Vernier isolastics

Hello all, I`m having a bit of a headache about the Vernier iso`s.
The problem is to set them you turn the adjuster in fully,then back of 1/4 to 1/2 a turn. Then retorque the engine bolts. Now,when the bolts are loose there is some movement of the engine on the iso`s, but when you tighten them this movement all dissapears leaving a rigid engine. Is this correct or should there still be some engine movement?
At the moment i run it with the iso`s set as spec, resulting in bad vides around the 2- 3000rpm mark.

My last commando did not have the verniers and it was a smooth ride at all rpm.

Chris r

Chris,
It's backlash in the adjuster threads. Keep opening up the adjuster and torquing down until you have a measurable gap and use that measurement as a starting point. After that it should be easy, simply do the maths adjust by the book to set the required gap torque up and check.
Cash

I've never found the "tighten up-back off" method to be very reliable.

With the Iso. mounting slackened off, I insert the feeler gauge, and then begin tightening the mounting in stages, periodically checking if the feeler still moves freely at each stage. If the feeler becomes trapped or starts to feel too tight, then I slacken off the mounting, back the adjuster off slightly and start again.

I've never found the "tighten up-back off" method to be very reliable.

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I didn't mean that.

Perhaps I should have wrote, set any gap as long as there is one when torqued up and measure it. Use that measurement to work out the final adjustment. Works for me no probs'.
I guess there's more than one way to skin a cat.

Cash

cash said:

I've never found the "tighten up-back off" method to be very reliable.

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I didn't mean that.

Perhaps I should have wrote, set any gap as long as there is one when torqued up and measure it. Use that measurement to work out the final adjustment. Works for me no probs'.
I guess there's more than one way to skin a cat.

Cash

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Cash,
Actually my answer was in response to blacklav's comment about screwing the adjuster in fully, and then backing off by 1/4 - 1/2 a turn. I wasn't disagreeing with anything you said (although I still think it's easier to do it my way - rather than attempting to work out how much to turn the adjuster). :wink:

As above: LAB is correct, Every Iso nut and tube as vairable slop in the threads, [lash] a couple of trials will determing how much lash there is and then back off the correct amount, or fiddle untill its correct.

Phew. Thanks for the replies guy`s.
I thought that was the way to get an accurate setting, but i was totally put of by the manufacturers instructions of backing off 1/2 turn.
Will adjust and hopefully get to ride at the weekend. Will keep you posted.
Many thanks
Chris r

L.A.B. said:

I've never found the "tighten up-back off" method to be very reliable.

With the Iso. mounting slackened off, I insert the feeler gauge, and then begin tightening the mounting in stages, periodically checking if the feeler still moves freely at each stage. If the feeler becomes trapped or starts to feel too tight, then I slacken off the mounting, back the adjuster off slightly and start again.

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Agreed. Feeler gauge is simple and works.

From the setting instructions you quote I'm assuming you have the same verniers as me. Strangely, that 1/2 turn back gave me a huge clearance when torqued up, around 18-20 thou. I eventually had the ISO tube faces squared off but they sit around 1/4 to 1/3 back from zero clearance with 25ft/lbs torque on the bolts.

Keith1069 said:

From the setting instructions you quote I'm assuming you have the same verniers as me. Strangely, that 1/2 turn back gave me a huge clearance when torqued up, around 18-20 thou. I eventually had the ISO tube faces squared off but they sit around 1/4 to 1/3 back from zero clearance with 25ft/lbs torque on the bolts.

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I don't think it's the threads on the Iso adjuster taking up slack so much as it's the tube itself. Compared to the steel collars on the original buffers and bushes, the MkIII iso tube is very thin walled and it always felt like it was taking a crush or bending as it was being tightened, the ID of the tube is way more than the 1/2" bolt and stud they're mounted on. It's one of the reasons I like the Hemmings over the MkIII. You keep the original buffers and bushes and it's torqued down before the adjustments are made. I would never recommend doing it, but I found that after you got it at 25ft/lbs you could do roadside adjustments with the MkIII's by just carrying a 3/4" wrench. A half a flat one way or the other was good for a few thou plus or minus due to the springy-ness of the tube.

Just an update on adjusting the Iso`s.
My incorrect theory was, if there was free movement of the motor from the frame all would be smooth.
Wrong ,it made it worse.

Eventually like Keith 1069 I only needed to back them of 1/4 of a turn to make the required gap.
Still vibrates through the bars at 2750 rpm though.
So I guess I`ll live with it.
Many thanks
chris r

If you've got time and your hands, try turning 1/16 turn in one direction at a time and see if you can tune it in to the "sweet spot". You have to run up throught the revs and gears to check each minor adjustment to see where the vides move, up or down the rev range. You might find a certain buzz in the pegs at one speed, and another in the bars at a different speed.

With enough playing around, you can find what works best for you.

Take a read on this and see if anything helps, I think I found it from a Hemmings search once.

"The workshop manual calls for a clearance of 0.010" (0.25mm); for a more comfortable ride you might let this go up to 0.020" (0.50mm) or for better handling at the expense of extra low speed vibration try 0.005" (0.12mm). On any Commando that's been "used" the clearance is often not the same at the front and back or top and bottom of the adjuster, so check all the way around. Remember to push the engine over in the frame away from the side you're checking and torque the mounting bolts to 40lbft. Whatever you do don't over tighten the Isolastics. The frame is not designed for a rigidly mounted engine and it will break. If one Isolastic unit is tight and the other is free then the frame will break very quickly indeed.

For racing, it is possible to tighten the Isolastics so there is effectively no measurable clearance. Do this by adjusting back from a tight setting until the thrust washers can be rotated by pushing them with the end of a screwdriver.

The engine essentially rotates about the rear Isolastic mounting. Consequently, the front unit moves more, wears more and has a greater influence on the transmission of vibration. Any play in the rear mounting is doubled at the rear wheel, play in the front mounting is simply matched in the rear wheel. Therefore it is possible to tolerate more play in the front mounting than the rear and get a more comfortable ride. Try varying the clearances a little and see what suits you best."

Dave
69S

Just been through this exact situation BlackLav. Set as per instructions, the verniers had no clearance whatsoever and there was (a lot of) vibration. Using the feeler gauge method takes time and patience, backing off the mounting bolts, adjusting the verniers, tightening the mounting bolts and then measuring the clearance, but it rewarded me last night with the smoothest ride I've had yet - bloody marvelous. Take the time and do it right, you shouldn't have to do it very often!

but it rewarded me last night with the smoothest ride I've had yet - bloody marvelous. Take the time and do it right, you shouldn't have to do it very often!]

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Glad you found the 'sweet spot'. Never have on mine even at excessive clearances of 15 thou front and back. Mine has always had a coarse buzz at 4000 + which I've tried to dial out with Iso adjustment and failed. That led me to crank road and piston balance (matching side to side), checking runout of crank drive and timing shafts, gearbox main shaft straightness and runout also, layshaft straightness, parts touching where they shouldn't. I still think its the box because when I press the gear lever in 4th (as if looking for 5th) the coarseness is significant. Putting my hand on the engine, head, barrels, chaincase or anywhere within reach at 70-75 mph everything feels super smooth. I just live with it now but it is annoying.

Ah the sweet spot, its like the perfect note that eric clapton is still looking for.
I`ll keep trying .
Its just that i never had this problem with my last commando on the basic rubbers, technology pah.

chris r

When it's right it's righteous.