Hard isolastic rubbers

I picked up my cradle and other bits from Norman White today, he's done a great job of converting to cotter pins and generally refurbishing the whole cradle / swinging arm assembly.

He also changed my isolastics as he said "Have you ridden this bike? If so, its a wonder you have any teeth left. The front isolastics are a pattern product with incorrect shore hardness rubbers" he went on to get quite cross, saying how people who made such parts gave a bad name on all the hard development work that was done in the day to get these bikes to be so good.

He showed me the difference between my rock hard ones, and new AN correctly made ones, the difference was quite staggering to be honest.

I didn't buy my old ones as they were already fitted to the bike, so I don't know where they were from. But I've got new AN ones in now and shall only buy AN ones in future!

I post this just as a caution to others who may be buying such products.

I remember sometime back around 10 years ago or so when the iso rubbers being sold were quite hard.

I was one of those stricken with Hard Iso Disease, and suffered for five years and then replaced with soft.

Personally, I feel the factor recommended 10thousands gap is too much as I can feel some swing arm movement, mine are set at 6 thou, a little foot peg vibration but a more secure tracking feeling.

Messing around with the front ISO clearance does not seem to make much difference unless super tight.

The many forum head steady threads show the concern that getting that area right makes a real difference.

1up3down said:

I remember sometime back around 10 years ago or so when the iso rubbers being sold were quite hard.

I was one of those stricken with Hard Iso Disease, and suffered for five years and then replaced with soft.

Personally, I feel the factor recommended 10thousands gap is too much as I can feel some swing arm movement, mine are set at 6 thou, a little foot peg vibration but a more secure tracking feeling.

Messing around with the front ISO clearance does not seem to make much difference unless super tight.

The many forum head steady threads show the concern that getting that area right makes a real difference.

Click to expand...

Norman gave me a lesson on setting the iso's his way, he said its best not to use feeler gauges but to adjust by feel, tightening them so there is barely discernible side to side movement but still free up and down movement.

Tony Smith gave me a similar lesson, he said to tighten them and back them of a touch, ride it and adjust, repeat until happy!

Neither of them used feeler gauges or could tell me what theirs were set to, other than say they were set 'just right' !

It's a privilege getting lessons from such qualified teachers!

I recently replaced my isolastics with "heavy duty" isolastics. I bought them because they were fairly inexpensive and I figured I didn't have much to lose. They definitively transfer more vibration to the motorcycle. As a matter of fact my oil tank dances around quite a bit at lower rpm's due to the vibration. On my next order I plan on going back to the genuine Andover Norton isolastics. I would say the only good thing about the firmer mounts is that the carburetor probably has an easier life. But overall I think the original isolastics are the way to go.

I think there was a difference from the 750 to the 850 rubbers, 850 being stiffer from what I've heard. My original donuts were supple, but cracked and stuck to the tubes so I replaced them with AN from OB.

Dave
69S

Trying to talk in absolutes on a Commando is as ephemeral as maintaining claim of fully fettered one.



Re: Isolastic solution and handling improvement

Postby hobot » Wed Aug 04, 2010 1:13 pm
Once a poured in place isolastic installed, its just the start of a sliding scale of SHORE measure curing.

Re: Hard vs Soft Isolastic Rubber

Postby john robert bould » Sat Nov 21, 2009 1:16 am
On the subject of Rubber, My little friend Dennis Lawton.Lawton Sales Weston Nr Crewe makes these rubber Isolastic's. I have collected the compound which is of a specified SHORE hardness. Problem is after molding they continue to CURE. ie get harder . Heat . TIME and to a lesser degree LIGHT continues the curing action. Having Seen my pal Colin's Harley 883 sportster "Shaking" i would have a guess and say the Norton set up is quite firm compared to. SO ..as your New Iso are on the stores shelf...they are getting Cured, Harder :?: ....Dennis also produce's Spitefire[plane] rubber parts...these are kept is black bags... Den keep's the rubber compound is freezers to hold back the CURING process...Make's you think what's happening on a hot summers day

And some more from last century comments
http://home.clara.net/captain.norton/cnn2sec33.html

I have an idea that the hard rubbers date back a little more than ten years and at the time, they were the only type available (certainly the Mk3 pattern). I'm pretty sure that the ones I had came in Andover Norton packaging which is no reflection on the current production but probably shows that they too had to make do with what they could obtain at the time.

Here's ole DynoDave Commeau measures over 2 decades ago... http://atlanticgreen.com/images/frontiso.jpg

hobot said:

Here's ole DynoDave Commeau measures over 2 decades ago... http://atlanticgreen.com/images/frontiso.jpg

Click to expand...

The chart legend does not reflect the charted results; what I mean is what each one is labeled as, does not reflect it's relative properties re: hard/soft.

You can't have "ultra soft" and "1989 hard" relatively close together, unless 75 original is softer than "ultra soft", and "oldstyle" even softer still.

The chart indicates that "utlrasoft" is only slightly softer than "1989 hard", and harder than the other two...

