KZ750H forks topping out

I think you could cut the spring. It would correct preload but not change the spring rate. That is as long as they are not progressive springs.

Mikaw wrote: I think you could cut the spring. It would correct preload but not change the spring rate. That is as long as they are not progressive springs.

They are progressive, but even so it is still easier for me to make up a few different length spacers and see what works best.

There should be some preload with the stock springs. You could use an old spring & spacer to figure out how much the spacer would jut out above the tube. assuming the old spring is within spec. or use the spec length + the spacer.

martin_csr wrote: There should be some preload with the stock springs. You could use an old spring & spacer to figure out how much the spacer would jut out above the tube. assuming the old spring is within spec. or use the spec length + the spacer.

Thanks Martin. I'll pull the springs and see how much longer they are than stock, then adjust the spacer length accordingly.

I have no idea how much preload your new springs should have, if any.

martin_csr wrote: I have no idea how much preload your new springs should have, if any.

I'll make up a few different length spacers and play around with the oil weight until I get it dialed in.

Mikaw wrote: I think you could cut the spring. It would correct preload but not change the spring rate. That is as long as they are not progressive springs.

Just for future reference, but cutting the spring will change the spring rate - it will actually increase it.

Consider a spring that compresses 1mm with 1N of force, a rate of 1N/mm. Now cut that spring in half. You now have two springs, and if you stack them both on top of each other with 1N on top of that, they will still have a total deflection of 1mm, but each shorter spring will be half of that - 0.5mm. So the new spring rate will be 1N/0.5mm = 2N/mm.

Halving the spring length will double the rate.

PVC pipe works good for spacers. Try flush with the top of the fork tube as a starter. That means there will be about 1" of preload with the caps installed.

As ED says above, use some PVC pipe to make your spacers up, its quick , cheap and easy, then, if you prefer a more robust spacer, either shorten your steel spacer to suit {using your modified PVC spacer as a guide}, or use what ever material you're happy with... I only used aluminium pipe for my spacers because my OCD said it was stronger, I have seen PVC spacers used with success, I've even used a couple of washers before to add preload and it worked well....

Irish Yobbo, thank you. I learned something new. I used to work in the garage door industry and would deal with torsion springs daily. All torsion springs are rated by IPPT. inch pounds per turn. If you had a wire size of .283 that was 40in long and you needed to replace it but only have a .250 wire you could install the .250 wire and make it 33 inches and be close to the .283X40 IPPT by making it shorter. So a rule of thumb was a smaller wire X shorter length or larger wire X longer length. With the understanding the shorter spring would have a shorter cycle life because it was stressed more to get the same IPPT of the larger wire. So it was always better to go up in wire size and make it longer to get an equivalent spring with a better cycle life, if you had room for the longer spring. Then you could really change things with the I.D. of the spring. So I do understand springs to a point but I had no idea there would be an similar effect of cutting a coil spring.

I read up and your correct, it will change the rate but not the load.

Thank You

Irish Yobbo wrote: Just for future reference, but cutting the spring will change the spring rate - it will actually increase it.

Consider a spring that compresses 1mm with 1N of force, a rate of 1N/mm. Now cut that spring in half. You now have two springs, and if you stack them both on top of each other with 1N on top of that, they will still have a total deflection of 1mm, but each shorter spring will be half of that - 0.5mm. So the new spring rate will be 1N/0.5mm = 2N/mm.

Halving the spring length will double the rate.

Thanks for the example - I'll let my kids cut a load of springs in half next time I have to teach Hooke's law.

Trying to avoid taking the top cap off the forks twice: does anyone have the dimensions of the stock spacers?