Isolastics MkIII Vernier Servicing

Joined
May 22, 2004
Messages
522
I converted the earlier isolastics on my 73 850 way back in 1994.

I have since set the gap to 08.00, but feel the 'feel' of them is perhaps a tad hard/ harsh. Additionally, at 60 mph I experience considerable 'white finger' on my throttle hand.

I am wondering if they should have the bushings replaced, after all living some temperature extremes since owning the bike, I am concerned that the bushings have hardened through age..

(I have browsed back some pages looking for a posting on this issue, but found little or nothing.)

I believe there are a variety of sizes or widths to replace the originals and a service tool for replacing..

On the face of it, this is a horrendous task , mainly of course, the rear mount.:shock:

Anyone care to enlighten me and their opinions.
Thanks.
 
Joined
Jun 14, 2003
Messages
747
Stuart SS,

Before you go changing out the isos, try changing their gap. The tighter that gap the more buzzz you get at highway speed. A looser gap results in less buzz, but sloppier handling. At least it works on my MK III that way.

Jason
 
Joined
Apr 7, 2004
Messages
1,691
This was posted by Mike T. From another Norton board. Changing Iso's with the least amout of stuff taken off the bike.
1. REMOVE THE TANK.

2. REMOVE THE PRIMARY (OPTIONAL -- SEE BELOW).

3. REMOVE THE HORN (OPTIONAL -- SEE BELOW).

4. REMOVE THE AIR FILTER(S) AND THE EXHAUST PIPES.

5. PUT THE BIKE ON THE CENTERSTAND AND FASTEN THE CENTERSTAND WITH SAFETY
WIRE, ELECTRICAL TIES, BUNGEE CORDS, ETC., SO IT CANNOT POSSIBLY
COLLAPSE.
DO NOT FASTEN IT TO ANY PART OF THE FRAME, BUT ONLY TO THE ENGINE PLATES
OR
SOME OTHER PART OF THE BIKE THAT HANGS ON THE ISOLASTIC MOUNTS.

6. SLIGHTLY LOOSEN THE NUTS ON THE LARGE CENTRAL BOLT THAT RUNS THROUGH
THE
REAR ISOLASTIC, AND ALSO LOOSEN THE NUTS ON THE HEADSTEADY.

7. PUT A SMALL HYDRAULIC JACK, ETC., UNDER THE MIDDLE OF THE LEFT FRAME
TUBE
(WITH PADDING TO PROTECT THE FRAME) AND SLOWLY RAISE THE SIDE OF THE
FRAME
UNTIL THE LEFT FOOT OF THE CENTERSTAND JUST LEAVES THE FLOOR. AT THIS
POINT,
THE WEIGHT OF THE FRAME DOES NOT REST ON THE CENTRAL BOLT OF THE REAR
ISOLASTIC, AND YOU CAN REMOVE IT EASILY. USING A SUITABLE DRIFT (A 1/2"
SOCKET EXTENSION WORKS WELL), TAP THE BIG BOLT LOOSE, CATCHING THE
VARIOUS
METAL PARTS OF THE ISOLASTIC THAT FALL FREE WHEN IT'S OUT. (BY THE WAY,
USING
A HYDRAULIC JACK THIS WAY IS ALSO USEFUL FOR GETTING THE BOLT BACK IN
WHEN
YOU'RE DONE, AND YOU CAN LOOK THROUGH THE HOLE WITH A FLASHLIGHT AND MOVE
THE
FRAME UNTIL THE PARTS ARE EXACTLY ALIGNED).

8. LOWER THE HYDRAULIC JACK. NOW THE FRAME IS HANGING ON THE POWERTRAIN
BY
THE FRONT AND TOP ISOLASTICS, AND THE TOP ISOLASTICS SHOW IT BY TWISTING
SLIGHTLY UNDER THE WEIGHT. LIFT THE REAR WHEEL (WITH A 2X4", BRICK,
ETC.)
UNTIL THE TOP ISOLASTICS ARE NO LONGER TWISTED. NOW, REMOVE THE SIDE
PLATES
OF THE TOP ISOLASTICS. (YOU DO NOT HAVE TO REMOVE THE ENGINE STEADY FROM
THE
TOP OF THE ENGINE).

9. THE POWERTRAIN IS NOW RESTING ON THE FLOOR, HELD UP THE CENTERSTAND,
BUT
IT'S ATTACHED TO THE REST OF THE BIKE ONLY BY THE FRONT ISOLASTIC. NOW,
PUT
MORE STUFF UNDER THE REAR WHEEL TO RAISE THE FRAME UNTIL THE CENTERSTAND
ALMOST COMES OFF THE FLOOR.

10. AT THIS POINT, THE FRAME TUBES ARE OUT OF THE WAY AND THE REAR
ISOLASTIC
IS COMPLETELY EXPOSED ON BOTH SIDES FOR REBUILDING.

