I have some XZ400 forks which I am using to replace my rusty and leaking XZ550 forks. I will put new seals in the XZ400 forks and keep the option of the air valves for adjusting the ride.
I read a post that said I should use the XZ550 springs in the XZ400 forks because the former are progressive springs and the latter aren't.
Is there anything else I should look out for? Thanks
That's right - the 16R model has progressive springs. You will need to swap spacers as well - the progressives are a fair bit longer.
The air caps are longer so you will have more pre-load than on the 550. That's fine for me as I'm more like a sumo wrestler than a 75kg Japanese teenager.
Many thanks - its great to have access to such experience on this forum!
To reduce the pre-load in the new setup, is it worth while cutting the XZ550 spacers down to account for the difference in cap lengths? Cheers
Unless you are a a 75kg Japanese teenager (77kg with sword) I'd build them with the spacer as is, then measure your sag and trim to fit.
wouldn't think there would be too many jap teenagers with a 2kg sword :o
Is "sag" something to do with the forks or how far my paunch extends over my belt? Either way I will stick with the longer XZ400 spacers. Even though I fantasize about being 75kg in skinny jeans, barring an attack of the big C, I don't think it will happen.
There is static sag which is the amount the forks drop from fully extended under the bike's own weight. Then there is race sag (commonly called rider sag) which is the amount from fully extended to where forks come to rest with rider aboard bike. You usually will need a couple of helpers to measure this. Might pay to do a search around for the recommended sag measurements, usually a percentage of full travel. Correct rider sag is achieved by preloading springs (spacer length in this case) If you have correct rider sag but no static (aka free) sag then you probably should have heavier springs.
Thanks, will do.
Working on the forks today I realised that I had got my wires crossed with respect to the spacers.
The XZ400 spacers are longer because the air caps extend further into the slider, AND the xz400 springs are shorter.
Therefore with the longer xz550 progressive springs in the XZ400 forks, I need the shorter XZ550 spacers. Even so the preload will be greater because I am using the XZ400 air caps as well.
Hmmm.
Sorry mate...and there I was thinking I was being as clear as anything, but I can see how I turned you around. Good to see you have the correct idea now.
Here's a video on sag (https://www.youtube.com/watch?v=t4m4ahZLRMY)
Lots to learn here. The videos are particularly helpful and I am moving in to totally new territory here.
I am introducing some preload with my setup. As I understand it, (after looking at the videos), I may need to shorten the spacers if I have too much preload and I need more sag. If I have too much sag (unlikely) then I can introduce some air to the forks, (say 1-3 psi) in order to reduce the sag.
Am I on the right track?
What are your fork oil recommendations given that I ride conservatively.
Cheers
Yes I think that's the idea. The stock setup is for a 75kg japanese teenager with a 1kg sword (thanks for the correction Dingleberry) and then as you eat more pies, you add more air. Up to about 36psi, then you have to increase the spacer length or ditch the XZ and buy a Harley.
I started with 10 weight, went to 15 on someone's recommendation, but it was horrible - the bike just skipped along the tops of the bumps I drained and went back to 10 almost immediately.
6 psi has worked very well in my '83 for many years.
Just checking the tubes.
One is nice and straight, the other has about 5mm run-out in the centre when held at both ends. Poobah.
Has anyone had a go a straightening forks themselves or is it best left to an engineering shop?
You can straighten your fork tube without much difficulty if you have a hydraulic press. You support the tube on V blocks either side of the bend with the high side up toward the ram of the press and gently have a go at it. Make sure you have a 'pad' of some sort to prevent damaging the surface of the tube. A piece of angle iron or plate to spread the load will do nicely, but don't let it slip when under pressure. It takes a bit of trial and error, and really helps to have a dial indicator to test the straightness of the tube.
It's been a while since I have done this, but I think that is the important stuff to know. ::)
If you don't have access to a press then best send out to a specialist shop that straightens them. A friend had his Aprila race bike forks straightened by a place in Auckland. He said the forks were so bad, they had creased on the bend and he was going to through them away. The company he took it to had a machine specially for straightening forks. He watched them put it through the machine and it even took the crease out, he was very impressed. Let me know if want the contact details of the place and I will find out for you.
"Trial and improvement for fork straightening" - sounds a bit like life really.
I haven't got an hydraulic press but it helps to know what to ask for. I've got a pretty good picture of what I need thanks.
