Fork springs

[Carl Howell]

Soon (before the MOT) I need to rebuild the front forks on my bike (Yamaha FZX250 Zeal) because someone put crap fork seals on or too much oil or something and now they are weeping a bit, not enough to reach the discs but its annoying. While its all apart I think it would be worth changing the springs as the front is wayy too soft for my liking. I'm thinking of firmer springs and thicker oil. Is there anyway to find out how much oil to put in the forks because no one makes a proper manual for it.

Are the springs universal or do I need to measure them to make sure they are the same length or something or are they bike specific?

Thanks, Carl
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Owned: 2002 Gilera DNA 50, Yamaha DT125R

Own: Yamaha FZX250 Zeal (FZR250 engine as a similar shape to a Hornet)

[Kickstart]

Hi

Forkl springs are very bike specific. Length and how stiff they are. Different lengths can be coped with to an extend with making up a different length spacer to fit between the top of the spring and the top of the fork.

Thicker fork oil will make the damping stiffer. It will not make any difference at all to how far the forks compress, just how long it takes them to compress.

A cheap way to make the forks stiffer is to use a bit of extra oil and so reduce the air gap above the oil. When forks compress the oil cannot compress, only the air can. The air gap thus acts as a spring.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Bezzer]

Springs are bike specific rated for the bike weight , ride etc you can't just stick any old ones in them and expect them to work right . While new aftermarket springs are usually worth it to improve the ride you can alter the oil weight to stiffen or soften the OE ones a bit. If you can't find the oil spec and quantity and there isn't another similar model you can compare it with then measure the oil height you've got now and put the same amount back in after you've done the fork seals- ie take the springs out and measure the distance from the top of the forks to the oil then when you replace it you can use a syringe and a bit of tubing to get the same level with the new stuff. That's assuming the level is right in the first place
Oil type all depends on what's in there now could be anything really best to start at 10w to see if that improves the ride for you then you can always uprate it if it's still too soft. Fresh oil
even it's the same weight that was in originally can make a big difference.

Edit - or what Kickstart says- too slow on the keyboard
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I used to be indecisive but now I'm not quite so sure.

[Carl Howell]

Do you think a suspension specialist would be able to help. Anyone know of someone good in the west midlands.

When I bought the bike the bloke gave me a FZR400 manual (my bike shared the same engine as the FZR250) saying its the closest match.

Thanks, Carl
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Owned: 2002 Gilera DNA 50, Yamaha DT125R

Own: Yamaha FZX250 Zeal (FZR250 engine as a similar shape to a Hornet)

[Kickstart]

Hi

A suspension specialist might well be able to help. Try Revs Racing in Halesowen. It is a tiny shop but hopefully he can deal with you quickly at the moment before the race season starts.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Carl Howell]

Thanks Keith. Will have to pop over.

Carl
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Owned: 2002 Gilera DNA 50, Yamaha DT125R

Own: Yamaha FZX250 Zeal (FZR250 engine as a similar shape to a Hornet)

[lonner]

[Carl Howell]

Just been to Revs Racing. He said the best thing to do is renew the forks (£85) and new springs are £70. I think it was £45 extra if I take the bike in so I will get the forks out.

Whats involved in renewing the fork internals? I know how to change the fork seals but that's about it. Is there much more to it than that and new oil?

Thanks, Carl
____________________
Owned: 2002 Gilera DNA 50, Yamaha DT125R

Own: Yamaha FZX250 Zeal (FZR250 engine as a similar shape to a Hornet)

[Kickstart]

Hi

As well as the seals there are also bushes, probably top and bottom. Might need new dust seals as well as hydraulic seals.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Carl Howell]

Will try and get them over to him next week or the week after then.

Thanks
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Owned: 2002 Gilera DNA 50, Yamaha DT125R

Own: Yamaha FZX250 Zeal (FZR250 engine as a similar shape to a Hornet)