Hard vs Soft Isolastic Rubber (2009)

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john robert bould said:
highdesert said:
Good questions, Stephen!
My 750's always transmitted less vibration with the same iso clearance settings than my 850s.
The only possible reason I can think of is that the 850's have heavier pistons.
In theory, it should not make any difference if the iso rubber's end caps have shims or adjustable threaded adjusters.
In reality, I don't know because I converted my 73 to threaded adjusters years ago and can't remember.

I do know that put in all new rubber donuts about eight years ago and the bike with same iso clearances does indeed vibrate more so.
I suspect I was sold the "harder" donuts.
If I was you, I would call old britts and mick hemmings and ask them specifically if the sets the sell now are considered "soft".
I would want the soft ones, if that is an option, and I will check on this next time I replace mine in a few years.

I can't see why there would be rubbers specific for a 750 and then an 850 because there was no change in the cradle specs they go in to, to my memory.
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Eight years ago.....maby time you changed them :?:
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I can't make a comparison, but I suspect the 850 barrels are a tad heavier than the 750s, but up until the MkIII I believe they used the same isos?
Add the electric foot and other gubbins and the MkIII motor must be significantly heavier, so I'd assume the rubbers would have been a different compound to compensate - just my guess :wink:
 
John, I DID just recently rebuild both front and rear isos with new rubbers and nylon washers, and difference in vibration is very significant, much reduced.
The new rubbers are softer than the old ones, and lubing the new rubbers and cradle with silicone lube so everything moves also helped.
Total about a four hour job, all within the frame with nothing removed other than the front iso unit.
 
Very interesting thread! I was planning to re-use the rubber bushes on mine since they are very low mileage, but John's info on the curing process puts things in a different perspective :eek: Let's see - 69 to 09, I imagine they're pretty well cured in 40 years - and probably a bit too hard as a result. I noticed that the front bushes were WAY off center when I took the ends off to check clearance. Guess I'd better include new rubber bushes when I get the Hemmings adjusters.
 
I've just restored a '72 Combat and fitted a new front Vernier from RGM and found it vibrated far more than I would expect. I've had to 'tinker' with the mounting a lot and have ended up with going back to some old, soft rubbers I had using pre-Vernier and this is now a lot smoother. One thing that has occured to me, in all my 'tinkering' is that the pre-Vernier is not so bad to adjust side clearance and not much worse than Vernier. The great advantage of pre-Vernier is that it is SO MUCH easier to remove and replace the whole unit on the bike. Removing and replacing an Iso unit with Vernier is VERY difficult and can only be done by force which 'flexes' the frame tubes, which is worrying. The other disadvantage of Vernier is that you can only adjust the side clearance on the vernier adjuster side.
 
I have to agree with you on the vibes situation. I really do think the one piece Vernier is made of harder rubber. Really considering going
to the soft RGM offering next winter.
 
The Hemmings vernier adjuster can be installed on the old style iso's with no mods. I replaced my 70 iso's and I thought the bike had lots more vibration than with the old rubbers. I never did get all the buzz out but I guess it's acceptable.
 
Vernier isos are not better than shim systems, IMO.

Topgun above lists some of the reasons why I prefer the original mk1 shim system, and sold my adjustable Vernier kit.
Mine was a Norvil kit from Fair Spares, which had the rubbers molded on the threaded "pipe" shaft:
https://www.norvilmotorcycle.co.uk/066130.htm

I do not know much about the other suppliers' kits but would assume they are all pretty much similar.

Sometimes it is better to fight the urge to "upgrade".
 
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Didn't DynoDave do a test on the various types of donuts? I sorta remember that the 'newer' ones were stiffer. But what is 'newer', and who manufactured what? I got my donuts and the new 71 style innards (all separate parts but still different from the 69/70 parts) from OB, so I assume they are Andover parts, whatever that means. I still have my old 69 donuts and they certainly are still softer than the Andover ones I put back in. Even after 50 years. But also I did pull my front iso off after about 3 months of installing the new donuts and the things had already taken a set towards the ground by about 3/8". I'm not sure unless we come up with some sort of empirical squish donut testing method that anyone would be able to tell what is what. The head spring did help with the low rev vibes on mine. I cranked it up as tight as I could get it and the front iso still took a sag to the bottom. I don't know what the rear ones are doing. Then also my center stand is on the frame, not the cradle, but I never use it anyhow. Been my experience that messing with the vernier adjustment doesn't do much for my bike unless I get to the extremes.
 
