is Triumph 5 speed cluster stuffed into a swingarm pre-unit Tri box, 54-62. Not that hard to do. The clutch is therefore triumph. T140 stator bolts thread into a thick flat plate bolted in place of an inner primary. Motor came from everywhere. Stock cam, single Mikuni, 750 cylinder and Atlas head, cheap compared to Commando heads, just drill to...
Click to expand...
 
74ok said:
baz

Post in thread '5sp triumph box, atlas head + lots more'

Brian Holzigal said:
This is of course a bitsa built over a few years from parts collected. The frame was pretty ordinary but staright with no loop and a few holes for chooper tanks I guess. Cheap. Very cheap, always a good starting point for a special. The gearbox is Triumph 5 speed cluster stuffed into a swingarm pre-unit Tri box, 54-62. Not that hard to do. The clutch is therefore triumph. T140 stator bolts thread into a thick flat plate bolted in place of an inner primary. Motor came from everywhere. Stock cam, single Mikuni, 750 cylinder and Atlas head, cheap compared to Commando heads, just drill to...
Click to expand...
Click to expand...
????
 
lotsa prior xtra/third iso discussion in this dedicated norton commando forum, first i've heard about not using a head steady

so also a new dedicated topic

not to mention the other thread has a ton of other stuff goin on

topic/subject is

extra ISO under gearbox head steady delete​

some part there ur missing????

then the link goes to 2 folks who went there & talked about it, including a vid
 
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74ok said:
lotsa prior xtra iso discussion in this dedicated norton commando forum, first i've heard about not using a head steady

so also a new topic
Click to expand...
The Dreer commandos had no head steady
I have my own iso norvil style head steady but it's not really necessary but I refitted just in case
 
It would take a lot of convincing me to delete / remove a head steady . Tried it once , around the block only .
A third one , welded in undercarriage style , I have tried out on a friend's machine . Many years back .
It's integral to isolastic handling to have one . Besides sloppy handling , the other 2 isos will not hop up and down as straightly as they should , and then wear out rather quickly . I use a Heim Joint type and will never go back . Lube all 3 regularly .
 
Torontonian said:
It would take a lot of convincing me to delete / remove a head steady . Tried it once , around the block only .
A third one , welded in undercarriage style , I have tried out on a friend's machine . Many years back .
It's integral to isolastic handling to have one . Besides sloppy handling , the other 2 isos will not hop up and down as straightly as they should , and then wear out rather quickly . I use a Heim Joint type and will never go back . Lube all 3 regularly .
Click to expand...
I can assure you my commando with the extra ISO under the gearbox doesn't need a head steady
But I choose to keep it fitted
 
baz said:
The Dreer commandos had no head steady
I have my own iso norvil style head steady but it's not really necessary but I refitted just in case
Click to expand...
If a rigidly mounted engine requires a torque stay, why doesn't a flexibly mounted engine require one? Your claim doesn't make sense. All large parallel twins have torque stays, AFAIK.
Without one, the engine will try to rotate in the engine mountings, so crankcase lug holes and cradle bores will ovalize and the corresponding bolts will loosen up. What happens to the 3 ISOs I can't imagine - the support system is statically indeterminate - and some of them will be subjected to increased compression as the loading shifts. Displacement pattern will be time/load dependent.

- Knut
 
I do not want to rubbish the Commando design, but if the handling depends on the head steady - that is ridiculous. You must be riding a bowl full of jelly. Herb Becker did something under the gearbox of Doug MacRae's bike to get it to handle. But a lot of old guys like to keep their shifty moves secret. I suggest that modifying a Commando frame, creates the risk of cracking it. I was once going to build a second bike. I looked at a Commando frame and rejected the idea. With a Commando motor, even a featherbed frame would probably crack. The torque output is probably much more than with any other vertical twin British motor. The Commando frame design is probably on the limit.
 
