Jett's 750 Kawa chopper...

[Prof]

Jett is new to motorcycling, but sold on choppers. Over a period of time we have talked about build possibilities and donor bikes. He developed a pretty clear oidea of what he wanted and finally got the opportunity to purchase a 1982 KZ750 twin in very good nick. A few weeks ago, he flew over to Victoria, picked it up and rode it to Willunga...


Once registration was transferred to SA, it was time to start work... ie one full on strip job...


Stock rake is 27-28 degrees. We'll be taking it out to 40 degrees, rigid rear end, raised steering head and girder front end...


Dropping off the rear shocks gave Jett a bit of an idea of how much the seating can be lowered. Rake now 33 degrees...


Clamped to truing frame and more stripping. Swing arm and rear wheel is retained to allow lining up on centre line...


Rear wheel is centred...


Steering head is centred...


Nest step is to locate new rear axle position. Bike is to e rigid and is a fairly narrow bike, so 4" ground clearance will be just the ticket. Here measuring below lowest point. Engine sump sits half inch below bottom of frame rails...


Rear wheel is chocked up as if sitting on ground. Wheel is to be moved 3.5" to the rear. Axle jig has been set at this distance and spirit level used to get axle to correct height...


Now to remove unwanted frame (most of it!). Cut position on down tubes is measured 40mm up from right side engine mounts which have a bolt running through the tube. This distance will allow fitting of slugs to be made to join new down tube pieces. Jet is new to fabrication so he cuts above the marked lines and will trim them back later. Cut lines are marked with a small pipe cutter to keep cuts perpendicular to the tube...


Had to include this speccy shot...


"Oh my God! What have we done!!" All but a small part of the lower cradle is retained....


Here 'tis... been 'chopped' now to turn it into a classic chopper that will be great to ride and a real head turner...


A few guys seeing the bike in its original state bemoaned the fact that is was to be chopped up. It was such a pretty bike. Well, that's what Michelangelo thought when he looked at that piece of marble that became his masterpiece 'David'. he wanted good raw material to produce a great result. So it is with choppers. Find a bike you like ... then chop it.

As of today we have built lower rear frame rails, centre seat post and backbone. Seat rails are cut out ready to weld and by the end of next weekend we should have the frame all welded up... so stay tuned...

By the way, Jet is looking to sell all the parts of the bike that have been removed... complete front end, headlight, gauges, bars. tank, side covers, rear wheel, guard and taillight. No rust and in perfect condition. Exhaust system is also in very good condition except for rust at the cross over tube, which we can weld up if someone is keen. If you want any parts call Jett on 0403 199 509

[Bearcx]

Holy cow! Ain't much left........

[Youngblood]

This will be interesting!

[Prof]

A quick peek at almost where we are up to on Jett's machine... rear guard has since been cut to length (short) and attached. Next weekend we expect to have the sissy bar done and be well into one of our unique CA king Queen seats. Jett has wanted to do a girder which we have begun planning, but I put the springer on so he could get an idea of the stance... but he is getting enthusiastic about the springer now!


Now that I finally have access to my photos, I'll get the build up to date... just thought you'd all like a look... I am really pleased with how the frame has turned out... and Jet is ecstatic, seeing his vision take solid form.

[Bearcx]

Great progress, and a cool stance. Like the springer front end, talk him into it..

[Prof]

Haven't had to talk him into it Dave. He came up today for a bit of a play and drool and stated he is sold on the springer. He wants to run the bigger 19" wheel with a twin leading shoe rather than the 18" so have to find one of them or marry a twin leader with a 19" rim.

He did a bit of grinding and made a red lens from a piece of car taillight for his microphone taillight. Will show you some pics shortly,

[Prof]

Back to the build...

We originally set up the axle position, 3" back and worked out correct height according to bikes final ground clearance. We are about to put the rear wheel in with axle plates so we can built the rear frame. Here doing a final level adjustment...


We are using an xs650 5x16 rear wheel because it has similar gearing to the original mag wheel. standard xs rear sprocket has 34 teeth. The kz rear sprocket has 36 teeth. Gearing it up by reducing the sprocket by two teeth allows for the difference in wheel diameters (5x16 is slightly smaller diameter) and also that the kz revs too much for out liking for highway cruising. We can also easily get 36 and 32 tooth rear sprockets for the xs wheel so we have a variety of options. Hub was polished, and a new rim laced to it with stainless spokes.

Once again we use a plumbob to centre the wheel and here can be seen setting up temporary axle spacers so we can tighten up the axle and set up the axle plates.


Axle plates aligned. Now to measure up for the 30mm heavy wall tube with mitre gauge...


Bending the two rear lower tubes. Marker is used once first tube is bent, so second one can be bent to the same angle...


Trimming to fit the rear of the engine cradle. Long weld area will guarantee a strong join. Care it taken to make the two pieces of metal a close fit with minimal air gaps which would cause tension and possible twisting as the weld cools. this is the initial cut, The cradle tubing needs to have all the point removed before welding.


Handy little home made gauge used here to get both axle plates the same angle before shaping the rear of the tube and welding...


With both lower tubes tack welded in place a heavy walled rectangular cross brace is fitted and welded in behind the original cross member. It ties the cradle to the lower rear frame tubes and provides a solid base for the single seat post Jett wants. Remember that there is more strain on a rear rigid frame than a sprung one. There is also a large unbraced area between the rear of the motor and the back wheel. so making this area strong is important...


