Advice with engine vibration

Hi. New to owning a commando and looking for advice on engine vibration. Have just got my MK3 on the road. Fair bit of vibration up to 3000rpm then smooths out beautifully. So riding at higher revs is like butter but uncomfortable at lower revs. As I don't know the bike well, or the isolastic system, I'm not sure if this is normal. I'd appreciate some feedback or thoughts. :?:

It's a vernier system so keep the big washers lubed up as they tend to dry out. I use a spay silicone but many use grease. Adjust as per manual , you have one we hope. That vibration range is normal. Some leave the rubber covers off the rear mounts to better adjust, lube , clean.

Yes a manual is necessary and friends that know Nortons can be very helpful . There might a INOA chapter close to you.

The spring from the head to the frame will help with low end vibration, but it won't cure it. There's an adjustment measurement, but I tightened mine up as far as it would go and that seemed best for me. The newer rubbers seem to be stiffer than the old ones, but then you probably get better handling too. Yours doesn't sound unusual.

The spring from the head to the frame will help with low end vibration

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There is a sweet spot and to find it can be a bit drawn out to find. However what works for me is; Vibration in the foot rests on over run tighten the nut two flats a time. Vibration accelerating slacken two flats. My brain is getting a bit addled these days so it might be the other way round but I'm sure you know what I mean.
Dave

Ged67 said:

Hi. New to owning a commando and looking for advice on engine vibration. Have just got my MK3 on the road. Fair bit of vibration up to 3000rpm then smooths out beautifully. So riding at higher revs is like butter but uncomfortable at lower revs. As I don't know the bike well, or the isolastic system, I'm not sure if this is normal. I'd appreciate some feedback or thoughts. :?:

Click to expand...

This is completely normal and as good as it gets for 1975.
In the MK3 riders handbook it is suggested that if you encounter more vibration than you care for when riding slowly, ie thru town, shift the bike to a lower gear so that revs will climb above 3000.
The beauty of the MK3 is that once revs rise above 3k rpm, it is smooth as glass all the way to the redline.
And smooth as glass all day cruising on the highway.

What cs sprocket are you running?
With most bikes, gearing the bike up reduces vibration. With a Commando, it tends to increase vibration, or at least it means more time will be spent in the shakey range.
A 21 tooth works quite well, smooth running comes in at just over 50 MPH in top gear.

Glen

I''m surprised that vibration at engine speed as high as 3000 rpm is considered "normal". I would not have expected N-V to screw things up that bad. On the MK 1 Iso's (or maybe MK 0 on the prototypes!) there was very slight vibration at idle, but it completely disappeared by the time you hit 1000 rpm. I've never ridden the later Cdo's with the vernier system, but I'd expect it could be adjusted to no vibration above 1500 rpm or so without deterioration of the handling precision.

The only issue we had with the Iso system on the two prototypes was that the back Iso was always needing adjustment. It turned out that the ends of the spacer tube was going slightly conical as it didn't have the collars on the ends. The Iso elements were moving inboard as the tube distorted.

I had a pre MK111 850 with extremely low miles, it had the original iso parts and rubbers in perfect shape and it was very smooth. I think all the bikes out there now either have replacement parts that are not the same(harder rubber) or very used up ones causing the problems we see today. See the attached photos for an example of an used up assembly

IMHO, this thread is really gonna grow, :shock: asking about Commando vibration will get a lot of discussion!

jimbo said:

IMHO, this thread is really gonna grow, :shock: asking about Commando vibration will get a lot of discussion!

Click to expand...

Its a joke thread...

Commandos don't vibrate...

Fast Eddie said:

Its a joke thread...

Commandos don't vibrate...

Click to expand...

Unless you're a pussy! :mrgreen: Okay, so maybe I'm one of those...

As Jimbo showed earlier, the iso rubbers go away with age, as did mine. And, as mentioned, mine got worse after replacing with new, as they were quite a bit harder (higher durometer) than the originals. Running a 22T countershaft sprocket forces me to stay in 3rd gear more than I'd like, and holds off the sweet point until after 50mph. However, after playing around with different durometer muffler mounts, I've found these have a rather profound affect on the vibration point and severity. I chalk up this effect to the long moment arm provided by the header pipe. Come this Spring, I'll be swapping them for an even softer rubber. We'll see what happens...

Nathan

Possible solution could be to attach a concrete vibrator to the bottom of the engine plates, and run the unit 180 degrees out of synch with engine vibes - cancelling some of the vibes.
Could provide electric power to unit through the accessory socket on frame.



