KZ 650 project

undefined undefined Hey guys, I'm new to the forum, so I'm not sure if the questions I have, have been covered already. Anyhow, starting a 1979 KZ650 project. Going to be doing a spin on the AC Sanctuary bikes. Ultra classic up top, ultra modern suspension, wheels, and brakes on bottom. Very similar to Dnell's kz650 fighter project. Zx6r front end, swing arm, and wheels.
Pictures to come!

Question, anyone know the stock rear shock length for these bikes?? I making this bike a runner, shooting for well above par in the turning/handling category. So I need to nail the rear shock and suspension work on this sucker. Moving top shock mounts down and forward like the AC Sanc. bikes. Shock ideas? Length?

Ps. I am no stranger to fabrication. I am a tig welder by trade and hobby machinist. Lay it on me!

Welcome Post some pics of your bike .and another showing what your plans are . We love pics .

pics are good. IIRC stock kz650 shocks are 13-13.25" Do you have any experience modifying a frame? Front and rear suspension are best considered together as raising/lowering the rear affects the front geometry and vice versa. I would determine how much custom work you want to bite off and select your suspension upgrades depending on that.

Thanks guys! Yes, I've built quite a few rigid frames for early Harley projects that I've done in the past, and have modified a bunch as well. I will be doing some structure bracing on the frame as I would like to do some heavy motor mods this upcoming winter. As for now, the motor runs well with good synced carbs and a kerker.

For this build I definitely want to move the "top shock" mounts down on the frame rails too increase shock angle a bit (as the AC sanctuary guys do). Anyone have shock preferences? I've heard good reviews on the TEC shocks. Best for the money?
Which leads to another question... Anyone know the shock angle the AC guys or any other "race handling" builders are using?

Fitting;
2006 complete ZX6r front end. (Brakes, suspension, wheel)
2006 ZX6r rear wheel, with 2004 ZX6r swing-arm.

Thanks guys! Yep, I have built and modified quite a few frames.

Fitting this bike with;
Complete 2006 zx6r Front end
2006 Zx6r wheels and brakes
2004 ZX6r swinger.

First order of biz on this build will be establishing the relationship between the zx front end and the rear shocks and swing arm. Going to move the "top shock mounts" down on the rails (as the AC guys do), and brace frame accordingly. Which leads to some questions...

Anyone have any shock preference? I've heard some decent reviews on the TEC shocks. There KZ1000 shock at 13.5 length seem like they may be a good bang for the buck. May need rebuilt for max performance. But sure do look good at 200 bucks....

Anyone know what shock angle is king for handling? What angles do the AC guys, or any other race/handling specific builders use?

1979 KZ650, good synced carbs and a kerker. Runs well! Will be doing some gpz turboing action in the winter so stock frame will need some bracing... But for now just focusing on getting the geometry and ergonomics on point.

moving the top shock mount is done to make the shock more progressive, It will be dictated by the length of your shock and desired swing-arm angle. Most guys move it 1-2" down the lower sub-frame rail. However the ZX6 swingarm does not have dual shock mounts so I assume you will be fabricating those. depending on how you do that I would expect that to add anywhere form 0-2" to the rear ride height before you have changed the shocks at all. In that case I would pay more attention to the swing arm angle, 10-13 degrees is considered the sweet spot.

things to note:
ZX6 forks are substantially shorter than stock, combined with moving from a 19" to a 17" front wheel a lot of ride height is lost.
The rake will change dramatically with your proposed setup, this combined with stiffer forks puts a lot more stress on the head-stock
ZX6 triple trees have significantly less fork offset.
Watch your rake and trail, I would use a calculator to run the numbers before committing to anything.
You will probably need an offset sprocket and/or notch the frame for the chain.

My order of operations would be:
figure out lower shock mount
dry fit swingarm and wheels front and back,
set rear ride height with a steel bar
measure rake and trail with stock forks and zx6 wheel - slide forks up triple tree to simulate ZX6 fork length
determine what rake and trail zx6 front end will leave me with
make adjustments to front geometry by changing rear ride height, or find different front end/ triple clamps if warranted
move upper shock mount
order shocks


Whats the application of the bike once complete?

Thanks! Good info. Yes i will be fitting lower shock mounts myself. Whats the best way to determine where the shock mounts should go on the swinger...? If your trying to do that first (without angle, and top shock mounts figured out?)
Would you recommend any other swingarm that might be a better fit over the zx6 swingarm?

On a dual shock swing-arm you want them as close to the axle as possible because this puts less load on the swing-arm which lets you build it lighter, but since the zx6 swing arm is a mono shock its built to with stand those forces and it doesn't really matter where you place them. You are getting the weight of a mono shock arm without the weight reduction of a single shock. not ideal. If you go this route watch the width. the KZ shock mounts will be narrower side to side.

Personally I would ditch the ZX6 swing-arm and go for a ZRX1100/1200 swing-arm. Lots of guys have done that swap, its already dual shock so that will save you trouble there. Alternatively Zephyr 750 swing arm if you don't want a braced arm look. Or GS110E for a period look but I'm not sure a 17" wheel will fit in there.

Whats the application? Show? Go? cruising?

Aww I see! The zrx and Xjr swingers were a few other options I had in mind, but I found that zx6 swinger in good shape for about 40 bucks on the ol eBay, so I jumped on it. Glad it was only 40 haha as I probably won't use it now.

I'm pretty meticulous when it comes to looks and quality, so the bike will definitely "show" but I'm building it to go! Of course it is only a stock motor, but I will be doing some heavy engine mods come winter time.

Any ideas on rear shocks? I've come across a nice set of ZRX shocks that are 14"... I've read on hear that they will obviously be sprung to heavy for a little kz650... And a bit long...

Are they adjustable enough to make work?

Thank!

Brady

Whats your budget for shocks? The problem with shocks that long in conjunction with your very short proposed front end setup is likely the rake, and probably the trail, will be extreme. Its hard to say what shock length will be appropriate until you settle on your other suspension components. shocks are easy to change, everything else.... not so much.

If you look at the Sanctuary builds you will notice how tall their bikes are, this really helps with ground clearance in turns. Additionally a higher center of gravity requires less lean angle to corner, while also allowing a faster turn in. Are you more interested in high speed stability or cornering performance? If you are interested I highly recommend Tony Foale's book - Motorcycle Handling and Chassis Design: The Art and Science.

DoctoRot wrote: I would pay more attention to the swing arm angle, 10-13 degrees is considered the sweet spot.

Can you explain this a bit more? Degrees between what? And under what conditions?