Here's a repost on the rear isolastic removal/replacement. Credit goes to Mike Taglieri. I added the stuff re Alternate Method.
From: Michael Taglieri
Date: Mon, 3 May 1999 01:30:01
Subject: Easier Way to Rebuild the Rear Isolastic
* See note at end re: alternate method I used on my 74 Roadster.
The standard workshop manuals for the Commando generally tell you that
the rear Isolastic mount can be rebuilt only by removing the engine, or
even the entire power train. Today, helping Chuck Contrino rebuild the
rear Isolastic on his '72 Interstate. I was finally able to test a
procedure I've been contemplating for a long time that lets you rebuild
the rear Isolastic without significantly dismantling the rest of the
bike. It worked very well, and this is how you do it:
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 (see Alternate Method below: on my bike it was only partially exposed), 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 help.
Once you've got the rear Isolastic exposed, the manual explains the way
to rebuild it. Chuck decided to install Mick Hemmings' vernier Isolastic
conversion collars on his bike, and I may wind up doing the same -- it's
astonishing how well-machined these pieces are. I almost wish I could
afford to buy an extra set to frame and hang on my wall.
Alternate method I used on my 74 Roadster
Rather than using the centerstand, I had my bike (a 1974 850) on my lift with the front wheel locked in the wheel vise, centerstand up. (No worry about tipping the bike over when jacking it off the centerstand and it is a one person operation.) No need to raise the rear wheel as described above, but it still requires the preparation described in #1 thru 4 above. Put a hydraulic jack under the engine plates with a piece of 2” X 4” wood on top of the jack to push on the engine plates. Jack it up so that slight pressure is placed against the engine plates. This will hold the engine/gearbox up when you remove the rear Isolastic bolt. Remove the Isolastic bolt. The end caps, PTFE washers, etc. will come out at this point. Remove the head steady side plates. Loosen the front Isolastic bolt, but do not remove. Now the only things holding the engine/gearbox in place is the front Isolastic and the jack.
Slowly lower the jack and the engine/gearbox will pivot off the front Isolastic, drop down, and the rear Isolastic will start to clear the “Z” plate. I left my primary on. The rear Isolastic would not completely clear on the right side as described by Mike Taglieri above on my bike as the primary case rested on the left frame tube preventing it from lowering any further. However it was low enough and exposed enough (about ¾ exposed) that I was able to get all the rubbers and buffers out of the rear Isolastic tube with little effort. In fact the right iso rubber was a very loose fit and almost fell out. The center and left ones were snug and appeared to be in good condition, but I replaced all three since I don’t want to do this job again anytime soon.
Installing the new isolastics was easy. I cleaned out the tube, greased it with silicon grease and greased all the isolastics. I put the left iso in from the left side. Then from the right side I put in the spacer, center isolastic, another spacer, and the right side iso. I had to tap the center iso in using a long ratchet extension as a drift. You do not need the Norton special tool to get the isos in—you just have to work them into the tube with your fingers. The grease makes it pretty easy. Then you have to add the end caps, PTFE washer, collar and boot. Now jack it back up to line up the hole. The hardest part was putting the long stud back through all the various spacers, Z plates, etc.
I use Mick Hemmings vernier adjusters. These can be used on pre 1975 Commandos without any modification. I understand the Mark III style is easier to use though I have never seen them.
