Project CB690 (KTM 690 engine in a CB550f frame)

goodoltup

Member
Work has begun on the frame jig. I have received several metres of 2x3" steel box section tube, which will form the frame of the jig. Instead of clamping it all together like some frame jig kits I have seen, I will weld it. One problem I needed to solve was making the steering neck cones for the jig. I decided that instead of making cones I could use the existing bearing cups. First I make some discs on the lathe. The bearing cups were then ground down to allow a light fit in the steering neck cups. The bearing cups were then tig welded to the discs. The third picture shows the welded assembly in the steering head. The welded assembly then went back on the lathe to have a 16mm hole drilled concentric to the bearing cups.
 

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goodoltup

Member
I used the mill at work to get the required angle on a small section of the tubing, and to drill the 16mm holes through both sides. The small bit was then welded to the frame jog upright, and 16mm threaded rod used to make the steering head holder. I don't have a lot of great pictures of this process, but hopefully from the last picture you can see the bit that was in the mill.
 

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stubsryan

Member
Sweet project mate. I’m really looking forward to seeing how this one pans out. Keep up the good work


Sent from my iPhone using DO THE TON
 

goodoltup

Member
This is my current welding setup. I ran a higher amperage line to a socket that is only used for the compressor and the welded. Only one at a time can be used, but that really should not be a concern. The welder has been doing great, I have no problems with it at all. It's a lovely piece of kit, cheap and cheerful.
 

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goodoltup

Member
Ok this is what it's all about. The frame is in the jig. I used a digital inclinometer to ensure that all the tubes were square to each other and that the headstock was set at the same angle as the stock KTM. This was really just for mockup, the real headstock angle will be set with the shock length once the frame is released from the jig. For the time being the most important thing is that the headlock is perpendicular to the jig, and that the frame is centred in the jig. Once all the measurements had been taken, the frame was tacked on the upright that is under the frame cross member. Next I will make a holder for the engine so it can be positioned in the frame while being kept in the same plane as the headstock. Then it can be positioned and the motor mounts mocked up.
 

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goodoltup

Member
Here I've made an engine mount out of some tube and remnants of the KTM skid plate. This allowed me to position the motor in one plane, moving it around until it worked. There were several compromises to make, namely if the motor was too high the injector interfered with the frame, and if it was too low the chain would rub on the frame cross member. A pretty good solution was found, in that the injector could be rotated a few degrees to allow the necessary injector clearance, and the motor could be positioned at max height and provide good chain clearance. Still necessitates the replacing of a frame tube, but that I was prepared for that, see a few posts ago where we priced up a precision bent tube.
 

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goodoltup

Member
This may be a big decision here, but I think I can use the original KTM swingarm. Think of the work it would save! I wouldn't have to manufacture a swingarm from scratch. The bearings would work, the rear axle would fit, it looks cool. Only problem is that it taking into account the 75mm the swingarm pivot is moved forward, the KTM swingarm would add 80mm to the wheelbase. And, of course, it's mono shock and not dual shock. I believe that I can have some clevises welded on (I won't do it) and I can machine off the boss for the mono shock, that should be trivial. The rear calliper would have to be mounted differently because it would interfere with the shocks, but again that is ok. I think I can live with this.
 

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Popeye SXM

Also used for MX
I like it. Moving the SA pivot forward and using the KTM SA is a good solution, keeps the pivot point close to the sprocket. I think the KTM SA looks great too
 

goodoltup

Member
I took the forks apart in preparation for shortening. Minor panic as for a couple of days I thought that they could not be disassembled far enough to replace the topout spring, but after searching the internet for pictures I did notice that there was a hidden snap ring that allowed them to come apart. I will be ordering a spring kit that shortens the forks but maintains the correct spring rate. Also new seal kit, of course.
 

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goodoltup

Member
Finished mocking up the tube and the motor mounts. The left motor mount is shaped so that it matches the shape of the stock sprocket cover. The right side one looks more like a simple triangle. The swingarm mounts will be made in 10mm plate, the front motor mounts in 6mm plate, all waterjet. The tube will be formed by a specialist mandrel bending company.
Also, I bought a cb550 tank. I like the gt550 tank better, but it would need tunnel modification in order for it to fit, and in order to keep this project running I thought it would be a good idea to minimise unknowns and potential problems as much as possible. I will keep the gt550 tank and maybe add it later for version 2.
 

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goodoltup

Member
My manager gave me an engineering drawing of an automatic transmission. It has hand written notes and a date from 1968. I'm very thankful, it makes a nice addition to the garage.
 

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goodoltup

Member
Hi, yes, it's been too long since I've done any real work on the project. I wasted a lot of time getting the CAD files for the plates and tube, and wasted more time getting them quoted and ordered. I have now, however, received the plates from the water jet company. I ordered a few extra just in case I make a welding or grinding mistake. I sent the DXF files with a PDF drawing of the part with dimensions, but the water jet people just loaded the DXF and started cutting, not realising it was scaled 2:1. You can see in picture two that the front motor mount plates are huge, twice as big as they should be. The water jet people recut them and sent them out next day, so no harm done.
 

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