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Author Topic: Head Shake - a.k.a tank slappers and what to do about them  (Read 12621 times)

Adder

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Head Shake - a.k.a tank slappers and what to do about them
« on: February 08, 2007, 01:17:01 PM »
If like me you struggled with massive head shake when first starting out, here's one or two causes and what to do about them. With acknowledgements to Dez, Macca and Snooey for invaluable advice last season...

Free play in the headstock: make sure there's no side-to-side movement on the headstock - tighten it up so that it's only just loose enough to spring back.

Front forks binding: this can happen when the forks twist after a crash or if the front axle is too tight and pulls the legs together. Prevent this by either leaving one side screw a little loose or by shimming the gap between the axle and the fork leg so it can be tightened both sides. You then need to make sure the axle won't come loose! See the next item:

Free play in the front axle: this is a big no-no and IME the biggest single cause of problems. Make sure the axle is tight against one fork leg at least and the screws can't work loose. You can hold them in place with grub screws in the bottom of the fork leg (need drilling and tapping on the kit forks) or use good threadlock. To keep one side loose enough to prevent the forks binding when you don't have clamping grubscrews, shorten the axle hole with a 4mm grubscrew or longer axle bolt in that side. You're looking for a gap between the head of the axle screw and the fork leg on one side only which you then fill with a spare shock-shaft o-ring. This will allow movement without excessive free play.

No rear damping: if the shock has too much air in and pogo's about, then the suspension geometry will be changing excessively. Re-fill the damper and make sure all the screws/mountings/etc are tight.

Steering damper: if all else fails, then fit a steering damper. This is useful on a bumpy track where you are being thrown around on the exit of a corner, where the steering gets thrown around a lot. To save money use an old buggy shock or a TC shock with a long/extended shaft and fit it between the steering upright plates and the top triple clamps (there's suitable holes already there on the TT). You only need to use 10w oil - much more than that and you risk slowing the steering response right down.
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Scott Adderson
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Thommo

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Head Shake - a.k.a tank slappers and what to do about them
« Reply #1 on: February 12, 2007, 10:06:47 PM »
Adder,

excellent advice and well written, only point I would disagree is about front axle, I feel that this must be bolted tightly to lower fork legs on both sides. If tightening both sides causes forks to bind then use shim washers or shorten axle as necessary.
Just my pennies worth  :)
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Adder

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Head Shake - a.k.a tank slappers and what to do about them
« Reply #2 on: February 13, 2007, 09:49:49 AM »
Only speaking from personal experience as a newbie with the TT! I'll qualify my comments about the axle as it's a valid point you've made and you certainly wouldn't run a real bike with the front axle loose! :

I've found the Tornado forks don't twist in a crash (unless you have a really serious off! ) so it's possible to leave one side slightly loose on the main bolt and the locking grub screw will hold it sufficiently rigid to minimise head shake as long as all else is in good order. I've not tried shimming the Tornado axle, but would imagine it's not a significant issue to do that with these forks.

I tried shimming my TT forks on the axle and that was OK until the first crash when they twisted, jammed and headshake was bad again :( If like me you crash(ed) a lot ;) you're no better off!

It was better with the TT upgrade alloy triple clamps and ground stainless forks, but could still twist and bind. Leaving one side deliberately loose and locking the screw or using an O-ring like Colin McCabe helps reduce this tendency.

If you were to use clamping triples, eg NF type, then twisting would be reduced/removed and you'd probably get away without making one side loose.
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Scott Adderson
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Whitham69

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Head Shake - a.k.a tank slappers and what to do about them
« Reply #3 on: February 13, 2007, 09:51:46 AM »
you can swap the two bolts over for one long nut and bolt, this should stop binding as well
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rhino131

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thank you
« Reply #4 on: August 13, 2007, 01:43:07 AM »
thanks to you guy my NF 506 is now driveable before i would get heavy on the thottle would go right into slapper and then tumble maked me sick and angry  not condusive to learning but your tips here really worked thank you so much need to photo my bike and post up here soon
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racer x 1

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Head Shake - a.k.a tank slappers and what to do about them
« Reply #5 on: April 11, 2008, 04:44:40 AM »
hey guys i have followed all the advice on this forum and have looked the bike completely over and i still have a really bad headshake under hard acceleration on a fairly bumpy road and track. i have given in and am now looking into buying a steering damper.  Which is best for a supersport bike? im looking at the small nf damper...
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Adder

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Head Shake - a.k.a tank slappers and what to do about them
« Reply #6 on: April 11, 2008, 12:21:22 PM »
We've found with Nev's TTn that you still get headshake if you run a steep rake angle on the forks, so it's also worth trying letting the forks out as well and see if that helps.

A bent layshaft or wobbly bearings in the back wheel or swingarm can also contribute, it's worth checking those as well before you do anything else.

A TC or buggy damper is ideal, you just need to be careful to get the length correct to prevent it jamming up the steering on either lock. It's worth using one with very free-running o-rings, if the action is sticky then you get unresponsive steering. You also need to bleed the shock well to ensure the piston doesn't push back out or suck in due to pressure changes or you get uneven left-right steering response - diaphragm-type shcoks are easier to do in this respect

I run a TC3 shock with modified shaft, bleed screw and 10w oil with large-hole pistons: any more than that and you slow the direction change down through tight corners.