The wheel is centred, but what about chain alignment? Here measuring the offset of the original sprocket...


... and the xs set up. Our new wheel differs by three mils... We will space out the sprocket by 2mm. Three or four mil out of alignment is not really significant, but like to get them with in a couple of mils...


Jett is very keen on a high steering head and large open space between the motor and backbone. We fabricate the seat post or of 50 x4mm tube (hydraulic pipe actually which is stiffer than mild steel). The bend allows it to be fixed close to the rear of the motor but leave plenty of room for the rider seat. and the electrics box. It is cut a bit longer than we may need...


We measure how high Jett wants the steering head and cut a backbone (same material as seat post) and make a temporary mount on top of the engine to see how it looks...


A straight line from steering head to rear axle looks the tidiest. At Jett's original steering head height this will make the seat too high with too big a gap above the carbies I talk him into a compromise...


Before we can do anything more permanent we need to brace the seat post via the rear engine mount, using 25x6 bar on both sides. This mount will also be well gusseted...


The seat post can now be cut to length and shaped to closely fit the backbone...


More tomorrow...

[Prof]

Before doing any more on the backbone and headstem we want to stabilise the set post against the rear of the motor on both sides.

So the motor can be easily removed and installed, the right side mounts need to be removable. The rear mount will be a short tab held in place by a pair of M6 bolts. Here they have been drilled and now the 25x6 welded section of the mount is being drilled for tapping. You can just see it curving underneath and to the right. To make the tapped holes accurate we begin to drill them first with the same size drill that made the top holes (7mm). We only drill deep enough to mark a decent centre and then use a 5mm bit so a thread can be cut. If we just started straight off with the 5mm bit, we could not guarantee accuracy...


It can now be bolted into place and...


... welded. A large 3mm gusset is run across the top and another one welded underneath. Idea of this gusseting is so the engine can effectively be a structural support to the frame. Ungusseted engine mounts would simply flex and do nothing for structural integrity. Notice the chamfers on the joints to be welded...


Other side similarly gusseted...


Because we want a smooth join between the flat pieces, best way is to put a tack at the bottom in line with the top piece. Gusset can then be levered into position to get a perfect join on the upper parts that will show the most. Steel ruler is used to ensure the joins are seamless...


Meanwhile Victor who is again joining in on the fun has been busy on the lathe making a couple of slugs to join in the new down tubes. Our tube is thicker tan the original so each slug has a step. Slugs a light tap in fit...


Slugs in place in the original frame. Notice the hole for plug welding (the second hole is hidden by the slug) and also that the tops of the slugs have been chamfered to make it easier to tap in the down tubes...


We are going to set up the steering head similar to the Harley style shown below. The down tubes will meet at the top of the steering head rather than at the bottom. This is a very strong and good looking set up and suits this frame where Jett is looking for an emphasis on height rather than stretch...


Measuring up for the down tubes. We have lightly welded to backbone to the seat post...


Working out how we will get on with the 550Ridikulus Rool... We want around 35 degrees rake to give us reasonable trail. However, we will have some leeway with all this when be build the girder Jett wants...


First down tube shaped up and fitted. We have put a small slot in the backbone to locate the plumbob string (red arrow shows plumbob). A close watch needs to be keep on this to ensure the steering head stays centred. Numerous checks need to be made as we tack weld the parts...


A slight tap upwards on the second downtube to get things spot on... If the right (as you look at it) frame tube looks at a different angle to the left, that's because it is! This frame is different on each side of the motor and caused a lot of head scratching when lining up the rear bottom frame legs...


Tubes being ground to take the steering head, which I have machined from a piece of hydraulic tube to take Harley bearing cups. I usually go this route as it allows more options down the track if the owner wants a springer, telescopic front end etc...


Steering head tacked on and Jett and Victor just have to see how it looks with Jett's tank...


While I line up and weld in the steering head using my trusty laser to keep an eye on things, Jett gets stuck into a trick gusset; this being the pattern...


Steering head now has to be boxed in. Here making up the bottom section out of 8mm plate. A bend back towards the down tubes will add a tidy touch in keeping with the curved gusset and angled seat post...


This tab fits between the down tubes and needs a sharp bend done by cutting, bending and welding...


Welded in...


Pattern for side boxing...


Once Jett's trick gusset is in place this will be one strong mother...


8mm gusset being cut to shape then finished on the linishing belt...


Cutting out the centre is done by drilling one 13mm hole and then running the band saw into it and turning around and cutting out the rest. Can also be done with a hacksaw or more holes and an angle grinder with 1mm cutting discs...


Some 'old school' work with a file... tiring if you are not used to it. Hacksaw, hand drill, cold chisel and files was all we had years ago... it was tough work on 12mm brackets! No wonder we'd take a couple of years to build out choppers...


Once fitted, the gusset is centred using a square here...


... and a verniers here...


More soon...

[Bearcx]

Great photos, Andrew. Shows good detail for anyone reading.

[Prof]

As long as it helps some folks with their own builds, Dave... heck of a lot of work for nothing otherwise.

[gages]

Hey Prof
I have the same model bike and am chafing a set of forward controls , is this something you could make and sell to me ? While you have one there ?
Cheers

[Prof]

Yes. Need to know what style of controls you want... plain, straight, curved, holey etc. Do you want fold up pegs or solid. Can be done in mild steel or stainless. Have a lookd at my website for some designs as well as builds on this forum... or send me pics of something youl like.