Handling

[leonardo269]

Hi,
     My K7 has a front end wobble if I do not hold the bars tightly. (for instance if I take one hand off the bars to lift my visor). (Tyre looks OK, wheel looks OK). It does it withoiut the brakes being applied.

Also, my newly reconditioned set of forks are rubbish! I can feel every bump and pothole in the road as I ride along. The stanchions have been re-chromed with new seals and internal bits with the correct amount of the right grade hydraulic fluid.

I realised that the handling on CB750's was a bit suspect, but the combination of these two faults is slowly driving me round the bend :blink: .  

Are these common problems with CB750? If so, has anyone suceeded in  putting them right?

Cheers,

Ray

[jimshea]

Ray,
At what speed does the wobble occur?? is it all of the time? if not, it sounds like a simple wheel balance issue; do you have balance weights on the front?

[Voxonda]

Hey Ray,

I would suggest to, also, check your steering head bearings.

Good luck.

Post edited by: Voxonda, at: 2007/02/03 09:50

[leonardo269]

Hi,

It does it all the time, but is most noticable at low speeds. If you relax grip on the bars it is quite an wobble.

When the tyre needs replacing (which is probably not that long) I think I will get the whole wheel rebuit on a new rim and fit a modern tyre.

That ought to do it.  

Cheers,

Ray

[leonardo269]

Hi,

I replaced the steering head bearings with a tapered roller set recently. There is no play and eveything is smooth as you would expect.

Cheers,

Ray

[SteveD CB500K0]

Two things spring to mind:

Are you sure about the front tyre? A low speed wobble is usually indicative of an unevenly worn front tyre. My VFR did this (tankslappers at 30mph) and a new tyre fixed it.

Second, if you can feel every bump through the front suspension, have you cocked-up the fork oil? It shouldn't be like that. Was it you who put in the ATF or were you just told that it was so?  Are the forks stiff when you bounce on the front with the front brake applied?

[leonardo269]

Hi Steve,
             There is nothing immediately apparent in terms of uneven wear, but I will have a good look at the front tyre when I get a chance. I suppose the best thing is also to jack the front end up, spin the wheel and check the wheel and tyre for wobble with a dial indicator.

Each Fork leg is filled with 150ml of Silkolene fork oil sae 10W, recommended to me by my local bike shop. What do you use?

The forks compress by about 40mm when they are pushed down with the front brake applied.

Thanks,

Ray

[Lane]

Sorry to butt in here.
Check out your swingarm - the bushings may be shot. Put the bike on the center stand and grab the rear wheel at the top. Push HARD side to side - there should be NO side-play at all, I mean none.
Even when the problem is in the back like that, it's expressed through the front end, because the front end moves side to side so easily. So bad swingarm bushings can cause folks to spend a lot of time looking at the front end, when nothing is wrong up there.
Funky swingarm will definitely cause the symptoms you describe, and be be absolutely dangerous in a turn - the bike can start to buck like a horse sometimes. Like having a hinge in the middle of the bike.
Fortunately, it's a cheap fix, but a filthy, pain in the butt job to do.

bill

[leonardo269]

Hi Bill,
          I will check the swinging arm when I get a chance (my bike does not have the centre stand fitted, so I will need to jack it up to do this).

The swinging arm has only recently been rebuilt and the bush and spindle dimenions were within tolerance so I would think it unlikely, however I do take your point and I will check it out.

Cheers,

Ray

[shifty_steve]

Hi, I also have a K7, with what sounds like the same problem, gone through everthing tyres, bearings forks, but never thought to give the swingarm a good check, almost feels like it starts at the back end but just been focused on the front, its been driving me mad.

Steve

[size=9]My first post, hello to all:) [/size]

[leonardo269]

Hi Steve,

 I checked the swinging arm, no problem. From the frequency of the wobble I would say that it has to be the front wheel or tyre on my bike.

Jacking the bike up and spinning the front wheel, I have observed an uneveness in the contact edge of the tyre that varies by about 1cm per revolution. (probably the last owners emergency stop!):woohoo:

My therory is that this flat on the tyre is probably causing the forks to continaully bob up and down and becasue of the damping effect,  compress the travel of the forks so that when I pass over a bump in the road they bottom out.

I have a spare (rusty) front wheel & (just about legal) tyre that might be worth swapping over just to test the point.

Cheers,

Ray

[shifty_steve]

Hi Ray, yeah I cant say I have noticed that much travel from front wheel or tyre, I had both new tyres fitted, rode 5 or 600 miles then realized the garage had fitted them wrong direction....very dangerous..so I ain't the most observant peg in the tin, made sure they are correct now though. This weekend I am determined to get to the cause, keep us up to date, fingers crossed with your test.

Steve

Ps; I did'nt think to ask but did you have this problem prior to forks refurb??

[leonardo269]

Hi Steve,
             I dunno, the bike was a rusty (and dangerous) bag of spanners when I got it. I never dared to take it out on the road. The steering head bearings were that notched you would have had to turn in 5 degree installments.

To top it all the brakes were shot and the forks were lubricated with 1/2 a pint of mud per side.

I honestly dont know how someone can do that to a motorbike.

Much better now, even with the slight wobble.:lol:

Regards,

Ray

[leonardo269]

OK - time for a bit of an update. I replaced the front wheel and tyre for a spare one that I had knocking about and it seems a bit better, although there is a fair amount of bobbing about from the front forks that indicates that the dampers are not working very well. (bearing in mind that I replaced the piston rings when the forks were rebuilt.

My local bike shop gave be SAE10W fork oil, but the Haynes manual specifies SAE10W-30. From the information I can determine the two figures relate to the viscosity of the oil in \"cold\" and \"at working temperatures\". with 30 being thicker than 10. This all seems to relate to oil that is going inside the engine, rather than inside the fork leg, so it is not completely clear.

The question is:- Is my existing oil too thin and could this be a reason for the lack of damping? Is it worth trying a SAE30 oil to see if this improves matters?

I have to do something this is ruining the riding experience at the moment.

Cheers,

Ray