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CR750 replica build
CR21:
--- Quote from: philward on October 25, 2019, 10:17:35 PM ---Thats exactly what I did Scott
--- End quote ---
Hi Phil,
Hope it turned out ok? I think a few people have done it, how accurate it is to an original I don't know but I think it will be in-keeping once it is all painted up.
Cheers,
CR21
CR21:
A little progress from today:
Oiltank
Oiltank brackets tacked on, ready to check chain-clearance etc:
Exhausts
The CR75O exhausts are a 'big' part of the appearance of the machine, and something that I would like to get looking tidy.
I believe on the original bikes each exhaust pipe was made of two pressings, which were then welded or seam rolled together. This left the appearance of a seam running at the top and bottom of the pipe. The headers were formed separately and were welded or clamped to the pipes.
Although the shape profile could be achieved with rolling or even sand bending rolled cones, the appearance of a seam is hard to achieve
The obvious next step was to give it a go...
So a good chunk of time was spent today trying out hydroforming! Something that I have watched many videos on and read about but never tried.
Quick trip out to pick up various fittings to allow the cheapo pressure washer to be hooked up to the sheetmetal assembly, tapped hole in the blanking plug for bleeding air out of the system:
The hardest part of the CR exhaust shape is the curve, so the first flat pattern was knocked up to test the curve profile section. Complete guesswork for the angle and diameter (scaled off of photographs) at this stage and purely for experimentation:
Seamed together and valve welded in:
Hooked up, with a little safety cage!
Pumped up around 400psi
Happy for a first attempt, but very wavy edges and some buckling :-\
The pattern next to the product:
Round two!
Stainless sheet, smoothed pattern shape, special attention on matching the two halves and having smoother curves:
The latest attempt above the first attempt and pattern:
What I have learnt about hydroforming today is that the pattern, weld penetration and consistency are key to repeatability.
And that it is with a bit more experimentation I could possibly achieve what I am after...
I think I am going to purchase off the shelf header pipes, however I may experiment with another process I have been wanting to play with for a while which is sand-bending...
Cheers,
CR21
Laverda Dave:
Wow, fascinating work. I like to have a go at most things buts hats off to you for trying hydroforming with that pressure and being successful.
Great thread, looking forward to the next installment and photos.
philward:
I think I've mentioned it to you before Scott, but when trying to calculate the visual up sweep on the pipes, don't forget that in the picture of Dick Mann on the bike, his weight is on the bike and hence the swing arm is pushed up. I positioned mine relative to the rear wheel spindle as a reference the the picture- but the bike was on the 'A' frame stand when I welded the exhausts together - with no weight on it (which looked the right up sweep). But when everything was assembled and I sat on the bike, the exhausts are lower than I wanted. Just a thought!
AshimotoK0:
Looking fantastic... talked to a guy yesterday at Newark who I get parts from and he told me he just recently sold a CR rear hub for £350 to somebody. Thought it might have been you Scott but seems not.
His was from the estate of Alf Briggs who was Honda UK's Service Manager from the very early 1960's and held all of the race parts at one time. Alf was a close friend of Mr. Honda and when they pulled out of racing Alf was allowed to keep all of the spares I believe.
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