Thanks too for the advice about the Auckland repair shop. I am now living about 6 hours away in Whanganui (Home of the infamous "Cemetery Circuit"). I'll try to find a local workshop. The railway workshops got closed in the town about 30 years ago, but its amazing what a legacy of engineering skills has been left behind.
Haynes recommends two methods for measuring the fork oil. By quantity and by measurement of the oil level from the top of the fork tubes. I imagine the critical thing is to have the quantity identical. Any thoughts as to what is the better method?
What version of Haynes do you have? US version of Haynes only listed the US82 spec. 257cc will fill your 16R forks to overflowing (and you will need 2 bottles).
Yamaha Specs are ...
| Model | Weight | Vol | Height |
| US RJ | 15w | 257cc | 152mm |
| US RK | 15w | 267cc | 127mm |
| Euro 82 | SAE 10w/30 SE | 249cc | 100-140mm |
| XZ400 | SAE 10w/30 SE | 272cc | - |
We don't have a spec for 16R models with progressive springs (with their different densities) and XZ400 tubes. I used exactly half a bottle in each (the bottle was not quite 500cc). That filled the fork to about 10mm under the thread with spring out and fully compressed. That was a bit harsh and I tipped a bit more out later.
By the way, I now use Castrol 10w fork oil from Supercheap - less than half the price of Bel-ray/Spectro from the bike shops that I used to use. I figure with Castrol you can't go too far wrong.
Some people use ATF. I don't know why exactly, it's dearer here than fork oil.
I have a generic RJ Haynes manual (1983) with the progressive springs illustrated.
This shows 257cc's of oil or 152mm from the the top thread of the tube with the forks fully compressed and without the springs in place.
I also have a Yamaha workshop manual for a 16R which specifies 249cc of oil.
Following your experience POD, I think I will go for measuring the oil level at 152mm below the top of the tube. (Fully compressed without the spring and held upright.) As a start, that should take in to account the longer thread of the aircap and leave me a few cc's of oil left over out of a 500cc bottle.
(BTW The XZ550 progressive springs that I have swapped over are 465mm long compared with 461mm in the Haynes manual)
Apart from what we are doing here, its curious that different markets have different specs for fork oil volumes. I would have thought all the forks in each market would be the same. Huh.
Is the 16R Workshop manual paper or electric? I haven't got one of those - any chance of a copy?
The manual I have is a paper copy in fairly good nick from a former Yamaha service centre. The Perfect binding is broken on the spine and I was thinking of having it rebound.
If it was useful I could separate the pages then scan it to create a Pdf document for your (generously shared) resources.
The manual I have is a paper copy in fairly good nick from a former Yamaha service centre. The Perfect bindings is broken on the spine and I was thinking of having it rebound.
If it was useful I could separate the pages and scan it to create a Pdf document for your (generously shared) resources.
For some reason the site won't let me add a jpg of the manual cover. POD, I will contact you by email. Cheers
Fork straightening went well.
I found an old school engineer locally who had a set of aluminum half round blocks to support each end of the fork and another one to press the bend out. "I've done a few of these" he said. How many forks are 55mm diameter? I watched and learned as he pressed and measured in a 6 tonne press. Finally a quick polish on the lathe. NZ$40. Sweet!
He gave me a tip for bad dents or nicks in forks. Fill them with silver solder and then polish them smooth on a lathe with super fine emery paper. Apparently solder sticks to hard chrome OK.
Happy bunny. Forks are now filled with 10w fork oil, assembled and ready to reinstall.
Thanks for all the advice
That's a nice price. Congrats.
Wish I'd had that tip before I ditched my spare forks
Finally got the bike back on the road today after the adventures of dealing with a bent tube and a bent triple clamp spigot.
First ride on the new forks felt like I was driving an old style pneumatic hammer. (10w oil in forks at recommended volumes, no air pressure, progressive springs and spacers from the '82 forks)
I would say that the preload is too much for my weight. I will do some sag measurements in the morning. If the sag is less than 30mm I will start by shortening the spacers.
Tested the static sag today after the hard as nails ride yesterday. 26mm between resting sag and sag with me on. I was aiming for about 30mm
I dropped the aircaps off the forks and removed the XZ550 spacers that I had put in on top of the XZ550 progressive springs. The length of the original spacers is 100mm. The difference between the length of the 550 fork caps and the longer 400 air caps is 10mm. As a guesstimate I decided to cut 15mm off the xz550 spacers.
After reassembly the static sag was a more workable 33mm. It will be interesting to see the difference in the ride.
33mm static sag on the front springs gives a good ride for my weight (85kg). Nice to be back on the road again.