isolastic replacement suggestions for a 72 interstate

Time Warp said:

Don't forget the secondary (inner) rubbers in the isolastic tubes.
I do not think the stock box heady steady is that bad (if it was more rigid) but the rubber cushions it uses have some limitations and the hanger spring might very well been to support those cushions.

Those cushions are certainly not there to take any weight, they are only a (intended) control for axial and radial forces within their working range (hence the slot adjustment, maybe with the wheels on the ground, maybe even with the rider aboard ? )

I will stick with my thoughts on where Dr B got the basic idea.

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I believe ? RGM has been making replacement isolastic kits for longer than even AN.
If they were 'no good the word would have been out by now.

There was talk some years ago of kits with harder rubber and maybe more vibration than stock, the maker ?

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Dr B???? Wasn't it Hooper and Trigg?

robs ss said:

A couple of questions:
That doesn't appear to be the standard bracket (that has the vertical stud the the trunnion is adjusted on) - what is it?
There looks to be an electrical connection to that bracket - why
Cheers
Rob

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I'm pretty sure I just ordered all the stock parts from the Mk3 list. The electrical connection is the red ground wire to the head. Normally the ring terminal goes under one of the Allen bolts to the head but on the CNW headsteady these bolt heads are recessed so I used one of the spring mounting bolts.
Russ
I can take a better picture if needed.

batrider said:

I'm pretty sure I just ordered all the stock parts from the Mk3 list. The electrical connection is the red ground wire to the head. Normally the ring terminal goes under one of the Allen bolts to the head but on the CNW headsteady these bolt heads are recessed so I used one of the spring mounting bolts.
Russ
I can take a better picture if needed.

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No - that's okay - thanks for the answers!

robs ss said:

No - that's okay - thanks for the answers!

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It was a bad angle to see what you wanted to see. This is better maybe..

batrider said:

It was a bad angle to see what you wanted to see. This is better maybe..

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Ahh yes - I see now - thanks again!

EstuaryBoy said:

Dr B???? Wasn't it Hooper and Trigg?

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Not that I am aware of, Mr Hooper (of V8 fame) suggested putting the Atlas engine in the frame Dr Bauer designed instead of the new engine intended for it.

Time Warp said:

Not that I am aware of, Mr Hooper (of V8 fame) suggested putting the Atlas engine in the frame Dr Bauer designed instead of the new engine intended for it.

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Electronic head steady?

COOL!!!

Fast Eddie said:

Exactly my thoughts Rob. I have always looked at that spring (and its hook) and questioned how it can possibly effectively counteract the weight hung from it. It’s not only the engine, the entire powertrain is hanging from it and the article above suggests that weighs 140lbs ! Surely that spring, or the tin plate hook holding it, can’t handle that? If it did, what would that do to long term effect of head gasket sealing etc If there’s a permanent 140lbs force trying to pulling the head off ??

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I made up a test rig to find out how much force these springs exert when installed as recommended. I had to extrapolate as my spring balance has a 22kg limit.
I estimate the coils, at 38mm (up from 24mm unloaded), will exert approx. 42kg force. I think this will have a relatively insignificant effect on the head gasket since a single lubricated 3/8" head bolt, correctly torqued, will generate about 1000kg force. (yes, for the purists, I realise I'm not talking Newtons)
Looking at the force diagram below, the only upward force imposed by the motorcycle on the drivetrain is the front isolatic. The rear Isolastic and rear suspension both impose downward forces. The head steady, if you have the Dave Taylor type, accepts no vertical force.
So, it appears to me, the job of the spring is to take some of that vertical upward force off the front Isolastic. What proportion? Can't say.
If you adjust it - as some do - to make the front isolastic bolt able to "slide", then it is taking all the load in its static state.
I also think its purpose is, not to extend the life of that Isolastic, but, rather, make it work better by relieving some of the shear force off it.
So... no - I don't think it is a bodge!

Okay nay-sayers - tear that apart!

... it is also evident (at least to me) that it cannot do anything to reduce the load on the rear isolastic. It has the load it has.

The only way to reduce that is to go on a diet, fat-arse!

Rob, so back to another discussion we had about how to park the motorcycle and give the isolastics break, if you diagram is correct then using the centre stand (assuming its cradle mounted) is the best way of relieving pressure on the rear iso?