THE "OPTIONAL" STEPS: IF YOU DIDN'T REMOVE THE PRIMARY, THE ISOLASTIC IS
COMPLETELY EXPOSED ONLY ON THE RIGHT SIDE, AND YOU WILL NEED SOME KIND OF
HOOK TO PULL THE RUBBER PARTS OUT. IF YOU DIDN'T REMOVE THE HORN, THE
FRAME
TUBES WILL BE PARTLY OUT OF THE WAY BUT NOT ENTIRELY. I RECOMMEND TAKING
OFF
BOTH OF THESE ITEMS IF YOU'RE REMOVING THE ORIGINAL ISOLASTIC RUBBER
PARTS,
BECAUSE IF THEY'RE TRULY STUCK IN THERE, IT'S A %$#@ OF A JOB TO GET THEM
OUT. ON THE OTHER HAND, CONSIDERING HOW AWFUL A JOB IT IS TO REMOVE THE
HORN, YOU MAY WANT TO TRY THIS FIRST WITH THE HORN IN PLACE AND REMOVE IT
ONLY AS A LAST RESORT. (BY THE WAY, IF YOU POUND ON THE CENTRAL RUBBER
WITH
AN ORDINARY DRIFT TO GET IT OUT, THE RUBBER ABSORBS THE SHOCK OF THE
HAMMER
BLOWS BEFORE THEY GET TRANSMITTED TO THE EDGES. THE BEST WAY IS TO POUND
ON
THE EDGES OF THE RUBBER BY USING A VERY LARGE SOCKET ON AN EXTENSION AS
YOUR
DRIFT).

REMOVING THE HORN: AS ANYONE KNOWS WHO HAS TRIED IT, THIS IS ONE OF THE
ULTIMATE BASTARD JOBS ON THE BIKE. YOU CAN DO IT WITH THE REAR WHEEL IN
PLACE BY UNBOLTING JUST THE FRONT PART OF THE REAR FENDER (TWO BOLTS NEAR
THE
TOP, TWO NUTS ON STUDS NEAR THE BOTTOM), AND FLEXING THE FENDER ENOUGH TO
"POP" IT OFF THE STUDS AND MOVE IT DOWN. THESE STUDS TURN OUT TO BE THE
BOLTS THAT HOLD THE HORN MOUNT, WHICH YOU REMOVE (TEACHING CHILDREN IN
THE
AREA SEVERAL NEW WORDS IN THE PROCESS). FINALLY, YOU CAN SQUEEZE THE
HORN
OUT OF THE SPACE BETWEEN THE FRAME AND THE FENDER -- MOVING THE REAR AXLE
AS
FAR BACK AS YOU CAN WILL
 
Joined
Oct 7, 2005
Messages
1,170
Stuart:

Does the tube between the left/right bottom/aft pair of Isolastics have a welded-on "top-hat" washer on each end? I'm assuming your comment about updating it means it does. If not, take a close look at the end of the tube. If it shows any evidenc of conical distortion, thatt can scr=ew up the handling/vibration compromise something awful.

When properly adjusted, there should be no vibration passed through to the frame and handlebars at anything above 1700 rpm. We spent a lot of development time getting the cut-off vibration below normal driving speeds.
 
Joined
May 22, 2004
Messages
522
Thanks for the input blokes..

I have had the gearbox out as ~ when restoring the bike I entrusted the motor and gearbox to another ~ (hmm) mechanic ~ MUCh against my inner- selfs better judgement ~

And 6 months later I had to remove and rebuild the gearbox. so have some idea about the procedure.. but your suggets are a bonus.

(And as for 'that" horn ~ when I had the gearbox out I chucked that *(&(9 horn over the back fence, and have fitted a (Japanese) car horn under the seat between the mudguard and the shock mount.. just snug! Plus much more effective! )

frankdamp

Your comment is enthralling and I will look into that in detail~ 8)

BUT

The bike died on a rally/ ride last weekend and has 'some' weird bizarre problem.. totally unrelated .. in fact won't run .. another drama! REALLY strange!! :shock:

I will post anothere quiz regarding this if I don't get anymore joy ~ as I did get it to run again last night - first kick - but it died after some 90 seconds.

Anyway

Can anyone add comment as to the optional replacement bushes and where I can get the kits.. ??

Thanks again
 
Joined
Apr 7, 2004
Messages
1,691
Just went thru this check you kill button by bypassing it in the headlight. And hot wire the key switch if that don't work.
 
Joined
May 22, 2004
Messages
522
norbsa48503
You could be right here, as I have been surmising the problem within the confines of the old grey matter..(LOL) and the ignition switch is one of the obvious options I feel is a potential.

It is definitely on the sloppy side in its operations. I did overhaul the kill switch awhile back as a matter of point, but still that is no guarantee that it is fault free ~ right !?
In fact I would or think I may fit a relay in conjunction with the ignition switch would be in order ~ plus a major repair of that horrible junction block just behind the coils!

Nothing would surprise me when it comes to those ^%% Lucas bullet connectors either.

I would like to replace the entire wiring loom and rewire it MYSELF ~ after all I spent many years in the trade. 8)

BUT the problem is getting supplies of the correctly colour coded wires!

That new Sprint is looking good too ~ but not so the $15,000!
 
Joined
Oct 7, 2005
Messages
1,170
In a magazine road test in 1967, the horn was described as "sounding like a bee under a bucket"
 
Joined
May 22, 2004
Messages
522
An Update

I checked teh setting on the verniers and they are still set at .008, so I have backed off the (MKIII) head steady just a tad , and will check how things go after that ...

Not sure whether to thank you or not Frank; as now I am chasing ~ "zero vibration above 1,700 rpm.. " :lol:

:wink:
 
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