poor handling

[evo]

Hello I,m new to this and was hoping for some advice.
I am experiencing very poor handling more noticeable at low speed (10mph) as if the bike or me were drunk! above 10mph cornering feels as if I were to relax my arms/hands the steering would took in. In a straight line at approx 30-40mph If I were to loose the handle bars they would escalate into a very nasty wobble. I have lifted front off the ground checked for play in the front wheel, handle bars, smoothness left to right all seems good. There is no play in the rear wheel. The bike is in a good well looked after condition and road beautifully until I had a slow speed drop to the left hand side. My rear tyre is squared and the front is due for replacement, I have not experienced this before on other bikes even with squared tyres is there anything else I could do or should I just replace the tyres and hopefully this fixes the problem.
Any advise would be much appreciated and hopefully I can go back to a more relaxed riding style.

[cyril]

Hi Evo.

Sorry to hear of your malady.

I have suffered bad handling twice on my bike.
1) First time the tyre pressures were low.
2) Second time post front end rebuild after head on smack.
The second time was a bit like you describe. (an unpredictable bucking bronco)
I only cleared it after unbiasing the front end.
I supported the front (engine on blocks).
remove front wheel, slacken lower yoke, triple clamp bolts, and headstock nut.
put axle back in place.
I tapped all the front end with a plastic mallet to free off any bias.
Tighten headstock nut.,
Check fork tubes are at same height (grove ring at bottom of triple clamp).
tighten yoke and triple clamp.
refit front wheel.
take for tentative test ride.

This worked on my bike,
I had spent a month chasing head stock bearing tightness / freeplay to no avail.

There is a steel fork brace as part of the mudguard,
hopefully it did not get twisted when you had your slow speed spill

Hope this helps
Chris

[evo]

Hi Chris and thanks for your reply.
I have checked tyre pressures, steel fork brace (part of mud guard) all of which are ok.
I am not 100% sure what is meant by Bias? This has been mentioned to me before as a possible solution, please can you explain.

Thanks again,

Tony.

[cyril]

Hi Tony.

Bias as in uneven loading / preloaded.

In my case although everything appeared aligned, and balanced, there was an uneven loading in the forks,
so when i dipped in for a bend the fork tubes were not taking the loads evenly,
either jamming up, or fighting each other,
It would alternately dip further into the bend, then straighten up
making it feel like the back end was skipping and trying to chuck me out of my seat.
after straightening up after a bend, the bike then had the wobble you indicated.

I think my fork tubes were jamming in the yokes when i installed the front end,
then i caused further bias, by repeatedly nipping up the headstock bearing. without fully freeing off the triple clamp.
i thought the headstock pre-load was the cause of the problem.
but un-biasing the front end,.getting it to settle to an unloaded condition before clamping it all back up cured the problem.

as your problem occurred after your spill, it is obviously the cause, and your forks taking an uneven load has probably caused something to move in the clamps, setting up an uneven loading / bias.

i mentioned the steel under the mudguard, as that keeps the geometry of your fork lowers aligned, if it has twisted slightly it will cause a bias all of its own, the easiest way to check is to remove the front wheel, then see if the axle pin aligns correctly, or has to be forced to go through both sides.

hope this helps you get it sorted quickly.

Chris

[evo]

Thanks again Chris.

I will get the front off the ground and use your advice. I will keep you posted of the outcome.

Tony.

[Rick76]

Thanks Chris for a very interesting and systematic account of the work on your NTV forks. I have recently drained and refilled my mod. k with (466cc atf) and think to follow your lead and check the stanchion alignment. I wonder if you or any members have experience of, a) different fluid characteristics - my forks feel a bit firm in cooler conditions - are thin synthetics more stable? and b) do variable rate type springs have a noticeably different action?
Also, concerning handling, I see from specs. NTV's have a 28degree fork angle and 116mm trail . Not a direct comparison but my old Norton dommie was, I believe 26deg and was v.stable and steered perfectly. Could this difference explain the NTV steering sensitivity?

[Jake]

Apr 14, 2011 3:10:08 GMT -5 Rick76 said:

.... I wonder if you or any members have experience of, a) different fluid characteristics - my forks feel a bit firm in cooler conditions - are thin synthetics more stable? and b) do variable rate type springs have a noticeably different action?

