ZXR400H fork rebuild

[ducatilover]

I'm going to rebuild the forks on the 600, they're ZXR600H1 units.

The ZXR factory manual says they take 5W oil, the bike they're on is a wee bit heavier, but I'm a bit under 60kg.
The ZXR400H weighed in at a claimed 163kg dry/189kg wet
My ZZR is currently dry and should be just under 180kg depending on how heavy the 'zorst is. (evidently there's not much ZZR left)

So, the question is:
Is it a good idea to put 7.5 or 10w oil in her?
From memory the ZXR was a harsh riding bike, but I have an extra 15/20kg or so.


Also, who stocks the seals and bushes? I can get seals from overseas, but cannot find bushes.

[spanner spinner]

are they shim stack forks or damper rod forks. If they are shim stack forks you can't change the fork oil weight with out causing a lot of other problems, the shims need to be changed not the fork oil weight. If it is a damper rod type you can change fork oil weight to alter the damping but it will be a suck it and see as far as what weight.

[ducatilover]

I am led to believe they're damping rod forks, racers in the U.K seem to run 7.5wt, so I've decided not to go with heavier fluid. I don't think it'll work on the road

Hope to have a rebuild kit in my letter box soon

[Robert Taylor]

I am led to believe they're damping rod forks, racers in the U.K seem to run 7.5wt, so I've decided not to go with heavier fluid. I don't think it'll work on the road

Hope to have a rebuild kit in my letter box soon

The seals are easy to get in New Zealand, several sources. Plus you are then supporting the livelihood of New Zealanders.

7.5 weight oil....are you aware that if for example you purchase 7.5 ''weight'' Redline ( at one end of the scale ) and then alternatively 7.5 ''weight'' Silkolene ( at the other end of the scale ) the comparitive rebound return speeds will be markedly different.

Rating suspension oils by motor oil SAE ratings is notoriously inaccurate.

[ducatilover]

The seals are easy to get in New Zealand, several sources. Plus you are then supporting the livelihood of New Zealanders.

7.5 weight oil....are you aware that if for example you purchase 7.5 ''weight'' Redline ( at one end of the scale ) and then alternatively 7.5 ''weight'' Silkolene ( at the other end of the scale ) the comparitive rebound return speeds will be markedly different.

Rating suspension oils by motor oil SAE ratings is notoriously inaccurate.

Have ordered within NZ (for once!), seals are bloody easy to get

The 7.5 I refer to is Motul, seems to be a popular choice in the UK (so they tell me)

Have you got an oil recommendation Robert? This is not going to be raced and I'm not exactly a nut rider (no peg scraping on this one) so I'd want something that gives me a reasonably mid-range damping rate with my mighty standard internals (sorry, I want to have 'em built by you, but $$$ is lacking)
Bear in mind I do have a small amount of factory adjustment.

[hayd3n]

check out www.pyramidparts.co.nz/ cheep and quick and reliable
%20 off if ur biikes not listed

[nzspokes]

Watching with interest as im about to do my forks. I may make some compression adjustably.

[ducatilover]

check out www.pyramidparts.co.nz/ cheep and quick and reliable
off if ur biikes not listed

My forks are listed Good shipping prices too, I'll have a good hunt 'round the site, might have to order a few bits and bobs

[Robert Taylor]

Have ordered within NZ (for once!), seals are bloody easy to get

The 7.5 I refer to is Motul, seems to be a popular choice in the UK (so they tell me)

Have you got an oil recommendation Robert? This is not going to be raced and I'm not exactly a nut rider (no peg scraping on this one) so I'd want something that gives me a reasonably mid-range damping rate with my mighty standard internals (sorry, I want to have 'em built by you, but $$$ is lacking)
Bear in mind I do have a small amount of factory adjustment.

Its a long time since I worked with these but as I recollect they have low tech cartridges in them.

Motul is one of the very very best suspension fluids and 7.5 wt is likely around 25 or so centistokes at 40 degrees celsius. It will be close to being ok PROVIDING the piston rings are not excessively worn and the top bushings at the top of the cartridges ( I think they are floating on these ) are not so worn that they bypass more oil than normal. This also assumes the shim stacks are still sealing firmly against the piston faces.

If you have to go to a much heavier oil to get a decent rebound control speed then it proves that there are internal issues

CYNICALLY, if you fit some of the dodgy cheap high friction seals on the market it may help to control any fast rebound issues!

[ducatilover]

Its a long time since I worked with these but as I recollect they have low tech cartridges in them.

Motul is one of the very very best suspension fluids and 7.5 wt is likely around 25 or so centistokes at 40 degrees celsius. It will be close to being ok PROVIDING the piston rings are not excessively worn and the top bushings at the top of the cartridges ( I think they are floating on these ) are not so worn that they bypass more oil than normal. This also assumes the shim stacks are still sealing firmly against the piston faces.

If you have to go to a much heavier oil to get a decent rebound control speed then it proves that there are internal issues

CYNICALLY, if you fit some of the dodgy cheap high friction seals on the market it may help to control any fast rebound issues!

I would have to agree with your recollection, ZXR400h1 forks are nothing special, maybe back in '89?
I've always used Motul and never had problems, so I'll keep using it.
I just realised, I don't think I have any rebound adjustment on these? I think it's just bound adjustment, unless it's adjusting both...argh.
I think I'll go with some 7.5wt oil, have to do my mighty GN250 also, so I'll biff some Motul 7.5wt in them too, they handle like a shovel anyway.

I'll have to think about upgrading these forks vs buying new ones.
Do you think they could perform well enough for very average road riding on a bike that's so fuckin' tarted up it'll never see any real action?

Fork seals make THAT much of a difference???

[Robert Taylor]

Yes, friction in fork seals and dust seals can be massive. Check out MotoGP and WSBK bikes, NO DUST SEALS. Here, we place a 6-7mm long vertical slit in dust seals and they open up that slit about .7 of a mm, when assembled onto the fork tube. NOK absolutely make the best fork seals. Good suspension work also includes getting rid of as much friction as possible

[ducatilover]

You learn something every day! Well, I just did

[Robert Taylor]

I would have to agree with your recollection, ZXR400h1 forks are nothing special, maybe back in '89?
I've always used Motul and never had problems, so I'll keep using it.
I just realised, I don't think I have any rebound adjustment on these? I think it's just bound adjustment, unless it's adjusting both...argh.
I think I'll go with some 7.5wt oil, have to do my mighty GN250 also, so I'll biff some Motul 7.5wt in them too, they handle like a shovel anyway.

I'll have to think about upgrading these forks vs buying new ones.
Do you think they could perform well enough for very average road riding on a bike that's so fuckin' tarted up it'll never see any real action?

Fork seals make THAT much of a difference???

These forks will see plenty of day to day action on road, the ultimate objective being to provide great chassis control with excellent compliance over nasty bumps. Great suspension is not only about racers, 80% of our customers are not racers.

[ducatilover]

What would you recommend, later model forks (say ZX6RB or something similar) or having these 400 forks set up?

[avgas]

I found the 5w I had in my H forks was a (slight) bit light for the way it was setup. So your on the right track with 7.5w. I probably should try other fork oils - but mostly use MOTUL.
If you can, as Robert said replacing anything you can get your hands on internal wise. I rode 2 different bikes (mine and a mates) and his internals felt like rubbish. It makes a massive difference.

I found f-all difference from having my forks on the H and the newer forks. But thats just me personally - and I tend to dial shit up till its rock solid anyways........so my advice will either cause you to have a shit load of fun or get you killed.