NC21 forks bottoming out

[tj2]

Hi my sons nc21 forks bottom out under braking. I have just replaced the oil and fork seals, but have not yet reinflated the forks to the correct pressure.
Could this be all it needs?
Cheers
Terry

[CMSMJ1]

Hi Terry,

The real reason will be that the springs are tired and that your son, unless he is a lightweight, will be too heavy for the springs.

inflating the forks can lead to blown seals - very low PSI if you do it and only if you've fitted OEM seals.

Easiest option is to find some pipe/spacer and preload the springs by another 10-20mm to stiffen it up.

Welcome to the site...

[Neosophist]

Mark has pretty much summed it up.

How heavy is the rider?

Are the forks actually bottoming out (do you hear them bang?)

The Honda forks of the NC21 / 24 are very soft and do compress a lot...

Air is good, 8 - 11psi (this is literally 1 pump of a small bicycle pump) but non-honda fork seals espeically the cheaper ones don't like air and will leak.

Maxtron do a set of replacement springs which you can get for the riders weight.

Or you can try using a longer metal spacer like Mark mentioned to increase the preload.

[Lane]

Use a cable tie/zip tie around the fork stanchion to find out how far the forks are travelling.

What sort of braking are we talking about? Does he ride it like he stole it?

[tj2]

Thanks for the replys.......
He is about 70 kilos (11stone) ish
He has only just passed his uk licence, and is still learning how to ride it

When I did the forks, I replaced stuff as it came out. I have no manual as a reference as to how it should be.

Do the springs go in with the tighter coils to the top or bottom?

Oil quantities were researched but could not find for NC21. So when refilled I used the specs from another vfr with trac so hopefully this would have been about right.

If anyone knows the correct info and is able to post it or pm it to me that would be great

Needs the rear stiffening also........................ but that is easy.......

Cheers for your help

Terry

[amorti]

Once it gets to that point you likely need new springs. Remember the original springs (designed for lightweight rice-eaters) have had the weight of a 180kg-ish bike sat on them for about 25 years now, so they will undoubtedly be compressed a bit. Hagon progressives from WEmoto are your best bet for a budget fit-all product. They will set you back about £80, and Hagon will also tell you what weight oil to use, and how much of it.

More oil (less air gap) will have the same effect as adding air. This increases the spring effect of the compressed air, increasing the spring rate. It is hard to say how much you can get away with without popping seals quickly, though. In general it's one of those ideas which was consigned to the history books many many years ago, and rightly so.

Adding spacers for more preload will simply allow the bike to use that much higher of the suspension travel. Can be useful, but there are problems with it. One is, it doesn't fix the low spring rate, so under braking the forks will probably still bottom out. Two is, you will have a job closing the fork caps.

Thicker oil is sometimes suggested. All this does is increase the damping, meaning the forks are undersprung and overdamped - they will bottom out just the same, but get there slower. The ride will become harsher too.

You will both be glad of the new springs, it's your boy's safety we're talking about after all. The difference from worn-out OE springs to new progressive's is astounding.

[Neosophist]

The forks are assembled like this.

http://images.cmsnl.com/img/partslists/ ... 9_0360.gif

Right Fork: 340cc
Left Fork: 345cc

Weight: 10-W

[tj2]

Thanks for that.

Oil level was about 50cc per leg low so adding the extra has helped.

Put 5psi in each and is better yet..........
But........................................











Both springs are a tad weak and will get replaced as soon as can afford.

Poor lad , just passed test and insurance cost almost £800 (which he has paid for himself)

But he says that its more than worth it for the fun he is having


Again thanks for your help

Terry

[duncan]

Glad you are enjoying your VFR400.The best mod you could possibly make is to fit Maxton springs in the front

[Pilky]

In the process of looking to buy a bike i found an NC21 for sale! £1000 with restrictors fitted. Great.
Went to look at it and my old man immediately noticed the front end was very soft but he umm and aah'd to himself and said that the vfr400s always had a slightly soft front end. He didnt look convinced but you know what its like when you buy your first big bike, you rush in and buy it (I did anyway) i paid a bit much for the nc21 but oh well its good fun.
Anyway within a week of riding it the front end bottomed out in Pentrefolas on the way to Betwys. I shit my pants.
Straight away we dismantled the forks and to our amazement there was little near no fork all in both forks! The guy who sold it told me insisted that the forks had been serviced before selling it (this was a dealer!) and that the forks must of leaked from BOTH forks within a week of having it. The guys on here pointed us in the right direction and we redone the forks luckily there wasnt any damage to the springs. I bought aftermarket fork seals in a hurry and after fitting them the fork oil seaped out of the top but as soon as we fit genuine honda fork seals it was perfectly fine and has been since.
I wouldnt recommend buying aftermarket seals. I dont know whether anyone elses have been fine but they certainly didnt work for me! Buy genuine ones!