Shore hardness

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john robert bould

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Sep 26, 2009
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I notice a few members having trouble with things cracking/breaking as late...Now i now Norvil produce EXTRA soft isos.."for added comfort" But as the engine now shakes more ...stuff hanging off the motor is more prone to fracture...When the commando was designed this vibration and rubber mounts must have been addressed? picking a shore hardness rubber that was just right...Goldie Locks.."this rubber is to soft..and this......." I know british rail engine mounts are precise? Can you see the engineer over riding years of rubber type? Saying , dont know what these mounts are. but we have a load in the stores, Lets use these up" Will it matter to a 200 ton 170ph passanger train?"
 
One of the first questions I had as I began refreshing my bike. I found little to no information on iso durometer values. In this world of sketchy aftermarket stuff, it is very relevant. Be interesting to see what comes up :idea:
 
IIRC it was DynoDave that published his list of cushion tests. Read up on how the isolastic cushions were 'fine' tuned by Norton before production to see their isolation depends on total mass of rubber being contacted as well as the softness factor. Softer cushions isolate sooner and better-deeper so would protect parts and pilot - until playing Cdo racer or a policeman on Cdo trying to catch the racer - when much turning loads involved or who'd bother with a Seeley and its roughness. Up/Dn vibes are the bugger so works a treat for my 2 Combats to make extra soft front cushions and fit old extra hard/stiff ones in the rear for comfort that don't end, until I'm racing away from chasers on modern solid mounted corner crippled craft that can't take the loads tamed isolastics can.
 
When I spoke to Norman White about this he was really quite annoyed, it "touched a nerve" as we say.

His main point was that the factory spent a lot of time and money establishing the correct shore hardness. So why do these people with lesser knowledge and resources think they can 'improve' on the design?!

His argument was directed mainly at those selling harder ones (like mine were) but the argument applies equally to softer ones I would suggest.

Norman did tell me exactly what the shore hardness should be, but I've forgotten. He also went on to say that new AN ones are correct, and in his opinion, the only ones to use.

I fitted them and they certainly contributed to my huge reduction in vibration.
 
There's a large difference between making the vibrations easier on the rider and reducing vibrations in a bike. Running nice soft mights might make the vibrations easier on the rider, but it's a fairly unwise choice on a bike that has issues DUE to how much motion the motor has. One has to keep in mind that the drive forces also go through these mounts therefore, chain pull and other forces start to become much much bigger problems with softer mounts.

I'm sure, as with most british engineering, that there's some room for improvement on the factory system, but softer is not the direction to go to address the actual problems. If rider comfort with the few vibes that are there is THAT much of an issue, I would strongly urge the purchase of one of those "king and queen" things that some call seats instead of messing with the mounts.
 
midnightlamp said:
There's a large difference between making the vibrations easier on the rider and reducing vibrations in a bike. Running nice soft mights might make the vibrations easier on the rider, but it's a fairly unwise choice on a bike that has issues DUE to how much motion the motor has. One has to keep in mind that the drive forces also go through these mounts therefore, chain pull and other forces start to become much much bigger problems with softer mounts.

I'm sure, as with most british engineering, that there's some room for improvement on the factory system, but softer is not the direction to go to address the actual problems. If rider comfort with the few vibes that are there is THAT much of an issue, I would strongly urge the purchase of one of those "king and queen" things that some call seats instead of messing with the mounts.
Click to expand...

Indeed, most aspects of a production bike can be improved, especially old ones! With the iso system, Tri-linking the whole assembly would probably be the improvement, but its a big job. And actually the stock set up does work well. But the shore hardness I would suggest cannot really be improved as soft = excess movement and harder = excess vibration. Maybe this is one aspect the factory boys got right (probably a job that was not done on a Friday)!
 
I think my recent silencer cracking problem is something other than the ISO rubbers, as these came from AN. Many years ago I fitted a set of ISO rubbers from Norvil, which I later found out to be of their own manufacture. These caused a bad vibe around 2,500 to 3,200rpm. Got a set from Norman & noticed a massive improvement.
 
I would mess with the mounts, I'd fit two more on the ends of a longer pivot shaft and attach them to the Z plates.
 
Two points continue to be missed. Soft cushions do not harm bike or rider but protect both - unless testing handling like a real racer with a determined police chasing on his Cdo. Stiffer cushions give better control so the racers or police have to get paid to test handling extremes while enduring the extra vibes. Alan adding any extra rubber mass in front or top isolastic type mount tends to transmit more vibes while making the hinge harder to onset. What ever shore value cushions are new tends to increase as they age and sag denser. Someday word might get out to bevel the fronts to please the sensitive princesses like me.
 
Re: Shore hardness

Postby Fast Eddie » Sat Aug 16, 2014 12:47 pm

When I spoke to Norman White about this he was really quite annoyed, it "touched a nerve" as we say.

His main point was that the factory spent a lot of time and money establishing the correct shore hardness. So why do these people with lesser knowledge and resources think they can 'improve' on the design?!

His argument was directed mainly at those selling harder ones (like mine were) but the argument applies equally to softer ones I would suggest.

Norman did tell me exactly what the shore hardness should be, but I've forgotten. He also went on to say that new AN ones are correct, and in his opinion, the only ones to use.

I fitted them and they certainly contributed to my huge reduction in vibration.
Click to expand...

Just measured Shore A durometer of a new set of Andover Norton vernier-style isos. Made multiple measurements on each individual rubber donut and found all measurements to fall in the range of 45-50. FWIW.
 
Someone earlier thread mentioned that rubber generally hardens with age so aircraft rubber gets tossed after a certain time even if never installed. Pouring formed isolastic cushions ran into this continuing curing harder effect. So what ever Shore value you start with increases with time and heat. Drilling holes in rubber like comnoz did sucks to me. There is a Goldie Locks solution, so keep on bouncing till then.
 
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