Isolastic Centering?

Tornado · Apr 4, 2023

Had another stab at adjusting the rear iso mount. I'm running the Hemmings adjuster in a MK2 bike, adjuster on the right/timing side b/c that seems to have more ease of access.
I have excessive vibrations, pretty much most of rev range. Previously had kept winding out the gap to try to solve, no real improvements. Gap ended up at 25 or 30 thou, with prying between SA and Z-plate. Moment I stop prying, gap closes right down to less than what a 5 thou gauge can slide between. Infact if I have it slid in before releasing prying, the feeler gets trapped, quite hard to pull out.
This seems to me to indicate the iso is off centerline somehow? How to check and correct?

Front shows lots of vertical movement while blipping throttle, both visually and by holding a finger on the iso abutments. Same is not true for rears, maybe a millimeter or so movement can be felt. Unsure what brand rear iso's are, less than two yrs since renewal. Could be the excessively hard compound ones. Fronts are vernier retrofit kit from Norvil.

L.A.B. · Apr 4, 2023

Tornado said:
Previously had kept winding out the gap to try to solve, no real improvements. Gap ended up at 25 or 30 thou, with prying between SA and Z-plate. Moment I stop prying, gap closes right down to less than what a 5 thou gauge can slide between. Infact if I have it slid in before releasing prying, the feeler gets trapped, quite hard to pull out.

Hopefully, the prying was done with the Iso. stud fully tightened. Prying with the stud slack would 'spring' the frame resulting in an artificially wide gap.

Even with the stud tightened, if the Iso. rubbers are stuck to the inside of the cradle tube then prying will distort them and when released will revert to their natural position, pulling the cradle back.

Tornado · Apr 4, 2023

L.A.B. said:
Hopefully, the prying was done with the Iso. stud fully tightened. Prying with the stud slack would 'spring' the frame resulting in an artificially wide gap.

Even with the stud tightened, if the Iso. rubbers are stuck to the inside of the cradle tube then prying will distort them and when released will revert to their natural position, pulling the cradle back.

Yes, stud fully at the 25 or 30 ft-lbs...this is the method when using the Hemmings adjuster as I understood it.
Am I seeing the gap/excess slack from drive/left end taken up by the prying, giving the measured 25-30 thou on timing/right end side? Releasing pry means all that gap then gets closed up by the rebounding effect you mention? So my iso's are not deep enough in from right end along the cradle tube?

L.A.B. · Apr 4, 2023

Tornado said:
Am I seeing the gap/excess slack from drive/left end taken up by the prying, giving the measured 25-30 thou on timing/right end side?

With the stud tight then that would be the total side play.

Tornado said:
Releasing pry means all that gap then gets closed up by the rebounding effect you mention? So my iso's are not deep enough in from right end along the cradle tube?

If the rubbers are stuck to the cradle then they could be pulling the cradle over to one side.

YING · Apr 5, 2023

Tornado,
I have the same bike as yours with the Hemmings adjusters.Only difference is that I put mine on the primary side.When I go to setting it, I put the bike on a scissors jack so to have it not setting on the center stand.This makes it easier to get the clearance you are wanting. I like the way the Hemmings work.Just my 2 cents
Mike

Stephen Hill · Apr 5, 2023

The Hemmings adjusters uses the stock bolts, rubbers, and spacer tubes. I don't see how the rubbers being frozen to the cradle would create a problem. As long as the bolts can slide in the assembly, adjustment should be possible.
If the bolts were frozen to the spacer tubes or the tubes bonded to the inside of the rubbers, that would make adjustment difficult. Or am I missing something?

L.A.B. · Apr 5, 2023

Stephen Hill said:
The Hemmings adjusters uses the stock bolts, rubbers, and spacer tubes. I don't see how the rubbers being frozen to the cradle would create a problem. As long as the bolts can slide in the assembly, adjustment should be possible.

Measuring end play or adjustment doesn't rely on the bolts (assuming you mean the rear Iso. stud and front Iso. bolt) "sliding" in the assembly because checking end play and adjustment of the Hemmings Iso. requires the stud or bolt to be fully tightened.

Stephen Hill said:
If the bolts were frozen to the spacer tubes...

With the assembly tightened then the bolt/stud and Iso. spacer tubes are locked in position and neither bolt/stud nor sleeves can move independently of the other.

Stephen Hill said:
...or the tubes bonded to the inside of the rubbers, that would make adjustment difficult.

If (note my underline of "if" in my previous post) then as I believe the large diameter pre-vernier rubbers are bonded to the sleeves, the rubbers cannot slide along the sleeves and if the rubbers then become stuck to the inside of the cradle tube, levering the cradle would most likely distort the rubbers which are likely to spring back possibly resulting in unequal gaps at each end.

