1978 KZ650 Bike Build

I was just checking out that guy's site the other day. I might have to go ahead and order some things from him if you're satisfied. I have a registered business, so should have no problem with shipping. 

Yesterday I drove to a nearby city to visit a guy for a parts trade.  He needed some Z1 OEM turn signal lenses and I needed a Z1 lower triple tree.  We both belong to a local vintage chat site but have never met.  While I was at his place I toured his stable.   He has about 20 bikes, including Kawasaki, Honda and Yamaha.  All of them are in first class shape.  He's currently restoring a 73 Z1 and a 72 H2.  

Both triple trees use the same shaft, and it's the same length and bearing configuration.  But the Z1 has a different angle between the neck post and the fork tubes, so I cannot mix and match.  (I was hoping to use a Z1 upper with the KZ lower.)  I'll go with the Z1 components because I have most of the parts needed to complete the front end.

Z1 triple tree is the top one.  KZ650  is the bottom one.
 

Holes for the brake splitter are the same on both.
 

 

I don't mean to bust your bubble but I think you should consider finding a KZ650 upper triple to match.

In the photo you posted the Z1 triple has quite a bit more fork offset then the KZ650 - looks like 10mm more at least. This will really mess with the handling as a couple mm difference here can have a big effect on trail. Increasing the offset (all other thing remaining equal) will decrease trail and make steering much more twitchy. Adjustable offset triples for racing usually come with 3-5mm adjustment either way - small changes here have a outsized effect. The KZ650 has great stock geometry i wouldn't stray too far from it, unless your are doing the complete package.

Doc is correct, get the 650 top triple clamp, the 900 clamps have more offset {less trail}. It was quite common here in Australia to fit Z650 triples on the earlier z900's for racing, the 650 triples have better geometry. I've just put a 650 on the road and am surprised at just how well it handles, especially compared to the 900's, very neutral steering and very stable at speed...

DoctoRot post=845781The KZ650 has great stock geometry i wouldn't stray too far from it, unless your are doing the complete package.


What do you mean by "doing the complete package"?   

Comparing the stock 650 to the 900 for discussion purposes.

Rake 27 deg vs 26 deg
Trail 108 mm vs 90 mm.

I have both triple trees but wanted to use the Z1 because I have pretty much an entire front end that I could use.  If I go back to stock 650 I need to buy the front end...forks, gauges, gauge mount, brakes, etc.
 

wrote:

DoctoRot post=845781The KZ650 has great stock geometry i wouldn't stray too far from it, unless your are doing the complete package.


What do you mean by "doing the complete package"?   

Comparing the stock 650 to the 900 for discussion purposes.

Rake 27 deg vs 26 deg
Trail 108 mm vs 90 mm.

I have both triple trees but wanted to use the Z1 because I have pretty much an entire front end that I could use.  If I go back to stock 650 I need to buy the front end...forks, gauges, gauge mount, brakes, etc.

 

Complete package would be changing fork offset, wheel size, forks, rake, wheelbase, swingarm angle, shock angle, ride height, etc...it all adds up

I'm not very familiar with the Z1 stuff but IIRC they use 36mm forks so that will fit the KZ650 triples so you can use the forks, wheel, and brakes. The only things that wouldn't fit are the gauges. You could have the Z1 gauge mounts welded on the KZ triple. Or you could just try the z1 triples out since you already have the parts in hand. 90mm is very little trail by modern standards, probably why the z1s were prone to tank slappers. What is the fork offset on both the triples? you can easily do a little calculation to see if its going to the realm of unsafe.

First of all, I appreciate that reply.  It's quite helpful.  My original plan was to mate a Z1 upper triple to a KZ650 lower.  But that fell apart when I saw the different angles on the lowers.  

I will have to measure the angles on the triple trees.  Will do that later this morning.  I hadn't thought about welding the gauge frame onto the KZ triple...it's something I should look at.  The gauge frame mount is quite different from a KZ mount so definitely not a bolt on.  I have a Z1 gauge mount but I don't have a KZ650 one, although they are quite common on ebay.  I think the gauges will fit either gauge mount.

Z1 forks are a bit longer overall...about an inch or so.  I didn't see that as a big issue.  Upper tube diameter is the same on both models as you pointed out.

The KZ650 used an identical front wheel to a 77 KZ1000, which is the same size as a Z1 but with a different axle and brake rotor mount.  (4 bolt compared to 6 bolt on a Z1)  I have a complete 77 wheel and was planning to use it.  No front fender yet though.

