Iso question

I think another issue is that they do not get installed properly. They need to be recessed just right, not too deep and not too shallow. Hence the need for the tool. They will never be right if they are not just so.

I understand that drilling holes in the hard rubbers can reduce the vibration.
Any ideas about the size and number of these holes ?

A few years ago I changed both front and rear ISOs with a set bought from RGM without a problem. I do believe prior to that harder rubbers were on the market in an attempt to reduce the low frequency judder between 2000 and 3000 rpm.
The only time I have experienced any buzzing through the bars was caused by over advanced ignition. A couple of years ago the buzzing came back this time through the bars and seat, the cause this time was from the drive chain. I had no idea that Renold had stopped manufacturing motorcycle chain I got hold of a box of Renold industrial chain (well it's just chain isn't it ). With advice and chain from Andychain the problem was solved. I now have a very smooth 850

Dave

Not a fan of doing the same job twice, especially jobs that should only be done once every 20 years or so.

However, the bike was virtually un-rideable with the new iso rubbers with serious vibes throughout the rev range, so I changed out the RGM items for AN ones last night.

What a difference. Got my bike back. Vibes are gone except for an acceptable buzz through the bars between 2,500 and 2,800 rpm.

The AN items are a much softer consistency, much like the ones I took out but in better ie new condition. The old ones looked ok, but were out of round and definately starting to deteriorate.

Also took the chance to install Hemmings ISO adjusting collars. These are a great bit of kit. When I returned from the first ride out, I was able to adjust the gap in a couple of minutes.

I replaced the original isos on my MkIIA 850 with A-N parts, which were a direct replacement, and very soft rubber - 2 bushes in the front mount and three in the gearbox cradle, all separate parts with spacers between.
I also fitted the Hemmings verniers and a DT headsteady with spring.

I fitted OEM type MkIII isos to my Combat, which are a two-piece assembly with the isos moulded on to the solid shaft with two integrally moulded bushes front and rear, which is threaded both ends for the fixed and adjustable collars.
I had to machine down the front mount to fit the front assembly. This bike used a box-section head steady with standard bobbin rubbers.

This setup was stiffer, and the vibes stayed a bit beyond 3K rpm, whereas the 850 smoothed out before this, but it still smoothed out OK.

The PR uses standard isos but with an additional bush front and rear, plus an iso head steady. I haven't run this set up yet, but it's definitely the stiffest of the lot.

RGM sell MkIII - type isos for earlier bikes which remove the need for machining the front mount. I have a set but haven't tried them yet.

MkIII iso rubbers are certainly harder than the 'genuine' A-N earlier type, but I presume this is to accommodate the additional weight of the ES gubbins?

Having significant experience dealing with poorly made replacement parts, and always a "how can this go wrong" view, the FIRST thought I had was to find information on original design isolastic durometer spec. What I found, was, nothing.... lot's of "I bought from XXX, and they work great!" Far too subjective, but, all there was to go on. The vernier conversion kit I bought had HORRIBLE quality stainless parts wrapped in newsprint, no maker name or part #. I spent HOURS reworking them to be usable. Good luck!

freefly103 said:

Also took the chance to install Hemmings ISO adjusting collars. These are a great bit of kit. When I returned from the first ride out, I was able to adjust the gap in a couple of minutes.

Click to expand...

There have been some reports of the Hemmings adjuster grub screws loosening up or loosing the soft tip. The screws are available from McMaster in a package of 5 p/n 93285A211 http://www.mcmaster.com/#93285a211/=shobqt if that link is not too old. I've had no problems with mine. I remember reading about some drilling out the original threads and tapping them with a larger screw too.

concours said:

Having significant experience dealing with poorly made replacement parts, and always a "how can this go wrong" view, the FIRST thought I had was to find information on original design isolastic durometer spec. What I found, was, nothing.... lot's of "I bought from XXX, and they work great!" Far too subjective, but, all there was to go on. The vernier conversion kit I bought had HORRIBLE quality stainless parts wrapped in newsprint, no maker name or part #. I spent HOURS reworking them to be usable. Good luck!

Click to expand...

To add more detail to beware of, the machining had deep tool marks from the turning process ("record groove") as well as a .030" convex profile. The flat teflon washer would have been gone in 100 miles. I had to surface grind/polish to repair. The guy selling them had no interest in hearing about any of it. Caveat emptor. :shock: