Checking rear isolastics in situ

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Jan 22, 2008
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Does anyone have a method of checking if the rear isolastic mounts need replacing, with the engine/gearbox in place?

I have vernier isolastics and have adjusted them front and rear at 8 thou with the bike free standing (i.e. off the centre stand and not leaning on the sidestand). I made sure to check the clearance after the engine bolts were tightened. The bike has a Taylor head steady, new swing arm pivot and bushes and swing-arm lock rings.

I can still get some movement (approx 1/8 inch) when I grab the rear wheel at the top and push it to and fro. If I do this on the drive side I can see the primary case moving very slightly from side to side relative to the frame tube, accompanied by a slight 'clunk'. How much movement, if any, should one expect at the rear wheel with mounts in good condition and correctly adjusted?
Thanks for that Trinorman. I read that post before on how to remove the isolastics without removing the engine/gearbox. I wanted to know what sort of movement at the rear wheel one might expect with a well set up isolastic mount and thereby avoid, if possible, doing any dismantling unless strictly necessary. Are you in effect saying the only way to check that the mount is serviceable is to take it out of the gearbox cradle?
I think that removing the rubbers is the only accurate way to see if the isolastic rubbers are still good. On mine, one of the rear rubbers literally fell out into my hand as I took the side cap off. They should be a snug fit. Also you need to check that the holes through the center of the isolastic bushing are still centered. With wear they move out of center as the rubber elongates.

Do you know how long the isolastics have been in place? Ever replaced to your knowledge? That could be one factor in deciding whether to dig in that deep or not. Of course if you do it now you will probably never have to do it again as long as you own the bike presuming this is not a bike that you put lots of miles on.

I think you will always have a little play when you move the wheel back and forth as you did. I just checked mine and I have about 1/8". My isos are set approximately .010" down to about.005" on each iso. I have never gotten the same measurement all the way around and figure as long as I can rotate the end caps I have enough. I use the Hemmings adjustable ends on mine.

Good luck!

You made some good points there, Chris. I have the bike for one year now, and so far as I can guess from the incomplete history, the vernier mounts have probably been on the bike since the late 90s. As you say, that is probably a good enough reason to dig deeper, sort the thing and not have to do it again for a long time. Thanks again!
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