another iso question

Is it possible for ISOs that are too loose to cause a high frequency vibration. I took my front mount out to replace the gaiters and while out I measured how many turns to get .010 clearance. 2 and 1/2 holes out from snugged up. I set the rear at the same and the vibration level is more like my BSA A10 now. More of a high frequency buzz than the heavy harshness I had been feeling with the adjusters turned out 1 and 1/2 holes as per the instructions that came with the iso kit. I moved them back in to 2 holes out but will not get to test ride till tomorrow.

MikeG said:

Is it possible for ISOs that are too loose to cause a high frequency vibration. I took my front mount out to replace the gaiters and while out I measured how many turns to get .010 clearance. 2 and 1/2 holes out from snugged up. I set the rear at the same and the vibration level is more like my BSA A10 now. More of a high frequency buzz than the heavy harshness I had been feeling with the adjusters turned out 1 and 1/2 holes as per the instructions that came with the iso kit. I moved them back in to 2 holes out but will not get to test ride till tomorrow.

Click to expand...

What RPM is it worst at....?
Check cradle fasteners for tightness
I dont use a feeler gauge...i just back them off till its gone by 2800 - 3000 rpm

Hi,
So, what are the rules of thumb regarding the clearance of the isolastics and at what rpm they occur and how intensely they are felt?
regards
Alan

I believe the workshop manual says to set iso so that a 12 thou feeler gauge slides between the Teflon disk and iso end cap flange, with engine pushed/pryed away from frame, taking up all play at other end of the iso. This is done with iso through bolt or stud at the spec'd 25 ft-lbs torque. Intent is to get around 6 thou either end when engine is not pryed over/centered.

If you have the mk3 suspensory spring at the head steady, this can be adjusted to tune out lower rpm vibrations, but at consequence of more higher rpm vibration (according to guidance on RGM website document).

On my 850 mk2 with Dave Taylor headsteady, suspensory spring, vernier iso adjusters front and back and fresh rubbers, I get most vibration around 2100-2700 rpm, enough to shake stock mirrors enough to blur image. Above 3000 rpm, things are much better, usable mirrors etc.

It could be the iso rubbers are too hard
What's the history of the rubbers?
Virtually all vibes should be gone by 3000 rpm
There really is no comparison with an A10 tbh

Mike, I found the threads so sloppily cut, (PMP) I had to adjust, nip it up, then measure/test ride. A couple checks & it was good.


JMWO

My850 Mk2 has been modded out to the Mick Hemmings adjusters and the AN one piece
iso rubber-tube. It has more low vibes than before. It is ok after 2800. At 3800 you can see
in the mirror better than any bike I have ever ridden. 10 thou on the clearance or maybe a
a trifle more. If I go more it is even smoother but then you start to get odd sounds as you
lay it into a curve.

Onder said:

My850 Mk2 has been modded out to the Mick Hemmings adjusters and the AN one piece
iso rubber-tube. It has more low vibes than before. It is ok after 2800. At 3800 you can see
in the mirror better than any bike I have ever ridden. 10 thou on the clearance or maybe a
a trifle more. If I go more it is even smoother but then you start to get odd sounds as you
lay it into a curve.

Click to expand...

Go too much bigger than 10 thou and you will start to get some really strange handling
I just back mine off until the engine can move up and down using a tyre lever
I've got no Idea what the gap is

With adjusters backed off 2 holes from snug the vibration in the bars is gone. Still some buzzing in the foot pegs throughout the RPM range. Not enough to be uncomfortable but you do notice it. What started me on this was a bad chain and sprockets that gave a very harsh feel through the pegs. Replaced them and noticed the underlying vibes. Perhaps I'm just chasing my tail at this point, and maybe the rear set controls have a bit to do with vibes in the pegs?

FWIW- Iso's were new RGM about 8 years ago, Dave Taylor head steady with suspension spring.

baz said:

It could be the iso rubbers are too hard
What's the history of the rubbers?
Virtually all vibes should be gone by 3000 rpm
There really is no comparison with an A10 tbh

Click to expand...

I compared it to the A10 because I had it dynamacly balanced last rebuild. The vibes are still there but balancing moved the worst of them to the upper end of the RPM range where I don't spend much time. Whats there now is a mild buzzing like what I was feeling on the Commando.

MikeG said:

With adjusters backed off 2 holes from snug the vibration in the bars is gone. Still some buzzing in the foot pegs throughout the RPM range. Not enough to be uncomfortable but you do notice it. What started me on this was a bad chain and sprockets that gave a very harsh feel through the pegs. Replaced them and noticed the underlying vibes. Perhaps I'm just chasing my tail at this point, and maybe the rear set controls have a bit to do with vibes in the pegs?

FWIW- Iso's were new RGM about 8 years ago, Dave Taylor head steady with suspension spring.

Click to expand...

8

Years.


The end.

What was the balance factor on your A10?

Onder said:

What was the balance factor on your A10?

Click to expand...

Off the top of my head I can't recall. I still have the paperwork at home, I'll look tonight.

Onder said:

What was the balance factor on your A10?

Click to expand...

Looked through the paperwork he gave me when I got the crank back. No balance factor stated, just weights of all reciprocating components and some calculations he did. IIRC, we never discussed balance factor, he asked me how I rode the bike and where average RPMs ranged and took it from there.

Just had an odd occurrence with my rear iso. (Just to match my "Front Iso - Strange" experience )
Cleaned and reset front & rear isos as part of the 12,000 mile service. Closed both up snug, cleaned them then backed them out 2 holes, as that's where I have found them to be best.
600 miles on and, on a ride last sunday, I noticed buzzing in the footpegs at 62mph (3500rpm) and the mirrors not as clear as usual.
Today I loosened the through-bolt (stud) and closed the rear iso up. It would only turn in a bit less than 1.5 holes - WTF??
So, again cleaned and wound the adjuster to a bit over 2 holes out, then locked it up. I watched the adjuster as I tightened the through-bolt (stud) nuts to see if it moved - It didn't.
Took it for a ride and all is well again.

I'm surprised that it closed up - especially over such a short distance. Thinking back, I believe the buzzing increased over the last 100 miles.
Anybody else seen something like this and have any idea why?
Cheers