James GSX750 chopper...

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Prof
Founder, Choppers Australia
Posts: 5625
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
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James GSX750 chopper...

Post by Prof » Thu Apr 21, 2016 10:25 pm

James found The Chopper Shed on the net and liked what he saw and came down to with his bike to make either a bobber or perhaps a chopper. Not having any experience with extended forks and raked frames he had a lot of questions.

Well, the easiest way to find out it to get on a chopper and ride it. First I sent him out on my Honda 750 shop bike. It has a 40 degree rake, 6" over forks, forwards, a lowered rear end, but retains the original seat rails, so you still feel like you are sitting up on the bike.

All the same, he came back impressed saying, "It steers itself".

OK. So now try my shovel. This classic chopper is much heavier than his will be and has 44 degree rake and 6" over forks plus a very low seating position.

He comes back convinced. "Wow. I definitely want to chop mine!!" "And I want it long and low."

We talk about the pros and cons of rake and trail and bike length, ie chopper versus bobber.

The chopper is a bit heavier steering at up to walking pace (about 35+ degrees) and jogging pace (40+ degrees). Doesn't easily go around tight roundabouts or T junctions.

But steers itself and becomes increasingly stable as speed increases. Very relaxing to ride. Though slower in the twisties, is very predictable. Front wheel will resist unexpected objects and keep you on the bike. Longer wheel base makes your chopper easier to rescue in a rear wheel skid. You sit down in the chopper rather than on top of the bike. Higher steering head allows for lower bars.

His GSX was already stripped so next job is to set it up on the raking frame. Frame is levelled and bike is levelled on the frame...
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Rear wheel centred...
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Front end centred. Line is dropped from centre of steering head...
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Put the laser in the steering head and see how well that is aligned. A bit off as most 70's and 80 Jap bikes seem to be...
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Time to cut. I mark the places and James gets on with the angle grinder...
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More places to cut, but we'll leave the seat rails intact for the moment just to keep things stable. All brackets get cut off too...
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With only the centre backbone left we try his tank. He doesn't like it being so short and checks out what I have to offer...
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Where does the steering head have to be? Forks are slid 6" down in the bottom trees and then set up against the steering head. We try 40 degrees and check to see if it will fit within the 550 RidikuluRool. A bit over, but close enough at this point. Blue line shows stock steering head and red line shows new angle and new steering head position...
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Down tubes are heated just below the steering head and bent to get out 40 degree rake. Then down tubes are measured and marked for cutting. Slugs need to be made to extend them, so 1.5" of clear tube is left above the engine mounts for the slugs. A tube cutter is used to mark the cut so we can keep it perpendicular...
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With a piece of timber as a guide forks are now set up in the steering head and we can measure the length of slug we need...
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Slugs are machined from hollow bar and the front end set up with laser and plumbob to get it all square. Down tubes were a bit of a pain and are pulled into line with a twisted rope...
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Front end tack welded and forks and front wheel put back. Blocks of wood give ground level... Just the ticket reckons James...
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Next up will be building the new backbone and setting it into the rear engine tubing. Then a longer swing arm to allow James to sit down in his chopper and after that we can build the rear frame, seat rails and set up the tank he has chosen...
Chopit'nrideit... Prof

Bearcx
Posts: 1898
Joined: Thu Oct 18, 2007 12:31 am
Location: Gawler, Sth Aust
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Re: James GSX750 chopper...

Post by Bearcx » Mon Apr 25, 2016 8:20 pm

Nice stuff. Good to see something different, too. Plenty of grunt in the old Gixxer motor.
The brave may not live long, but, the cautious do not live at all.

Prof
Founder, Choppers Australia
Posts: 5625
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: James GSX750 chopper...

Post by Prof » Mon May 16, 2016 8:56 pm

We've made some good progress on the GSX chopper in the last week or so...

James mate machined up some 6" over slugs out of stainless. Slugs are fine if correctly made and fitted. They got a bad name in the seventies because of dodgy work and some silly folks having the join below the bottom triple tree. When you makde them do it right... Keep the join within the triple trees (ie max 6" [150mm] in length), start out with solid metal bar, extend a section below the thread that locates (firm sliding fit) inside the fork tube, keep the metal as thick as possible especially around the "o" ring.

You can see the features mentioned here. Top of slug has a pair of machined slots for ease of tightening. Tube alongside is original spacer. This will be cut to allow for the extra extension on the bottom of the slug. The more the rake, the less tension needs to be on the springs. For a 40 degree rake I will actually reduce the spacer or if there isn't one the spring length by and extra half an inch.

I also run an 8mm hole down the centre of the slug with a counterbored M8 socket head cap screw and 'o' ring to make it easy to add fork oil. That has been done here though it cannot be seen in this photo.
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Swing arm lengthening...
James in of more than average height and sitting on the chopper showed he would be a bit squished, especially as he wants his seat to be low. One longer swing arm coming up!

We decide on 90mm extension. Pivot is cut off and ends of tube is squared up...
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Plating is also squared up...
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Pivot tube is cleaned up and tubes cut to give the extra length. Because the swing arm will be plated both sides we don't need to go the extent of machining up slugs. Instead we cut a couple of extra pieces of tube that in this case are a nice fit inside the swing arm tubing...
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Inner tubes are pressed in and plug welded...
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With extensions welded in place we can now set up the pivot tubing...
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Running the bolt through the pivot allows us to measure each side from the axle plates to make sure it is square...
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A couple of pieces of round bar are used to check parallel...
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Pivot tube is centred against a mark we initially made...
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Swing arm is welded up and rechecked, then installed on chopper and a final check for square...
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Plating is still to be done, but can wait while we get more pressing jobs done...

Givin' 'er some backbone...

James has chosen a current model Sporty tank which is a bit longer than the 80's style Sporty tank he was going to use and looks much better with this chopper now being longer. So off with the seat rails and cross bar to allow the frame tubes to be narrowed...
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They need to come in a couple of inches...
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A string line is run down the centre of the chopper so we can get the tubes equal distance from the centre...
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I suggest heating, bending and lengthening the backbone will be more work and not look as good as simply starting from scratch...
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James gets into the action...
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This you young blokes is a hacksaw, the essential ol' skool chopping tool; no electric stuff back in the day! Here the blade is reversed so we can trim the tubing to allow the new backbone to fit...
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New backbone tacked in place at the steering head...
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Lining things up at the back. The tubes are heated and bent into final alignment with the backbone We cut out a little too much of the tubes at the bottom, but this will be plated anyway and is quite fixable though better if it hadn't happened...
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Tank sitting in place...
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James wants to drop the rear of the tank into the tubing, so next job will be some panel beating of the tank...
Chopit'nrideit... Prof

Butcher
Posts: 26
Joined: Thu Jan 09, 2014 9:50 pm

Re: James GSX750 chopper...

Post by Butcher » Tue May 17, 2016 6:51 pm

Never seen a Harley with 4 cylinders before !!!! (lol) Lot of work in this lads, on yer - wished I had a fraction of yer ability.

What's happening to the flathead next to it ?

Prof
Founder, Choppers Australia
Posts: 5625
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: James GSX750 chopper...

Post by Prof » Tue May 17, 2016 9:32 pm

Perhaps they reckoned if Indian could do it so could they!

Flat head next door is Walla Bob, my 1942 WLA. Been in the family since the early fifties.

Has just had electrics upgraded to 12 Volts and an auto advance retard of a sporty added. Generator doesn't want to charge atm, but once that is fixed up it should be ready for a few decent rides.
Chopit'nrideit... Prof

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