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Offline Milord

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MK1 Cornering instability
« on: 04 September, 2019, 09:41:24 PM »
Hey biffers and biffettes,

Been a lurker since I purchased the bike but this is my first post, and it's a biggie, so thanks for taking the time to read!

I've recently bought a 26,000mi 2009 cbf1000 mk1 (8 months ago) straight from a 2012 cbr125r so an upgrade is an understatement! Still in love with the bike and I feel as safe as ever on the road compared to some of the gutless 125s around.
Partial service history so no evidence of servicing of head bearings, swingarm or anything of the like.

Within the first few months of riding (and I do like to ride spiritedly) I noticed instability while mid corner at around 70mph onwards. Upon inspection of the tyres I found that the previous owner threw on a set of touring orientated Bridgestones and seemed to only ride in a straight line due to the squaredness of both front and rear tyres. I assumed the uneven wear was the main culprit and I may have been leaning right on the edge of that worn/unworn section causing the instability.
I bought some pilot road 4s and got the head bearings replaced (as I got some wobble while taking my hands off the bars) which did improve handling quite a lot but the instability remained.

Now when I say instability I'm talking about when I lean at speed the front end feels extremely light, the handlebars wobble and the rear seems to bounce up and down. The bike does not feel happy.

It's all very scary when it happens and just wanted to know if any of you owners have came across the same problem or know where the issue might be stemming from.
Could it be rider error and I just dont know how to position myself on the bike?
There are a few scuffs which tells me it's been dropped on the left side, could it be a bent frame?
Do I just need to upgrade the suspension package because the stock ones are poo?

You might begin your reply by saying I bought the wrong bike for high speed knee down action but it's a heck of an all rounder bike and cant see myself riding anything else for the money I bought it for.

Notable mentions about the bike regarding handling:
I have standard forks and shock (set at 4)
Newish PR4s with balanced wheels
New head bearings
Stock handlebars
Seat set to lowest position
I doubt aerodynamics will be much to blame but it's worth mentioning I have:
Full lower fairing
MRA screen with additional visor (both set to lowest position)
Rubberized hand/wind guards
Luggage rack (yes it occurs with and without boxes)

Your input would be much appreciated fellow riders!

Offline Admin

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Re: MK1 Cornering instability
« Reply #1 on: 04 September, 2019, 10:18:18 PM »
Have those new head bearings been rechecked since being fitted?

It's usually worth rechecking them once they settle in, that's all I can think of tbh..   :038:

Offline ushirlo

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Re: MK1 Cornering instability
« Reply #2 on: 05 September, 2019, 05:33:32 AM »
set rear shock at 5 or 6....
replace oil in front shocks to thicker one.....

Offline FLIZ

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Re: MK1 Cornering instability
« Reply #3 on: 05 September, 2019, 09:04:48 AM »
Tyre pressure’s,  Play in wheel bearings,  Check for play and re-adjust head bearings if necessary. Top yoke nut loose. Obviously check wheel alignment if you suspect bike may have been dropped. Standard suspension isn’t what I would call poo, but obviously does wear out and can be improved on, depending on what you want.

Some biffers the bars “wobble” on deceleration especially if you take your hands off the bars at that time. Mine used to very slightly but needed worn tyres replacing, new tyres on now no wobble. It seems to be tyre wear/road surface sensitive, imho.
I did once road test a biffer that this wobble was “violent” take your hands off and got a proper tankslapper, I didn’t buy it, was fitted with top box n rack.

Sorting out problems like this can be a minefield, be methodical, one thing changed at a time, road test after each change/ adjustment, on the same piece of road so you get the same conditions. Good luck with it, let us know how you get on.

Lots of other biffers on here for help n advice, just ask away.   

Offline edger

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Re: MK1 Cornering instability
« Reply #4 on: 05 September, 2019, 09:29:17 AM »
You could try  pulling the fork tubes up through the yokes , this puts more weight over the front end "pushing the tyre into the road " .
I find that sitting well forward  shifting  your bum/knee about helps (but we are not talking
Marc Marquez here :mfrlol: )
Also you could increase the fork spring pre -load  by fitting a spacer above the spring and below the top fork nut,
Have a look on the search button there is a nice thread showing how to do it.
I did try filling with a heavier oil but I found it just made the ride harsher

Offline edger

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Re: MK1 Cornering instability
« Reply #5 on: 05 September, 2019, 12:59:12 PM »
I just measured how far I have my forks pulled through by and at the moment its 12mm
Although you may find it speeds up the turn in a bit and the first time you ride your favorite road /corner  you may find you turn tighter than you expected. :430:
Also if you have enough leg try putting the seat on the highest and the bars on the lower setting as it tilts you forward a bit.
But at the end of the day its a case of trial and (not to much) error  to get it as you like it.
But when you do its all worth it !