It’s all a matter of taste with suspension settings.....

I bought some progressive fork springs from Hagon
when I first got my bike and fitted them together with
15w oil. But not everyone likes the front suspension
setting this firm.....

One of the things I discovered with front suspension
is that, how hard or soft the rear suspension is
can effect front end steering. Within limits, the harder
rear suspension is then the slower the steering and
vice versa ( softer rear = quicker steering.)

I set my suspension up on the road. I took the bike out
on a Sunday morning, and raised or lowered the rear
suspension until I obtained a setting that I liked .....

Tyre pressures are also crucial....Again on my bike
they're set fairly high at 42 psi rear and 36 front.....

[professore]

I have my bike set up like this and it suits me great.
Prof.

[cyril]

Hi Rick76.

Sorry but i have no expertise or experience of fluid characteristics in forks, nor of chassis design parameters.

I was Just glad that my front wheel was still round, and main frame not buckled after my prang.
fork inners became banana profiled, lower yoke bent (straight forks would not align with upper yoke),
and the braced mudguard buckled, as was my radiator, its lower mount, and fan shroud.
other minor parts needed mending, and front axle although not straight was within acceptable limits.

I have eventually worked out why I could not adequately set my headstock pre-load, after fitting taper roller bearings.
It would appear I had been pinching the outer rim of the upper seal between the outer race of the upper bearing and the Adjuster nut, instead of pe-loading the inner races of the bearings.

Eventually resolved by shimming between the upper bearing inner race, and upper seal until i could set up the pre-load, without binding the steering. (old lock-washers with external tabs removed fitted perfectly).

Obviously the outer race of Taper roller bearings are taller than on ball bearings.
something i did not consider when swapping them.

Now i understand why i could not get the set-up right, i am confident that it is eventually sorted.

Chris

[cyril]

Well the shimming of the upper inner bearing has done the trick.
400 miles and no hint of any wobble in the headstock.
Previously it was less than 300 miles before it became wobbly.

Does anyone know how to get the swinging arm bearings out?
I have a spare swinging arm, but it has defeated all my efforts to remove the bearing
There must be a way without causing damage to the housing.

Chris

[Jake]

May 20, 2011 17:20:15 GMT -5 cyril said:

Does anyone know how to get the swinging arm bearings out?

Sorry Chris, not a job I’ve ever tackled.....

I guess you’d probably need a ‘presser’ or’ puller’
type tool to remove the bearings....
You may find information on Youtube (e.g. see link below).

www.garagenight.tv/replacing-swingarm-bearings/

Or use correct size socket, hammer and centre punch?
Which may not help, since there are bearings on both sides.

There's some useful tips on the 'Thumper Talk' forum:
Check out the hint from DRZinMD in the thread below....

www.thumpertalk.com/forum/archive/index.php/t-360681.html

Good advice is to have new bearings available, in case you
damage the existing ones (or if it ain't broke don't fix it).

I notice the Haynes manual isn’t that helpful…..
See chap. 6, pages 6.15 - 6.17.

wbieniec.kis.p.lodz.pl/moto/ntv/manual/6.pdf

If you manage to solve this one, let us know
how you did it......

[cyril]

May 20, 2011 17:20:15 GMT -5 cyril said:

Does anyone know how to get the swinging arm bearings out?
I have a spare swinging arm, but it has defeated all my efforts to remove the bearing
There must be a way without causing damage to the housing.

Chris

Well got the Swing arm bearings out at last.
No joy with pullers even grinding arm tips to thin slivers.
Prised dust seals out with screwdriver.
Pressed bearing on shaft side out using sockets and 8" G clamp.
Tapped Bearing out on opposite side using same socket and long 3/8" extension.

If you have no G clamp, Drill one grease plug to about 13mm and drive them out from opposite sides using a socket, and long 3/8" extension
The restricting factor is the inner bore which passes across the arm at the pivots.

The grease plugs sit on a shoulder in the bearing housing.
you cannot press directly on the outer bearing shoulder to remove it.

The grease plugs (item 7) will be damaged in either respect.

I hope this is of some use.

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[Rick76]

Hi Cyril, best wishes for 2012 and congratulations on your s/arm job. Have you been weaving about for all this time ? I'd just like to say thank you for the excellent post, if ever I get problems it'll be the business.