vernier isolastic adjustment

From the INOA Tech Digest (table 4-1, page/section 4-5)

Vibration up to 3k rpm

Front OK

Rear mount tight (remove 0.005")

3k to 5k rpm

front tight (remove 0.005")

Rear OK

0k to 5k rpm

You have to be careful which replacement rubbers to use as some can be a lot harder than the original ones, one fix is to drill holes into the sides of the larger diameter rubbers. Would be good to know who does the softest MK3 rubbers as otherwise its best to keep your old rubbers and use the Mick Hemmings vernier conversion. I have only gone vernier on the front about 15 years ago and that did not change the vibration levels, they still switch off at 2500 rpm.

Cross check your settings with a feeler gauge to establish what you have actually got set. What type of head steady do you have? Do you have a Mk3 one piece rubber or the Mick Hemmings adjuster fitted to one side?

Hi Gerald

Have you added the the Mk3 spring tension mount to the head steady? It took a while to get it set right on my MK3, definitely worth persisting with.

Regards

Katherine

Dear Gerald,

Vernier adjustment is not all it seems, there is always some slack in the threads of vernier adjuster, when you adjust you have to have through bolt slack , when you tighten it don't be surpriseed when your clearance vanishes. check clearance with feeler gauges with through bolt tight and see what you actually have!, then adjust as necessary.

regards Martin

Vibrations when the isolastics are set correctly are more often than not the result of "pirate" rubber elements made to the wrong specification. This is known of the vernier type as well as the old type. Ask Norman White about his experiences with rubbers the customers had provided from questionable sources, or any other reputable Norton mechanic.

You measure between the PTFE washer and the outer end dish. It matters not which side you measure as the gap centralises. Once you have nipped up the main bolt, use a wooden lever to put some pressure sideways on the mount and then measure and re-adjust as required.

You are checking with the bike off the centre stand aren't you as this can be really misleading. I used to do mine on its wheels and with the prop stand blocked up and packing under the RHS footrest to get it as near level as possible. I always used feeler gauges even with the "vernier" (which are no such thing really) isolastics.

Hi Gerald, The centre iso tube should be able to move 0.006" (or whatever you set) between the two side caps. If you have fitted a Mk3 Isolastic 1 piece rubber to a Mk 2 850 you will also have to fit the Mk 3 mount as they are a different length.(or shorten it) The way to get away without this change is to fit the Hemmings modification which just replaces one end cap but uses the original Mk2 850 rubbers. What exactly have you got?

Hi Gerald, I no longer have the Commando but used to aim for .008".

I can't remember how many holes there are but ISTR 8. So backing off 5 holes should give you (5/8)/20 (assuming 1/2" UNF) which would give you over .030"...... One hole would give you just over .006".

Substitute numbers as required in my calculation but that looks far too slack.

Actually, it won't be 1/2" UNF as it's the thread on the mounting rather than the through stud we're looking at. So you need to see what the pitch of the thread on the mounting is.

Ian - you were correct as the through bolt is 1/2 x 20tpi CEI and the mounting is 3/4 x 20tpi - 1 full turn on the vernier adjuster is 50 thou so 1 hole is just over 6 thou

I have been using a Norvil "vernier" for 10 years now and with that 3/4" thread 4 to 5 holes gives me appx 008/011" depending where its measured. I also had the isos machined square a few years ago and the front had 060" taken off the RH to allow it to sit straight and cure the weave and pull to the left. A washer takes up the space on the LH. Torque is 25lbs/ft. My rubbers are quite soft but if i try to reduce to 006" the high frequency vibes return. So bearing in mind Andovers comment who knows what hardness of rubber is fitted. Certainly i can install them with fingers only but that could mean they are undersize.