As for whether the rubbers can stick or not, then one (Mk3 vernier) Iso. rubber was so tightly attached to the inside of my Commando's cradle tube that I ended up having to destroy it before it would come out.

Once again this is "if".

RoadScholar · Apr 5, 2023

If you have the ISOs that use shims for clearance they could easily be positioned to cock the drive train to the left. Lazy Norton mechanics used to, and maybe still do, shim the front ISO on the left and the rear ISO on the right because it is easier, much quicker than equalizing both sides of the 2 lower ISO mounts.

If you plan to use the shim method than I suggest setting the shims on the left front and the right rear. Than remove the ISO shims from the front, clean them up measure the total thickness and divide by 2, put equal shim stacks on both ends, same for rear.

The RGM verniers are a better way to go with a modest increase in the PITA factor...

Best.

L.A.B. · Apr 5, 2023

RoadScholar said:
If you have the ISOs that use shims for clearance they could easily be positioned to cock the drive train to the left. Lazy Norton mechanics used to, and maybe still do, shim the front ISO on the left and the rear ISO on the right because it is easier, much quicker than equalizing both sides of the 2 lower ISO mounts.

It's the Hemmings vernier so there are no shims (existing shims would usually be removed) although they could be used to centralise the cradle.

hhh · Apr 5, 2023

RoadScholar said:
If you have the ISOs that use shims for clearance they could easily be positioned to cock the drive train to the left. Lazy Norton mechanics used to, and maybe still do, shim the front ISO on the left and the rear ISO on the right because it is easier, much quicker than equalizing both sides of the 2 lower ISO mounts.

If you plan to use the shim method than I suggest setting the shims on the left front and the right rear. Than remove the ISO shims from the front, clean them up measure the total thickness and divide by 2, put equal shim stacks on both ends, same for rear.

The RGM verniers are a better way to go with a modest increase in the PITA factor...

Best.

This could all be for naught given the likely wide tolerances in the frames. Having them all on one side may not even be enough to center the swing arm properly with the headstock.

Tornado · Apr 5, 2023

Stephen Hill said:
The Hemmings adjusters uses the stock bolts, rubbers, and spacer tubes. I don't see how the rubbers being frozen to the cradle would create a problem. As long as the bolts can slide in the assembly, adjustment should be possible.
If the bolts were frozen to the spacer tubes or the tubes bonded to the inside of the rubbers, that would make adjustment difficult. Or am I missing something?

The issue seems to be the cradle wants to sit off center towards right side. So far over that any adjuster gap setup on right side while prying cradle to left (to take up all left side gap), gets fully closed up upon releasing the prying force. So right side is always hard against the adjuster and this gives poor cradle motion and lots of vibes. LAB suggests the rubber assemblies may not be properely centered along the cradle tube, stuck to inside of the tube while sitting closer to one end than the other.

It seems many place the adjuster (oem vernier and some times hemmings type) on primary side. Is there an important reason for this that i've missed?

L.A.B. · Apr 5, 2023

Tornado said:
It seems many place the adjuster (oem vernier and some times hemmings type) on primary side. Is there an important reason for this that i've missed?

According to the OldBritts instructions, the Hemmings adjuster replaces the front "left-hand mounting". The instructions for the rear simply say: "Use the same procedure as fitting front mount...".

Theoretically, the Hemmings adjusters are (approximately) the same width as the abutment (narrow front, wide rear) that it replaces so it shouldn't matter which side the Hemmings adjusters are fitted at either the front or rear.

The original Mk3 rear vernier adjuster was placed on the left-hand/primary side and the front adjuster on the right/timing side.
Although the Mk3 rear assembly could be reversed (so the adjuster on the right), the Mk3 front adjuster has to be fitted on the right-hand/timing side of the assembly.

The pre-Mk3 vernier front conversion kit adjuster could also be fitted at either end (with the threaded Iso. tube reversed accordingly) because the pre-Mk3 front abutments are the same width whereas the Mk3 threaded adjuster is wider (and the Mk3 mount tube shortened at that end).

Tornado · Apr 5, 2023

L.A.B. said:
According to the OldBritts instructions, the Hemmings adjuster replaces the front "left-hand mounting". The instructions for the rear simply say: "Use the same procedure as fitting front mount...".

Theoretically, the Hemmings adjusters are (approximately) the same width as the abutment (narrow front, wide rear) that it replaces so it shouldn't matter which side the Hemmings adjusters are fitted at either the front or rear.

The original Mk3 rear vernier adjuster was placed on the left-hand/primary side and the front adjuster on the right/timing side.
Although the Mk3 rear assembly could be reversed (so the adjuster on the right), the Mk3 front adjuster has to be fitted on the right-hand/timing side of the assembly.