“Softer” and “harder” is very subjective... softer / harder than what?!

I recall Norman White getting quite emotional about this, “all these people messing around with things they don’t understand” he said. “The factory put a lot of effort and testing into the right rubber. Why don’t people just buy the right bloody ones”.

Andover rubbers were ‘the right bloody ones’ according to Norm.
 
What are the numbers according to "Norm"?
It seemed the "right ones" were not available for a while and I was super disappointed I could not get soft early ones. To this day-mine are still the originals from 72 combat.
Sure my combat shook like crazy (bars, mirrors, mufflers, gas tank, and oil tank) at idle (ultra low frequency resonance) but all vibes were gone by 2000 rpm. Now a days guys talk of vibes over 3K as though it's normal. Not for me thanks...
I go for the blue ones..... and the one piece adjustables are the brown ultra soft (gag me with a spoon).
Hard vs Soft Isolastic Rubber (2009)
 
Norm did tell me the numbers dd, but I can’t recall.

And yes, ‘correct’ rubbers weren’t available for some time, hence I guess the different versions appeared on the market.
 
AN sells the softer rubber as per the original spec. For a long while the tail wagging the dog lead them to sell the harder version, that tail was chopped off over 6 years ago and the correct hardness rubber re-introduced.
 
i realize that this thread is a resurrection, but just to ad some info...

because there the factory no longer exists, the market has swollen to include a number of Me-too's, the sell apart which looks like the original factory item but isn't. in the case of the premk3 i can verify that what was supply as iso rubbers were not fit for purpose. in this case the vendor was providing parts from Norvil, so if you are fitting into a premk3, insist on Andover norton .

PM me for details if interested in my saga...
 
Would that be the Norvil ones made with some off the shelf std metric tube that fits where they touch which is no where.
 
I knew DD did that work. But what are the S1 donuts and where do you get them? DD seems to indicate they're not available any more. Remember hobot would drill holes in them to soften them up? Maybe that's what needs to be done.
 
DogT said:
I knew DD did that work. But what are the S1 donuts and where do you get them? DD seems to indicate they're not available any more. Remember hobot would drill holes in them to soften them up? Maybe that's what needs to be done.
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IIRC Hobot was trying to use an aftermarket 1 piece of the MKIII adjustable style. It was obvious by the width and diameter (and actual use) they were very stiff. He and I discussed a possible softening procedures. I had done this work in the early 90's so as we now know, the early individual components are available again and seem to perform well enough and not hard as a rock...
If you have an old 1 piece hard style then just hang it on the "wall of shame" with any other norton junk you may have purchased over the years. AN, RGM and Norvil all have parts on my WOS.
 
850commando said:
i realize that this thread is a resurrection, but just to ad some info...

because there the factory no longer exists, the market has swollen to include a number of Me-too's, the sell apart which looks like the original factory item but isn't. in the case of the premk3 i can verify that what was supply as iso rubbers were not fit for purpose. in this case the vendor was providing parts from Norvil, so if you are fitting into a premk3, insist on Andover norton .

PM me for details if interested in my saga...
Click to expand...

You do realize that Andover is as close to factory parts as technically possible?
 
elefantrider said:
Vernier isos are not better than shim systems, IMO.

Topgun above lists some of the reasons why I prefer the original mk1 shim system, and sold my adjustable Vernier kit.
Mine was a Norvil kit from Fair Spares, which had the rubbers molded on the threaded "pipe" shaft:
https://www.norvilmotorcycle.co.uk/066130.htm

I do not know much about the other suppliers' kits but would assume they are all pretty much similar.

Sometimes it is better to fight the urge to "upgrade".
Click to expand...

Your problems were that the verniers are a bad design it’s that you got them from the wrong supplier.

And no, not all of them are the same. Never make that assumption.
 
DogT said:
The Hemmings vernier adjuster can be installed on the old style iso's with no mods. I replaced my 70 iso's and I thought the bike had lots more vibration than with the old rubbers. I never did get all the buzz out but I guess it's acceptable.
Click to expand...

You can get the verniers for the pre-MkIII bikes from Andover now. I just got a set.
 
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