KZR's Bikes of the Month for 2024

KZ750H forks topping out

More
31 Aug 2020 10:30 #834078 by Mikaw
Replied by Mikaw on topic 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.

1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.

Please Log in or Create an account to join the conversation.

More
31 Aug 2020 10:38 #834082 by calum
Replied by calum on topic KZ750H forks topping out

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.
The following user(s) said Thank You: Mikaw

Please Log in or Create an account to join the conversation.

More
31 Aug 2020 10:44 #834083 by martin_csr
Replied by martin_csr on topic KZ750H forks topping out
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.
The following user(s) said Thank You: calum

Please Log in or Create an account to join the conversation.

More
31 Aug 2020 13:00 #834091 by calum
Replied by calum on topic KZ750H forks topping out

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.

Please Log in or Create an account to join the conversation.

More
31 Aug 2020 13:38 #834093 by martin_csr
Replied by martin_csr on topic KZ750H forks topping out
I have no idea how much preload your new springs should have, if any.

Please Log in or Create an account to join the conversation.

More
31 Aug 2020 14:55 #834095 by calum
Replied by calum on topic KZ750H forks topping out

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.

Please Log in or Create an account to join the conversation.

More
31 Aug 2020 15:31 #834096 by Irish Yobbo
Replied by Irish Yobbo on topic KZ750H forks topping out

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.

1981 KZ750 LTD
The following user(s) said Thank You: Nessism, 750 R1, calum

Please Log in or Create an account to join the conversation.

More
31 Aug 2020 16:06 #834101 by Nessism
Replied by Nessism on topic KZ750H forks topping out
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.
The following user(s) said Thank You: calum

Please Log in or Create an account to join the conversation.

More
31 Aug 2020 16:51 #834107 by 750 R1
Replied by 750 R1 on topic KZ750H forks topping out
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....
The following user(s) said Thank You: calum

Please Log in or Create an account to join the conversation.

More
31 Aug 2020 18:16 - 31 Aug 2020 18:20 #834111 by Mikaw
Replied by Mikaw on topic KZ750H forks topping out
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

1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.
Last edit: 31 Aug 2020 18:20 by Mikaw. Reason: content, spelling

Please Log in or Create an account to join the conversation.

More
01 Sep 2020 01:37 - 01 Sep 2020 01:39 #834130 by calum
Replied by calum on topic KZ750H forks topping out

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.
Last edit: 01 Sep 2020 01:39 by calum.

Please Log in or Create an account to join the conversation.

More
02 Sep 2020 05:31 #834201 by calum
Replied by calum on topic KZ750H forks topping out
Trying to avoid taking the top cap off the forks twice: does anyone have the dimensions of the stock spacers?

Please Log in or Create an account to join the conversation.

Powered by Kunena Forum

If you like KZR Please consider making a donation. Thank you.

KZRider is free, but not without cost.

Please consider chipping in a few bucks to help cover the cost of running the KZR servers.