Seven Fifty cafe-racer. Rear mudguard.

From the very beginning of project I decided that my Honda Seven Fifty cafe-racer will have clean frame  triangle. As CB750 frame triangle is too large I decreased it by intake system, electrical component and chain guard. But all the time I was haunted by thought about completely unprotected air filters and  the main menace for them which is rear wheel and all debris it could throw forward in motion, especially while riding on the wet road.

After quite an intense thought I came to conclusion: the only solution of question is so called hugger: the fender which mounted to the swingarm and “hug” the wheel. As I cornered idea, I worked it out and designed that fender on principle “close to invisible”. As for hugger material, between reinforced plastic, fibreglass and aluminium I, naturally, chose aluminium.

I never before made metal fender from the scrap, but it promised to be interesting experience, so I took the remains of soft 3mm aluminium sheet (dunno which alloy exactly it is) and started bending, banging, tapping  and so on, round after round. I used sandbag and all special hammers I made or modified when was working on the seat base. I was not certain in result and I was so concentrated on work that I made no slightest try to take camera and shoot the process.

After some time I realized  that I was moving in right direction so I doubled my efforts and soon got quite sufficient result. But I needed English wheel to make fender surface more smooth and thus decrease time of hugger surface grinding.  Fortunately, one friend of mine built the English wheel in his garage (which placed in less than kilometre from mine) and what was even more fortunately this my friend visited me occasionally right after I finished fender tapping.

His English wheel had only one set of rollers, but even so I was able to treat most of the hugger surface. It was pleasure for me to work on English wheel, so may be in future I’ll get the same tool in my garage.

I shot illustration for further process so, that’s how my mudguard looked after English wheel and initial side cutting:

As you may see, I made its’ design similar to front fender. Its’ width is 168 mm, so it completely covers sides of 160mm tire. I also formed flat area to mate it with swingarm cross piece.

Even after first stage of sandpapering fender looked good:

Then was time to mount it initially on swingarm:

And to check how it fits the frame. I made special wooden spacer which, when it is mounted to swingarm and frame, imitates fully compressed shocks.  Thus I checked possible collision of parts and found that fender fits into the frame perfectly and has sufficient gaps in all positions.

My next issue was fender mounting.  I mounted bottom part of hugger to cross piece of swingarm by three bolts.

I made reinforcing plate for this mount:

But to be sure that hugger withstand all possible load and vibration, I made additional bracket which connects fender and chain guard. I made it in one piece and then it was welded inside and out of hugger. As a gap between wheel and mudguard is more than sufficient, I mad inside part of bracket a bit bigger than it was need to make fender more inflexible.  And that’s how it all looks:

And how it works:

Sandpapered hugger, ready to be painted in black:

Mounted to the swingarm:

And with the wheel:

How the bike looks with all latest updates I’ll show in one of the next posts.

 

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