Sorry I had too much to drink over the holidays.

BritTwit said:

Possible solution could be to attach a concrete vibrator to the bottom of the engine plates, and run the unit 180 degrees out of synch with engine vibes - cancelling some of the vibes.
Could provide electric power to unit through the accessory socket on frame.

Sorry I had too much to drink over the holidays.

Click to expand...

Stupid idea.

Its orange !

I recall reading about the process of getting the isolastic system to work during development.
The early hope was for a complete removal of all vibration from idle to red line. Rubber that was soft enough to remove vibration at idle was overwhelmed at higher rpm , so vibration came back in large quantities right at the rpm range where the engine is used most.
Harder and harder rubber was tried until smooth running was attained right to the red line, however this meant some low speed vibration came back as the hard rubber needed some revs before it would do it's job.
Good compromise I think, rev it up a bit and the vibes are gone. It's a motorcycle, they are meant to be ridden with some gusto!

On another note-
Frank said
'On the MK 1 Iso's (or maybe MK 0 on the prototypes!) there was very slight vibration at idle, but it completely disappeared by the time you hit 1000 rpm. I've never ridden the later Cdo's with the vernier system, but I'd expect it could be adjusted to no vibration above 1500 rpm or so without deterioration of the handling precision."

Best to keep the idle to 1000 or above in order to get some oil to the cam to extend it's life. 1000 rpm+- is a fairly lazy idle for a Commando, much lower and it starts to sound like an East hope one lunger powered Crab Boat coming into dock!

twin carb idle
https://www.youtube.com/watch?v=7sSjSy_75tw

Glen

BritTwit said:

Possible solution could be to attach a concrete vibrator to the bottom of the engine plates, and run the unit 180 degrees out of synch with engine vibes - cancelling some of the vibes.
Could provide electric power to unit through the accessory socket on frame.


Sorry I had too much to drink over the holidays.

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something like that just might work :mrgreen:

We need someone to test the different rubbers available, and I have heard of persons drilling small holes into the rubber to relax them a little. Commoz to the rescue! (Of course he has a whole different system on his bike.)

Fast Eddie said:

jimbo said:

IMHO, this thread is really gonna grow, :shock: asking about Commando vibration will get a lot of discussion!

Click to expand...

Its a joke thread...

Commandos don't vibrate...

Click to expand...

You are partly correct Eddie if an owner does however feel some minor unpleasant tingling the cure is simple.
First switch off in machine affect.
Second apply more polish to it.
This constant polishing with the engine off and the machine preferably indoors is am told guaranteed to solve the issue.

I must to my shame admit my own bike vibrates at 3000 an i can't find time to polish it out. So i just don't ride at 3000 it's much more fun above there anyway.

Atlanticgreen has some info on the rubber densities, but it's not complete as I remember. The rubbers in my 69/70 still looked sort of OK when I removed them, but they were certainly not as stiff as the replacements I got from OB. Don't know if that was due to age or what, but the PTFE washers were completely gone, so it was pretty loose and I don't remember much of any vibration early on. I get a little buzz in the pegs now but I can see things in the mirror from idle up.

Now I remember why I got rid of Isolastics all together way back in 1980 and coverted to a Featherbed frame, I don't suffer vibrations at all, get the balance factor right and smooth as all through the revs range.

I also remember weather plays a big part with Isolastics and how your bike handles on the day or night.

Ashley

When Norman White saw the iso's (of unknown origin), fitted by the PO to my '74 mk2a he was really annoyed, he ranted on about how the factory spent time and effort establishing the correct shaw hardness (?) and that folk with less than a fraction of that resource or knowledge are selling various "upgrades" some harder, some softer, but all "unproven".

I fitted new AN parts and they seem fine to me, although I changed many things at once so cannot make any 'back to back' claims.

But Norman's rant made me realise the rubber isn't just rubber, that the whole concept of the bike is designed around these rubber parts, and that they were designed and specified as such for a reason. So it seems to me that it just ain't worth the risk in not buying genuine parts given their importance and the fact that telling good from bad by visual inspection alone is impossible to any of us lay folk.

Just IMHO of course.

I think handlebar width and shape is a factor too. Too wide and things start moving. Add bar end mirrors and you've really got some parts out there whipping. I'd like to keep the bar ends so I plan to cut down the bars as short as possible. Problem with the MK3 is the stock right hand switchgear/brake master cylinder can foul the tacho at certain angles if the bar is too short.