Gsxr 1000 k1-4 swingarm into a slingshot frame

[KennyKak]

Has anyone here ever put a k1-4 gsxr 1000 swing arm into a 750 slingshot frame. I know it's been done but not sure what linkage, dogbones and shock to use. I have a complete K4 rear end and unless I'm being really numb here (there is a strong possibility of that) it doesn't look like it will all go together.

Edited August 6, 2023 by KennyKak

[Upshotknothole]

I've got a K4 1K swing arm in my slingshot 7/11. The top shock mount is the biggest issue, you'll need to move it up and back to get the linkage working how it's supposed to. I'll see if I can find some photos of how mine is set up. People have also done busa swing arms by lowering the bottom linkage mount.

[Upshotknothole]

The welds aren’t pretty, but the geometry works really well. I believe the Penske shock is for a K4 1K as well, but not positive. I think it uses the K4 linkage as well, but can’t remember and I’m out of town at the moment.

 

 

[KennyKak]

I've bought a cbr 600rr shock as it's a bit shorter so might be able to fabricate a shock mount that uses the original top shock mounting points. Fingers crossed

[Joseph]

2 hours ago, KennyKak said:

I've bought a cbr 600rr shock as it's a bit shorter so might be able to fabricate a shock mount that uses the original top shock mounting points. Fingers crossed

It indeed makes more sense to make a replacement steel mount that you can bolt to the original fixing points than to weld stuff onto the frame

[KennyKak]

It's not a million miles out but the shock may come down abit as I've just drilled the old dog bone and may need to be a little longer. I've got a K1 750 I can check against once it stops bloody raining. 

[Upshotknothole]

I checked on mine and it is using the stock K4 dog bones. 

[KennyKak]

I've tried both the slingshot and K4 linkages. The slingshot sits the shock lower making the top shock mounts lower and easier to make. But I know the dog bones mount differently to the slingshot swing arm (K4 underneath and slingshot over the swingarm). Im just gonna stick with the K4 linkage with 140mm dogbones and keep everything as close as it should be for the K4 set up. Don't fuck with what already works and all that

[Joseph]

I'm building the plans for a laser cut/welded bolt on shock mount to raise and push back the shock, i'll let you know how it goes

[davecara]

Have a nose at my Slingshot thread, a lot of work went into the knuckle and top shock mount on that to make it work right. Granted, mines for a K8 but the principles will be broadly similar

[Upshotknothole]

I can try and go out to my garage later and take some more photos of how mine is set up. I'll also measure my shock, as it's a Penske and I've always assumed it was for a K4, but who knows.

[KennyKak]

14 hours ago, Upshotknothole said:

14 hours ago, Upshotknothole said:

I can try and go out to my garage later and take some more photos of how mine is set up. I'll also measure my shock, as it's a Penske and I've always assumed it was for a K4, but who knows.

The k4 shock is bigger so that looks about right. I've just used the cbr600rr to save a little space

[Digs]

I fitted a k3 arm to my 7/11 build, but I designed the linkage from scratch around 3d scans and simple BREP models of the frame and components. In the end I used a Showa BFRC shock from a 2018 gsxr 1000r as I had some fouling issues with my original bmw shock and then other issues with the Kawasaki shock... But, there are definitely other ways to do it and achieve similar results.

If you want minimal modifications the big thing you need to do - to make your life easy - is replicate the lower shock mounting position. The original lower mount location will make your life a nightmare if you try and use it.  Also - as mentioned above by @Upshotknothole- the top shock mount needs to come out a fair way. You can get ballpark for this with a decent side elevation photo of the bike. 

Definitely check out @davecara’s thread too, he’s put a lot of good info up and done alot of the hard work.

Food for thought:

You need to work out the motion ratio you’re aiming for. 

You need to make sure the mounts you make can take the loads applied (they’re big) 

what’s your static swingarm angle? 

How much sag will you have? 

Does the shock you are planning on using have the correct spring rate? 

Are you getting the shock revalved? 

The k3 swingarm has a 28mm axle, what wheel are you using? 

it’s also a good idea to test the range of motion without the shock spring, helps you spot potential issues before finding out about them while riding. 
 

light reading: 

http://www.promecha.com.au/leverage_linkages.htm

https://www.datamc.org/data-acquisition/suspension-data-analysis/anti-squat-geometry/

technical reading:

https://link.springer.com/article/10.1007/s11081-019-09475-w

Couple of useful diagrams:

books that might help: 

https://www.classicbikehub.uk/News/article/motorcycle-modification-keeping-your-project-safe

https://books.google.co.uk/books/about/Motorcycle_Handling_and_Chassis_Design.html?id=84hF-qoR5I8C&printsec=frontcover&source=kp_read_button&hl=en&newbks=1&newbks_redir=0&gboemv=1&ovdme=1&redir_esc=y#v=onepage&q&f=false
 

 

 

 

 

 

 

 

 

Edited August 23, 2023 by Digs

[Ians]

Hi there I’m trying to do this with my slingshot frame but having issues with lining sprockets up hopefully someone can help

thanks ian

[Ians]

Just looking again it’s got a 7” rim not 100% sure if this is a k4 rim and could I get a smaller wheel to fit the k4 swing arm 

[Digs]

So I’ve put a 6” rim in two slingshots, they’re not k4 rims but zzr1400. I needed to machine down the rear sprocket carrier to make it work.
 

