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CB750F Tank modification and welding

carterbaker208

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I've got a 1981 CB750K that I've been preparing for a cafe conversion, naturally I didn't like the tank shape where it swoops down close to the seat. My options were to:

A. Cut that off and weld it back together, retaining the original tank
B. Get a new tank and risk having to modify the tank to fit my frame

I chose to get a different tank that already had the shape/lines I wanted. Naturally I picked up a 1975-78 F sport tank that has IMO the perfect lines for a cafe racer. Upon getting the tank, it sits too high on the frame, and the bottom is just a little too thin to fit onto my '81 frame. With that being said, this is what I'll be doing to make it work with my frame:

1. Front tank mounts will be cut and moved up on the tank and welded back on
2. Bottom side of the tank will need to be widened to fit on the frame, so there will be a lot of cutting and welding to make that happen

Has anyone had experience with this before and have suggestions or ideas to help this process go smooth? I'll be doing it either way, just curious to see what's out there. I haven't seen an 81' with a 78' tank on it for a reason I think lol.

Follow along has I keep you all updated, hopefully I won't completely screw things up. I invite suggestions and pointers to help this build go smoother.

Thanks!
 
I agree with you on the lines of the SOHC F tanks - classic.

I have not done the mod you plan, but have made tanks from scratch (avatar pic). It is very challenging indeed. I used 16ga sheet ( that's actually a DOT reg. if it matters), it is a bit harder to form, but welds up easier than thinner gauges. Also, on tanks - unlike body panels - it's better to do a continuous bead, rather than spot stitches, to get a sealed seam. The stitching tends to create porosity. Another thing I do is coat the seams from the outside with a Caswell epoxy before priming to ensure a seal (I don't like using it as a liner).

Good luck!
 
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