Picture here: http://www.moto-5.com/Forum/viewtopic.php?t=438

The NF friction damper appears to work OK on Mario's SF501, he just used a single o-ring on that.

Alternatively Formby Models sell their own damper for the bikes, check their website for details.
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Scott Adderson
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racer x 1

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Head Shake - a.k.a tank slappers and what to do about them
« Reply #7 on: April 11, 2008, 03:07:49 PM »
how large are the hole(s) in the piston?
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Adder

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Head Shake - a.k.a tank slappers and what to do about them
« Reply #8 on: April 11, 2008, 04:50:42 PM »
1.5 rings a bell...
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Scott Adderson
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Head Shake - a.k.a tank slappers and what to do about them
« Reply #9 on: April 12, 2008, 01:12:48 AM »
thanks
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danharding

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Re: Head Shake - a.k.a tank slappers and what to do about them
« Reply #10 on: June 05, 2010, 11:21:27 PM »
Hi sorry for digging up an old thread after a little help please.

I have now done a few mods to my second hand TTe and it is now driving very nice apart from a head shake at speed.

Fist off its a fairly stock TTe running a HPI 15turn silver can with Lipo battery whilst I get used to controlling it and getting it setup.
 
I have raised the front and rear ride height,
Moved the scratch bars back,
Fitted grub screws to the under side of the forks to get the front shocks to work and not bind,
Fitted the TTnitro steering damper,
Added some lead to get the battery up to 300g

Today I have got it driving the best it ever has done handles real nice, turns well, sits up well but when it gets up to near top end it starts to head shake,
It was really bad when I first took it out (no rider) I then put the rider on (standard TT rider looks good but weighs a ton) this has calmed the shake down a lot to almost non existent but its still there just.

Any ideas what I can try?
I'm also in 2 minds weather to keep spending money on this one (wish list so far = front brake, nylon scratch bars, proper steering spring and damper setup, revo shock, new body and rider, decent forks) trying to get it right OR just say sod it and buy the new TT SB5 ? ? ? ?
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John Veal

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Re: Head Shake - a.k.a tank slappers and what to do about them
« Reply #11 on: June 06, 2010, 08:19:13 AM »
Dan,
I've not seen a SB5 with any headshake, they just go fast and look stable.
But you can't get one just yet, so;
Re-check Adder's first point, grip the bike tightly with one hand and grab the front wheel with the other and pull the wheel and forks sideways to find any free play. This can be anywhere from front wheel bearings, axle screws, fork clamps to loose headstock screws, headstock bearings or even loose chassis screws. If you've had a few end over end crashes it's worthwhile changing the headstock bearings anyway, they are undersized and fragile in my opinion. Also check wheel alignment and chassis alignment (ie no twist) and finally wheel balancing. Some of my wheels required a hefty piece of lead to balance out.
Any slight free play or out of balance may not be noticeable on a well set up bike, but add a rock hard rear shock and it'll be magnified.

It's worth noting that most racers use springed steering and seperate damper. The dampers are run with either no oil in, or very light oil (5 - 25wt).
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steliosh

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Re: Head Shake - a.k.a tank slappers and what to do about them
« Reply #12 on: June 06, 2010, 09:21:59 AM »
One reason for a head shake at speed may be a bent wheel or badly glued tire, front or rear (or both!)... As speed builds the shake gets more violent...

I noticed this on my KP09 with my 4-year old wheels and tires: My old front wheel was slightly bent. While I was using the 27T motor, it would headshake only at top speed... Then I switched to brushless 13.5T and it started shaking almost everywhere, the brushless being more powerful and keeping the front end of the bike light almost at all times, when the throttle was open.
I changed to new wheels, took care to glue both tires as well as I could and the headshake was almost gone!
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KP09e turned to KP10e, TT FM1e, Ricky CR250, Anderson M5 Cross, TT SB-5, Venom GPV-1, Kyosho HOR (x2), Kyosho Mk1 (x3)!!! TT KT8 kart...

danharding

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Re: Head Shake - a.k.a tank slappers and what to do about them
« Reply #13 on: June 06, 2010, 11:52:03 AM »
Thanks for the replies guys yes springed and separate damper steering is on the list of things to get.
Bearings probably will need replacing then as I've had several big offs since I've started.
Thereís no free play in the front end all nice and solid.
The rear damper is probably on the slightly soft side rather than rock hard it feels nice to me but I donít know how soft or hard it should be, but its got a 1 hole piston about 1-1.5 mm with 60wt oil standard spring and lots of ride height spacers, its running about 125mm at the back I cant get 130mm as I donít have enough spacers.
I will check the wheels for trueness and balance; do you just spin them on the axle and check for dropping to one point??

Cheers Dan H
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scott c

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Re: Head Shake - a.k.a tank slappers and what to do about them
« Reply #14 on: June 06, 2010, 02:24:56 PM »
Stelios you nailed it. I was getting bad tank slappers at speed w/ my tt nitro and crashing violently.
Finnally noticed the paint being rubbed off the inside of the front fender. The tire had no glue
at all from the factory. Problem solved.
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