Rear iso conversion with eng & GB in situ?

Bonzo

Bonzo

VIP MEMBER
Joined
May 8, 2022
Messages
847
Country flag
I tried searching for this topic, but it led me to a dead link (probably vintage).

My '74 mk2 is held up on its original shimmed isolastics. I have the front & rear vernier conversion kit from AN and bought them as a winter off the road project.

Currently my bike has the head off, so was thinking it might be a good time to have a go at the front iso, whilst the ex pipes are off, and leaving the rear until winter.

Then, reading NW's book, came across the section about the replacing the rear iso's on post '70 machines.

"Removing the power unit completely to replace the rear iso's is not entirely necessary. Remove rear wheel, release shocks from s/a, coil & brackets (done), head steady (done), front iso (would be done), ex system (done), oil hoses and finally rear iso stud. The sub assembly can be tilted forward enough to expose the rear iso tube enough to extract the rubbers".

If anyone has used this method to get to the rear isolastic, my question is, does this translate in reality?

And if so (or not), any tips?

I'm contemplating tackling the job as I know it will need to be tackled at some time, and if Norman's wording is to be believed, I have a disassembly head start.
 
Last edited:
www.accessnorton.com

Newest Member with a few questions

Hello everyone...I have been absorbing as much of the excellent information and advice on this forum over the last two weeks. I have the opportunity to purchase a '72 Combat Commando, and am well aware of the issues with the Combat spec engines. Engine had a total rebuild ten years ago, with...
www.accessnorton.com www.accessnorton.com

According to Holmslice it isn't possible to change the one-piece tube Mk3/vernier conversion rear Iso. without stripping the bike down, however, I replaced my Mk3's rear Iso. with the power unit (engine, gearbox, primary, swingarm, rear wheel and cradle) in the frame.
www.accessnorton.com

Getting to the REAR ISO Rubbers!

Ok, I have just ordered all new iso rubbers from Phil at Fair Spares. It has been ten years since I replaced them last, and I think back then I got the "hard" rubbers because it has always vibrated worse. Back then, I removed and replaced the rear iso rubbers all while in the frame. I remember...
www.accessnorton.com www.accessnorton.com
 
Last edited:
The front housing goes easily with the timing side adjuster cap off (or might have been the right side)
The rear was installed with the cradle in place.

If you have the bike part disassembled going through it it would be easy in place.

Rear iso conversion with eng & GB in situ?
 
Time Warp said:
The front housing goes easily with the timing side adjuster cap off (or might have been the right side)
Click to expand...

There's no way the front Iso. can be fitted with either the adjuster or fixed abutment "off" as both have to be screwed onto the tube...
Rear iso conversion with eng & GB in situ?


...and no need to do so in my opinion as it should go back as one assembly:

 
I did it that way multiple times when I was making the lower spring support which needed the Isolastic housing removed for drilling.
The engine needs to be raised slightly (iirc) but easy that I recall.
I would rate the Commando as an easy and enjoyable bike to work on once the Rubics cube of it is worked out (Perhaps like folk who attempt fitting the plastic airbox the right way up instead of inverted with a counter clockwise twist)

Maybe a RGM unit is different but the AN being somewhat of a copy must be similar dimension wise.

Rear iso conversion with eng & GB in situ?
 
Time Warp said:
I did it that way multiple times when I was making the lower spring support which needed the Isolastic housing removed for drilling.
The engine needs to be raised slightly (iirc) but easy that I recall.
Click to expand...

Yes, you raised the engine as you were "making a spring support" but you cannot fit the front Iso. assembly between the frame lugs with one cap off as there would be no way to refit it and what owners would usually be doing, simply replacing the front Iso. assembly with the engine in its normal position as demonstrated in the video.

Time Warp said:
Maybe a RGM unit is different but the AN being somewhat of a copy must be similar dimension wise.
Click to expand...

No, it's (basically) the same as both types must fit between the frame lugs.
www.rgmnorton.co.uk

VERNIER PRE MK3 FRONT ISOLASTIC CONVERSION KIT, FULL (WITH END CAPS AND PTFE''S)

050484C ISO KIT PRE MK3 ISO KIT RGM NORTON VERNIER ISOLASTIC KIT
www.rgmnorton.co.uk
 
Last edited:
I have done it (just to see if it could be done - lol), but it does take quite a bit of disassembly…. I did it on a 1970, so it had the cross member for the center stand - which complicates things a bit. You need to be able to support the frame while you are doing it. I removed the tank, seat, battery, battery box, oil tank, carbs, air filter, exhaust, front engine mount, rear wheel, and the headsteady. I was able to leave the primary in place. The power unit is then slid forward, and the engine pushed upward to get the rear isolastic out from its frame mounts. Can easily be done in a day. FWIW.
 
