Tank and rear guard on CB750 project for sale...

[Prof]

I recently bought a CB750 that needed a bit of work before being rideable. Carbies need setting. Needs a tank and trimming back of the stock wiring loom and a bit of cleaning. It came to me with the stock rear guard and a Maltese cross taillight, which to me just doesn't look right, so I've made up a new rear guard as well. Should be ready for purchase in a week or so.

It's a chopper that I built for a customer years ago and has been through a few owners since. Current owner suddenly needed the money and unfortunately couldn't get it on the road.

I'll have a couple of pics up when the tank and guard are mounted, but I thought I'd show you a couple of things now.

The frame was originally set up in The Chopper Shed for a diamond tank, but this was missing. Fortunately I had another one here that needed some moulding and paint. It also is a bit too long, so I have had to cut off the front tab and run a bolt through the tank itself.

With it bolted at the rear mount I use this sharpened bolt to mark the underside of the tank...


Knife points to the mark. A quarter inch hole is drilled at what I hope is the correct angle...


It is within a couple of mils and I get everything lined up with the die grinder. Next job is to machine up a bung that welds into the tank through which this bolt goes. The socket head cap screw is counter sunk into the bung, but clever me forgot a photo...


The tank builder also machined up this threaded cap. You can see the hole drilled through the centre and out through the side to prevent a vacuum in the tank as the fuel is used. Problem is that the petrol will just squirt out the hole... needs a bit more obstruction...


I drill out the bottom of the cap (It's too heavy anyway), so we can put in a rubber washer. Bottom is finished flat with a drill that has its point ground off (I have made up a set that I use for jobs like this) ...


To hold in the washer, I make a slight undercut (arrow)...


Underside of washer is grooved with the angle grinder and then a hole drilled to one side. Once this is pushed into the cap it will create a winding enough path to prevent fuel spurting out


Here pushed into the cap...


For a bit of fun, I counter bored the top to fit a penny...







Rear guard next...

[Prof]

I wasn't planning to do a post on this fab, but decided to because; 1. I think it is the best looking rear guard treatment for a chopped CB750 that does not have seat rails Konged and 2. there are some sheet metal procedures worth showing. This is not a big or complex job in fact total fabricating and fitting took under three hours.

This exercise was made a little easier by copying the rear guard on my shop CB which I made some years ago. Taillight is standard Lucas...


Main section is measured up, marked up on paper and transfered to 1.6mm steel sheet and cut out with the angle grinder 1mm blade...


Paper pattern and cut out...


Parallel guide lines are drawn on the steel to help me keep the folding even and here I have poked it into my big folder and progressively bent it by hand. You can use a couple of pieces of angle in a vice with 6mm spacers on each end for speed of folding...


Second piece of sheet metal welds into the rear and holds the taillight and acts as a number plate support. Modern aluminium numberplates are very fragile and crack and bend just by looking at the suckers. Support is a necessity.

Pattern is made and held onto the steel sheet. Use a texta to quickly mark the edges. Don't try and draw around the pattern just do a cross hatch style of marking...


Final shaping done at the vice. When cutting metal in the vice keep it horizontal with a piece of 50mm angle and G clamp...


Bent to allow the number plate to clear the rear tyre... about 30 degrees. Again you can use two pieces of angle one end held in the vice with a G clamp on the other. See earlier posts where I have shown this technique...


Getting the correct width and smooth curve by hand bending over the anvil. A piece of 75mm pipe in the vice is just as good...


Keeping two pieces of thin sheet when one of them is curved can be a challenge... sorted out by a couple of clamping pliers. Red arrowed clamp is clamped to the curved body and acts as a place to mount the second clamp and hold the two pieces together...


Bronze welding is easier to do inside a fold and requires less heat and therefor creates less distortion...


Drilling the mounting holes. Texta patches allow scriber mark to be easily seen...


Block of wood in the vice allows the metal to be positioned perpendicular to the drill. For anything under 2.5mm, use a step drill for accuracy and also roundness of the hole. In thin metal, the ordinary twist drill will tend to make a triangular hole...


Mounted for marking off second set of holes...


Block on its side this time...


Marking out for the taillight large hole. Find centre, then measure centre to edge of taillight and mark on guard...


Now for small holes. Measure centre to centre of mounting bolts...


Halve this measurement and mark each side of large hole centre marking...


To keep them square, measure from bottom of number plate support. This way number plate and taillight will be sure to be square to each other...


Drill with step drill...


One problem with these taillights are the brass threads for the lens screws. They are only pressed in and if the screw protrudes they can be popped out... I have about four of these in my collection...


Best solution I've come up with is to cut out a piece of tube rubber and make a flexible gasket to space the taillight a couple of mm from its solid mounting...


You don't want the wiring drooping and getting worn out by the tyre. I glue in a piece of plastic tube to slide the wires through. It needs to be big enough to take the wires and what ever connections you have on the ends. Also, leave a gap at each end for easy threading and joining of wires...


Last job before painting is to drill four holes to mount the number plate. I always include a captive thread for each bolt; in this case four M5 nuts bronze welded to the rear of the mount...


On this chopper, wiring goes over the stock rear plastic guard section, so I need to drill a hole with the step drill in the plastic...


Wires supplied are too long. Black is the running light, red, brake light... checked on the battery...


Wires cut so they don't droop onto the tyre, but are still long enough to grip while joining to supply wires. These electrical strippers are very handy...


Bullet connectors are used. Taillight side has male on the running light and female on the brake light so wires can't be connected incorrectly. Soft plastic covers to cover the female connection are Narva as are the terminals...


Supply wiring is fed through the plastic and connected and the guard installed...


Nice tidy finish to the chopper in my opinion. I think the previous owner's choice of seat spoils the lines and comfort, but that is easily remedied...


Now just have to finish off a few wires, mount and hook up the carbies and we should have a nice running chopper ready for its new owner.

Although my shovel chopper is my first choice, the CB750's come a close second, reasonably light, sufficient power for comfortable cruising and easy to work on single overhead cams. I'd happily ride a well set up CB750 chopper around Australia... in fact I am looking forwards to doing some interstate trips on the springer, TCS Rigid Suspensioned CB I am building in the workshop as time allows. Let's keep these beauties on the road.

Hope this thread has been helpful...