Please Educate me on the Mk2 Isolastic

It's time for me to learn about the isolastic's on MK2 750. At this point I would like to know what I need to order to replace my current rotting iso's. I have already read volumes on this subject but unfortunately I don't know how much of this info applies to my bike.

Should I be looking at the MK3 conversion?

Will I need to modify or replace the Iso housings to accept the conversion?

Do you have particular Iso's you like or dislike?

Gary

Re: Please ducate me on the worls of Mk2 Isolastic

Gary,
What I know, which may be subject to revision, you can do 3 or 4 things. Replace the original parts, gotten from OB for about $90. But you have to do the shim thing and figure that out.

Other thing to do is the Norvil conversion, I don't think it requires any changing of your current setup. Grandpaul also sells the same outfit, I think. At least that's what I gleaned. I think it has vernier adjustments, so no shims are required, but it is a different setup than original.

Another option, OB parts for $90, and the Hemmings vernier adjusters, I think they are about $150, but I haven't checked the price lately. They just replace the outer bushings on your current setup. That's what I'm going to do sometime.

There has been some discussion about early 750 and later 750 and 850 rubber bushes. You don't want the later rubbers, because they are too stiff and will give you more vibration. I'm really unclear on this though. I replaced my bushes with the OB ones, original part numbers and it seems to have more vibration than I remember, but I was riding with really old bushes, and the exhaust parts were banging on the iso nuts. It does seem to be getting better as I put miles on the bike. Some people have even drilled holes in the bushes to make them softer. I had a discussion via emal with Phil at Fair Spares and he sells the original soft bushes. I almost wish I had done that than the OB ones, but I don't have anything to compare so I can't really say what the deal is.

That's been my experience, good luck. What ever you do, I'd like to hear how it works out.

Dave
69S

Re: Please ducate me on the worls of Mk2 Isolastic

I redid my MKII as it was originally set up.... I think I re-shimmed it after 3000 miles or so. But even with the stock isos shimmed snug, the bike didn't handle very well, especially fishtailing at slower to moderate speeds, and at idle, the motor shook like a pole dancer. The best improvement I made was the Dave Taylor headsteady, with the Taylor upgrade, it was like night and day.

Re: Please ducate me on the worls of Mk2 Isolastic

MkIII

There, you've been educated.

Re: Please ducate me on the worls of Mk2 Isolastic

DonOR said:

I redid my MKII as it was originally set up.... I think I re-shimmed it after 3000 miles or so. But even with the stock isos shimmed snug, the bike didn't handle very well, especially fishtailing at slower to moderate speeds, and at idle, the motor shook like a pole dancer. The best improvement I made was the Dave Taylor headsteady, with the Taylor upgrade, it was like night and day.

Click to expand...

That's the best I've heard of improved headsteadys, I've also heard that the original are nearly as good as the new improved ones from Dave Taylor to OB to CNW. So far I'm sticking with my 69 setup, and I may go to the boxed one as an improvement. Maybe it just depends on how hard you push it, I'm a pretty conservative rider at my age.

Dave
69S

Re: Please ducate me on the worls of Mk2 Isolastic

swooshdave said:

MkIII

There, you've been educated.

Click to expand...

Dave,
Come on Now! I didn't even ask about the head steady and look their helping! Besides I haven't seen a good iso thread in at least a couple of week. Anyway this thread is really important because its for me!

By the way, hows that home made head steady treating you! I like the thought of putting one of those together!

Re: Please ducate me on the worls of Mk2 Isolastic

T95 said:

swooshdave said:

MkIII

There, you've been educated.

Click to expand...

Dave,
Come on Now! I didn't even ask about the head steady and look their helping! Besides I haven't seen a good iso thread in at least a couple of week. Anyway this thread is really important because its for me!

By the way, hows that home made head steady treating you! I like the thought of putting one of those together!

Click to expand...

THe bike is rock-solid feeling on the road. Three things I attribute that to: Headsteady, swingarm spindle clamps and MkIII Isolastics. It could only be better with two more rod ends like hobot has but I don't want to take that much effort yet.

Re: Please Educate me on the worls of Mk2 Isolastic

Dave, what is different about the MKIII isolastics and the earlier ones? As far as I know it's just the dimensions of the front and rear mounts?

Dave
69S

Re: Please Educate me on the worls of Mk2 Isolastic

why isn't the stock headstedy considered to be isolastic?

Re: Please Educate me on the worls of Mk2 Isolastic

After reading what others have done with still more or less annoyance of vibes I did something different. Bench grinder trimmed off Ms Peels and Trixie's front large doughnuts to a 45' angle leaving ~1/4" untouched rim to contact tube ID.

The rear iso most just pivots a tiny bit with front hopping up/dn, plus tire thrust loads push through it and over time tends to sag, so I stuffed two extra left over doughtnuts in there w/o trimming them softer more progressive as above. Bob Patton stuffed his chuck full by 6 large ones!

I forget the brand but put in the adjustable type on Trixie Combat that required 1/4" trimmed off the RH front mount tube. Extra hassle if other styles avoid machining. Still good to make sure tube ends square.

The very absolute least effective rod placement is the head steady, Gosh even factory only put in one peashooters worth of rubber restraint. I rate it maybe 5-10% out of Peel triplex, so if Taylor or other top steadies please you both in smoother and securer sense then you have some idea how freaked out I am to have a Commando that flat disappears out from under and never scares you.

Of late -like last few days discovered how much rear tire state and thread texture can feed back as if engine getting though. Beside direct feedback via suspension seems also to go in and out of engine vibes to let some frequencies similar to engine get through. Almost all isolastic issues disappear with increased rpms [straight upright] now I've a sense of why some don't seem too.

