isolastic query

Hi, i'm a new commando owner (1973 mk 5) and novice mechanic trying to acquire the skills to maintain my machine as a regular user. My current issue is with the rear isolastic and my vague understanding of the mechanics of the thing. The bike appears to have had vernier type isolastic adjusters retrofitted (collar with lots of small screw holes drilled around) - the front isolastic is good and tight and I'm running it on the assumption that it has been correctly set. The rear one developed a bit of play which could eventually be seen by waggling the back wheel side to side. On inspection the rear iso, adjusting collar with all the holes drilled around it was loose, running back and forth (by hand) on the threaded rod. The grub screw, presumably to lock the collar on to the rod, was also loose. So i slack off the big end nut on that end of the spindle / rod (at the z plate) with the bike on its wheels (weight off the centre stand/engine) and reach in to turn the collar up tight, back off a third and tighten that grub screw up as best i can with a tiny metric allen key. Note that there is about a half inch of thread visible from the outside of the collar to the inside of the frame. Tighten up the big end nut and put the bike back up on to its centre stand. To my surprise i can still turn the collar round by hand. After some trial and error i find i can get that collar good and tight by screwing it right up before locking down the big end nut but this seems to give no clearance and I'm wary of running the bike with the isolastics set too tight. Hope this makes sense, any ideas welcome
cheers
Stu

Welcome to the forum Stu.

stu said:

On inspection the rear iso, adjusting collar with all the holes drilled around it was loose, running back and forth (by hand) on the threaded rod. The grub screw, presumably to lock the collar on to the rod, was also loose.

Click to expand...

Edited: As the information I gave may not be correct for your vernier kit.

stu said:

Note that there is about a half inch of thread visible from the outside of the collar to the inside of the frame.

Click to expand...

Well, it doesn't sound right? Is the second collar there?

Go here and read it until you understand it. Then start adjusting.

http://www.members.shaw.ca/randell/isolastics.html

Dave
69S

There is no need to do anything with the big nut on the end of the main iso through bolt, just leave it tightened.

The adjustment is made purely by turning clockwise or counter clockwise the retro fitted threaded adjuster.

And yes you lock it in place with the allen to hold it once set.

HOW you set it is you tighten the adjuster just so you cannot get a 8 thousandth feeler guage between the adjuster and the cradle end cap it is right next too, then you back off adjuster until you have about an 8 thou clearance.

This assumes that there is no clearance on the other side, in other words the TOTAL slack in the entire iso is 8 thou

Too tight and your foot pegs will vibrate, too loose and you will have no vibration but you can feel the rear wheel moving side to side.

Don't know where you got the idea of backing off a quarter turn from the adjuster being snug, that is HUGE.
Ya gott do the feel guage thing, the manual says 10 thou, I personally use 6 thou as that snugs up the rear and I don't mind a little foot peg vibration, racing Commandos run pretty close to no clearance for sharpest handling.

dog T - thanks, i've read that page a few times and it's helpful, the more info the beter.

LAB, thanks for the welcome.
From images etc online I think my set up may be a retrofitted mick hemmings vernier adjuster ? on the left side only. On the RHS the collar is plain (no drillings) and snugged up tight with a washer and a rubber boot over.
The thread i can see could be the inner barrel of the 2 piece adjuster collar since it is obviously of a larger outside diameter than the spindle rod apparent at the bolted end.

1up3down, cheers - you've described pretty much what I'd been doing. It seems surprising that it's only that tiny grub screw keeping the collar fixed tho. For some reason I had imagined that the nuts on the thru bolt (spindle) would squeeze up the rubber internals to help hold that collar tight.

Still reading up on all of this . .
Stu

stu said:

From images etc online I think my set up may be a retrofitted mick hemmings vernier adjuster ?

Click to expand...

Yes it could be the Mick Hemmings type.

There is another (Norvil) version which has the fixed adjuster secured by the grub screw so perhaps disregard what I said in my previous post if it is the MH type.
http://www.norvilmotorcycle.co.uk/techtalk04.htm

For some reason I had imagined that the nuts on the thru bolt (spindle) would squeeze up the rubber internals to help hold that collar tight.

Click to expand...

nope, they got nothing to do with any iso adjusting, leave em alone

and yes, you are correct in thinking how can that little grub screw hold the threaded adjust in place

Point of fact, the very first theaded adjusters sold had a thin allen grub screw, and that thing was supposed to hold it all in place when you tightened it down

however, often it tightened down directly on top of one of the threads, thereby slicing away the nylon little grub allen tip and affording very poor tightening purchase

and so we milled away a good quarter inch of threaded area and bore all the holes out bigger and fitted a bigger allen so it would bear down on a flat area instead of on a thread, problem solved

The threaded adjusters were conceived by the legendary Brian Tyree in the nineties while on a ride home from the Norton National in Utah puttering back home on his Commando and musing about a better way than to "shim"

Brian patented his threaded adjuster idea and asked Mick Hemmings to do the marketing.

I bought one of the very first sets and experienced that the little grub screw would NOT hold in place.
So Heinz Kegler and I milled a flat spot and bigger holes, I think now they are sold that way, you may have an earlier set.

Let us know if you have any more questions

I have the Hemmings adjusters.



The grub screw is still pretty small and has a nylon tip on it. Mick says not to tighten it so the nylon gets squished off. I haven't had any problems with mine getting loose.

