Update to head stock / fork movement

[ian tomo]

Posting this as a new thread, so apologies if it should have been tagged onto my previous.

Anyway,after reading replies regarding excessive movement to forks, I decided to strip and re-build. Replaced steering ball bearing race with taper roller, happy days there. There was definitely play in the fork bushes, and the oil was thin, grey, and smelly. When i put micrometer on bushes there was hardly any wear. Ordered new ones anyway, seals and dust wipers. The bike is ex police, (don't know if that is relevant?) and had progressive springs fitted, both were 485mm, so after the strip down and clean, they went back in. Decided to use 10w oil to stiffen up the rebound. All went well and off I popped for a test ride.

My findings.... I can't honestly say I notice any difference as yet. When braking quite hard the forks depress about 5" (tie wrap on sliders). When I go for an emergency stop and get the ABS to kick in the forks depress a further 1/2". Tie wrap slides to 3/4" below lower yoke, an overall travel of 5.5" which if I am not mistaken is about bottoming out????
I don't get any indication of it bottoming out, no bang or clunk, Should there be ? It doesn't even feel like it dives, but it must be?? Jacked front wheel up after 30 miles, and no movement in forks or head stock.
Having read all the threads, following fork rebuild, the overall consensus seems to be an improvement in handling, accelerating, cornering, braking etc,
It may be my inexperience or lack of knowledge of motorcycle cornering dynamics, but can't feel any noticeable difference since the fork refurbishment.
I would really appreciate your comments and thoughts.
Thanks Ian

 

[dwalby]

I can't honestly say I notice any difference as yet.

Having read all the threads, following fork rebuild, the overall consensus seems to be an improvement in handling, accelerating, cornering, braking etc,
It may be my inexperience or lack of knowledge of motorcycle cornering dynamics, but can't feel any noticeable difference since the fork refurbishment.
I would really appreciate your comments and thoughts.
Thanks Ian

Its been many years since I experimented with mine, but I'm pretty sure you're not going to notice a huge difference just by changing oil. Another option is to add preload to the spring, or get a stiffer spring. Either of those things will raise the front end ride height, which will change the steering geometry a bit, and give you more available fork travel while riding. And, coming off of a sportbike onto the ST, I can guarantee you that a few front end tweaks is not going to turn it into a racebike, so don't expect miracles.

 

[Mcreviver]

Is there a plastic PVC pipe spacer on top of the right fork spring? I put Progressive springs in mine and one spacer came with the kit. I think the spacer is around 3" long.

 

[dwalby]

Is there a plastic PVC pipe spacer on top of the right fork spring? I put Progressive springs in mine and one spacer came with the kit. I think the spacer is around 3" long.

I don't have the Progressives, but I seem to remember hearing that their recommendation was to toss the right spacer and use the single spacer they provide for the left side. Of course, you can always adjust it to your own tastes, their recommendations are only a starting point.

 

[broc11]

I can't honestly say I notice any difference as yet

Hi Ian, just considering upgrading the front suspension on my own bike, so it's interesting to read your findings.
How many miles are on your bike and what is the rear shock like?
I have just ordered a new wilbers 640 for mine, and have more or less decided to go for hyperpro fork springs, with maybe 10wt oil.
but I think I will just wait till the shock is fitted before I touch the forks, the pan is never going to handle like a fireblade regardless of what upgrades I make.

 

[vinny]

Ian, the fork dive you are experiencing is probably due to the anti-dive valve on your left caliper assembly. If you have not bled or flushed the brake fluid lately, you may want to do that and make sure there is no air in your front brake system. If the anti-dive valve is working correctly, there should not be 5.5" of travel when applying the brakes. I have never measured the amount of fork travel during braking, but it's not that much... maybe a good reason to apply a tie wrap and check it out myself so I will know. Hope this helps you out.

 

[Jim Van]

According to the RaceTech "Bible" , with you sitting on the bike ( off the centerstand of course ) , the front forks & and rear shock should be 1/3 compressed. The length of spacer in the front forks and your & the bike's weight determines how much the front forks compress. Adjust the spacer length accordingly.

The spec. on the front fork travel is 150 mm. So you should measure about 50 mm static compression.

 

[ian tomo]

Thanks for response all. There is a metal spacer on top of RH fork, I did measure it, I think it was just over 3". The bike has only done 36k miles, and had fluid changed at 16K, according to police service sheet that came with it. if I want to add preload do I increase the length of the spacer in the RH fork only? I changed out brake fluid about 5 months ago if that sheds light on the issue? I didn't strip down anti-dive when re-building forks, so never got my head round how it works. I think I will measure the sag and see what that is....... before I weld the slider to the lower fork, It won't bottom out then

 

[dwalby]

if I want to add preload do I increase the length of the spacer in the RH fork only?

