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Not making a lot of progress as another build keeps on getting in the way.....
But was lucky enough to come across an Africa twin hub on ebay....a rare item nowadays! It does mean I can have a twin disc spoked front wheel though and, as far as I can judge there'll be no clearance issues with the calipers. It was an easy fit as well....spindle size the same as Suzuki....a couple of spacers and its bang in the middle!
Not so much stopping power at the rear though....a Transalp hub....using it mainly because I had one lying around feeling lonely....and because it looks the tiniest bit like a Manx hub! Had to make up a stop for the brake plate and a spacer but again an easy fit.....and chain line is dead on too....
Finally came across a reasonably priced donor bike on ebay which should provide pretty much all the bits I need....
Its a decent runner but one unwelcome surprise.....
You often see that broken lug on CB500's.....usually caused by the bolt seizing in place and then people trying to hammer it out.... this one though caused, I suspect, by engine bars being mounted to it and coming off?
Not to worry....the motor will be getting a rebuild anyway so it can welded when its all apart!
So, onto the frame in the next few days.....this pic of a Paton is fairly close to what I have in mind....
So, onto the frame.....basically my plan is to make it in sections and then assemble them on the jig later
In the pic above you can see how they've used short lengths of tube at the top front and lower rear engine mounts, much like a Ducati frame....something I'll be copying.
In the past I've found its best to use longer than necessary bits of tube and only cut back to correct length after final welding....otherwise the weld tends to 'bite' into the edge and leave it looking a bit untidy.
The frame itself is going to be in 16g tubing but for these joints have decided on 10g.....
It can be a bit tricky to weld the washer centrally to the tube so I screw them down to a piece of wood first....
So, onto the first section....front downtubes.....
I've spaced them out by 8mm either side to give enough clearance to fit the exhaust pipes....I hope
Next job is to cut the tubes where they attach to the headstock, any gaps that need filling with weld means distortion....something you don't want especially there!
So, I find a bit of tube with the same id as the headstock od...though here I had to slit it and widen it....then carefully tack it in place over the tubes, being careful to get it square and at the correct angle....
Then run a holesaw down inside the tube....with lots of lube!
Which, if everything is set up right gives a really good fit....thats just a spare bit of tube for checking btw....not a really long headstock!
Next, on with the main top section of the frame....I know it looks like a bit of a concertina but will be addressing that later.....the idea is to make sure carbs, head etc are all easily accessible with the engine in the frame
And then the first 2 sections assembled into the jig....and btw the reason they seem to be multiplying is that I always make a trial piece in cheap erw tube and then when I'm sure its right make a copy in proper stuff!
Next job is to add the diagonals that run from the lower rear engine mount back up to the top shock brackets....
That finishes getting all the main mounting points on the frame finished.....leaving just bracing tubes....and mounts for stuff like rad, coils, airbox etc
So, out of the jig and see if everything fits together!
Which it does....surprisingly! A couple of small problems....nothing too major and a stroke of luck with the carbs.....2mm clearance to the tps....
Swingarm mounts are just tacked in but the triangle where they sit will eventually be plated in both sides.
Getting close with the frame now....a couple of detail pics....
And a try out with some bodywork on.....and on its wheels. I got talked into seeing sense and now going for a rear disc though I think caliper mounting is going to be tricky....front wheel will be a 17" too....the one on there at present is a 19" borrowed from a Triumph Tiger!
Thanks Steve, all the mounting points will be cut flush after welding and then fitted with rubber bungs....I'll be trying to resist the temptation to paint it gold though!
Not really sure Steve, am slightly tempted by a Ducati look...red bodywork....gold frame....but next week I'll probably be thinking something completely different!
And some temporary rad mounts.....eventually there'll be a bit of a shroud there to direct air to both the rad and the air intake which will be just inside the tube marked 'R'!
Also, had a go at the tank....this one is just a mock up from scrap steel sheet....I taped the edges so I could fill it with water to measure the capacity....1.9 gallons.
Was having a lot of trouble getting the shape right so it fitted under the grp cover....then it occurred to me to make another mould of the top of the tank and try it that way....
Not exactly a perfect fit....wish I thought of that plan 2 or 3 hours earlier!!
Finished making the actual tank in ali but kept on looking at the way the tank cover overlapped the frame at the front....
In the end decided I couldn't live with it.....it won't take long to alter I thought.....3 days later and nearly a whole tin of filler....
Well.....bit of a long answer...originally I'd just planned to link the downtubes and main frame rails with tube a bit lower down
But there is a big cast lug on the front of the cylinder head that is unused on any of the 500 twins....no idea why its there at all
So at first I just made the triangular plate to give an extra engine mount to the sleeved holes in the downtubes which are also mounting points for rad and duct
I had some concerns that maybe the lug wasn't used because of differing expansion rates causing problems and was thinking I could always delete it later on if need be....but then thought no....its not as if its a pre unit Triumph!
With that decided I just added a stub of tube around the engine bolt and welded tube to that to brace the two
The other plus of doing it that way is when I finish weld it theres a good chance the headstock will distort one way or the other a bit....I'll have it checked and pulled straight if need be but by leaving the bolts out whilst that is done there'll be less stress involved.....
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