Jett's KZ750 chopper #3 rear guard, sissy bar, tank...

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Prof
Founder, Choppers Australia
Posts: 5622
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
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Jett's KZ750 chopper #3 rear guard, sissy bar, tank...

Post by Prof » Wed Jul 29, 2015 9:10 pm

As we got to Jett's rear guard, I was notified that the 45 degree coverage no longer applies. This was music to Jett's ears as he was pretty keen to have a short rear guard. First step is to work out where the guard is to finish and measure with a dressmakers tape...
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Then mark the guard. You can easily make this instrument to mark a square line on the edge. Base is ½" square tube. The marking line (RHSide) is equidistant from each end...
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Guards and tanks are pain to secure while you cut. Jett's guard is held in this Chopper Shed special clamp, made from some water pipe, the clamp itself will be recognised by anyone who has lapped their valves... an auto valve compressor welded to the frame...
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Wheel is mounted and axle pulled tight to the front of the axle plates. This ensures the wheel is centred, so the guard can be centred over the wheel. Wheel is then removed and we drill holes in the cross member and guard. A couple of threaded 8mm plates are welded to the inside of the guard with everything assembled. Mounting holes in cross member are drilled oversize to allow some movement for final alignment...
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With everything bolted up we tackle the sissy bar which is the rear mount for the guard...
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A pair of bottom mounting tabs with 10mm holes are made. The sissy bar will on the inside of the tabs so keep things straight and narrow otherwise the tabs would be threaded. Tabs here are being aligned for welding. A 10mm rod is passed through the tabs and measured from the rear of the axle plates (Red arrows). Yellow arrow shows chamfers ground into axle plates and tabs so weld will penetrate whole of metal and can then be ground flat...
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Some discussion follows on sissy bar height. The most comfortable height for the pillion is padding up to the shoulder blades... and he wants a happy honey on the back doesn't he. He doesn't want to go too high, so a slight compromise is made. Jett has some medallions he wants to use on the bike, one of which is this belt buckle for the sissy bar. A narrower top would have looked better, but a wide curve is needed to accommodate the buckle... so we draw out the sissy bar on the floor. As Da Prof always says... "begin with a centre line and use a set square to keep both sides even"
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I have a number of formers for making sissy bar tops, but none fits Jett's requirements, so we knock up another one for the collection and get to work heating the 16mm stainless round bar. There is a bit of a knack to getting the curve even... a bit too involved to explain here.
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A close up of the former... a large piece of pipe, and two pieces of angle iron...
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Marking for second set of bends...
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Getting the nest set of bends takes care and patience...
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First set being checked...
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All bends completed and being checked...
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This is how it will look. "Marvellous!" says Jett...
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Ends being marked for trimming. Double checked with tape measure from centre of top curve...
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A flat needs to be cut into the bottoms of the sissy bar. Here, set square is used to get them vertical...
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Getting cuts parallel...
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Flat is blacked with texta...
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Then set in place and marked with a scriber. They will be drilled and tapped to M10 x 1.75 to suit a couple of stainless button head bolts. Stainless fasteners come in only the coarse thread of each size...
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Guard/sissy bar bracket is made from some stainless angle. Engineer's ruler here is being used to make sure the bracket is evenly located on each sissy bar leg...
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Bracket being heated and shaped to fit curve of guard...
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A piece of paper is ideal for measuring around curves, here being used to mark mounting holes that will be an equal distance from each edge...
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Guard blacked and marked with a scriber...
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Bracket welded to sissy bar. Don't weld around the bar as it will weaken it. This is especially true of stainless. I have built up some extra weld to leave a flowing line. It also reduces a potential stress point by the weld being at an angle and not straight across...
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Threaded plates being welded under guard...
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Bolts done up lightly...
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... and final square checked before tightening. We had to run a long bar through the top of the sissy bar and give it a bit of a twist to get everything into final alignment...
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Next job is to build seat and pad it so we can set up the mid controls. Jett also has a very cool tail light which he have been modifying an will mount soon..
Chopit'nrideit... Prof

Bearcx
Posts: 1898
Joined: Thu Oct 18, 2007 12:31 am
Location: Gawler, Sth Aust
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Re: Jett's KZ750 chopper #3...

Post by Bearcx » Sat Aug 01, 2015 12:07 pm

Good progress. Love the sissy bar, looks awesome.
The brave may not live long, but, the cautious do not live at all.

Prof
Founder, Choppers Australia
Posts: 5622
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
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Re: Jett's KZ750 chopper #3...

Post by Prof » Sat Aug 01, 2015 8:45 pm

Bear wait until you see the finished sissy bar... it will be very tidy..

Fuel tank mounting is next...

Jett bought the tank off the internet. I can't stand the ugly fuel outlet, but Jett likes the overall shape and size of the tank... and I agree with him there.

