NC30 Racetek fork reassembly and setup.

StrayAlien · Post by **StrayAlien** » Sun Sep 22, 2013 11:38 pm

Hi all,

My '93 NC30 racebike has racetek fork internals with a 85 spring. I bingled it in May and bent the forks and heaven and earth would not get the bottom damper bolts out so they had to be machined out by the repairer.

Now I have two small boxes of parts to put back together. Fair enough I can get em back together ... BUT how to make sure they are set up correctly?

First big question is: how to calculate and set up the initial preload? These forks have an external top-out spring so preload calculation is not so simple.

I am about 85kg with gear, bike is probably about 175kg or so wet.

Ballpark rule of thumb guidelines welcome here - as long as (I guess) it can be fine tuned with the top nut preload adjusters then we're okay .... I guess.

All help welcome.

magg · Post by **magg** » Mon Sep 23, 2013 1:53 am

You have the usual top out spring of 2-3 coils located on the outside of the damper cartridge?

StrayAlien · Post by **StrayAlien** » Mon Sep 23, 2013 1:56 am

Yep. That part is stock. The racetek setup is valving and a (longer) spring replacement - so there is no tube spacer - there is a 'shim stack' of washers at the top of the spring.

magg · Post by **magg** » Mon Sep 23, 2013 2:51 am

Using RaceTech's handbook, they suggest that with a rider sag set at 25-35mm, preload should be 5-25mm. If preload needs to be at either extreme then they recommend a spring rate change.

The other approach is to adjust the preload to get bike sag 25mm and rider sag 35mm. If you cannot get these sag figures using the existing preload range then the spring rate is wrong.

The generally held view is that the rider sag should be 25-30% of the available travel (front or rear) with race bikes closer to 25% because tracks do not have many big bumps.

magg · Post by **magg** » Mon Sep 23, 2013 2:55 am

Forgot to mention that the OEM top out spring has no bearing on sag or preload adjustment.

StrayAlien · Post by **StrayAlien** » Mon Sep 23, 2013 3:19 am

Thanks magg. What I am after here is how to set up the initial spring preload as I reassemble for forks so that the adjustments you speak of can be made using the fork-top adjusters after assembly and installation back on the bike.

Even with zero preload set on the top, the springs will have already preload on them after reassembly, and those suggested preload figures you mention have to include that initial preload .. and because of the top out spring, the preload is not purely how many mm the fork spring was compressed for installation (as I understand it). So, setting the initial preload on these forks does not seem so straight forward as a non-top-out-spring fork.

Unless I have it wrong, that 5mm you speak of does not equal 5mm on initial spring compression because it does not take the top out spring into account. I believe these forks are actually *longer* after assembly that would would think because the top out spring is doing it thing and (well) stopping stuff from topping out.

.... or do I have it all wrong? Forks are a little mysterious ...

I'd like to avoid the guesswork and having the initial preload nowhere in the ballpark for the top adjusters to do their thing, rather than needing to remove and dissasemble the forks, change initial preload a bit, reassemble, try the sag setup again, and if the adjustors are not in the ballpark, dissasemble etc.

I believe the stock setup has a tube like thing to set initial spring preload but the racetek does away with the tube and uses washer 'shims' under the spring collar to set it up. I'll get some photos up here tonight.

Before I bingled it I could get the sag right with whatever initial preload the fork has internally, so I am aiming to get it somewhere near that again.

edit: just saw this: "the OEM top out spring has no bearing on sag or preload adjustment". Racetek manual says it does, but I am no expert.

magg · Post by **magg** » Mon Sep 23, 2013 3:33 am

The "long" top out spring that is fitted to much newer fork designs will affect the preload/sag setup process but the OEM type does not. The OEM top out spring is a simple attempt to stop mechanial comming together when/if the forks fully extend.

Your "initial" preload is the washers on top of the spring which can be changed simply by unscrewing the fork cap. If the settings were ok before the crash why do you need to change them after the repairs?

StrayAlien · Post by **StrayAlien** » Mon Sep 23, 2013 4:28 am

Thanks magg, you are a legend. I was hoping it was much simpler than it sounded.

Re 'why change", it is more a matter of I do not know how they were before! After the crash I had no real use of my right arm and a mate helped me with the fork top-end dissasembly and the tops were whipped off and dismantled before you could reach for a ruler and a notepad.

But, I am happy to have the opportunity to put them back together from scratch and learn more about them and setting them up.

Thanks for ther advice. And .. if you are in sunny Melbourne some time, my shout.

NC30 Racetek fork reassembly and setup.

NC30 Racetek fork reassembly and setup.

Re: NC30 Racetek fork reassembly and setup.

Re: NC30 Racetek fork reassembly and setup.

Re: NC30 Racetek fork reassembly and setup.

Re: NC30 Racetek fork reassembly and setup.

Re: NC30 Racetek fork reassembly and setup.

Re: NC30 Racetek fork reassembly and setup.

Re: NC30 Racetek fork reassembly and setup.