Quickies question though: how did you arrive at the conclusion about direction of load in your diagram?

Not sure I’m a ‘naysayer’ but I have been a ‘questioner’ and still am. When you say the main purpose of the spring is to relieve some of the sheer force off the front iso, what do you expect that to do in practical terms, how will that advantage manifest itself ?

Fast Eddie said:

Rob, so back to another discussion we had about how to park the motorcycle and give the isolastics break, if you diagram is correct then using the centre stand (assuming its cradle mounted) is the best way of relieving pressure on the rear iso?

Quickies question though: how did you arrive at the conclusion about direction of load in your diagram?

Not sure I’m a ‘naysayer’ but I have been a ‘questioner’ and still am. When you say the main purpose of the spring is to relieve some of the sheer force off the front iso, what do you expect that to do in practical terms, how will that advantage manifest itself ?

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First question - No. In fact, I think, putting the bike on the centre stand will increase the load on the rear iso. You will still have "B" acting there but, since the rear tyre is off the ground, "A" will also have to come through the rear iso.
I think that, being on the centre stand, it will reduce the load on the front iso, because of the cantilever effect of the suspended swing-arm.

Second question - Simple moment-arm diagram around the rear iso shows it has to be true, In practical terms, what to you think will happen if you were to pull the central bolt out of the front iso. I think the engine would drop onto the frame rails. Therefore the frame is pulling up on the front iso.

Third question - If the iso rubbers are already distorted by a force, then they will be less compliant to absorb vibration. The only exception to this would be the upward component of the vibrational movement - because, of course, that would be relieving the shear. So the total effect, I think, would be worse performance at absorbing vibration - kind of the same as having stiffer iso rubbers.

Ref your first point; it’s early here and I posted before coffee. Yes, if your diagram is correct, the stand will not give the isos a break. A Jack mounted under the frame rails will do, which was my earlier thought on this.

Ref your second point; these things might seem obvious to you. That’s probably cos you’re clever.

Ref your third point; all good theory. But personally I’m more interested in its effect on an already good set up, not in relieving symptoms of old crushed / worn isos. Hence my eagerness to hear your before and after ride report sir...

Fast Eddie said:

Ref your third point; all good theory. But personally I’m more interested in its effect on an already good set up, not in relieving symptoms of old crushed / worn isos. Hence my eagerness to hear your before and after ride report sir...

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Yep - I'll do that!
I intend to try a matrix of upward force vs front isolastic setting.
On each setting I'll ride it for a while and make notes.
I guess you could call that a "seat-of-the-pants" investigation. Mainly subjective, of course!
I'll start with sliding iso bolt and 1.5 holes back-off on the iso.

robs ss said:

Yep - I'll do that!
I intend to try a matrix of upward force vs front isolastic setting.
On each setting I'll ride it for a while and make notes.
I guess you could call that a "seat-of-the-pants" investigation. Mainly subjective, of course!

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Now I’m even more eager...

Fast Eddie said:

I have a hard time believing that the stock head steady rubbers (same part number as the exhaust mount rubbers) can effectively take any real weight of the engine unit. And if they did, it wouldn’t be for very long!

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They certainly couldn't take the weight of a 850 mini exhaust silencer which weight nothing...

The power unit is suspended by the Isolastics so there should be no actual weight hanging from the head steady rubber mounts.

Indeed LAB, which was kinda my point in my post (quoted above) which I wrote in response to an earlier claim that “the spring (and top isolastic coushions) are indeed suspending the engine”.

I just noticed Carl Hokanson that I have mentioned, is a member here - @Carl H !

Like I said, I'd trust his iso kits ANYTIME, ANYWHERE.

grandpaul said:

I just noticed Carl Hokanson that I have mentioned, is a member here - @Carl H !

Like I said, I'd trust his iso kits ANYTIME, ANYWHERE.

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Thanks for that. Because so many , including myself had trouble getting the front units in, I have been turning them down by .100", so they are more like the size of OEM front isos. I never could figure out why the fronts were so large on the OD of the rubbers, when the rear were just like OEM size and slide in without lots effort. It takes me about 15 minutes to do, Plus clean up time of my lathe, But I got tired of getting questions from buyers why they struggled ( to put it mildly) to fit them in the front cradle. It's a dirty job, But someone has to do it... ;-))) Carl H