Project Fuel Injected Turbo FZR250, half

Magnet is a good suggestion. Or maybe circlip pliers that can grab the lip. I found tipping it upside down and banging it on the bench can also work. Blowing compressed air around can also loosen it by blowing it off the seat. You don't need to remove the seats if you are measuring spring installed height. Only if you need to make new spring bases. The attached drawing is what I ended up making. I may have also made a couple with even thicker base, maybe 1.4-1.5mm thick. I just measured a standard one and it has a .98mm thick base.

 

I've fitted the spring I modified and put the shock in the bike. With standard dogbones it sits low at the back. If I hold the bike at the same height as the original shock and dogbones, with the new shock I need 10mm shorter dogbones which I'm going to have to make. Once fitted I'll go through measuring shock travel versus wheel travel again to check for differences and also to record exactly what I end up with if further changes are required. The comparison with the original setup will be interesting as well.

 

Yeah, agreed. I doubt I would notice a small change. I have seen comment about different length dogbones making the suspension harsh which might be pointing to a rapidly rising rate. Originally it does rise but it's pretty linear as far as I measured which was up to about 90mm wheel travel

 

[QUOTE="ruckusman, post: 152728, member: 2491 "I got as far as contemplating grinding the buttons on the underside of the buckets."[/QUOTE]
I'd be very careful. The force to open the valve needs to be applied to the valve stem. Reducing things like this, or more particularly stem height above the collets, can result in the force being applied to the spring retainer or collets. The other thing is that the inside of the buckets has a radius. Reducing the button will move that radius closer to the edge of the spring retainer. New cam grind would be the safer option but then you run into lobe clearance problems and as I recall it's already snug.

 

Short dogbones made and fitted. The bike is setup and ready to remap the shock ratio

 

I just thought of something else. Going the cam grind route will have the buckets 2.5mm further out of their bores. Is there a danger of them being canted over as the cam lobe starts to push down?

 

The results may be indicating a bit of flex in my setup for measuring the ratio. I will get a chunk of steel and do it once more to see. the jig also bottomed out at 65 turns
I have made another set of measurements as per the attached image. The ratio was reasonably close apart from initially. That initial movement would normally be covered by rider sag. There's nothing really horrible about it from my perspective. I set the first values to "10" so the "Y" axis scale remained reasonable.
Ratio1 is with standard dogbones, Ratio2 is with 10mm shorter dogbones.

 

As I understand it, the effect will be the opposite of what you suggested. Wheel movement results in hardly any shock movement early on.
Anyway, I made the rig a whole lot stiffer, made sure to remove slack before starting measurements, and got a completely different answer.
I'm going to set it up with the standard shock and dogbones and do those measurements again.
The ratio is closer to 1:1 with the short dogbones so that would make the suspension harsher if nothing else changed, but I have a much softer spring and the shock is adjustable so hopefully will allow the damping to be tweeked for a decent ride.

Living and learning.

 

Right. I have put a bit of thought into this. The ratio I have been graphing is the overall ratio at each increment of wheel movement of 1.25mm. So the graph is of total wheel movement up to that point divided by total shock travel at the same point. Technically I should be plotting the instantaneous ratio, or in other words the amount the wheel moved from the last point divided by the amount the shock moved from the last point. I did have a look at this but it's quite noisy which is likely to be a limitation of my setup. It showed a trend and if I was a bit better at this I probably could have smoothed the line.
I did go ahead and record the movements using the standard shock and dogbone layout. The end result was a bit better start to the graph but generally the same. Ignoring the first 10 data points the graphs have a similar slope. Both have a slightly rising rate. The difference is that the short dogbones result in a lower ratio throughout, there's less leverage on the spring and damping.
Where I see this being a problem is if you simply put an R6 shock into a 250 and make 10mm shorter dogbones to retain ride height, the slightly heavier R6 spring in conjunction with the reduced ratio, could result in the bike being over-sprung. I haven't tried it yet but I'm near certain that the 250 would benefit from a lower spring rate. Definitely for solo riding, maybe!

 

Dogbones being lightened a bit. I might decide to take a bit more off. It'll be easy with the jig I made. Just bolt each one back on and run a cutter across.