Clunking Boxxers

[NCR600]

Just finished fitting up the 02 Boxxers to the FRM 125, including making a brake hanger to make the 185mm discs work. On the shakedown run in the street I discovered the things have a pronounced 'clunk' when pulling the wheel up over a gutter. They don't do it when I just charge at it, only when I pull the front up over, or off a gutter or step.

I can't replicate the noise by jumping up and down on the bars, or discern any play in the headset.

I give up! Anyone got any ideas what this noise is?

Cheers!

[roasted]

top out?

dont know the fix.

[lotec]

top out. heavier oil in the rebound leg should do the trick but boxxers have a little bit of negative travel to stop this (the newer ones do anyway) they must be rebounding mighty fast :?

[NCR600]

I was thinking top out, but the noise is too violent, like something letting go under pressure, like a spring noise. It's weird that it won't do it statically, only when on the move. I've got some more work to do on the hanger tomorrow to get the alignment spot on, so I guess some more intensive investigation is in order.

[lotec]

i dunno... Ive heard some pretty evil / violent top out noises having ridden psylos with a very minimal amount of 5wt oil in them haha seriously my bet would be that, the reason its not happening when standing still (you're standing beside the bike or on top of it compressing them) is you cant push them down and jump off them fast enough to make them top out, stand on the pedals on the bike while standing still, compress the forks as hard as you can and quickly pull the front wheel up to lift it off the ground... i bet they will do it then

[NCR600]

Hmmm, I've got 15wt in each leg, 150mm from the top with the spring out & fork compressed. They don't seem to be rebounding hugely fast, but I've got some 20 & 30 wt oil hanging about from my days racing stupid old Ducati historic race bikes, so I'll bung that in the rebound side and see what happens. Should be close to the mark anyway when I manage to get the heavy ass springs in there.

[Ryan]

Whoa, easy there dude, 20-30w oil is way too heavy for Boxxers unless you're one seriously heavy individual yourself. Rockshox forks aren't renowned for the durability of their seals as it is, using oil that heavy would be begging for trouble.

[lotec]

maybe there's a problem with the rebound leg then? i run like 7.5 wt oil in my rebound leg and they don't top out too harshly ever they've only topped out like once or twice what Ryan said i think oil that heavy is begging to blow the seals

[RaID]

Whoa, easy there dude, 20-30w oil is way too heavy for Boxxers unless you're one seriously heavy individual yourself. Rockshox forks aren't renowned for the durability of their seals as it is, using oil that heavy would be begging for trouble.


he is running 02 boxxers (ie before the "newer" damping cartridges)
so you need to run heavier oils to make them work decently
this is not needed in 03 n later model boxxers

definately sounds like a top out problem
try running a heavier oil, i that doesnt help raise the oil height by a few mm
also try slowing down the rebound by the adjuster (but dont expect a huge difference in adjustement available there)

[DWNHLR01]

I have exactly the same problem with the boxxers on my Orange.

[NCR600]

It's deffo a top out problem, I haven't tried heavier oil yet, I'll wait till I get the stiffer springs.

Shouldn't there be a top out bumper or hydraulic cushion or something? This is a pretty violent sort of noise.

[lotec]

newer boxxers have negative travel springs to stop topout (although if they rebound fast enough you'll still get it a tiny bit) it could be possible that when someone serviced the forks they put the parts back in the wrong way and put the negative travel springs on top of the cartridges not underneath them, if you were desperate and know what you were doing you could strip the fork down and check every-things in the right order... i don't know if 02 boxxers have this though but i really don't see why they wouldn't, from what i know the internals were unchanged between 02 and 03

[SKT]

My mate and I are running '03 Boxxers.
We both think 10 weight is prob a bit heavy, seems to cause spikes here and there. 7.5 weight or something close for sure. Even 5 weight if your fairly light.

One thing ot check is that the valve in the rebound leg is in the right way. You may laugh but I have had a bike mech (not a very good one for sure) put that valve in upside down resulting in no rebound control at all.
It's easy enough to check, download the manual and crack 'em open, lay e'm out. You are gonna need to change thta oil anyways, might aswell see if it's built right.

[NCR600]

Well just to give some feedback on this old thread, I got some heavy springs (Thx to Bill@DhD) and pulled the forks apart and put them back together properly with 20 wt oil in the rebound side and 10 wt in the compression.

I drilled out the nylon ring on the compression side (seems to be a common mod on the net, so i thought I'd try it) and assembled the compression valve correctly (the top spring was just floating around inside the damper rod)

The rebound damper rod seems to be ok, but the nylon 'hat' on the top of the piston is broken, so I've got no click adjustments, but I bodgied it up enough to have a positive stop at each end of the adjustment. Anyone know if you can just buy the nylon bit as a spare, or do I have to buy a complete rebound damper assembly?

They still clunk on top out and make noises I can only put down to spring slap, but I guess they must all do that, cos I can't see anything wrong with them!

Thanks folks!