Are they supposed to be like this?

I'm fitting some RGM isolastic mounts to my '73 850 and either I'm missing something or they aren't designed very well.

The problem is that the overall length of the mount assembly is determined by the adjuster which is used, primarily, to set the clearance over the iso's ptfe washers.

At the moment it looks as if; when I have the correct clearance over the washers the overall length is 1mm too long. If I tighten everything up I can force the assembly between the frame lugs and then I could probably move the adjuster to provide the correct clearance over the washers which would tend to spread the lugs a little.

It would have been better if the inner sleeve of the assembly had been longer, such that it protruded through the adjustable cap, then the “fixed” cap could have been used to set the overall length to fit between the lugs; leaving the adjustable cap to be used independently to set set the clearance over the ptfe washers.

Has anyone had any problems with the RGM kit or does it work ok despite its shortcomings?

Cheers! ~ Gary

Just weld it all up . If that doesnt work , I know someone whos pretty good with No 8 wire . :?

ggryder:
You didn't mention whether your problem is with the front or rear or both, but here is my recent experience in fitting Norvil vernier isolastics:
(Note that the Norvil units are locked by tightening the main thru-bolt, unlike some other designs.)

Rear unit - no problem at all.

Front unit - holy dooley! Actually, I kind of expected some drama, having read previously that some machining is required when converting front iso's.
1. The distance between my frame lugs is 150mm. The manual says it should be 152.27 - 152.52. That was the main problem.

2. The MINIMUM stack length of the new kit was 150.7mm when assembled to the mounting tube - ie an interference fit like you have. And that without any clearance for the iso.
To make it fit, I machined 1.5mm off the left hand (short) end of the mounting tube, to retain the same lateral positioning of the engine in the frame as with the original shimmed iso's.

3. The length across the isolastic (inner) tube with the fixed collar fitted was 150mm. Once the above machining was done, this tube protruded beyond the adjusting collar, preventing it from being locked by tightening the main bolt. I shortened the tube by 2mm.

Bear in mind though, I haven't put the bike back on the road yet, I'm still working on the engine.

One thing I unfortunately didn't consider when doing this work: In the interest of keeping the engine assembly parallel to the frame, it's better to have front and rear adjustment collars on the same side of the bike. I put mine on different sides, as suggested by the Norvil fitting instructions.

Cheers
Martin

Thanks for taking the time to explain your fix Martin. I was thinking of modifying the iso kit so that it worked how I believe the Hemmings conversion works, so that the iso clearance adjuster works independently and doesn't affect the overall length of the unit, but now I think I'll do something similar to what you did. I'll machine something off somewhere so that the assembly fits correctly between the frame lugs when the iso clearance is correct. Any subsequent adjustments will most likely reduce the overall length by 10 or 20 thou' and the lugs will spring to take that up. Not elegant, but useable.

Having now understood how the isolastic adjustment works it seems pretty pompous of Norton to christen them "Verniers".

Cheers! ~ Gary

Are you sure they are the correct length ones?? There are two types, The first type needs to have the iso tube machined down to the MK III size the others were made to fit the pre 75 type.

Yes ? , excuse my ' digression ' . Sitting them on the dineing room table for a few days may reveal the whole of the intricacies . Whats the rush . :?

That kind of differing measurement is common to frames that have been tweaked previously, and/or manufacturing innacurracies that several people have reported here.

Different vernier adjust designs and variable factory clearances mean no set answer to fit but close looks and decisions where and how much to trim. The front tabs ain't that solid a mount point as tend to twist tubes but are about impossible to spread wider, and boy have I tried on Trixie with all thread spreader and block knocked up between the down tubes.