I do not think my MK3 Seeley frame would ever crack. But race tracks are not thousands of miles in length, and a Seeley frame costs a bomb. The head steady on my frame is double braced fore and aft, and has rose joints which will allow the top of the motor to vibrate slightly sideways. The rest of the motor is rigidly mounted. When I got the Seeley, I had seen what it could do, and I had kept track of it for a considerable time before I could buy it. But I could not get the Laverda 750 motor. I think the 850 Commando motor might lighter, and even better.
 
mdt-son said:
If a rigidly mounted engine requires a torque stay, why doesn't a flexibly mounted engine require one? Your claim doesn't make sense. All large parallel twins have torque stays, AFAIK.
Without one, the engine will try to rotate in the engine mountings, so crankcase lug holes and cradle bores will ovalize and the corresponding bolts will loosen up. What happens to the 3 ISOs I can't imagine - the support system is statically indeterminate - and some of them will be subjected to increased compression as the loading shifts. Displacement pattern will be time/load dependent.

- Knut
Click to expand...
A standard commando dosent have a torque stay !
And my commando has MK3 ISOs front and rear
It has a MK3 type under the gearbox this is empty IE no rubber (I didn't want to alter damping effect of the standard setup)
I have a norvil type headsteady but I have tried it without the headsteady fitted (as the Dreer commandos) but I prefer to keep it fitted
None of this is needs to be imagined
 
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acotrel said:
I do not want to rubbish the Commando design, but if the handling depends on the head steady - that is ridiculous. You must be riding a bowl full of jelly. Herb Becker did something under the gearbox of Doug MacRae's bike to get it to handle. But a lot of old guys like to keep their shifty moves secret. I suggest that modifying a Commando frame, creates the risk of cracking it. I was once going to build a second bike. I looked at a Commando frame and rejected the idea. With a Commando motor, even a featherbed frame would probably crack. The torque output is probably much more than with any other vertical twin British motor. The Commando frame design is probably on the limit.
Click to expand...
Yes
You have told us this many many times before
You are entitled to your opinion
And as I have said to you before the featherbed frame also depends on its headsteady
But like the commando it was very successful in racing and on the road
 
acotrel said:
I do not think my MK3 Seeley frame would ever crack. But race tracks are not thousands of miles in length, and a Seeley frame costs a bomb. The head steady on my frame is double braced fore and aft, and has rose joints which will allow the top of the motor to vibrate slightly sideways. The rest of the motor is rigidly mounted. When I got the Seeley, I had seen what it could do, and I had kept track of it for a considerable time before I could buy it. But I could not get the Laverda 750 motor. I think the 850 Commando motor might lighter, and even better.
Click to expand...
That's rather naive, but since you haven't actually ridden it in years, it probably doesn't matter. Even my brick shithouse Rickman has cracked.

Facts: Colin Seeley was renowned for his lightweight designs, unsurprisingly they had a tendency to crack.

And as I have said before, when I ordered the Rickman chassis in 1975 I had also considered a Seeley build, but every Seeley Commando (750s, and 850s, all MkIIIs) that I looked at in race paddocks had a cracked frame, mostly around the swinging arm pivot.
 
here's a quote from above 1st post/link

Brian Holzigal said:
Motor came from everywhere. Stock cam, single Mikuni, 750 cylinder and Atlas head, cheap compared to Commando heads, just drill to 3/8" bolts. There was no need for a top steady as I fitted a 3rd iso mount under the swingarm, cradle to frame a copy of the top one under the oil tank which gives good stability and allows vertical movement. This setup triangulates the swingarm pivot. I have this on other Norton Commando specials
 
