Front end ain\'t right after Yoke change (update)
 

Please help - I've taken the day off to ride my bike !!! I changed the top yoke yesterday for a more bling item. Today the bike feels very different on the front end. I'm fighting the bike to keep it in a straight line and it feels like it wants to lean over all the time. In a straight line it feels unstable.

I just took off the top yoke I had and put on the other one. It was a bit tight but all went on ok. Forks are 4 rings showing through yoke on both sides. I never slackened off the bottom yoke. I did need to apply the front brake to get the top yoke to fit on properly.

What have I done - it really does feel very different - must have done something wrong! Nothing else changed on front end. No suspension settings changed anywhere. Nothing changed on rear or any other chassis part !!

I've come straight back home because it's just not right.

Oh and i'm on the normal 24.5 degree steering angle. The steering lock still works so I don't think I've put it on the 23.5 degree angle by mistake.

[Edited on 28-5-2004 by ziggi]

[Edited on 29-5-2004 by ziggi]

have you checked both old & new yokes have the same hole centres, it sound as if this new one has made the fork ange steeper.

Ziggi,

Might be a silly question but did you compare the new yoke to the old one before you fitted it?

If it was a bit tight to fit, it may be that the offset between the forks and steering stem is slightly different from stock. For example, if the offset is greater than stock, that would have the effect of changing the fork rake and shortening trail which would make the bike feel a bit unstable.

Hard to diagnose accurately without actually seeing the parts in question but worth checking out IMO.

Out of interest, who supplied the yoke?

Cheers, Neil.

erm... I bought it off Jasper who had it on his 748. Could that be it! Is there a difference in the 748 Yoke and 996S yoke? And no I didn't even think to check which is typical of me!!

mmmh...does sound strange.

I wouldn't have thought it possible to have made any changes in the steering head angle, just by changing the yoke.:puzzled:

Its the actual steering head tube that is rotated to adjust the head angle, and you would know if you had done that!

Just offer your old one upto the new one you have and see if the hole centres are the same...I'm sure they will be but it will rule that out.

Sounds to me that something else has been altered without your knowhow as you changed the yoke.

Have you refitted the steering damper? Are the clip-on pins located correctly in the small indentations on the back of the yoke. Did you loosen the stem nut when removing the yoke in any way?

Uhmmmmm....can think of anything else:puzzled:

you won't be able to change the geometry just by replacing the top yoke - think of it as just a way of linking the forks to the steering damper and you'll see what i mean.

You may have loosened the headbearing somehow, or the steering damper is rubbing on the tank or something else

I seriously doubt you have altered the geometry - would be one hell of a cheap way to do so! :lol:

[Edited on 28-5-2004 by DJ Tera]

I'm betting that in the excitement of fitting the bling bling new yoke, he's forgotten to refit the steering damper (either at all or properly?)...would explain all of the symptoms suggested.

If not...soza:roll:

I'm pretty sure the top yoke for a 748 is the same as for 996S. Just checked the parts cat and it's the same part number.

Regarding changing steering geometry, a different top yoke CAN alter the geometry! It's a bit hard to explain but I'll do my best.

Imagine if you will a vertical line, that's the line down through the centre of the steering shaft. Now, if the offset between that line and the line down through the centre of the fork legs is identical for both yokes then the forks will be parallel to the steering shaft. Now, imagine altering the offset of only the top yoke. The forks are no longer parallel to the steering shaft.

So, if the offset on the top yoke is even marginally different than the offset of the bottom yoke, by the time you translate that over the length of the fork legs, it will have made quite a large difference to the trail.

This is what I suspect is going on in your case. It would also explain why the new top yoke was slightly tight to fit on as the holes in both the top and bottom yoke would not be in perfect alignment (axis wise).

Ducati use a similar principal to allow adjustment between 24.5 deg and 23.5 deg rake. The difference is instead of playing with yoke offsets, they adjust the overall angle of the steering shaft in relation to the headstock on the frame.

My advice would be take the top yoke off again and compare against the original. Bear in mind that any difference would only have to be very slight.

Cheers, Neil

But surely if the centres were different then then the yoke simply wouldnt fit?

If the distance has changed, and the new yoke fitted, then either the forks have been bent to fit or the stem nut ( and associated bearings etc) have been forced...both very difficult to do I would have thought?

Still going with the steering damper!!!

AAaawww...my head hurts:(:puzzled:

[Edited on 28-5-2004 by Harv748]

Thanks for all your replies and yes my ohlins damper is fitted :D

First thing is Jasper now has my original yoke so I can't compare it. To fit this new yoke I have to offer it up - it won't go straight on so I have to hold the front brake and push the forks down and push on the yoke so it fits on the centre nut. Any other way and the centre nut don't line up with the middle yoke hole.

Correct Harv, which is exactly the reason why I thought this was the problem, the yoke being tight to fit.

