Thank you for the link to the Sonic Spring site. I have contacted Sonic Springs asking them about the 81 GPz550 application because the catalog lists 82-83 KZ550. Probably the same fork spring. No comment about spacers either.
Side note: Progressive Suspension fork spring 11-1111 fits 81-83 GPz550 models.
Sonic includes a section of PVC pipe with their springs. Cut to length for your application and desired amount of sag. When I rebuilt my 750 forks I cut the spacers so they were flush with the top of the tubes at full extension, then with the cap there was a small amount of preload.
As Texas points out, the 81 gpz550 uses different springs than the 82/83 gpz550. 82/83 were much smaller in diameter. The fork tubes were smaller diameter and the wall thickness was thicker so that left less space for the springs so they were a lot skinnier. But many companies assume they were the same so their kits come with incompatible springs depending on what you ordered.
I just cut down the factory spring which increases the rate nicely and use a longer spacer of PVC to make up the difference. You have to dress the cut end properly which is easy using a propane torch. But it works great, is very affordable, and puts the factory springs to use. I had many laying around from previous spring swaps.
Somewhere I had a post showing what to do, but I haven't been able to find the last time I checked.
I bought these same progressive springs for the same bike off Ebay last year, they were $88 minus shipping.
I tried to order straight rate springs from Race Tech but they had no idea what length the springs were suppose to be !? Like you said they only listed '82 and up... got tired of waiting for somebody to work on it for me (they never returned the second email) so just ordered the ones on Ebay
No issue with installation and the ride is much better, no more brake diving (well not as much) The OG springs are extremely soft, or maybe I am too fat
Here is the Sonic Springs reply which was very quick.
Hey Steve, thanks for contacting us.The description shows 82-83, but those are also the correct parts for your 1981 GPz550 as well.sonicsprings.com/catalog/index.php?cPath=29_302Please let me know if there is anything else we can do to help.
I am not sure what fork springs are installed in my GPz550 but it dives too much. I initially thought the fork springs were aftermarket because the spacers were thick steel and rusted too. I replaced the steel spacers with PVC spacers but decided to upgrade.
Thank everyone for the replies and insight. Dennis Kirk is selling the 11-1111 for $97 shipped vs Sonic $105. Either one is better than current state.
The parts fishe doesn't lie. I'd trust that over what Sonic says. That said, I like Sonic and would get their springs over Progressive. The founder of Sonic is a member of The GS Resources and a real standup guy. You can PM him there with any questions. He's always available to help.
Went through the same circus with Works Performance. They kept sending me the springs for 82-83. I finally got fed up and ordered springs for a 750 based on the dimensions they listed. Lo-and behold they worked great. I have 4 of these bikes plus several used forks for the 81, and they are all the same...36MM OD forks. I don't know where these companies got the idea that 82-83 fork springs were the same as 81. Maybe because the 82-83 Kz550 A (standard) models used the same spring, or at least the same diameter spring, as the 81 gpz?
I decided to buy the Progressive Suspension fork springs instead because I have had such a favorable experience with PS fork springs in my GS1000E. Although I have not owned a lot of GPz550's, I have bought extra GPz parts when the opportunity arose. A couple of years back I purchased a set of clean 81 GPz550 fork legs on Ebay. I did want share a couple of photos of the fork spring installation which are interesting.
Photos show 1. Mystery fork springs ( straight wound) removed this last Sunday. 2. PS 11-1111 which were about the same length & 3. Fork springs from the above Ebay purchase. I took some measurements which are shown in Pic # 2.
Installation was easier with a center stand. PS recommended 1.25" spacer in addition to existing spacer. A little confusing because the 81 GPz550 has no fork spring spacer. I went with the existing 1.30" spacer. Hopefully some of this info. is informative.