isolastic replacement suggestions for a 72 interstate

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batrider said:
I kept it stock and used the rubbers from Andover Norton. Vibration same. Fairly easy job using a variation of the Mike Taglieri method. I didn't want to take the bike halfway apart to install vernier isos.
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What is the Mike Taglieri method?

Never mind, found the thread.
 
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SteveC said:
It does appear to be weight bearing. I fitted one to my 750 and tightened it until I could move the front iso bolt back and forth by hand, so certainly the load was taken off the front iso. It doesn’t take the load off quite as well at the back, but it does reduce it.
Definitely worth fitting in my opinion, reduced my tick over vibrations - no more mudguard (fender) shakes at idle.
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Ah, the best part of idling is the front forks jump up and down. The guy in the car next to you bumps his passenger to show it, but before he looks you grab the front brake and it stops. The little things that amuse.
 
grandpaul said:
If properly adjusted, the engine is sat in place even if you extract the front mount bolt. Of course you can not operate the bike without the bolt, but the spring (and top isolastic coushions) are indeed suspending the engine. Remember that the engine is counterbalanced on the rear isolastic pivot, by the swingarm and rear wheel/tire assembly.
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GP, could you point me to a photo of how the spring is installed?
I don't have one, but am interested.
Cheers
Rob
 
robs ss said:
GP, could you point me to a photo of how the spring is installed?
I don't have one, but am interested.
Cheers
Rob
Click to expand...
Only picture I can find at the moment, I'll look for a close-up later...
isolastic replacement suggestions for a 72 interstate
 
The cNw head steady seems to come with the drilling/tapping for this (see photos below) - that is, to mount item #2.
Item #8 appears to pick up on the front tank bolts?
Anyone done this? Views?
Screen Shot 2021-01-21 at 11.01.37 am.pngcnw_head_steady3.jpg
 
Is anyone aware of work being done to validate the upward force of these springs?
My 650 engine weighs 43kg - not sure what a commando engine weighs?
If you knew the "spring constant" (k) for that spring and the amount of deflection of the spring required for it to fit over the spring saddle and under the trunnion (x) you could work out how much upward force it generates.
I wonder how close it comes to neutralising the engine weight?
Then, of course, there's the fact that the spring isn't acting vertically (looks to be about 20 degrees) which would mean that if it were to magically have 43kg equivalent force, only 40kg would act vertically and 15kg would act horizontally forward.
So, maybe like statically balancing these engines, there is a compromise to be made.

Someone (was it comnoz?) put a compression spring under the engine, acting off a cross-member.
 
robs ss said:
Is anyone aware of work being done to validate the upward force of these springs?
My 650 engine weighs 43kg - not sure what a commando engine weighs?
If you knew the "spring constant" (k) for that spring and the amount of deflection of the spring required for it to fit over the spring saddle and under the trunnion (x) you could work out how much upward force it generates.
I wonder how close it comes to neutralising the engine weight?
Then, of course, there's the fact that the spring isn't acting vertically (looks to be about 20 degrees) which would mean that if it were to magically have 43kg equivalent force, only 40kg would act vertically and 15kg would act horizontally forward.
So, maybe like statically balancing these engines, there is a compromise to be made.

Someone (was it comnoz?) put a compression spring under the engine, acting off a cross-member.
Click to expand...
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 ??

Obviously the spring isn’t intended to take all of the weight, only some of it. So that then raises the question as to how much value it is adding.

If extending the life of the isolastics is the aim, my own thoughts on this are to use a frame mounted lift when the bike is out of use over winter, that (I believe) will reverse the load on the isolastics, giving them a break.

Isolatics seem to last a good few decades normally. If my frame mounted lift helps increase that by another decade or so, I’ll call that ’problem’ solved and move on to the next ...
 
Fast Eddie said:
If extending the life of the isolastics is the aim, my own thoughts on this are to use a frame mounted lift when the bike is out of use over winter, that (I believe) will reverse the load on the isolastics, giving them a break.

Isolatics seem to last a good few decades normally. If my frame mounted lift helps increase that by another decade or so, I’ll call that ’problem’ solved and move on to the next ...
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Actually, doesn't the centre-stand essentially do that?
Well, not really, as I just measured it takes 25kg to lift the front wheel.
What I have done though, for cleaning purposes, is to cut a 12 1/2" length of 2" x 1" pine and use it a a manual "jack" under the front iso. It effectively lifts the front wheel off the deck.
If you stored a bike like this it would reverse the static load on the front iso. The rear tyre is already off the ground.
I'll have to give that bit more thought!

Edit: an additional thought is: are we trying to extend the life of the isos or trying to improve the effectiveness of them while riding? If the mass of the engine is not bearing down on the front iso, will it work better?
 
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robs ss said:
Edit: an additional thought is: are we trying to extend the life of the isos or trying to improve the effectiveness of them while riding? If the mass of the engine is not bearing down on the front iso, will it work better?
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I think this is the heart of the matter. I seem to remember an old Norton Service Note that said that the top iso mount should be adjusted so that it is taking some load and not just tightened when in place. I tried this and it seemed fairly tough to achieve.
Perhaps the spring is a later attempt to achieve this?
I can’t pretend to know the physics of the spring, but speaking as someone who has fitted one, if you remove the front iso stud and look through the hole as you tighten the spring, you can see the iso tube rising and aligning with the frame holes.
I kept the top iso bolts loose when doing this, and then tightened them once the front iso holes were more or less aligned and the stud had reasonably free movement. In other words, you could put the stud in by hand without the use of a mallet. Perhaps the spring is just an easier way to preload the top head steady?

It does seem logical that the engine will vibrate more freely if it doesn’t have to fight engine weight in one direction?

Just looked up the service note - N3/51
 
SteveC said:
It does seem logical that the engine will vibrate more freely if it doesn’t have to fight engine weight in one direction?
Click to expand...
I agree - If the front iso is not already vertically compressed (due to the weight of the engine) then it will impart less vibration to the frame and rider
 
Maybe the isolastic tubes could have dual coil spring carriers that extend out from the bottom side.
They could then have preload adjusters.

There is also electro magnetism which might allow in motion adjustment.
 
robs ss said:
Actually, doesn't the centre-stand essentially do that?
Click to expand...
I honestly don't now now!

My assumption was that with the rear wheel on the ground, which is connected to the cradle, forces would be trying to push the spindle up into the rear frame iso mount. Whereas, supporting the frame, with the wheel off the ground, would do the opposite.

I was also thinking primarily about the effect of the spring on the rear, rather than front iso, as the rear has a harder life dealing much more with all sorts of forces related to accelerating, braking, cornering, etc, than the front does.

I guess a good starting point here would be to clarify the actual intended purpose / function of the spring...?

Now that I have exposed my entirely uneducated assumptions, I'll sit quietly at the back of the class whilst those who know what they're talking about speak...
 
Did NOBODY read my previous reply regarding the fact that the spring is NOT holding the weight of the engine?

It is merely counterbalancing the effective weight of the engine from it's balance point from the REAR isolastic, with the main box section head steady carrying some of the load.

There are TWO points to contend with, when adjusting the spring:

1. You don't want the two top rubber buffers to tear.
2. You don't want the front isolastic rubbers to get squashed.

Balancing the affair out to where the front bolt can simply slide in place results in acheiving BOTH.

Now, this does not bode well for the REAR isolastic, which is then tasked with bearing the brunt of all the imposed forces, once the front iso is simply tasked with smoothing out the engine vibrations.
 
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Buy the individual buffers and keep the original shim design. That way, you can still replace the tall buffers individually when they eventually go out of round.
 
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