Topic: cb250 constant vibration ??? assistance needed

[750goes]

Moderators  - if I put this in the wrong forum spot please move it to where it should be...thanks

Guys,
my 1993 cb250N has a constant vibration in the fornt end - it is there from 50km/h to 80km/h - I bet it is still there after that as well.

it seems to be from the front end and you can feel it through the handlebars, like hanging on to a whacker packer - but no so severe...
it does not affect steering or turning the bike either left or right at speeds..

History
The front suspension was very hard so 2 weeks ago I drained and replaced the fork oil - old oil was cruddy, replaced with 10w oil to the correct amount in each fork, and nearly broke my arms off with the first bump I hit after a test ride..

I emptied equal amounts of oil from both forks until I got a lot smoother action on the forks and am comfortable with the feel of the front end and how it responds.

they are now firm and move probably 4" or a bit more in travel I can see on the fork tubes.

Steering head bearings were a bit loose - I have tightened the lock nut maybe 3/4 of a turn....they are a little bit "notchy", but I have not greased or inspected them yet...(little ball bearings I hate)

Front axle is tensioned correctly  and front rim is not warped/buckled (comstar), and seems to be balanced well..wheel bearings (front) appear to be fine also (have not inspected or greased them yet)... there is no play in the wheel ....

any thoughts or suggestions (nice ones)....

it seems to have a "zinging" noise vibration  - I don't know how else to explain it...

thanks for your replies

[bryanj]

Sounds like you need to strip and clean out the forks/dampers plus change the head race bearings as any "notchiness" is bad. You can get tapers to replace the balls

[scunny]

get the front end in the air and check your bearings. as Bryanj said, time to pull the forks apart and clean them up. I would still check the balance of the wheel tho

[nickjtc]

I would still check the balance of the wheel tho

Ditto.

In what condition is the tyre? Correct tyre pressure? Look at the easy things first before tearing into the more complex stuff.

[mlinder]

Oil Fork for our old CB's is 10 weight.
Dunno what it is on yours.
I know that my other bikes always used much less than 20w too.
The oil is the first thing that 'dampens' the up and down motion of your forks. If it's too thick, you'll havew a VERY stiff ride. You'll feel every bump in the road.
Running with too little oil will cause your springs to wear out prematurely. Sounds like the springs are now handling the initial damping until the 'washers' reach teh oil, where it's back to too stiff.

[750goes]

thanks for the replies

bryanj - I thought that might be the case - I was probably looking for a magic genie to appear so I would not have to do it myself...
scunny - the wheel is balanced - I spun it about20 times and it ended on a different spot each time...
nickjtc - tyre is 60-70% tread - and is fine - air pressure is also ok - checked each morning and once a week at the garage.
mlinder - mine is 10w - or thats what I put in it - I may even go a bit lighter.. 

Results will be posted but  I think the following will be done
1- replace the fork oil with lighter weight - and give them a real good clean out
2- replace the races and balls with bearings

Question - when I filled up with fresh oil the fork had in the following order of removal
 - top nut
 - flat washer
 - small spring about 2" long
 - longer fork spring (not removed)

I only pulled out the top spring and washer and filled the oil from there, did not take out the long spring...
I also drained it for about 10 minutes with some pumping of the forks via the handlebars..

should that small spring be at the top or down the bottom as per the following picture from a microfiche if I can get it to post here

http://images.powersportsnetwork.com/fiche/images/Honda/1993/Motorcycles/1911_FRONT%20FORK.gif

It looks a bit like number 5 sitting on top of number 2....I have no real history on the bike either as to what when and if any work has been done on it....and by who as well...

as usual any replies much appreciated - my manual is at work so will not be able to look at it until tomorrow

[HondaMan]

How much oil are you installing? I think I remember my CB/CL350s took 6 ounces and my CL77 (305cc) took 6.5 ounces.
(CB750 is 7.0-7.5 ounces).
Front axle: try this: centerstand the bike, get the front wheel in the air. Then loosen the fork caps on the bottom,  make sure the axle is properly spaced between the legs, and retighten. Most of these bikes have fork caps that are made so that one side will be parallel and flush to the fork bottom when tightened: this one gets tightened first. According to Honda, circa 1970s, the "flat and flush" part is supposed to be at the back, with the "gap" at the front, for "proper stress management" of the lower forks. (Huh?). I've seen them both ways, right out of the crate, from Honda, so I dunno which is best in real life. I've always switched them to the rear when working on them, and found smoother fork response afterward.

On a different topic: I'm getting ready to make ignitions for Terry and Steveko, would like to ship to all you guys at once. Which kind did you want, Stock coils, or Dyna-compatible?