Ziggi, you've just answered your own question. If you had to do all that to get the yoke on then the offset is definitely wrong.

Looks like you'll need to get your original yoke back!

Cheers, Neil.

Thanks everyone for your help - you know how it is when you change something and think "oh bugga, what 'ave I done"

That is quite normal if the weight of the bike is on the front wheel or fork lowers as the weight of the bike tries to push the towards the ground and moves the front axle slightly forward. If wheel is on the ground applying the front brakee and rocking forward allows the top yoke to drop into place. Sounds to me as though you have disturbed the top bearing nut, the one that comes through the centre of the top yoke and have it to tight, putting to much pressure on your head race bearings. I would try backing it off 1/8th to a 1/4 of a turn.

[Edited on 28-5-2004 by skidlids]

Good point Kev, and worth checking before incurring any further expense.

Ziggi,i have fitted your yoke without any problems at all.It went straight on,If there was a difference surely yours woudn't have gone on the 748!It's not a problem if you want it back.I honestly can't see ANY difference and there is no way,imho,that changing the yokes should effect the steering.But i've been wrong many times before!!!:)

Ziggi anyway you can take a pic and post it. We might be able to see something that you can't.

OK, so that large centre nut - the one with the long slot and the holes round the edges, that's supposed to turn is it? I've taken off the yoke and tried to move the centre nut and I can't move it. I was a little over zealous with the hammer trying to put it on first time, until I discovered the front brake trick. So I think skids is right and I've put too much pressure on the centre nut and hence on the head racers.

So how do I turn the centre nut ?

Jasper - I'm sure it's me who's done something wrong - no worries mate.

Can't move it ! maybe it is to tight then, I use a set of right-angled circlip pliers that I insert in a couple of the opposing holes.

I've got a small piece of flat steel plate. I push it into the slot and then put an adjustable spanner on it.

Right - it's seriously shagged. I took everything off again, slackened the center nut (eventually using mole grips and a rag). It was tight. Slackened by about 1/8 of a turn. Fitted all back together. Took her out.

First off I thought oh it's all back ok. Still was turning in fast and then the front end felt like is was washing out all the time. Maybe that's supposed to be how it is. Really gave it some stick around the dual carriageways. It wasn't right but at least it was tracking in a straight line ok.

Then when I had slowed down, I found I couldn't put any steering input to the bars. Everything I did ther bike push back on me and it feels like the damper is turned right up. Stopped, backed the ohlins right off to nothing.

The steering feels and sounds like the head bearing are like sand, hard to turn handle bars - oh bugger again. Managed to get home - bit like riding one of those funny bikes that steer the opposite way to the way you steer.

SO have my head bearings gone? - I think they have - they feel dreadful !! How do I fix them and how much will it cost?

Cheers all

Fixing them shouldn't be a real problem, depends how much of the work you can do your self. I deal way would to be to remove the top yoke and bars then drop the front end out complete with bottom yoke. Then remove the adjustable headstock from the frame and the bottom yoke from the forks after first getting a measurement of where exactly it is positined on the forks. From this point anybody with the relevant tools should be able to remove the old bearings and fit new ones.

That's way too much for me. I don't have the tools to do this so it's gonna have to be a shop job.

zigg,
if you can raise the front of the bike off the floor ( suspend it from joists/chock from underneath) try the steering from lock to lock. it should be smooth not notchy.
this should tell you if your head bearings are (censored!)
:)

Just a quick update to say that all is fine now. It wasn't the steering head bearing but 2 problems:

1. The yoke must have been slightly different as the part that goes down to the steering lock was catching on the lock stop. It needed grinding back.

and

2. The castle nut under the top yoke was too tight (not the center nut)

At least it's alright now :)

Glad you sorted it!

Result!:DWas it worth it?

Colin,
Regarding your quote: "The castle nut under the top yoke was too tight (not the center nut)"
The castle nut under the centre nut is the steering adjustment tube...it should not move! What exactly have you done to "make it alright"????
I have all the tools to adjust/dismantle the headstock..plus I have done it at least three times...plus I have a yoke we can measure to compare...plus I live in your town and am offering assistance if required!
Call me if required.
Richard

Ricky you can have more than one kind of 'tight'...


eg

ranging from tight as an 18yr old nun, to tight as a northern burd

Either of these extremes will provide dodgy handling, so you wanna aim for somewhere in the middle :lol:

[Edited on 15-6-2004 by DJ Tera]

DJ,
Memo to Self:
Dear Richard,
Remember..There are more colours than "BLACK" and "WHITE".
:roll:

I'm glad my analogy helped ;)

I didn't sort it - someone else did namely P&H. They took it all apart and put it back together. I thought thats what they said - not the center nut but under that. They also machined the top yoke so it didn't catch on the lock stop.

Was it worth it? No. As with most stuff I learn the hard way.