Vibration Experiences

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Scout63

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Now that I've been riding my Commando for a couple of months, I'm finding that I'm losing some parts to vibration. Other than the sheared engine mount bolt and missing engine mount bolt that I've posted already, I noted today that I've lost the lower front fuel tank washers, rubber washers and nut. I lost the kick start mount bolt a few weeks ago. Luckily I have bags of replacement parts from over-ordering from Old Britts.

Is this normal? Should I just be going over the bike every few rides front to back with a set of wrenches? I sort of hoped that all of the hype was just that. I still need to fine-tune the isos, but that won't help frame mounted parts. It hasn't lessened how much I love this bike, but I think I need to adjust my expectations. Ben
 
It's normal, although some do seem to vibrate more than others. (I've had eight of them now.) Everywhere a nut is, replaced it with a "nylon lock nut." That is a good start IMO. These bikes vibrate, and bits do tend to go "missing in action."
 
Something is not right if you are losing parts to vibrations, the Commando motors do shake around from the iso mounts but still shouldn't be losing parts or shearing bolts, so something is way wrong on your bike, I convered my 850 to the Featherbed frame in 1980 and in all these years since with hard mounts and a balanced crank I have only lost one muffler nut and the top gearbox nut in the last 38 years, but I think forgot to tighten the gearbox nut when I was working on the gearbox at the time.
If you have sheared off engine mount bolts then it seems something might not alined or something out of whack, my Norton was a everyday rider since I have owned it from new and was semi retired 6 years ago with a lot of miles under its belt when I brought a new Thruxton, so if I was you I would be looking for the cause of you major problem, but of course as part of any maintenance is going over the bike checking for lose nuts and bolts, I am still running with all my original engine mount bolts from the factory to this day.

Ashley
 
In my experience, no, it’s not normal. As mentioned above, even if the engine vibrates, the isolastics should prevent what you describe.

At the risk of asking the obvious... are you sure you’re tightening things up enough / properly ?
 
The only time I've ever experienced enough vibration to rattle anything loose was when my counter sprocket was beginning to wear enough to hook. I couldn't tell much about it until the entire clutch/primary were off.
 
I agree, I wouldn't say this is normal.

The only things I've had fall off fell off because I forgot to tighten them.

Compared to my Ironhead the Norton is a silken magic carpet ride, vibration is only an issue when she's motionless.
 
Yeah , your bike got shakes , for normal vibration some caulking on threads helps things stay where they should .... since I redid ISO’s and added spring to DT head steady I don’t need the caulk , I do use ny-lock nuts on front tank mounts though ....
 
You've got something somewhere that's outta kilter if your Commando is vibrating that bad. Now my rear mudguard does a real hootchie koo when the bike is at idle and the mirrors are fuzzy under 2300, but after those speeds she gets pretty close to my GL 1000 except for the chain drive.
Original ISO's were smooth at .010", but these new ones had to be opened up to about .014" if I'm remembering correctly..... At 10 it felt like a meat grinder. Open gap hasn't affected handling either, which was concerning me a lot.
Keep digging and you'll find the issue.
 
"The parts that fall off of this bike are of the finest British manufacture. "
Today I replaced a bolt and nut that disappeared from the rear fender.
 
Thanks for the feedback. I’ll keep watching everything. The bike feels pretty smooth now that I loosened the isolastics a bit. I’m hoping that earlier iso tightness caused the engine bolt problem, and the loose fasteners are in the rear view. I’m using nylock nuts where possible and blue loctitie. I’ll report back in a few hundred miles.
 
This seems too much.

I have found that vibration can come from all sorts of places.

Firstly and most obviously badly adjusted Isolastics.

Then working from from the back.

Out of balance or badly fitted tyres

Worn forks or steering head bearings.

Loose fork brackets on the forks.

Tanks touching the frame. This is common

Unevenly torqued engine and gearbox bolts

Misaligned primary and rear chains

Bad carb balance. This one is real and surprised me.

Tappet clearances

Bad engine balance. You can't really check this without full dismantling things but in the worst case a friend found totally mismatched pistons that were very different in weight.

Random bits like sidecovers stands guards being loose and rubbing at certain rpm

Clutch and rear chains nuts being loose.

If it vibrates that badly you may need to work your way front to back looking for the source
 
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It isn't normal. Iso's are the obvious thing to check but to add to the list of other suggestions, too tight chains can be a problem too.
 
Scout63 said:
Now that I've been riding my Commando for a couple of months, I'm finding that I'm losing some parts to vibration. Other than the sheared engine mount bolt and missing engine mount bolt that I've posted already, I noted today that I've lost the lower front fuel tank washers, rubber washers and nut. I lost the kick start mount bolt a few weeks ago. Luckily I have bags of replacement parts from over-ordering from Old Britts.
Click to expand...

Hi Ben,
My first thought is, what's the state of your crankshaft? Was it ever balanced / rebalanced for the conrods as pistons fitted? Dynamic balancing can work magic! Are you running h.c. pistons? Is your crankacase a genuine matching pair, or a set of cobbled together parts?
If fitting adjustable iso mountings can't cure the excessive vibrations, I suggest you send in the engine lower end for a real surgery.

-Knut
 
I used to have parts vibrate off the bike (rear view mirror, rubber foot peg etc). In went the lightweight pistons and longer rods. Vibration reduced by 1/3. Smooth now and no worries.
 
That vibration sounds excessive. That said, I use blue Loctite on most fasteners on my Commando and have never had anything vibrate off.
 
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