Stu, you have to realize that the 1/2" bolt tightens up on the inner sleeves that hold the rubbers, and that all tightens up against the frame. The rubber donuts are the isolaters for the engine, cradle and gearbox and swing arm from the frame. The adjuster lets you set the clearance between the frame and the cradle, usually speced as 0.01", but many people play with those dimensions. Currently I have my rear set at .02 and the front at .01. I've tried the reverse and it doesn't seem to make any difference on my bike.

I use a 2x4 to press against the z plates and the swing arm to press the cradle over away from the adjuster, my rear one is on the RS because I have the S exhaust. Use feeler gauges to set your clearance. It probably won't be the same above, below and up and down. I set for the tightest place. Same on the front, take a 2x4 and press the front engine mount away from the adjuster and check the clearance. You should also have a plasticky shim between the 'mounting tube cap' and the 'collar' the adjuster being one of the collars.

Once you see mechanically how they work, it will make sense. Look at the parts here http://www.oldbritts.com/1971_g9.html , but the best way to understand it is take off your front engine mount and play with it on the bench. Then you'll see what's going on.

Dave
69S

Well now you've got me wondering as well. The adjustable iso's I put in my 71 had no grub screw on the adjuster side at all, just on the fixed side? Not sure exactly what I'm looking at in your picture DogT. :?:

They are the Hemmings vernier adjusters. They replace items 25 and 43 here http://www.oldbritts.com/1971_g9.html One on the front and one on the rear. Your choice of sides, but easiest left front and for me right rear because of my S exhaust. It works on any non-vernier iso setup.

Dave
69S

I guess my real question is, should the adjustable end of mine have a lock(grub) screw to keep it from moving once adjusted? As I recall there was none provided and no provision to put on in that end, only on the fixed end.

I don't know which setup you have. Did you get instructions with it? Where did you get it and which style is it, I think there are 3 or 4 styles out and about. I found the Hemmings the easiest to do for me since I had already replaced all the innards.

Dave
69S

MikeG said:

The adjustable iso's I put in my 71 had no grub screw on the adjuster side at all, just on the fixed side?

Click to expand...

I think what you probably have is the earlier version kit from Norvil.

http://www.norvilmotorcycle.co.uk/techtalk04.htm

Fully screw the long abutment on the right hand side of the isolastic and tighten 2BA grub screw.

Fully screw the long adjuster to the left hand side of isolastic.

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Thanks LAB, that's what I have. Any problems with them loosening up?

I've two version of vernier isolastics, one like the Norvil and a one off alloy version. Both have small set screws to 'lock' the adjuster from turning to change gap and both worked fine but neither has nylon tip though both bare onto threads. I've had too many too tight set screws so didn't nip mine up very hard yet didn't seem to matter as gap setting held. MIght not even need them. Every bike has some quirks in alignment so the advised gap are just ballpark initial settings. Gaps all loosen up some in a few 100 miles so what may initially transmit annoyance might disappear. Soft air tires cause less isolastic isolation than hard aired tires and tires condition so dominates the sense of a smooth sure handling Commando you really can't fine tune gaps till good tires on both ends. I was a bit disappointed with myself and my current Combat most a year using up old hard worn tires till like new used tires put on for return of the famous Cdo sweetness w/o touching the gaps.

Look up or maybe LAB can tell us the TPI of the adjusters then just go by that for close enough gap initially.

My fine tune method is carry wrenches to release iso bolt nut then tweak the adjuster caps a tiny bit then clamp iso nut down and ride a ways then get off and do again more or less for best sense of smooth vs sure footed. I leave the set screw loose during this process which can take a few trips over days to get sense of best compromise. Much as I crave to dice the turns i more prefer the nice smoothness so tend to set mine to looser side of normal.

MikeG said:

Thanks LAB, that's what I have. Any problems with them loosening up?

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I have an 850 MkIII with the original factory vernier Isos. and I have never known those to loosen off, but I have no experience of the Norvil kit.

hobot said:

Look up or maybe LAB can tell us the TPI of the adjusters then just go by that for close enough gap initially.

Click to expand...

The Norvil adjusters are 3/4 -16 UNF, apparently.: post117421.html

A quick note to say these turned out to be the retrofitted Mick Hemmings isolastic adjustable collars. I rang up and ordered a half doz of the nylon tipped grub screws and a dedicated allen key. These arrived next day and fitted perfectly so now riding with no vibes and the collar seems to be holding its position with 2 screws fitted.

So... are you DEAD sure the wheel wobble you see is indeed the isolastics moving? The swing arm pivot on all pre-MKIII bikes is an engineering brain fart, LOTS of slop designed in. There is a fix, it's fairly straightforward. Watch closely at the swing arm pivot where it contacts the engine cradle as the wheel is move to and fro. A helper makes this much easier.

Cheers for the eyes up - I'm aware that there is an element of sideways play in the swing arm / spindle joint and that is definitely on the list to look at. The iso cups are solid now tho and have brought the slop to within managable levels (and cured the buzz !) Immediate job for this w/e is trying to eliminate a bit of clutch slip so slowly getting familiar with the different bits of the bike (while its not earning its keep getting me to and fro work). Out of interest, the swing arm / spindle fix is a retrofit beef-up bracket fitted externally ? I may have come across an article about this but yet to investigate properly.

A nod and the to do's done so far. MIght just try adding ATF to the primary which might un-grime the plates slipping w/o clutch apart, which ain't that big a task. Its tricky to weld the gussets on w/o distorting the swingarm all the way to the axle slots but has been done. Think about adding the spindle stabilizer collars too. The feel of the isolastics depends a great deal on the state of the tires and their inflation levels.