Clutch Snatching

[racerdave]

HI
I have a 98 storm
its a great bike, just one or two niggles
If i try to pull away smartish the clutch seems to grab and I end up pogoing down the road
if I pull away like an old man there is no problem
Any ideas ???
Up to 8000revs she pulls like a train then it goes all fluffy
are there any rolling road tuners in the herts beds area
who can sort this out for me ??
thanks David

[Wicky]

See this thread as crotch snatching phenomena is a bit of a mystery, and R&D is trying to find a solution as we speak

http://www.vtr1000.org/phpBB3/viewtopic.php?f=9&t=23016

[AMCQ46]

you will be surprised with these bikes how effective the old man style getaway is, you dont need lots of revs to get the clutch out, then once it is out then nail it. worked for me for 6yrs till a replacment clutch fixed the problem on mine

[tony.mon]

+1 on that.
So far my fastest drag strip time (11.6 for the standing 1/4) is using the old man pull away.

Still hoping to crack it into the tens, though, if I can figure out a clutch grab fix.

[benny hedges]

im sure you got less than 11.6 last year tony..... i'll go get me stubs out and have a look

[benny hedges]

Up to 8000revs she pulls like a train then it goes all fluffy

im wondering what cans you have???? have you fitted shorter cans????
mine wouldnt pull past 8 - 8500 with some art stubbys on, so i went back to my full length laser cans and it bounces off the limiter again

also, in an attempt to get better mpg out of the bugger after a record low of 59 miles to the light with a 19L tank, i dropped the mains down from 195/200 (dynojet sizes) to 185/190

it is a lot more economical but very wooly up top....so the bigger ones will defo be going back in.
if i want fuel economy i'll sell it and get a cg125!

when's the last time you looked at your air filter & plugs btw?

[tony.mon]

A little update- progress has been slow, sorry.

But I might be on to something.

I have been trying to understand what causes this problem- it must be mechanical, and therefore fixable, but as far as I know no-one's pinned it down.
Some report a result by changing some clutch components, and I've tried changing everything over the years, with no real cure.
But the parts you take off show no signs of obvious wear, and don't measure up any differently, not substantially anyway.

But over the years I've collected a fair few clutches, and a close inspection has revealed wear grooves on the spigot that goes into the centre of the clutch springs form the basket, and also on the outside surface of the well where the clutch spring sits.
It seems that the clutch spring is flung outwards under centrifugal/centripetal force, and pushes itself against the relatively soft aluminium alloy of these two surfaces enough to wear grooves, where the spring sits when fully extended, i.e. clutch fully engaged, where it spends most of its time.
All of the used clutch baskets and centre plates show wear, to a lesser or greater degree, of the ones I have (five or so sets).

So how to explain what's happening, and then stop it?

I think that the likely explanation is that the springs extend under clutch slipping/hard takeoffs, and when they're almost home, they "jump" into the grooves, like a roulette ball does when it gets into a slot. This has the effect of forcing the clutch home fully, and the plates resent this with a graunching noise, and the clutch appears to grab, even though you've kept the clutch lever at the same bite point.
It's the engine speed increase which applies more sideways centrifugal/centripetal force the the spring, and whereas it was happy to sit on the edge of the lip up to the point where you open the throttle more to induce a little more slippage, the extra force acting sideways on the springs make them press outwards into their "fully home" grooves.

How to overcome this?

I considered fitting a slim metal hard chromed sleeve over the centre boss, between it and the spring, so that the spring would slide along it.
But it couldn't be full length when the clutch was disengaged, and so would rattle like a Ducati when the clutch wasn't home- not a good choice. Shame, as I had found a lgth of old curtain rod from a wardrobe that fitted perfectly....

But then I considered holding the springs in place.
The "lower" end of the spring, nearest the engine, is a fairly good fit in the bottom of the well.
However the top, which is held in place by the clutch spring bolt, has only a flat washer, which allows the spring to slide out sideways from under it:

and this means that the spring can come into contact with both the inner edge of the spring post and the outer edge of the well.
Modifying this is easy; all you need is to cut off the original flat washers and fit ones with a slight lip or return:


They have been made up by a very helpful forum member who has access to titanium and machining tools.

The original washers are captive (I think the threads are rolled onto the bolt after the washer has been slid onto the bolt blank) which means that they need to be cut off, a bit fiddly, but no problem. Or you could choose lightweight button headed Allen bolts to replace them, they're not strength critical except in tension.

The new dished washers hold the spring in place top and bottom, and should prevent the spring from pressing outwards against those surfaces, holding it centrally in each well.
Here they are fitted:


I wanted to change nothing on the clutch except these springs, so that I didn't inadvertently change something else which had an effect,but as a preliminary test I'd already fitted the clutch basket and clutch centre with the least wear from the selection I had, and so mine wasn't really grabbing much, or at all, really.

So fitting these to mine isn't a conclusive test.

However a local (to me) forum member has a bike that does it all of the time, so I'll be fitting a set to his and we will report the findings once the testing is complete.

But I'm feeling quietly confident on this one; just kicking myself that I hadn't noticed the wear marks in the clutches before

[lloydie]

Looks promising tony .
Mine grabs like a wombles so it would be good if this sorts it :-)
Keep up the hard work

[AMCQ46]

looks like a promising hypothisis, good to see the grey matter still working
and as my replaced clutch is starting to get a little bit grabby [nothing like the old one which wouldnt work above 3000 revs without grabbing], so would be looking at this as an easy addition

[VTRDark]

It seems logical to me Tony. It will probably be better on wear and tear on the clutch plates as well, as the springs will permanently sit more square on rather than slipping to the side, so I would think the plates will wear more evenly.

Good work.

(:-})

[Xenocide]

Looks interesting. I'll be following.

Mine does it sometimes but you've got to be giving it some beans to make it happen. I'd imagined my clutch basket fingers were grooved but i've not bothered looking

[TonyW650]

looks interesting,
Mine does it when its gets hot and stuck in traffic, was amusing when I almost lost the other half off the back when it did it in hastings and she wasn't paying attention.
bounce bounce oi what you playing at was her words lol
did it a few times last year and once this year

[sirch345]

That certainly sounds promising to me Tony, it'll interesting to hear the outcome when you get time to fit those dished washers to a clutch that does grab (as you mention). Keep up the good work

Thanks for the good quality photo's

Chris.

[AMCQ46]

Tony, are you also still working on the solution to Snatch Clutching? I seem to remember discussing that over a few beers in Wales as well

[Kev L]

Why would you want to stop snatch clutching oh strange Celtic one?