Growing nuisance...

For a period of time my 850 has had some vibration at about 2300- 2800 rpm on the road. This is only noticeable in 4th and has increased more with time, also it manifests itself for the most part through the handlebars. The mirrors are rock steady and instruments are not affected at all. It is a felt thing like more in line with a low frequency heavy sort of sensation through the bars.
Anyway going to begin looking through primary & clutch, move into the ISO's, & give the alt. rotor a good lookover. Once I move above the 2800 rpm mark she smooths out as if nothing is amiss, but she is old and I'm going to give her a good check. This zone has always been present but to a much lesser degree.... I don't know.... I shall before it's over.

Could be worth giving the entire bike a good going over for loose bolts.
Although the engine is the energy that excites the vibration, the overall stiffness (or lack thereof) of the entire chassis determines how that vibration feels.
My guess is that some parts have worked their way a bit loose with age.

At the same rpm in 3rd it is not there ?

Change out the fork oil as well. Once you have looked at the obvious single sources, then start looking of the combinations as it could also be speed related. Could even be something like the grips getting old.

4th is direct drive so its taking the gears in the box out of the equation and does not add anything back in. It could be road speed related so try the same speed in 3rd and as TW suggests same revs in 3rd to gain more info.

I'll go poke about a bit if not too hot today & mosquitos aren't very aggressive. Believe I'll make a discovery in the primary region, at least that's my suspicions for some reason mainly because that's the only area I've not explored in years... Mind you it's just a hunch.
Front end fresh built, swing arm/rear suspension same, fasteners gone over.

My first guess would be that your isolastics have aged and are now compressed enough to be transmitting vibration to the frame at certain RPM's. Maybe it only happens in 4th gear because of the difference in leverage each gear has applying force between the frame and the isolastically sprung drive train... What kind of headsteady do you have??

Check the kickstand. They can make an annoying vibration if loose. Zip tie it to the frame for a test.

It could be the muffler's baffles , I am investigating something similar, and have real John Favill bean cans, one seems to be rattlely when I give it slap, and could cause a vibration/ low frequency heavy sort of sensation. I am going to swap it out and see.

Well...…. It is done. Suspicions verified in primary... Too much slack in chain. Adjusted, switched over to ATF for lube oil, 15 mi. trial run, & vibration all but gone. At least back to where the norm has always been. Bike back to having a Norton-ish feeling on the road.
Considering the age and a mere 22,000 or so miles very little wear shows on anything. I did some adjustment last year without opening the primary, but laid it open this time to avoid any misjudgment on my part which is probably how this came to pass.
Anyway pulled plugs and did several full rotations to ensure it was adjusted according to the tightest section of the chain run leaving it like a turd sliding in silk underwear.

Good news ! ... nasty discription ... glad all good , several yrs ago had similar issue ,turned out battery tray had broken where it joined frame on left side , was a painful fix .. yours more routine

Glad you found it.

A buddy of mine has a 72 Interstate that was making nasty noises in the primary and when we took the cover off found the primary chain hitting the bottom of the inner cover. He had assembled it with the cover o-ring pinched at the bottom so all the oil had leaked out. A couple years without primary oil and the chain was toast.

This one had fresh oil & a new o-ring, but had been adjusted some months prior just using the peekaboo holes in the outer cover. I guess as I turned the chain adjusting the tension back then that I just wasn't as careful as I should have been.
Let this be a lesson to me lest one day I coast through on a task ending up with some serious damage to my bike. So now begin and come back go over and finish up perhaps the next day.... I can go without a cruise for one day and suffer no ill effects.... I think I can at least.

Going years without going into the primary is asking for troubles, maintenance is very important and primary chain and lube change should be done regularly as doing oil changes, even if the bike is only ridden on occasions or little ride time maintenance should be kept up, its so easy pulling the primary case off for inspection in side to make sure things are right as well doing the clutch plates maintenance is also important, remember these parts do a lot of work, its not only motors, gear box, forks etc etc all need servicing regularly even not riding for sometime the maintenance still need to be done.
I had a friend come around on his Norton a long time ago and ask to look inside his primary as I think it has a problem, well as soon as I took the cover of it the chain was so loose and there were marks on the top and bottom of the case from it flapping around, had rollers missing on the chain and his clutch basket was also a mess, I asked him how long ago its been serviced and he told me he has never been inside of it from the day he brought it about 4 years earlier, his clutch was stiff and the chain was dry as, but got it in time before the chain would have gave up it was so close.
After I replaced the primary chain and serviced the clutch, even his rota had signs of just about to throw it in, and when he took it for a ride he came back and said its working great the best it been and no more vibrations and it handled a lot better, I asked him why he didn't notice it and his answer was "I thought its was normal" some people just should not own a British bike, I ended up doing all the servicing on it till he sold it a few years later.
Even not being used much a yearly service is still important even if it hasn't done many miles, as soon as my Norton or any bike for that matter when things change whether a noise or rattle or just something different I always look into the cause, as little things can turn into bad things, keep your maintenance up and you will get long life out of your bike, it has worked for me after 43 years on the road its still going strong and has never let me down, because I keep it well maintained.

Ashley

Big ten-four on above post .....

I've been in it before taking things down... not like it was neglect. I just didn't open it to adjust it last time, which won't happen again because you miss the big picture. Anyway you're trying to preach to the choir.

Was just thinking of what I put up Ashman.... I wasn't intending for that to come out as rude as it looks. Anyway I left it as is and offer up apologies for the appearance of it.

jbruney said:

I've been in it before taking things down... not like it was neglect. I just didn't open it to adjust it last time, which won't happen again because you miss the big picture. Anyway you're trying to preach to the choir.

Was just thinking of what I put up Ashman.... I wasn't intending for that to come out as rude as it looks. Anyway I left it as is and offer up apologies for the appearance of it.

Click to expand...

All good, doing the chain adjust without taking the cover off has its problems, a bit more time helps, but its not a big job to me and I wasn't trying to preach, maintenance is very important for me anyway, I must be doing something right as my Norton has always been very reliable, yes its had its share of worn parts but getting on top of it before it become something major, after 43 years doing this I know every nut and bolt and little tricks that I have learned the hard way, it all pays in the end.
Anyway you got on top of it and enjoy your bike and give it a pat on the tank and say well done when you get back home safely after any rides.

Ashley

You too. After having her all this time when something comes up I pretty much go to the area which has the issue. It may appear to be something other but I do recognize where she's ailing, and luckily the cure is generally easily put right with adequate applications of $. Most times it only needs elbow grease and patience.

My Norton is no show boat and its starting to show its age, but the workings are well looked after and less money to spend on it helps with fuel and clean oil so its on the road always or when needed, having 3 bikes on the road I don't like things breaking but spend the money on maintaining it goes a long way for reliability and less money fixing things that fail in the long run.

Ashley

They have their maintenance, though in the same respect they also almost talk letting you know when things aren't right in one area of function or another. Hardly ever has it quit without some indication of a problem existing. I like to think of the engineering & design style as old world transitional at it's best for the cost. They want to run, corner, accelerate, attempt to stop. What more could one desire for under 2K when new?