Trixie Combat is a test for me to get factory issue to most optimal state while still staying Norton. I know how good that can be, as long as not pressing your luck on handling limits - especially in increasing throttle sweepers that invite ya to stay on it till THE Jello Jollies onset. Comparing pretty smooth already Trixie with Ms Peel makes me think of riding a puddle of jello, little jiggles wiggles, jostles and hums with slight hesitations-tremble resistance in forks.

Will fit new Dunlop 404 110x18" to Trixie tonight and be rid of the 120 Dunlop dual 80 on 20 off road cleated tire and see what clears up and then diddle the iso adjustor off their default install ~.010".

Of Note the tractor tire is what Peel wore that I could not for the life of me upset or break loose w/o severely over doing it into blinds. Part of the reason I got such sneers from sport bikers, till later w/o the risk some squids take.
Never did try full street tire on Peel in her prime set up. Don't care if no one believes me but with simple fork mods and 3 rods, I know the Commando equation has been totally solved - throw in the ole towel and wrap it up to go.
Flabbergastingly Fabulous Uncanny Unapproachable!

So earlier tonight I happen to start pricing the front and rear Iso's. I was looking through the Old Britt’s parts list and I noticed a modification for the MK2 mount to fit what I believe to be a MK3 iso. I am still in the pre -powder phase and thought I better sort this issue out now rather than later.

Is the addition of the MK3 isos's to the MK2 a common modification or am I making this up as I go along?

Is the veneer style adjuster synonymous with all MK3 iso's or just certain models?

There was a change in the front and rear iso mountings at some point. If yours has a longer side on one side than the other, look at your front mount and you'll see it. That will determine what you want to do, but my understanding is you can use the Norvil or the Hemmings adjuster on either. But don't trust me. Do your own research and ask before buying.

Dave
69S

Re: Please Educate me on the worls of Mk2 Isolastic

DonOR said:

why isn't the stock headstedy considered to be isolastic?

Click to expand...

Cuz it's just a couple rubber things like the exhaust mounts.

Re: Please ducate me on the worls of Mk2 Isolastic

DogT said:

Gary,
What I know, which may be subject to revision, you can do 3 or 4 things. Replace the original parts, gotten from OB for about $90. But you have to do the shim thing and figure that out.

Other thing to do is the Norvil conversion, I don't think it requires any changing of your current setup. Grandpaul also sells the same outfit, I think. At least that's what I gleaned. I think it has vernier adjustments, so no shims are required, but it is a different setup than original.

Another option, OB parts for $90, and the Hemmings vernier adjusters, I think they are about $150, but I haven't checked the price lately. They just replace the outer bushings on your current setup. That's what I'm going to do sometime.

So it sounds like the only advantage it the MK3 iso's is the vernier adjustment. The same advantage applies in adding any of the other vernier style adjusters. It appears dialing in the isos can be a tricky process. I would like to hear both arguments in favor and against the vernier adjusters.


There has been some discussion about early 750 and later 750 and 850 rubber bushes. You don't want the later rubbers, because they are too stiff and will give you more vibration. I'm really unclear on this though. I replaced my bushes with the OB ones, original part numbers and it seems to have more vibration than I remember, but I was riding with really old bushes, and the exhaust parts were banging on the iso nuts. It does seem to be getting better as I put miles on the bike. Some people have even drilled holes in the bushes to make them softer. I had a discussion via emal with Phil at Fair Spares and he sells the original soft bushes. I almost wish I had done that than the OB ones, but I don't have anything to compare so I can't really say what the deal is.

How many of you 750 owners would like to testify about the use of 750 iso's over the 850?

That's been my experience, good luck. What ever you do, I'd like to hear how it works out.

Dave
69S

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I got the local engineering works to do the same as Hobot mentioned and take ¼” off longer side of front iso mounting, back didn’t need any altering to fit.

McVic

I think if you upgrade to the real MKIII iso's there is machine work to be done. You should be able to avoid all that by installing the Norvil type or Hemmings adjusters and original spacers and bushes. I would opt for not having machine work done, I think it's just an unnecessary expense.

I wish others would chime in, I'm still a bit confused about it all, although I did it using the shims and my old collars, but new spacers and rubbers.

Dave
69S

Re: Please Educate me on the worls of Mk2 Isolastic

DogT said:

Dave, what is different about the MKIII isolastics and the earlier ones? As far as I know it's just the dimensions of the front and rear mounts?

Dave
69S

Click to expand...

I had though the only difference between the MK2 & MK3 mount was it its length. I didn't realize the MK3 iso's were also a larger diameter. So a modification to the MK2 mount would then need to include both cutting it to length and boring it to accept the larger iso's?

dave,
I think you just answered my question while I was trying to reply!

The Mk 3 rear isolastics will fit without problems in your mk2.
The front iso mounting tube will have to be machined to accept the mk 3 iso adjusters.
the tube must protrude 1/4 of an inch from the plates,on each side, doing this by hand is not recomended.

In my view, the patented iso adjusters from Mick Hemmings are superior. they fit without machining or other modifications.
Also, a Dave Taylor head steady is a real improvement, I initially was sceptical about this thing, but the handling of my
bike improved significantly after installation of thr D.T head steady.

You can't argue against the vernier adjusters. There is no argument. Reshim just once and you'll end up with additional capacity to your profanity dictionary.

I just went through this on my Commando and decided against the old style with the shims. The rear iso will accept the adjustable Mk III type w/o any mods. The front is easy as well but you HAVE to have the Mk III mount otherwise the iso mount will have to be modified being too wide. Good luck!