Offline Art

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Re: MK1 Cornering instability
« Reply #6 on: 05 September, 2019, 01:17:18 PM »
Assuming the problem isn't due to your 'spirited riding'  :192:

I'd go back to basics and start off by checking the suspension rebound, if there's too little or too much adjust the suspension accordingly. Adjustment should be made bearing in mind the weight the motorcycle is carrying and how it carries that weight. You need to factor in your weight, pillion weight, luggage weight and how that weight is distributed (large or heavy top boxes don't help here). The rear suspension is adjusted by means of a pin spanner and extension bar found in the onboard tool kit. The front suspension is not adjustable. Its been mentioned to replace the fork oil with thicker oil and modified distance collars so if you want to you can. However before you can expect any benefits from such work or other modifications you first need to strip, inspect and service the forks. If the root cause is a worn fork spring, worn bushes or other component then it doesn't really matter how thick the oil is, how long the distance collars are or what other modifications you make.

There are many other factors that could contribute to instability and most of them should have been covered in the MOT inspection. That shouldn't stop you checking out the obvious things such as the wheels spin true and free, wheel bearings, swinging arm bearings, rear shock & pivot bearings. If you want to rule out the likes of the screen, top box, hand guards or whatever you can always remove those items one at a time and test ride to see if there is any difference. After that you need to contact a qualified mechanic for proper diagnosis.

Offline Ali-bear

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Re: MK1 Cornering instability
« Reply #7 on: 05 September, 2019, 03:34:51 PM »
The bar wobble is commonly experience on these bikes, but usually its on deceleration from 30 or 40mph when the rider releases the handlebar. Worrying when it happens but easily avoided!
Not sure what could be causing your issues, but there are lots of things you can check. Tyres, wheels and bearings. Suspension sag, free movement and damping. Drive chain condition and adjustment. Are the forks straight and not twisted in the yokes after a spill. Are the wheels aligned. Anything loose that shouldn't be?
Designed in Japan, assembled in Italy, fiddled with in Britain

Offline Milord

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Re: MK1 Cornering instability
« Reply #8 on: 05 September, 2019, 08:40:58 PM »
Thanks for all your replies folks you've given me lots of homework to do! :152:

Passed an MOT this April with no ads.
Alignment and balancing of wheels have been checked upon fitting the PR4's, I did ask the guys at the shop to unpinch any bolts around the forks as a precaution.
Head bearings have been checked and adjusted after they've bedded in, although like I said I still experience a small degree of handlebar wobble at times. Could this be translating in to the lean wobble perhaps? I have consulted my local mechanic who thinks it's the head bearings, they adjust and test free of charge but I can always seem to get them to wobble a few miles down the road and dont feel like taking the piss and turning around. I am aware this is a common problem and I've almost given up on trying to eliminate it entirely... is this wrong to think?

I did forget to mention the forks have been raised through the yokes, but at about 8mm.

Today I took some time to pump the tyres, adjust shock preload and check for play in wheel bearings. Chain could do with tightening. I will have to take these things day by day as I'm in between houses and all I have right now is the Honda toolkit. In addition to that, I find it hard to replicate the wobble trying to find a road with a suitable speed limit...or with little traffic :121:

As I've bought the bike I've been going through my own servicing and checking it off since their was not much history to the bike, just for that piece of mind. What I'd love to get done next is the swingarm and forks, probably being the most neglected of components (in my novice opinion :001: )

For all your other suggestions I will slowly but surely work through them and report my findings. Didn't expect such a wealth of knowledge on day 1 of posting so it's all appreciated!

Offline edger

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Re: MK1 Cornering instability
« Reply #9 on: 05 September, 2019, 09:08:34 PM »
Check the fork internals there is not to much you can do short of a replacing worn parts, but a good flushing out with paraffin  or something similar  pump them up and down you will be surprised at the amount of sludge, metal swarf  you will get out , Repeat till its clean , leave the fork tubes suspended upside down over night to make sure they are dry and refill with oil obviously make sure they are equal.
As the ad says every little helps!!

OH ! and by the way what part of the country are you in?
« Last Edit: 05 September, 2019, 09:17:27 PM by edger »


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