1977 KZ1000 Restomod

wrote:

Do i see a 750/1100 Zephyr rolling chassis and fuel tank in the back ground ?!?!

 

Could be...

wrote:

Thanks guys, a lot of good info. Sounds like the best thing for me to do is wait till the rims arrive and then get it up on the wheels to see where I'm at. The C-profile that holds the shock mounts is pretty rusty so chopping them and moving the mounts onto the inside of the triangle is an option. This will be a single seater so moving the mounts forward won't be a problem. The mounts need to be moved out about 5-6mm anyway. Is there a range I should stick to for the shock angle?
If I still need to bring the front up a bit I can get the bottom of the top yoke milled out. Can probably get about 20mm doing that. After that it's time to get a new top yoke made... hoping to avoid that (but it would be my own fault for skipping a step in the planning). 

Here's some more info: 
- Shock length: 365mm +8/-2 (thought it was +2/-8... oh well)
- Offset is a lot smaller than stock. Around 40mm +/- (going off pictures, can't find my notes...).





 

The angle of the shock will dictate whether or not the shock has progressive, regressive, mixed or neutral characteristics. Most people want a progressive shock that gets stiffer through the travel. The stock shock mounts are close to a neutral rate because they approximately follow the radius of the swingarm. if you move the upper mount rearwards they become regressive, if you move this point forward these shocks become progressive; to a point. The moment when a shock goes from only a progressive rate to mixed rate (progressive at first then regressive) is found at full suspension compression. While the swingarm is at its uppermost point (full compression) draw a line through the axis of the shock (eyelet to eyelet). Next draw a line from the swingarm pivot to the upper eyelet. if the angle between these two lines exceeds 90 degrees then the shock is mixed or even fully regressive. if it is less it is still progressive.

Because your swingarm dimensions are unknown it is hard to determine what angle would be best. if the lower shock mount has moved 2" back it has created a more progressive shock. A general rule of thumb on these bikes is the shock should be close to the angle of the rear frame hoop. maybe slightly steeper. you can see this change from the KZ1000A/B to the KZ1000J

The other thing to consider is the shock was spec'ed for a certain valving based on geometric conditions. If you change these dimensions around it will make the shock behave differently, for better or worse. That is why its best to order custom shocks after all other changes have been made because the difference can be accounted for in length and valving.

 

Yoshimura and Moriwaki, and now AC Sanctuary us about 35.5 degree  {54.5 depending on which side you measure}  shock angle and a swingarm angle of between 10-14 degrees for correct anti squat on these old bikes, Doc's 11-13 degree swingarm angle fits perfectly in these measurements. Geometry measurements also depend on what size, diameter wheels are used, usually a slightly steeper steering head angle and less offset for  17 inch wheels , for example, AC Sanctuary use 23.5 to 24 degrees of rake and 40mm triple tree offset with 17 inch wheels, they use 24.5 to 25 degrees rake with 45mm offset for 18 inch wheels... These bikes also use a slightly longer swingarm around 490mm to 510 mm and a fork length of 790mm to  800mm...

@DoctoRot: Good info - thanks That will make it a bit easier to figure out where to put the mounts. The shocks are for the ZRX1100, so I'll use that geometry as a template. EDIT: I'll get some numbers for the swingarm tomorrow.

@750 R1: Thanks for the numbers - you posted at the same time as I did

Is the frame going to get some more bracing?

wrote:

Is the frame going to get some more bracing?

Yeah, I have a bracing kit on the shelf. Need to figure out the rest of the changes so I can get it all welded in one go.

There are also rake and trail calculators online , they are handy to use when you have specific measurements to work with for getting trail measurements, ideally you want trail around 100mm/4 inches, a few mm either way won't hurt but to little trail and it will be very nervous and prone to head shakes, and too much trail and it will be harder to turn in, great in a straight line though...  

www.rbracing-rsr.com/advchoppercalc.html

Took some measurments today.
The GSX-R swingarm has the same spacing from the pivot bolt to the lower shock mounts as the stock swingarm. The axle is 30mm further down and 55mm further back with respect to the bottom shock mount. The new shocks are 20mm longer.
I'll wait until the rims get here but the plan at the moment is to move the top shock mounts to the same location as the Z1000J. After that I'll see if I need to drop the top yoke down or not.

Put a few things together today so I can see how the riding position is when the footrests get here. Would be interested in opinions on whether I should go with scantily clad or fully naked:

 

 

 

 

 

I'll wait until the rims get here but the plan at the moment is to move the top shock mounts to the same location as the Z1000J. After that I'll see if I need to drop the top yoke down or not.

These shock brackets give you the top shock mounts location you need...

 
 
 

Thanks, but it looks like they would just adjust the angle of the shocks without actually reducing swingarm angle. I'll have another look when the wheels are on.

Calum, just remember that you have no weight on the suspension yet, they should drop a bit in height once loaded up.. 365mm is longer than stock but you have a longer arm , It would be easier to move the rear mount back on the swingarm than move the top shock mounts, we are making up a pretty comprehensive jig to drill the holes for new top frame mounts on my frame, Its a lot of work to get right.  Have you actually measured the swingarm angle in its operating position ? Again, I'd do that with engine weight and wheels on, maybe weigh the engine and stick something with near the same weight in the frame, its better than bolting the engine just to check...  Just thinking out aloud here to try and help with some idea's...

You don't need a complicated jig to relocate the upper shock mounts but they are nice if you do this frequently. I made this crude jig to locate the upper shock mounts when i relocated them on my 750G. Triangulate the upper mount off the pivot and the lower shock mount. When I machined the mounts I had a 1/4" pilot hole pass all the way through so I could pass through some 1/4" rod side-to-side to make sure the mounts were on the same axis. Their location is just as exact as the stock mounts, if not more so.