Actually its much easier to change the left side, that's what I'd do. Ideally you'd like to extend both sides by the same amount, but I've never noticed any difference between doing that and just adding twice as much to one side and none to the other.

 

[broc11]

the fork dive you are experiencing is probably due to the anti-dive valve on your left caliper assembly

I didn't even know there was an anti dive valve there,I had some vague idea it was somewhere inside the right fork for some reason.
I am seriously thinking of getting the hyperpro fork springs,see how the new shock 'pans' out first though.

 

[vinny]

I didn't even know there was an anti dive valve there,I had some vague idea it was somewhere inside the right fork for some reason.
I am seriously thinking of getting the hyperpro fork springs,see how the new shock 'pans' out first though.

This is an easy check... sit on the ST and without applying the front brake, push down on the handlebars... the front end should depress slightly. Now do the same thing but this time apply the front brakes, there should be a noticeable difference in the amount of give in the front end... and it should be less. IF it is the same as without the front brake, then the anti-dive is not working.

 

[broc11]

IF it is the same as without the front brake, then the anti-dive is not working

Thanks Vinny, I'll do that and see what the story is. ride safe

 

[vinny]

Now do the same thing but this time apply the front brakes, there should be a noticeable difference in the amount of give in the front end...

Need to clarify this statement... the front wheel needs some rotation for the anti-dive test, since it is the action of the brake rotor which engages the anti-dive.

 

[broc11]

Need to clarify this statement... the front wheel needs some rotation for the anti-dive test, since it is the action of the brake rotor which engages the anti-dive.

Yeah I tried what you said, in order to pump the forks when the bike is stationary I need to pull the front brake anyway,otherwise you can't get any pressure on the forks,the forks seem very soft and bouncy whilst doing this, there doesn't seem to be any rebound resistance.
I will hopefully have my new shock fitted next week and I'll see how the bike rides then, I think I need new fork springs and oil though, not sure how to check the anti dive,I'll have to ask a mechanic about it, I presume there is an anti dive mechanism on my 01 VFR800fi too?

 

[George]

Brake fluid has nothing to do with the anti-dive valve. When the brakes are applied, the brake caliper pivots forward and "closes" the valve inside the fork thru a mechanical linkage. That being said, it's possible the valve is clogged tho I've never experienced that myself.

10W might still be too light. I mix 50/50 10 and 15 for mine. (Brand name fork oil, don't recall the name right now.)

I know, on totally stock bike, the forks can compress far enuff to pinch the brake line where it passes thru the bottom triple clamp. There's a hose clamp there which get bent far enuff to KEEP the hose compressed. Locked front brake. (Steve Bunis did it in 96, hard on the brakes and hit a square edge pot hole. Talk about yur sudden stops. )

Anyhoo, adding more spacer length can help. I would add a little to each side instead of a lot to one side, ya don't wanna bind yur springs.

Keep us poSTed. (Hope to make it to Ireland in the next couple years. Attending Pan-STOC would be a treat.)

 

[broc11]

I will keep you poSTed for sure George, you'll have a great time over here, cead mile failte and all that. great roads here for biking but I suppose it's very small compared to the distances you guys can travel over there,
good things come in small package though, as my mother used to say.

 

[vinny]

Brake fluid has nothing to do with the anti-dive valve.

Well... yes and no. It takes engaging the brakes to activate the anti-dive valve. True, once that happens, it is mechanical. Lets suppose there is an obstruction in the left side caliper or lines (say jelled fluid) and the left side is not getting any pressure. Yeah, I know... that's a stretch, but it is possible. Thanks, George for all your insight.

 

[George]

Tru-dat, Vinny. All the parts gotta work together. On the standard 1100, the anti-dive valve is in the left fork, on the ABS it's on the right. Assume it's on the right on all 1300s?

 

[broc11]

Jacked front wheel up after 30 miles, and no movement in forks or head stock.

Hi Ian, which head bearings did you use,and did you get oem fork bushes,seals etc? I priced all the parts at davidsilver,a bit expensive,but they have the genuine stuff.
also did you rebuild your anti dive valve? the rebuild kit for it is around ?32+vat.
I am going to put a zip tie marker on later on and see how much fork dive I have,there is around a 1/4 play in my forks also,fore and aft. hard to tell if it's the fork bushes or the head bearings causing it.
thanks

Update, tried the zip tie test,forks are diving 5" and that's just normal braking,so I imagine if I was hammering on the brakes she'd bottom out.
Got a mechanic to check the forks with the front jacked up,there is play in the fork tubes so I will need new bushes,might as well change the head bearings too,rebuild the anti dive valve,new seals etc.
I wonder is there new 0 rings or whatever necessary for the tops of the forks? debating whether to get new hyperpro fork springs, or maybe just put in a bigger spacer to stiffen up the oem springs a bit.
The touring season is nearly over here,but she will hopefully be ready to rock next year.going to get the swingarm powder coated and install new bearings this winter.