speed weave

Maestro, SEI-V

speed weave

Postby pedro » 30 Mar 2017 18:20

My 501/350 has developed a nasty habit of weaving at anything over 85/90 mph, it feels as though it could develop into a tank slapper if I keep it screwed on, so I don't.
I have checked wheel alignment, tyre pressures obviously, today I thought that I would renew the head race bearings just in case. Don't you love it when you have changed the balls, got it all back together, just picking up your tools, when you see a ball bearing on the floor looking all innocent. Took it to bits again, replaced the errant ball, put it back together, adjusted very carefully, went for a test ride and nothing has changed. Not sure where to look next. It seemed to start after changing to some raised clipons and so I'm wondering if the altered riding position is to blame. However, my other 501/350 is a Strada with even wider, higher bars and is rock steady. Any suggestions?
pedro
 
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Re: speed weave

Postby norbert » 30 Mar 2017 19:49

Hi Pedro,

One thing you can try with the fork:
-Get the wheel out
-loose the four allen who fix the tubes in the two ... (don´t know the word for it) of the fork
- get the axle of the wheel in
-Open the tubes on top, so the springs can come up
-raise the fork as far as possible
-in that position fix these four allen screws

Doing this, to my purpose the elements of the fork shoud be aligned as good as posible.

There is no play in the swingarm and the rubbers are still ok?

good luck
norbert
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Re: speed weave

Postby huub » 30 Mar 2017 20:11

check the sag in the front forks, with you sitting on the bike you should have > 75% of the suspension travel left.
if the springs sagged the shorter forks cause the steering angle to be steeper.
i had a 350 that could go into a vicious tank slapper when pushed hard around bumpy corners because of sagged front suspension.
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Re: speed weave

Postby Mepstein » 30 Mar 2017 22:12

Can you switch front wheels between bikes and see if there is a difference.
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Re: speed weave

Postby George 350 » 31 Mar 2017 11:57

Hi,
Three things to ask/check:
Firstly, Are you running a steering damper on the Sport but not on the Strada? The standard Sport steering damper could, if not 100%, be the cause. It doues't take long to remove it to check if it has made matters better or worse.

Secondly, Front tyre wear - is it getting worn? Is it the same make as on the rear, and the same make/size as on your Strada? If the wear is ok, what pressures are you using? The numbers in the blue book really don't work (for me) and I now run 32/35PSI front/rear with Bridgestone BT45's. (I weigh 11 stone). Raising the pressures could well be what is needed.

Finally, and this might sound crazy, but have you checked that the rear shocks are both damping ok?
Whilst not normally a trait associated with Morini's, anyone who rode a 1970's/early 1980's Japanese bike would have known about high speed instability, and changing from the standard shocks to something European worked wonders as a weave curer.

Happy hunting for the cause and fix.

George.
George
350 sport 1978, 350 Strada 1978
George 350
 
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Re: speed weave

Postby pedro » 31 Mar 2017 17:15

Thanks to everyone for your suggestions, Norbert, the word you are looking for is yoke, top and bottom yoke (Our American cousins call them triple tree's I believe)
I have reset the forks as you suggested and changed the fork oil, no difference.
George, Steering damper on or off, no difference. the tyres are good Avon roadriders at 30/32 psi which has served me well on road and track.
The rear dampers are next on the agenda, I spoke to Stuart and he says that a weave almost always comes from the back end. The swing arm is good, and this is a new thing, so it is a possibility that a shock is on the way out. A family wedding means that it will be a few days before I am able to swap shocks, but I will and will let you know the result.

Pedro
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Re: speed weave

Postby harrymuffin » 31 Mar 2017 18:27

Hailwood had that problem on the Honda 500-4. In the TT 1967 he just screwed the throttle open even more, starting to weave as he opened up exiting the bends and kept on weaving till he shut off for the next bend - put down as a power weave and still beat Agostini.
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Re: speed weave

Postby pedro » 31 Mar 2017 20:05

I don't somehow think that my little Morini is putting out the kind of power that the 500/4 did, however, the cause could well be the same, I saw Hailwood at post TT Mallory that year on the 550/4 and my respect for him became godlike worship. That thing was evil until he took off the rear shocks and threw them in Mallory's lake and fitted a set of Girlings. That trip was memorable for another reason as well, I was 16 years old and weighed about 9 stone, I had just passed my test and had ridden up from Kent on my 500cc 88SS Norton with my 17 stone mate on the back with a side wind all the way up the M1, I could hardly walk for a couple of days after.

Pedro
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Re: speed weave

Postby norbert » 31 Mar 2017 20:39

:lol: :lol: :lol:
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Re: speed weave

Postby pedro » 08 Apr 2017 20:06

Just an update, since my last post we have had my stepsons wedding and have been babysitting the grand-kids while Mum and Dad went off on honeymoon so no chance to play motorbikes.
Anyway, I took the springs off the Hagons to check them, really expecting that would be where the problem would lie. No chance, damping is perfect, and so I put them back together again, while they were off I took the chance to thoroughly look for movement at the swing-arm, none. This problem has only arisen since fitting new higher rise clip-ons which alter the riding position, previously it was fine on track but uncomfortable on the road for any distance. As I could find nothing wrong anywhere I decided to raise the suspension units to their hardest (highest) position, therefore putting more weight forward. It has improved things, the weave now doesn't come in until above 90 (on a private road of course) and then is improved further by laying forward. I think that I will have to accept it as it is, and if I take this one on track again I will have to lower the clip-ons again.

Pedro
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Re: speed weave

Postby norbert » 08 Apr 2017 21:22

Hi Pedro,

have you tried to pass the tubes of the fork a bit upwards trough the yokes?
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Re: speed weave

Postby pedro » 08 Apr 2017 22:00

Norbert,
No I haven't yet, although I have thought about it, but not sure what it would do to the steering geometry. Is it something that you have tried?
pedro
 
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Re: speed weave

Postby norbert » 09 Apr 2017 07:13

No, I myself have not tried that, but I´ve seen some people doing that. I guess it should make the steering a bit more agil. I think with the longer 500 swing arm that you have, it may be worth trying it.
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