Don't understand you point g-paul but the chart is useful and informative to me who has measured the range of deflections on idle, throttle snaps and harsh on & off road loads, so chart reveals the load range that's developed on cushions' defections. Dyno graphed the range we can expect, though not accounting for the continuing hardening rubber curing on shelf or installed. Of all the C'do character the disappearing act is the most appealing to me, so i just bevel them more or less to taste. To me all the front cushions are too harsh otherwise. I have not seen enough deflection at front to engage the small cushions, at least with the last few decades of cushions nor with my beveled ones, so don't know why they are there anymore. Frank the Norton test pilot said all the early C'do he tested isolated about 1800 rpm, which is close to where past Peel disappeared though Trixie takes a few 100 more rpm but geared way lower so both go smooth about same speed, lower upper 30's mph in top where I spend a lot of time doing in 'peace'. My bud Wes's '71 before bottom end seized d/t worn out rod shells and original cured iso cushions with 1/8" gap and 19T sprocket would pound me till 55 mph, which was about 10 mph faster than traffic congestion on our local hwys, ugh. Everyone modifies about everything else to suit, so consider some bench grinding next time front mount in hand.

hobot said:

Don't understand you point g-paul

Click to expand...

Perhaps the name labels for the different donuts are misleading.

RELATIVE TO EACH OTHER, the "ultrasoft" graph curve should appear on one end of the chart, and "1989 hard" (or the actual hardest sample) should appear on the opposite end.

I'm only thinking in terms of depicting of linear, relative, logic.

One other way to describe it would be that the graph line on one end should be the softest, then next one over should be slightly stiffer, then stiffer yet, then the hardest.

The way this chart reads, they must certainly be softest to hardest from one end to the other, but the legend titles do not describe that in relative terms (to each other). So, "misnamed" labels...

Oh ok now i got ya, you take issue with the named grade of a cushion not matching its actual charted placement-compliance. Somewhere out in www space is a shore testing grading of various cushions but I've not found it so far. After reading for decades about all the cushions after Frank Damp tested isolation below 2000 are too hard I assume new ones will be, so bevel em back to what the ingenious designers had in mind. My Combats feel like worn out lawn mower powered cable and fabric biplanes on grass field compared to moderns heading out my drive way, but then the Commandos feels like it lifts off surface in tautness while the moderns get more buzzy and loose jiggley. I've been given rides on a number of moderns, rubber mounted HD's, Goldwings and 6 cylinder sports curisers to still feel the engine getting through on top the road texture, but not my C'do's. Yet my stock Trixie feels like a tractor compared to Peel complete disappearing act I could not feel anything of a cycle under me but the patch grip harmonics w/o the annoyance of insignificant imperfections for uncany sense of UFO or turbo fan jet thrust smooth magic. I've ordered stuff to objectively measure monitor and record what's getting through bars and pegs so can pass around for pecking orders and diagnostics to help others get similar flying carpet w/o any fringe flapping to spoil the trance.

Fast Eddie wrote;

He showed me the difference between my rock hard ones, and new AN correctly made ones, the difference was quite staggering to be honest.

Click to expand...

My isolastics are about 8 years old. I fitted them and bought them from Emery. It looks like I've got some more retailing to do as there is a reasonable suspicion that mine will be rock hard. Without direct comparison, it's hard to know what you have fitted. Sometimes this forum is just too good. :lol:

I mention that the way the iso isolate is working against the mass of the Earth so tire conditon and air pressure made a lot of difference on threshold and deepness of the isolation onset. When air borne Peel and Trixie rattle-vibe like a solid frame till touch down smooths out again. Suspension quits oscillation in a couple bike lenghts flight. I've some easy places to catch air at home and some friends so not talking about MX crest to crest jumps, so far. If someone does find hardened cushions I'd sure be interested if they'd try the cushion edge beveling back to smoothness with good handling or not. Some have mentioned attempting to drill sideways though them but drilling thick rubber sucks.

I understand you g'paul
Logic suggests every thing you have stated is correct....ultra soft and hard..these are the book ends? The concept of ultra soft being harder than stock..well makes no sence at all. unless stock are in fact ULTRA,ULTRA soft...i think the shore hardness [to which us laymen cannot test] should be the measuring tool. Iso mounts could be so vairable,,,what would wider soft rubber,compaired to narrow hard rubber produce..same result?
Someone deceided the original rubber size and shore , this produced a all round performance ,not to much vibes, and acceptable movement between the engine and frame, the softer the rubber the more the exhaust's jumped about,and carbs shook the fuel into froth!
No wonder the carbs worn quickly, sliding up and down in a vibro machine :!:

grandpaul said:

hobot said:

Don't understand you point g-paul

Click to expand...

Perhaps the name labels for the different donuts are misleading.

RELATIVE TO EACH OTHER, the "ultrasoft" graph curve should appear on one end of the chart, and "1989 hard" (or the actual hardest sample) should appear on the opposite end.

I'm only thinking in terms of depicting of linear, relative, logic.

One other way to describe it would be that the graph line on one end should be the softest, then next one over should be slightly stiffer, then stiffer yet, then the hardest.

The way this chart reads, they must certainly be softest to hardest from one end to the other, but the legend titles do not describe that in relative terms (to each other). So, "misnamed" labels...

Click to expand...