74ok said:
here's a quote from above 1st post/link

Brian Holzigal said:
Motor came from everywhere. Stock cam, single Mikuni, 750 cylinder and Atlas head, cheap compared to Commando heads, just drill to 3/8" bolts. There was no need for a top steady as I fitted a 3rd iso mount under the swingarm, cradle to frame a copy of the top one under the oil tank which gives good stability and allows vertical movement. This setup triangulates the swingarm pivot. I have this on other Norton Commando specials
Click to expand...
I think the "triangulation" he talks about comes a poor seventh to the original top iso on commandos.
Look at the frame drawing - I have marked to original isos as F, R & T - the one under the swingarm pivot as NEW. The new one has comparatively little vertical separation from F & R so can't possibly be a effective as the, existing, upper one. It is also in one of the dirtiest areas on the bike.
Sounds like fixing a problem that does not exist with a substantially inferior "solution".
Cheers
090AF67D-D9A0-4C9E-A2A6-CFEC8F6A0ED8.JPG
 
robs ss said:
I think the "triangulation" he talks about comes a poor seventh to the original top iso on commandos.
Look at the frame drawing - I have marked to original isos as F, R & T - the one under the swingarm pivot as NEW. The new one has comparatively little vertical separation from F & R so can't possibly be a effective as the, existing, upper one. It is also in one of the dirtiest areas on the bike.
Sounds like fixing a problem that does not exist with a substantially inferior "solution".
Cheers
View attachment 118025
Click to expand...
I think the Dreer third ISO was roughly in the middle of the bottom frame tubes. That is where I added one on my Fastback, but chose to keep the head steady as well. The position you show has been used for an across-the- frame link by others, in addition to a head steady, as I recall.
 
jan nelder said:
I think the Dreer third ISO was roughly in the middle of the bottom frame tubes. That is where I added one on my Fastback, but chose to keep the head steady as well. The position you show has been used for an across-the- frame link by others, in addition to a head steady, as I recall.
Click to expand...
I think you're wise to keep the head steady - and the Dave Taylor style is very effective without impeding up & down/fore & aft movement.

I do tend to think a fourth iso is a bit like a fourth leg on a stool.

Cheers
 
robs ss said:
I think the "triangulation" he talks about comes a poor seventh to the original top iso on commandos.
Look at the frame drawing - I have marked to original isos as F, R & T - the one under the swingarm pivot as NEW. The new one has comparatively little vertical separation from F & R so can't possibly be a effective as the, existing, upper one. It is also in one of the dirtiest areas on the bike.
Sounds like fixing a problem that does not exist with a substantially inferior "solution".
Cheers
View attachment 118025
Click to expand...
No
The extra ISO goes under the gearbox
Not behind it
 
robs ss said:
I think you're wise to keep the head steady - and the Dave Taylor style is very effective without impeding up & down/fore & aft movement.

I do tend to think a fourth iso is a bit like a fourth leg on a stool.

Cheers
Click to expand...
"I do tend to think a fourth iso is a bit like a fourth leg on a stool."
Maybe think of a chair then 😂😂😂😂👍👍
 
baz said:
A standard commando doesn't have a torque stay !
Click to expand...
Not a traditional one, but I think the rubber mounting (and the additional spring on the Mk3) does limit back/forth movements (pitch rotations). It certainly limits roll rotations. Granted, it's an imperfect system, and the reason why my crankcases and cradles have ovalized mounting holes!
The Norvil racing-type head steady is far more effective of course.

The problem with a 3rd large ISO support under the gearbox is that distance to the CoG of the powerplant is small, so torque forces becomes quite large. There is no effective counteracting force couple in that design, and a different design is called for. Not easy to realize without obstructing the function of the other two supports.

baz said:
And my commando has MK3 ISOs front and rear
It has a MK3 type under the gearbox this is empty IE no rubber (I didn't want to alter damping effect of the standard setup)
I have a norvil type headsteady but I have tried it without the headsteady fitted (as the Dreer commandos) but I prefer to keep it fitted
None of this is needs to be imagined
Click to expand...
Huh? I don't doubt the existence of your set-up in any way! I guess you altered the support under the gearbox into a nonworking support because the idea didn't work out?
By my comment "What happens to the 3 ISOs I can't imagine", I was addressing the displacement behavior in general of such a support system.

- Knut
 
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