Setting Front Preload on a '02 - Wrist Twisters
 
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post #1 of 26 Old 04-22-2009, 05:02 PM Thread Starter
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Setting Front Preload on a '02

I took my ‘02 919 for its first real aggressive ride last weekend. I did a 400+ mile day that mostly consisted of spirited cornering (8-9/10ths pace). The week before, I mounted a stock '04 shock courtesy of another WT member. The ‘04 shock noticeably improved the rear end. With the shock in place, I was able to quicken the pace enough to reveal some shortcomings on ’02 front suspension:

1. Going into corners, the brake dive was a bit un-nerving. It unloaded the rear end to the point that it wanted to move around. This wasn't even hard braking, just adjusting corner entry speed
2. Also, when leaned to the edge of the tire, the 919 struggled to hold its line. With counter-steering and leaned pretty far off the bike it wanted to run wide in some high-speed sweepers.

I attribute both of these to the front being sprung too softly for my weight, (185lbs in full gear). So off to the garage…

I measured front (loaded) sag at 45mm, too soft for my tastes. I opened up the forks, removed the stock spacers, and cut some new ones out of PVC. Standard 1 inch PVC from Home Depot is the right size.

The stock spacers measure 150mm. I cut 2 lengths of PVC 160mm and 165mm, which reduced to 159mm and 164mm after filing, smoothing, and deburring.

I installed the 159mm spacers, put it back together, and torqued all the bolts to spec. The sag is now 36mm (9mm increase in spacer size reduced sag by 9mm). The front end was already lowered 7mm in the triple trees. I lowered it another 8mm to account for the increased ride height. So how does it ride…

A quick test ride showed that brake dive is reduced and the front feels a bit firmer, which is what I wanted. Hopefully, I’ll be able to hit the corners again this weekend to see how it handles.

It was a fairly easy mod and it only costs $3. Depending on the level of improvement, I may be buying some new springs…we’ll see.

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post #2 of 26 Old 04-22-2009, 05:07 PM
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I'd be interested in this. Good start on a write-up. Maybe smell a sticky coming on. Or at least an addition to the helpful topics.

What should the sag be?

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post #3 of 26 Old 04-22-2009, 05:30 PM Thread Starter
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Quote:
Originally Posted by cmurphy84 View Post
I'd be interested in this. Good start on a write-up. Maybe smell a sticky coming on. Or at least an addition to the helpful topics.

What should the sag be?
There are some different opinions on this, but the consensus seems to be:
30-35mm street
25-30mm track

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post #4 of 26 Old 04-23-2009, 10:37 AM
 
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Thanks for the report, keep it comming. Did you take the forks off the bike to fit the spacers?

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post #5 of 26 Old 04-23-2009, 11:05 AM Thread Starter
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Quote:
Originally Posted by ilovheros View Post
Thanks for the report, keep it comming. Did you take the forks off the bike to fit the spacers?
No, but you do need the front wheel off the ground. Just loosen the pinch bolts before your remove the fork caps. The hardest part was cutting the new spacers exactly even and deburring them. You don't want any PVC shavings clogging the valving.

If the spacers are pre-cut, the job only takes about 15 minutes.

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post #6 of 26 Old 04-23-2009, 01:44 PM
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post #7 of 26 Old 04-23-2009, 03:38 PM
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It'd be nice to have a detailed pic write up. IF you have to change it again snap some pics and post em up if you dont mind. Ive got the same problem with my 03. The front is squishey and adding preload to the rear to make that feel better just makes the front feel worse.

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post #8 of 26 Old 04-23-2009, 05:43 PM
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Just happen to have a set of forks laying around. The procedure is simple.

Loosen Pinch Bolt:


Loosen then remove fork cap:


Loosen the 14 mm lock nut then unscrew the fork cap. 7 to 8 turns is the proper amount for cap removal and replacement.


Remove spacer:


If you select 1" PVC tubing be sure the OD is 34 mm or damn close to it.
Cutting the exact length is up to you. There are many different ways to do do it.

Replace in reverse order.

Measure sag

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post #9 of 26 Old 04-23-2009, 06:19 PM
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post #10 of 26 Old 04-23-2009, 06:31 PM
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Quote:
Originally Posted by barton664 View Post
Where's the spring in there mr mike?
Down that black hole It's easy to fish out.

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post #11 of 26 Old 04-23-2009, 06:36 PM
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Quote:
Originally Posted by MisterMike View Post
Down that black hole It's easy to fish out.
Any major differences on a 07 with the adj front end?? Procedure wise that is



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post #12 of 26 Old 04-23-2009, 06:42 PM
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Quote:
Originally Posted by barton664 View Post
Any major differences on a 07 with the adj front end?? Procedure wise that is
Glad I got you on the right track Brian


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post #13 of 26 Old 04-23-2009, 07:31 PM Thread Starter
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Quote:
Originally Posted by MisterMike View Post

If you select 1" PVC tubing be sure the OD is 34 mm or damn close to it.
Cutting the exact length is up to you. There are many different ways to do do it.