Mounting tabs need to be drilled, so we black the tab with Texta and use an odd leg caliper to find centre. A piece of paper will work quite well too...
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Automatic punch is the most accurate way of centre punching prior to drilling. It makes only a very small indent which I now enlarge with a normal centre punch. Advantage of the auto punch is that the centre can be easily seen whereas it tends to be hidden when using the thicker centre punch...
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Finding the centre top of a round tube is most easily done with this contraption. First, the bike is set up perfectly level. Then this instrument (made at TCS) is set up up level and pressure applied to the pin as it is slid along the tube... It leaves a nice clean line in the texta-marked tube. I've used this for years. The other way to find the right position, is to set up the tank with a spirit level along the bottom and then mark the backbone through the drilled hole in the tank mounting tab ...
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Drill bits wander, especially if they have been inaccurately sharpened. Getting the tank level is critical, so after centre punching, I used a centre bit followed by a 3mm bit and then a series getting larger until we achieve the right size hole for the threaded bung.
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Area around the hole, ground a few mm lower so the threaded bung will not protrude...
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When setting up the bungs for welding, I screw in long bolts (yellow arrows) so I can ensure they are vertical. This is done by sighting them up against a square (red arrow). As you can see, the rear bung needs straightening up a little before welding...
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One of the bungs bronze welded in and polished back. Look at the bung and you will see that the thread starts 10mm down. This prevents cross threading; which can often happen when trying to support the tank and line up the bolt at the same time...
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Job done.... Along with the button heads, a neat job and easy to keep clean...
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Top engine stay/coil mount and mid controls next on the list...
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5622
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: Jett's KZ750 chopper #3 rear guard, sissy bar, tank...

Post by Prof » Thu May 05, 2016 9:02 pm

I'm all for forward controls for those long hauls, but Jett is sold on a position between forward and mid controls. So that's just what we gunna do!

This set up makes for a bit of a challenge. It puts the pegs just behind the alternator and electronic pickup protrusions. Things 'r gunna be tight mate!

First is to set the chopper perfectly level (see wedge [arrowed])and then measure from a known point that will work for each side, the rear axle plates...
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Requires removal of excess bracketry. By the way that tool is cold chisel, a much used old school tool...
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Foot peg mounts need to be removable in case they are bent in a prang (old school for accident) and so the engine can be removed. Here we are centre drilling a couple of pieces of 25 x 12 mild steel ready for threading and tack welding to the frame. They are 75mm long to allow a long weld top and bottom to reduce stress on the thin jap frame tubing...
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Spirit level is used to keep mounts vertical. G clamped and tack welded...
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Both sides double checked with tap measure and welded...
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We work out height pegs need to be. This chopper will be running high pipes and although it is considerably lower than stock, it can still get up quite a lean in those sweeping bends. I like my heels to touch the ground just before the bike scrapes in a lean. That way I know just what is going on. Jett thinks that is pretty cool and opts for the same set up. We set the height at 230mm above ground level.

Here we have the vertical peg mount sitting on the threaded mounts and have made up a piece to be bolted to the mounts we have tacked to the frame. The vertical will be welded to this. These parts on both sides are fabbed from 10mm stainless which will be polished...
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Top of both verticals will be neatly curved like the tacked on pieces. Here's how we do it. Red arrow is half the total width, marked with the verniers on texta. This centres the hole. This same measurement is marked from the end (blue arrow)...
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Centre punched with automatic punch (for accuracy) and then the indent deepened with a centre punch...
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A divider is now used to mark a half circle to be cut out...
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Virtually the whole curve can be cut with a 1mm blade in the angle grinder. Blue arrow shows the last little bit to be trimmed. Then I finish it on the linishing belt or you can use a file...
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When tapping a thread use lubricant (red arrow). Before removing the thread tap clean it with kero on a tooth brush (blue arrow)...
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Height is double checked on gear shift side which has a straight vertical mount...
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Marking gauge is great for marking the locating line for the two holes. An odd leg caliper or old verniers is quite effective also.. You can pick up a variety of calipers and dividers cheaply at swap meets...
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Drilled and ready to weld. Number on cover is height to centre of threaded hole...
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Rounding the ends and marking using a dividers off each hole...
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Brake side needs to be set out an 35mm. Best way to get an accurate and tidy bend is to cut half way through with a 1mm blade, bend, weld the cut and polish back...
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Bend checked against height (232mm) and for square...
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Tacked on one side and then squared up the other way...
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Before second tack, distance from rear axle plate checked. Expect to make the occasional mistake and have to break a tack. It's all part of fabbing from scratch...
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As soon as I get some more time I'll finish showing how we have done the rest of the foot controls...
Chopit'nrideit... Prof

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