Edited to add...the angle on the Z1 triple is 33.5 deg plus or minus 0.5 deg.  The angle on the KZ650 triple is 13.5 deg plus or minus 0.5 deg, so much flatter.  The KZ650 triple fork holes are approx 5 mm wider than the Z1 fork holes, which reduces the angle a bit more compared to having equally spaced forks.

The rake is defined by the headstock, so if I went with the Z1 triple I would have the same rake (27 deg) as a 650.  The trail is defined by the headstock AND the offset on the forks, so it would be a bit less due to the forks being closer to the frame.  I could probably work out the geometry to see how much less....will work on that this aft.  Gotta take the dogs for a walk.

Measuring the "angle" of the triple clamps is going about it the wrong way. To find the offset you measure the distance between the centre of the steering head hole and the centre of the clamp holes,  this value will be your offset. The longer forks won't matter, I just fitted GPZ750R1 forks to the 650 and they are about 25 to 30mm longer due to the GPZ having top mounted clip on style handlebars, just slide them through until you have the correct length. Changing the clamps won't change the rake, the frame determines the rake, the only way to change the rake, apart from cutting off the steering head and rewelding it at a different angle , is to raise or lower the front or rear of the bike. If you bolt on the Z1 clamps you will have the same rake and reduced trail due to the Z1's bigger offset. If the 650 clamps are wider than the Z1 parts you'll need the 650 spacers and axle to make it all fit. If it were me I would sell the Z1 parts and get the correct 650 parts. Trail works out the opposite to what you've said, less offset, forks closer to the steering head,  means MORE trail.That's why the 650 clamps {less offset} have more  trail, the bigger offset 900 clamps have less trail... 

Edit    I just ran the numbers through a rake and trail converter I use, using measurements from my 650 and using the Z1 triple clamp offset {60mm} and it came out at 4 inches of trail, or around 101mm, The extra degree of rake on the 650 helps keep the trail from being to small. I'd be quite happy with that as a trail number, Its close to what I aim for when building a modified bike. I have a gpz750 r1 that i'm in the process of modifying at the moment, 100mm is that target trail for the front end modifications i'm doing...

Thanks for that clarification 750R1.  

On the rake...I think we are agreeing.  The KZ650 frame determines the rake regardless of what triple tree I use, assuming of course that it fits.

On the trail, I see what you are saying.  (I had the triple tree backwards to normal when I was measuring.)  The imaginary spot on the ground from the rake angle is in front of the front axle.  So a bigger offset will result in less TRAIL. 

I measured the offset to calculate those angles.  The Z1 was 60 mm.  The 650 was 25 mm.

Bigger offset will result in less TRAIL, You're having fun with the terminology today..    Also, the 650 Triple clamp offset is 45mm, Just measured it...   Yes, Rake is the angle of the steering head on the frame, you can alter it with ride height alterations, for arguments sake, if you use longer rear shocks, you'll raise the rear of the bike, if you then measured the rake of the frame, even thought it hasn't physically changed on the frame, the angle , when compared to horizontal , in this instance, the ground, has changed, slightly reducing the angle of the steering head or rake .  Its quite tricky getting everything correct, there are specific formula's used at both ends of the bike and there's a lot involved.  I often wonder how badly some of the conversion/cafe racers i see REALLY handle....

Sorry!  I meant TRAIL but my head was thinking something else I guess.

I will have to re-measure my "650" triple tree but I'm pretty sure I measured it correctly.  It must be from another bike.  

OK, so I've done a little research and here is what I know.

First of all, I believe (not 100% certain) my frame is a 1978 B2.  I assumed it would be the same as a '77, which has a 27 deg rake.I confirmed my triple tree offset is 25 mm.  I did some Inspector Clouseau work to see if there are any markings on it.  The lower part has no markings.  (Neither does the Z1 lower, which I am pretty sure is a Z1 lower.)  The upper part has numbers on the underside that you can see in the photo below.

I checked the 1981 KZ650 service manual on this site and it shows three different 650 models with rake angles between 27 deg and 29 deg.  Corresponding trails are 108 mm with 27 deg, 113 mm with 27.5 deg and 115 mm with 29 deg.I bought my 650 triple tree on ebay.  It was advertised as an '81, and I assumed it would be the same as a '78.  It most likely isn't.  I'm guessing it came from the second or third models mentioned above.Just wondering what the trail would be with a 25 mm offset with a 27 deg rake?

Forgot the photo.....