Replace in reverse order.

Measure sag
The procedure is pretty simple. 1 inch PVC is the correct size.

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post #14 of 26 Old 04-24-2009, 06:52 AM
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Quote:
Originally Posted by tpoppa View Post
The procedure is pretty simple. 1 inch PVC is the correct size.
Please provide the ID and OD of the 1" PVC

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post #15 of 26 Old 04-24-2009, 07:12 AM Thread Starter
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Quote:
Originally Posted by MisterMike View Post
Please provide the ID and OD of the 1" PVC
OD=34mm
ID=25.4mm (1 inch)

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post #16 of 26 Old 04-24-2009, 07:30 AM Thread Starter
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I got a chance to ride a little yesterday. The personality of the bike is very different. Here are my intial impressions:

Stock 150mm spacer
-Plush, soaked up bumps easily
-Brake dive was too much for my tastes
-During aggressive cornering feedback was numb, I couldn't really tell what the front was doing.

159mm spacer
-The squishy, mushy feeling is gone
-Firmer, I can feel every little bump in the road (I prefer this)
-Feedback is more active, I can tell what the front is doing.
-Brake dive is reduced
-Aggressive cornerning, not yet maybe tomorrow.

Overall it feels better. After I put some more miles on it, I will likely do some fine tuning. I think I'm going to try a 156mm spacer next.

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post #17 of 26 Old 04-24-2009, 07:39 AM
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FWIW: If Ohlins still sells the springs for the 02- 03 bikes, they are well worth the money. If nothing else you get rid of the stock progressive windings. Then you can really do some fine tuning with spacers.


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post #18 of 26 Old 04-24-2009, 07:58 AM
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ok... having a bit of trouble here...

loosened choke bolt on triple tree... blue top cap not wanting to cooperate.... this thing don't have lefty threads does it??

cause i really don't wanna break nothing..



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post #19 of 26 Old 04-24-2009, 08:04 AM
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Try reversing the order:

Loosen the fork cap before you loosen the pinch bolt on the upper triple.
This way the fork is securely gripped & you can get better leverage.

Threads shouldn't be reversed, the caps are probably tight because they've never been removed since they were first assembled.

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post #20 of 26 Old 04-24-2009, 08:05 AM
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Quote:
Originally Posted by barton664 View Post
ok... having a bit of trouble here...

loosened choke bolt on triple tree... blue top cap not wanting to cooperate.... this thing don't have lefty threads does it??

cause i really don't wanna break nothing..
The fork is held secure by the lower triple.

Standard RH threads. The blue top cap can be stubborn. I suggest a 6 point box wrench or 6 point socket. The cap is aluminum, one slip and the cap will look like crap.

Same thing goes when you replace the cap. The fine threads will strip if cross threaded. Always start the threading process by hand.

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post #21 of 26 Old 04-24-2009, 08:35 AM Thread Starter
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Quote:
Originally Posted by barton664 View Post
ok... having a bit of trouble here...

loosened choke bolt on triple tree... blue top cap not wanting to cooperate.... this thing don't have lefty threads does it??

cause i really don't wanna break nothing..
The '04 - newer fork internals are different. The stock spacer is a different size. The cap comes off the same way. The pinch bolt will lock the cap in place, so you definitely need to loosen that first. Since you already have preload adjustment on the '04+, a new spacer may not make any difference unless you already have the preload set to max.

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post #22 of 26 Old 04-24-2009, 08:41 AM
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Brian you keep talking about how Big you are, but why are you letting a little blue cap destroy you?

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post #23 of 26 Old 04-24-2009, 08:43 AM
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Quote:
Originally Posted by tpoppa View Post
The '04 - newer fork internals are different. The stock spacer is a different size. The cap comes off the same way. The pinch bolt will lock the cap in place, so you definitely need to loosen that first. Since you already have preload adjustment on the '04+, a new spacer may not make any difference unless you already have the preload set to max.
He is not replacing the spacer, he is replacing the springs.

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post #24 of 26 Old 04-24-2009, 08:55 AM
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Quote:
Originally Posted by zookmor View Post
Brian you keep talking about how Big you are, but why are you letting a little blue cap destroy you?
i am capable of turning it... whether it wants to turn or not....in either direction.... but experience has shown me that before i turn to brute force it is sometimes prudent to ask if there are any special considerations... i kinda wanna ride it again and if i "F" up that little blue cap i am gonna have to climb into my wallet before i can ride again... ...



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post #25 of 26 Old 04-26-2009, 06:50 AM
 
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Would it be possible to take get an adjustable prelaod setup from a 04+ 919 to put right into a 02-03?? I have the '02 and was looking to get the Ohlin's springs but have had trouble finding them. So it may be a better idea to get find a wreaked 04+ and take the springs(if different) + adjusters from there.

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post #26 of 26 Old 04-26-2009, 07:48 AM
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The damping rods are different, too...

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