Isolastic movement

Is there any Norton data or other sources of data that give reasonably accurate numbers for engine vertical and front/rear maximum travel (assuming isolastics up to par)?
I note that there are larger diameter mounting rubbers and smaller diameter mounting buffers. This suggests to me that movement would be at least enough to compress mounting rubbers far enough so that mounting buffers would come into play.
Anybody know?

Thanks,
Ed

Yes.






I concur with your observations.

The closest data you are going to find is hardness ratings of the rubber isolastic components.
See this thread. https://www.accessnorton.com/NortonCommando/shore-hardness.17329/
But it won't tell you how this translates into measurable movement.

Tough question. I'll think about it.
Rubber dries out . People neglect lubrication .
Inner buffer rubbers I've seen turn to dust from neglect.
The best Iso's I've experienced were softer Andover outer/ main rubbers with plenty of lube.
These would be maximum internal up / down travel .
Early models.

You can look at the gap between your primary and the LHS Z-plate. This is usually my indicator of what kind of condition the isolastics are in and, if you see evidence of contact, how much clearance is not enough. I also use this point on the bike to judge how much lateral movement there is in the rear isolastic. Place your finger so that it bridges the gap and give the rear wheel a shake - feel the movement and adjust accordingly.

Didn't Hobot do an extensive study on the engine motion with isos? He was doing a 3 point rose joint suspension at the time (which he mistakenly referred to as a Watts Linkage). Search his posts for "rump rod".

APRRSV said:

Is there any Norton data or other sources of data that give reasonably accurate numbers for engine vertical and front/rear maximum travel (assuming isolastics up to par)?
I note that there are larger diameter mounting rubbers and smaller diameter mounting buffers. This suggests to me that movement would be at least enough to compress mounting rubbers far enough so that mounting buffers would come into play.
Anybody know?

Thanks,
Ed

Click to expand...

what are you doing with the info if you can get it?

jan nelder said:

what are you doing with the info if you can get it?

Click to expand...

I would like to know when mounting non-standard items to either the frame or the isolastic unit whether the isolastic movement will cause destructive contact.

Ed

Thank you all for giving this question some thought. Dave, I will try to find Hobot's info.

Thanks,
Ed

Rubber can AGE considerably diferantly . Can go real hard & remain tough , dry out and crack , or go soft and soggy .

The the buffers are that , or ' Bump Stops ' .

EUROTHANE ones have been produced . Theres many grades .

A few people have solid mounted unaltered balance Commando ( crank ) engines . Or had ISO's maladjusted tight , so no movement .

My observation is 2 1/2 to 4 1/2 is ' The Range ' if everythings aligned .

A variable with rpm hydraulic telescopic dampner , maybe trying pirateing a steering one , might stop the pogoing at idle . 500 rpm .
mine was smooth at 1100 up . But lateral rock at speed cranked over on undulateing surfaces . The Top Mount allowing ' roll ' .

Hobots top mount was CROSSWAYS , to eliminate that . A good trick is a third ISO engineered UNDER the G'box . Triangulates loads
at wider restraints . Benificialy alters stress distribution .

A proper fancy pants ' single plane ' mount for your extra gear ( & exhausts ) would be a Un Cost Cutting feature . They could have made them so they were twice as expensive , or more .
Like Ducati's .

APRRSV said:

I note that there are larger diameter mounting rubbers and smaller diameter mounting buffers. This suggests to me that movement would be at least enough to compress mounting rubbers far enough so that mounting buffers would come into play.
Anybody know?

Click to expand...

Logically, yes, or the smaller diameter buffers wouldn't need to be there. However, the Isolastic assemblies must also be capable of resisting the total output from the power unit as it pushes the remainder of the bike plus the weight of the rider (and passenger, etc.?) along at the Iso. mounts.

There's approximately [Edit] a 3/16" - 1/4" gap between the inner Iso. tubes and outer tube end caps so only that much free movement in any direction from the central position before the Iso. becomes 'solid' so the Iso. rubbers and buffers ideally need to restrict movement to 3/16".

Does it really matter how much movement there is [ presuming we are talking about up and down movement ]. I have run my iso's with 5-6 thou clearance for a long time now and using a Ludwig style head steady. Initially I had no handling problems or any vibration, but eventually the rubbers started giving out and I had metal to metal contact on the overrun. I replaced the front iso with RGM Heavy duty rubber kits and found I had bad vibrations but no handling problems/. I got pissed off with that so removed the rubbers and trimmed them down so they were a loose fit. It hardly made any difference. I have no vibrations above 50 mph [ 21 tooth sprocket ]

My conclusion. Next to no rubbers is fine. If you want to replace them, then probably go back to the original quality ones as they possible are softer then the H D ones. Having buggered front iso rubbers did not present me with any handling problems, and that's most of what matters.

My side cushions are made of a very hard plastic. They don't wear [ have not had to adjust them for over 7 years. ] I think they are made of the same material as the ones in Ludwig's head steady design. They don't transmit vibrations as far as I know because when the original rubbers were stuffed, there was no vibration.