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Author Topic: Widen tubular frame at swingarm pivot  (Read 1072 times)

Offline G-Tron

  • Posts: 9
Widen tubular frame at swingarm pivot
« on: Apr 30, 2017, 17:25:09 »
Hey guys.

So I'm planning a wider single sided swingarm in my shaft drive KZ750.  It's about 45mm wider than the stock swingarm.  Removing that much material from the frame will leave it extremely weak.

It's shaft driven so I can't narrow the swingarm as you'd have to take all the material off one side only (the other side locates the driveshaft to the motor) which will offcourse leave the rear wheel 45mm to the one side.

I can't find any examples on the net of how people have done this on an 80's tubular frame.  The singarm pivot is right where 3 tubes come together.

My one idea is to do the following:

-Machine down the outside of the frame so it's flat at the pivot point exposing the 3 connecting frame tubes. (It will still be held together by the inside "flange")
-Weld on a new (say 12mm) steel plates of the appropriate shape to the outside of the frame "overlayed" onto the 3 tube joint giving it some more width and reinforcing.
-Machine a new pivot hole into the plates, about 25-30mm larger in diameter than the original swingarm pivot holes.
-Now, with the material added to the outside, go ahead and machine the inside of the frame to gain the 45mm extra width required. Weld up the inner sides of the 3 frame tubes for strength.
-Machine some new metal round tube bushings with say 10mm wall thickness and weld them into the holes mentioned above. Both inside and outside.
-Finally thread these bushings to accept the swingarm pivot bolts.
-Weld in some additional bracing and gussets to the frame as required.


This picture illustrates the setup I'm working with.

http://www.partzilla.com/parts/search/Kawasaki/Motorcycle/1983/KZ750-N2+Spectre/FRAME/parts.html

Let me know if you think my approach is workable and safe or if there is a better way?
« Last Edit: Apr 30, 2017, 17:29:02 by G-Tron »

Offline G-Tron

  • Posts: 9
Re: Widen tubular frame at swingarm pivot
« Reply #1 on: May 01, 2017, 03:04:19 »
some pics to help with what I'm referring to






Offline G-Tron

  • Posts: 9
Re: Widen tubular frame at swingarm pivot
« Reply #2 on: May 01, 2017, 03:13:05 »




Offline G-Tron

  • Posts: 9
Re: Widen tubular frame at swingarm pivot
« Reply #3 on: May 01, 2017, 03:28:18 »
Another option is to cut out the entire pivot point, then laser cut an appropriate steel profile with sections that protrude into two legs of the frame prior to welding.  Once welded it can be threaded for the pivot bolts, or it can eb cut to accept a seperate round bush with thick walls can be threaded for the pivot bolts.


Offline doc_rot

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Re: Widen tubular frame at swingarm pivot
« Reply #4 on: May 01, 2017, 06:59:40 »
What about rebuilding or replacing the motor with a chain final drive? I know a few guys have converted their kz1000's to chain drive. IIRC all it takes is swapping output shafts, i would suspect it is doable on the kz750 as well, then you would have a ton of swingarm options. Unless you have access to a frame jig i would avoid cutting out the pivot mounts.
« Last Edit: May 01, 2017, 07:02:10 by doc_rot »
---------------------------------
'78 KZ1000  Project

'80 KZ750 Twin Project

Offline hillsy

  • Posts: 4104
Re: Widen tubular frame at swingarm pivot
« Reply #5 on: May 01, 2017, 07:00:11 »
Not sure what swing arm you are trying to fit, but your priority is to make sure the drive shaft is correctly positioned first up, then wheel position, etc.


It may be the case that your donor swing arm simply won't work.

Offline G-Tron

  • Posts: 9
Re: Widen tubular frame at swingarm pivot
« Reply #6 on: May 01, 2017, 09:45:40 »
What about rebuilding or replacing the motor with a chain final drive? I know a few guys have converted their kz1000's to chain drive. IIRC all it takes is swapping output shafts, i would suspect it is doable on the kz750 as well, then you would have a ton of swingarm options. Unless you have access to a frame jig i would avoid cutting out the pivot mounts.

I did consider this option but I really want to keep it shaft driven.  That and I've already collected all the new swingarm bits I plan to use...


Not sure what swing arm you are trying to fit, but your priority is to make sure the drive shaft is correctly positioned first up, then wheel position, etc.


It may be the case that your donor swing arm simply won't work.

I've taken a liking to the goldwing single sided swingarm.  It's not the easiest route but I want this for the bike.  The swingarm will be used upside down and the driveshaft location looks like it will be in the correct place yes. The driveshaft tunnel is bigger than the kz750 so should allow for some spacing to one side if required. There is a u-joint right at the entry which allows some angle if required.  I'm also not against offsetting the engine 1-2cm to the left if necessary.




Offline J-Rod10

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Re: Widen tubular frame at swingarm pivot
« Reply #7 on: May 01, 2017, 10:16:58 »
As mentioned, if you don't have a frame jig, I wouldn't cut the pivot. It needs to be perfectly straight.

Offline G-Tron

  • Posts: 9
Re: Widen tubular frame at swingarm pivot
« Reply #8 on: May 01, 2017, 10:59:23 »
As mentioned, if you don't have a frame jig, I wouldn't cut the pivot. It needs to be perfectly straight.

Noted thanks.  Looks like it will be down to welding in the added metal supports and then machining the insides for clearance.  I have access to a good welder and a machine shop. Unfortunately they aren't the same people.


ps:  I see you're from slipstream cycles.  I've had my eye on your universal rearsets for a few days now.  Planning to pull the trigger on them shortly.  Any dotheton special pricing? :)

Offline J-Rod10

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Re: Widen tubular frame at swingarm pivot
« Reply #9 on: May 01, 2017, 13:24:18 »
Noted thanks.  Looks like it will be down to welding in the added metal supports and then machining the insides for clearance.  I have access to a good welder and a machine shop. Unfortunately they aren't the same people.


ps:  I see you're from slipstream cycles.  I've had my eye on your universal rearsets for a few days now.  Planning to pull the trigger on them shortly.  Any dotheton special pricing? :)
Appreciate the interest. We're currently running them on sale at $100.