The pre-Mk3 vernier front conversion kit adjuster could also be fitted at either end (with the threaded Iso. tube reversed accordingly) because the pre-Mk3 front abutments are the same width whereas the Mk3 threaded adjuster is wider (and the Mk3 mount tube shortened at that end).

So this means I don't have to spend the effort trying to swap my Hemmings rear unit to the left side, as there's no magic cure to be found there to my current issue. Thx.

YING · Apr 6, 2023

Tornado said:
So this means I don't have to spend the effort trying to swap my Hemmings rear unit to the left side, as there's no magic cure to be found there to my current issue. Thx.

Tornado,
Use whatever side that you find easiest to get at.
Mike

Tornado · Apr 12, 2023

Had another fiddle around with the iso's. Definately something going on with cradle sitting closer to right side than the left at rear. With right gap at 6 or 7 thou, left is more like 15 or 18. Front is very slightly closer to right by maybe 2 or 3 thou. Readjusted the Dave Taylor headsteady according to an Old Britts document I have.
While watching a mkIII restoration video, they were placing the gearbox in the cradle plates and pointed out importance of fitting a spacer washer btwn GB top lug and left side cradle plate to prevent plate distortion. Checked and there is none on my bike. Plate has a significant deviation from the straight edge. Could this be causing the iso offset issue some how?

jan nelder · Apr 13, 2023

Tornado said:
Had another fiddle around with the iso's. Definately something going on with cradle sitting closer to right side than the left at rear. With right gap at 6 or 7 thou, left is more like 15 or 18. Front is very slightly closer to right by maybe 2 or 3 thou. Readjusted the Dave Taylor headsteady according to an Old Britts document I have.
While watching a mkIII restoration video, they were placing the gearbox in the cradle plates and pointed out importance of fitting a spacer washer btwn GB top lug and left side cradle plate to prevent plate distortion. Checked and there is none on my bike. Plate has a significant deviation from the straight edge. Could this be causing the iso offset issue some how?

I think the washer is part of the design, to allow easier gearbox removal in frame, so cannot be omitted- unless you have a pre-Commando box fitted...

johnm · Apr 13, 2023

Tornado said:
Had another fiddle around with the iso's. Definately something going on with cradle sitting closer to right side than the left at rear. With right gap at 6 or 7 thou, left is more like 15 or 18. Front is very slightly closer to right by maybe 2 or 3 thou. Readjusted the Dave Taylor headsteady according to an Old Britts document I have.
While watching a mkIII restoration video, they were placing the gearbox in the cradle plates and pointed out importance of fitting a spacer washer btwn GB top lug and left side cradle plate to prevent plate distortion. Checked and there is none on my bike. Plate has a significant deviation from the straight edge. Could this be causing the iso offset issue some how?

It may not be causing the issue but its definitely wrong and you need to straighten the cradle and add the washer to the left side

Tornado · Apr 13, 2023

johnm said:
It may not be causing the issue but its definitely wrong and you need to straighten the cradle and add the washer to the left side

Yes i'm planning to have a go at correcting this issue. Read a few older threads on the matter and seems some used a pry bar to re-straighten the plates. Unsure where they pryed against. Would not want to do it against the GB shell incase of damaging/deforming it.
Thinking to rig a jack screw assembly. Couple of wood blocks placed on inside of the plates, all thread or full thread bolt with some nuts and heavy thick washers, some holes drilled in wood to located the bolt ends. Winding out the threaded nuts to force washers into wood with great amounts of force in controlled fashion should work if I can get enough clearance.

seattle##gs · Apr 13, 2023

Have you loosened the top GB mounting bolt and see if the cradle will spring back a little?
I have seen several Nortons where the owners have left out the washer/spacer (3/16" I believe). Not unusual. Loosen the three mounting bolts.. motor-to-cradle and get enough room to shove in the spacer/washer. Tighten the three bolts and put a straight edge on the cradle, both sides. That should solve this problem.

acotrel · Apr 13, 2023

Many things probably depend on what you are trying to achieve - better handling or more comfort. Herb Becker modified the isos and got Doug MacRae's bike to handle. When I am faced with a problem, I am never averse to re-engineering. If the rear iso was filled with a teflon bush, the cradle would be forced to rotate around it in the vertical plane. The handling might not then depend on the head steady. It would depend on the location of the front iso.

Isolastic Centering?

Tornado

L.A.B.

Moderator

Tornado

L.A.B.

Moderator

YING

Pittsboro,NC

Stephen Hill

L.A.B.

Moderator

RoadScholar

L.A.B.

Moderator

hhh

Tornado

L.A.B.

Moderator

Tornado

YING

Pittsboro,NC

Tornado

jan nelder

johnm

Tornado

seattle##gs

acotrel

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