Forks - fitting springs to match my weight

This turned out to be much trickier than I expected. Not the job, just ordering the springs.

I got in touch with Lee Finney (aka (Fat) Finski from the Bemsee board) at Performance Techniques and asked for a quote for FZR400rrsp springs. Turns out no-one makes rrsp springs as such, so Lee needed more details so he could match them up. So I removed the forks and stripped one leg.

First you undo the large top nut with your hand over it to stop the inners popping out (note - undo this a bit while the forks still attached to the bike). Once thats out, compress the fork, lever the washer out the way and with a spanner on the pre-load nut (small one on the top) use another spanner to undo the locking nut. Then just screw off the top. Now you can remove the washer and the spring - have some clean kitchen roll handy as this will be oily. The oil that came out was black. I didn't think anything of it until I poured the new oil in which was almost clear.

Whilst your here you may as well check what you have. So, with the forks compressed, measure how far down the fork tube you have to go before you hit the oil (basically you are measuring the air gap). I just put a measuring tape down there, but you can use cable ties or straws or anything. The air gap I had was 40mm. Thats odd, the manual says it should be 106mm. So I measure again. 40mm. Can't be, no-one could be 66mm out when putting the oil in? So I got a measuring jug and tipped the oil into it. Says in my book that there should be 433ml of oil in there, so as some had come out on the spring, I should have less. I managed to spill some on the floor, but the jug still managed to hold 450ml! Had a word with Rob Jones, he reckoned I was lucky the fork seals didn't just pop out under braking. I won't say who filled the forks but they are an official Yamaha dealer (who I won't be using for servicing work again any time soon).

So, the dimensions of what I removed were:
Spring metal thickness = 4.5mm
Length = 360mm
Diameter of spring = 37mm
Inner fork tube diameter = 40mm
Outer fork tube diameter = 43mm
Washer thickness = 2.5mm
Gap between coils = 14.5mm
Fork oil = slightly more than 450ml

Lee didn't need all these but they are here for completeness.

So Lee got on to his suspension guru's and eventually I had some springs and spacers. The dimensions of these are
Spacer length = 110mm
Spacer diameter = 37mm
Spacer metal thickness = 1.3mm
Spring length = 250mm
Spring diameter = 37mm
Spring metal thickness = 5mm
Number on spring = 9.0
Gap between coils = 8.5mm

So I strip the second fork and as I pull the spring out it makes a scratching noise. Hmmm, the other one didn't do that. So I put them side by side and this one is:
- Bent!
- 15mm longer (375mm against 360mm)
- Has bigger gaps (15.5mm against 14.5mm)

Oh well, at least it will all be better when its re-assembled. I turned the forks upside down and pumped them for a bit to get all the oil out. I then left them upside down in an oil tray for a few days. Looking at the bits on the bench and it dawned on me that I hadn't got addtional washers from Lee to sit between the springs and the spacers. Luckily, I have a spare set of RR forks, so I just nicked the spacer from there (1.6mm thick, 37mm diameter just in case anyones curious). I then cleaned all the bits with compressed air before I installed them. I put the forks on the bike and to help make life easier I used some string to hold the internals up (see pic) and to keep the forks compressed. To measure the air gap I used a bit of clear tube. Once I was happy that the level was right I double checked with a pencil, marked in the same way (level should be 106mm from top with fork compressed and no spring). Once the oils in, lift and drop the internals to bleed them, when you have a nice consistant movement and no noise, its done.

I then undid all the string and put the spring in (bit that says 9.0 at the top), washer from rr forks, spacer, 2.5mm washer, cap inner and then cap outer. First one went together easy. Second one was a bugger getting the cap on, so I took the fork off the bike and used the following method: Put a rag over the top, put hand over rag, bend over and use your chest to push the cap down, twist the fork tube with your other hand to do up the cap. Went on easy this way.

Thats it for now, I will set the sag when I get a chance, its easier with two people. Various images below, all clickable to see larger versions.

it won't spring up that hard, but it will spring up rrsp inners hold the 14mm pre-load nut on the top to get the locking washer undone top = rr fork inners, bottom = rrsp fork inners left = bent and different length springs coming out, right = new K=tech kit going in rrsp spring at the front, K-teck gubbings to the rear what is says on the K-tech box new spring new spring can you see the bend, where the coils to the right don't touch the bench?
Back to Race Results and Reports or Home Page or Trackdays and Racing