NSR 125 forks not returning "optimally"

Stowelly · Traffic Copper Joined: 25 Oct 2009 Karma :

Any idea what could be wrong with these? thought it could be as one of the seals was leaking and its lot a lot of oil

basically, most of the time they return to the top reasonably well, not quite straight away as they should, but there are the odd times where the feel a little notchy.

is this likely to be an MOT failure?

skatefreak · World Chat Champion Joined: 06 Feb 2010 Karma :

Hey,
Yeah, compromised fork seals are an MOT failure and if leaking a lot will cause problems.
To be honest it sounds like that bike is on the verge of being a death trap, cant be very safe, if both forks arnt returning to the same position you wont have the front wheel running true and it can also cause problems when cornering...

I would say to be on the safe side get some seals (around 10 bucks) and oil and sort them out...

-Jvr

Stowelly · Traffic Copper Joined: 25 Oct 2009 Karma :

DrDonnyBrago · World Chat Champion Joined: 03 Jan 2010 Karma :

Is the damping adjustable? Have you used thicker fork oil?

Spring could be knackered, did you measure the free length of the spring when you had the seals out and the forks apart? Was it within tolerances?

Stowelly · Traffic Copper Joined: 25 Oct 2009 Karma :

pretty sure you cant adjust the dampening on the nsr forks.

used 10 grade fork oil, so if anything its a bit lighter.

didnt think to check the spring lengths etc, but they didnt look knackered??

it seems its about £6 for each spring from honda, so if i can change these without taking out / replacing the seals i could do that i guess?

taz4626 · Renault 5 Driver Joined: 30 Aug 2009 Karma :

the nsr125 forks also have replaceable bushes as i did a set on a mates nsr the other week as he had similar issue (it failed the mot for not returning quick enough)

might be worth changing the bushes aswell 5 quid a bush from david silver if i remember rightly

alains · World Chat Champion Joined: 08 Jul 2004 Karma :

i used grade #20 instead of #10 because it will bang on bumps
if you are a lightweight you can use 10
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dextersaurus · World Chat Champion Joined: 25 Mar 2009 Karma :

Maybe it's the springs?

How old is the bike? been off-roading? Wink

Heavier oil, and replace the bushes too...

When did you last cahnge the oil? Fork oil has a tendancy to oxidise, so releasing the air from the forks could have a noticable difference.

But i do stick to my thought that it's the springs. The bike will probably have taken quite a beating in it's time... You never know who's been trying to wheelie it Wink

Dunc

Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

If the fork seals have been done recently, I presume the foks have been stripped.
Two thoughts occur to me, and they may be completely off the wall, but worth a though.

If its the last 'bit' of travel, where the springs are almost completely decompressed so not offering much spring force to return them, then 'something' wrong in the damper could be causing them to stick.

Who 'did' the forks, and could they have been assembled wrong?

When stripped, were the damping internals completely cleaned?

Were the fork sliders painted or anything?

Wondering if there are, or should be 'top-out' buffers on the ends of the damper rod, so that the damper rod cant be stretched or damaged at full stretch. If these have been put back on wrong, could be fighting the spring at the top of the stroke.

Next up, depending on which way up the damper internals are and where they work, sediment from oil fork-oil could have collected in the damping holes or grooves, giving a higher damping force at that point.

On the CB125 forks and many more, there's also a taper groove down the bore of the fork leg, so that at the top of the fork stroke, the oil has a smaller passage to squeeze through than when its heading towards the bottom, if the damper rod is has been re-assembled with something missing, or not tightened up right, possible that the damper seal is sat over the end of that relieve groove so giving an inordinately high damping force at the end of the travel.

MIGHT be worth just going back over whats been done, checking, and double checking against the book, cleaning everything meticulousely.

Amazing how so many times a 'quick rinse' can be more unhelpful than not cleaning.... dislodhing that 'little' bit of shit that wasn't doing any harm, and putting it somewhere it will!
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