[750goes]

thanks Hondaman,

I  will look at the axle tomorrow,  I measured in resonably well the required amount - as per the manual, not sure of the exact ounces measurement - but somewhere around 250ml - I have since taken out probably 40ml from each side (I don't think I got all the old oil out even after pumping them for a while)

I have standard coils...so happy with those...I don't intend to swap to a dyna anywhere in the near future (I have recently bought 10 condensors, and a while ago got several sets of new points -1&4 style with a few 2&3's)

let me know when and where you want the money sent for the ignition set ups..

[Sam Green Racing]

Did the bike have the vibes before or after you changed the fork oil.  If it had it before, check tightness of handle bar and engine mountings.

Sam.

[750goes]

Thanks Sam,

It had the vibes before I changed the oil.......
I have already checked all engine mounts - they are all firm and been retorqued  - none were loose
will check the bars tomorrow - 

[HondaMan]

thanks Hondaman,

I  will look at the axle tomorrow,  I measured in resonably well the required amount - as per the manual, not sure of the exact ounces measurement - but somewhere around 250ml - I have since taken out probably 40ml from each side (I don't think I got all the old oil out even after pumping them for a while)

I have standard coils...so happy with those...I don't intend to swap to a dyna anywhere in the near future (I have recently bought 10 condensors, and a while ago got several sets of new points -1&4 style with a few 2&3's)

let me know when and where you want the money sent for the ignition set ups..

OK, I'll build up a "stock" unit for you this next week, along with Steveko's and Terry's "big bling" units.   

[750goes]

thank you,,

[crazypj]

Is the wheel actually round? Tyre seated correctly ( sorry, just had to ask)
PJ

[HITMAN]

It's a shot in the dark but, at one time I had a cat spray my front wheel.  Noticed it the next day and hosed it off the rotors, and went about my day.  The bad was it left an oily spot on the rotors the created a vibe at 30+ with the normal drag of the caliper.  Took the rotor and pads off and cleaned them with brake cleaner, as soap and water didn't cut it.


Problem fixed, but the neighbors ferrel cat is on my list

[750goes]

pj,

yes, tyre is round, so is rim and is balance, and located on rim correctly..

[750goes]

hitman,

there are a few cats in the neighbourhood, so I suppose I will give the rotor a quick scuff up with some emery paper to see if that lessens the vibration as well....

[HITMAN]

Just be sure to use something like brake cleaner aggresively to cut any oils, I always thought my experience was a fluke but it would be simple if yours was the same or similar.

Let us know what up. 

[HondaMan]

hitman,

there are a few cats in the neighbourhood, so I suppose I will give the rotor a quick scuff up with some emery paper to see if that lessens the vibration as well....

Off the topic a little...     Steveko has asked for a shipment of his electronic ignitions soon: do you live close enough to him that I could send yours together to save you guys some postage $$$ ?

[750goes]

H'man,

I think Steveko lives in Victoria, I am in NSW - I will send him a PM or email if possible and let you know asap...

thanks

[Dave L]

HI
It may be worth checking the back end , it could be the rear shocks or the bushes.
Also check the back wheel and tyre.
On my 550f2 the rear shocks are not very good and on the lower settiings this did cause some of the same issues you have discribed.

Regards Dave

[HondaMan]

H'man,

I think Steveko lives in Victoria, I am in NSW - I will send him a PM or email if possible and let you know asap...

thanks

OK. I don't know where those places are on your map: I'm kinda AUS-illiterate...

[750goes]

puts me about one state away and say 700 kilometres as a guess

[Terry in Australia]

G'Day Charlie, don't worry about it mate, it's probably just farked, ha ha!

Seriously though, try pulling the forks apart properly and cleaning the goop out of the sliders, then refilling them with ATF. ATF is good for most Honda forks, and the side-benefit is that it swells seals if you're too slack to replace the old ones.

Mark, (HondaMan) Charlie is in New South Wales, (Gay Capital of Oz, hence the CB250) and is about 500 miles north of me and Steve K0 in Victoria, but if you want you can ship them all to me or Steve, and we'll send Charlie's up to him, for when (and if) he ever gets off that sheila's bike! Ha ha, Cheers, Terry.

[750goes]

#$%* Terry I thought Melbourne was the "Garden" state - needing all that fertilizer you spread from time to time....

Yeah the 250 is a bit of a sheilas bike but it will have to do at the moment - the other gas guzzler the Jackaroo is sitting on the lawn, because it's out of rego - and needs 4 tires and a windscreen as well...

as for the forks they are due for a good go over - just haven't got the time over the weekends to do it at home - all tools and equipment are at work premises..


will get Trevor to give me a hand when he comes back from Brisbane- that Geoff's useless,  all he does is sit on his arse - no help at all (ha ha)...his K2 is coming along real nice...