This is the only video I've found showing the rear iso replacement on a MKII bike with engine in frame:

 
I simply removed the head steady, put the bike on the center stand, connected my engine hoist to the back of the bike, pulled the long stud and then jacked up the rear of the bike. Had just enough clearance to remove the old and install the new. 1974 MK2A but with a K&N air filter - don't know if the plastic or ham can air filters would be a problem - don't think so. Did pay attention while jacking to make sure no wiring/hosed/cables were in danger of being damaged.
 
marshg246 said:
I simply removed the head steady, put the bike on the center stand, connected my engine hoist to the back of the bike, pulled the long stud and then jacked up the rear of the bike. Had just enough clearance to remove the old and install the new. 1974 MK2A but with a K&N air filter - don't know if the plastic or ham can air filters would be a problem - don't think so. Did pay attention while jacking to make sure no wiring/hosed/cables were in danger of being damaged.
Click to expand...
Did you need to remove the primary covers?
 
Tornado said:
Did you need to remove the primary covers?
Click to expand...
No - they stay with the power unit and there's enough clearance behind them that the frame can come up. I was looking for a picture but can't find it. I'm thinking I may have had the mufflers off - seems like they would interfere.
 
Late in from a long day at work, so just catching up with your comments & links.

Thanks very much gents.
 
L.A.B. said:
Yes, you raised the engine as you were "making a spring support" but you cannot fit the front Iso. assembly between the frame lugs with one cap off as there would be no way to refit it and what owners would usually be doing, simply replacing the front Iso. assembly with the engine in its normal position as demonstrated in the video.
Click to expand...


I raised the engine enough to thread the timing side cap on with the Isolastic assembly in the housing as per the photo as I have told you.
The housing might have been non attached to the engine case but forget, no hammers, no forcing parts involved (Sorry Mike)
Its simple, not going smoothly, stop.

Once a Commando needs new Isolastics it will need many other things checked so little point in trying to do on a fully assembled bike.
 
Time Warp said:
I raised the engine enough to thread the timing side cap on with the Isolastic assembly in the housing as per the photo as I have told you.
The housing might have been non attached to the engine case but forget, no hammers, no forcing parts involved (Sorry Mike)
Its simple, not going smoothly, stop.
Click to expand...

Originally, you said;
Time Warp said:
The front housing goes easily with the timing side adjuster cap off (or might have been the right side)
Click to expand...

That's only attaching the Iso. mount to the engine but you said nothing about fitting the Iso. to the frame giving the impression that the Iso. assembly could be fitted with either the adjuster or abutment off.

My point was that it is not possible to fit the Iso. assembly (to the frame) with one end cap missing.
 
That is fitting the Isolastic housing between the frame lugs. (Obviously you can not fit or remove a cap when the housing is between the lugs)

The housing in with one cap off which makes it easy to fit to the engine, raise engine above lugs enough to fit the cap and lower into place to fit the main cross bolt.

The lugs are a set inside measurement so reducing the Iso width makes it easier and that small reduction makes all the difference (that I found)

As far as the rear Isolastic installation, just as the picture.
Lower the unit (The front was in in that pic) to gain access, clean the tube, lubricant and a corkscrew rocking action to fit it. (Not just try and push it in)
 
Time Warp said:
That is fitting the Isolastic housing between the frame lugs. (Obviously you can not fit or remove a cap when the housing is between the lugs)
Click to expand...

Yes, that was my point as all you'd said, in the beginning, was: "The front housing goes easily with the timing side adjuster cap off..."

"...goes easily..."?

Once you had responded with more detailed information about exactly what it was you were doing (jacking up the engine, fitting the Iso. mount to the engine then fitting the end cap and finally lowering the engine into position with the Iso. mount attached) -then made sense.
 
marshg246 said:
The Red Rubber grease AN sells makes it much easier and I NEVER use tools - my 72 year old fingers can still do it. I've only ever used the vernier isos from AN.
Click to expand...
Are you saying you can get enough clearance shifting the power plant still in frame to fit the rear MKIII iso or was this only for the rear MKII multi-piece iso assembly? I'm planning out how best to replace my MKII rears....
 
Tornado said:
Are you saying you can get enough clearance shifting the power plant still in frame to fit the rear MKIII iso or was this only for the rear MKII multi-piece iso assembly? I'm planning out how best to replace my MKII rears....
Click to expand...

The Mk3 rear vernier Iso. can be replaced by moving the engine/cradle assembly forward in the frame.
 
I asked this in my thread on ISO Centering but that has wondered off topic recently so I'll re-ask here:

Is there a reason the MKIII rear iso has two larger diameter bushes while the MKII rear has three? I'd think the heavier MKIII with bigger batt and starter gubbins would want a beefier iso mount, no?
 
You must log in or register to reply here.

Similar threads

Britstuff
How much lateral rear suspension movement is acceptable?
2
Replies
30
Views
769
ilikevelos
I
S
Help Required-Rear Hub Rebuild!!
Replies
10
Views
466
Shelby-Right
Shelby-Right
K
Layshaft BALL Bearing Upgrade - "in situ" - Techniques And Tips Help?
2 3 4 5 6
Replies
105
Views
6,169
B+Bogus
B+Bogus
robs ss
Saving the Rears Iso's?
Replies
10
Views
757
L.A.B.
L.A.B.
G
Norton head removal
2
Replies
25
Views
1,158
Thomasa
Thomasa
Back
Top