You need to find out the distance from the wheel centre to the inside face of the sprocket. For a standard slingy wheel it will be 100mm, ideally you should aim for 105 with 6” rim to not run too close to the tyre. Also bare in mind you may want to run a 525 or 520 chain to help with the clearance if you run a larger offset. 

Picture here shows how much I had to remove. 

 

 

[Upshotknothole]

I run a K4 6" wheel in my K4 swing arm no problem. No way in hell you're gonna get a 7" rim to work without a jack shaft.

[KennyKak]

With the complete k4 rear in place I can't get the wheels to line up without major work and still risk the chain fouling the frame. I do have a spare 750 wheel to try wich looks like it could fit and all line up. There isn't alot of space on the sprocket carrier to machine off so any machining would have to be done to the hub. When the weathers a little nicer I'm going to put the engine in the frame wich should show me I anythings twisted as no one else has had as many issues doing this conversation 

Edited April 4 by KennyKak

[Jonny]

On 8/20/2023 at 1:37 AM, Digs said:

I fitted a k3 arm to my 7/11 build, but I designed the linkage from scratch around 3d scans and simple BREP models of the frame and components. In the end I used a Showa BFRC shock from a 2018 gsxr 1000r as I had some fouling issues with my original bmw shock and then other issues with the Kawasaki shock... But, there are definitely other ways to do it and achieve similar results.

If you want minimal modifications the big thing you need to do - to make your life easy - is replicate the lower shock mounting position. The original lower mount location will make your life a nightmare if you try and use it.  Also - as mentioned above by @Upshotknothole- the top shock mount needs to come out a fair way. You can get ballpark for this with a decent side elevation photo of the bike. 

Definitely check out @davecara’s thread too, he’s put a lot of good info up and done alot of the hard work.

Food for thought:

You need to work out the motion ratio you’re aiming for. 

You need to make sure the mounts you make can take the loads applied (they’re big) 

what’s your static swingarm angle? 

How much sag will you have? 

Does the shock you are planning on using have the correct spring rate? 

Are you getting the shock revalved? 

The k3 swingarm has a 28mm axle, what wheel are you using? 

it’s also a good idea to test the range of motion without the shock spring, helps you spot potential issues before finding out about them while riding. 
 

light reading: 

http://www.promecha.com.au/leverage_linkages.htm

https://www.datamc.org/data-acquisition/suspension-data-analysis/anti-squat-geometry/

technical reading:

https://link.springer.com/article/10.1007/s11081-019-09475-w

Couple of useful diagrams:

books that might help: 

https://www.classicbikehub.uk/News/article/motorcycle-modification-keeping-your-project-safe

https://books.google.co.uk/books/about/Motorcycle_Handling_and_Chassis_Design.html?id=84hF-qoR5I8C&printsec=frontcover&source=kp_read_button&hl=en&newbks=1&newbks_redir=0&gboemv=1&ovdme=1&redir_esc=y#v=onepage&q&f=false
 

 

 

 

 

 

 

 

 

Just to add to the reading list, I can recommend Motorcycle Tuning: Chassis by John Robinson. It's like my Bible.

https://www.amazon.co.uk/Motorcycle-Tuning-Chassis-John-Robinson/dp/0434917249

 

[Digs]

On 4/2/2024 at 8:27 PM, Upshotknothole said:

I run a K4 6" wheel in my K4 swing arm no problem. No way in hell you're gonna get a 7" rim to work without a jack shaft.

I’m assuming it’s a typo and he meant 6”

[Digs]

12 hours ago, KennyKak said:

With the complete k4 rear in place I can't get the wheels to line up without major work and still risk the chain fouling the frame. I do have a spare 750 wheel to try wich looks like it could fit and all line up. There isn't alot of space on the sprocket carrier to machine off so any machining would have to be done to the hub. When the weathers a little nicer I'm going to put the engine in the frame wich should show me I anythings twisted as no one else has had as many issues doing this conversation 

It’s all very tight fitting wider rims or larger offset carriers/wheels in a slingshot frame. I had to do a lot of modifications to get my 6” rim to work and some single shear calculations to make sure I still had enough material left.