Wednesday, April 18, 2012

Sprocket and rear brake carriers

The driven sprocket is bolted to a casting with five vanes on the rear side. These vanes then push against a set of rubber blocks with provide a degree of shock absorbing to the rear wheel. The casting bears the marks 'SNW', a Japanese company that produced wheels and ancilliaries for Triumph, and is date marks: 2|0 |9 8|9 - the 20th of September 1989. 



The sprocket carrier had been painted red by a previous owner, along with the wheels. The paint had not adhered well in some places, and was damaged in others. So I decided to strip it off and then to repaint it silver. I like the red on the wheels though so will be repainting them in the same way as the previous owner decided. 


 Despite the paint having fallen off in some places, it was very hard to shift from others. Isn't that always the way. So I gave it two doses of stripper with a good scrub each to boot each time.

Even after that, some of the red paint was still ingrained in the casting, leaving a pink blotchy appearance.
 I gave it a dose of Hammerite Special Metals primer. I also did the rear brake carrier whilst I as at it.

 As I have written before, the Special Metals primer covers very well indeed but does not flow terribly well. So I had to rub it back afterwards. I used wet and dry 400 grade paper for that. The blotchiness reappeared the primer was thin but I felt it was an adequate key for the silver paint I wanted to use.


 Ages ago, I'd read in that wheel paint works well on Japanese castings in a classic bike magazine ( I think it was Classic and Motorcycle Mechanics but can't be sure). That article said the high aluminium content in wheel paint meant it was also pretty resistant to temperature so could be used on engine cases. Anyway, the formulation is intended for application to alloy wheels so I figured it would work well on these components too.


The paint went on very well - good coverage and flowed well, tolerant to runs. However, the surface had quite a bit of texture to it (looked great, felt rough) which would be hard to keep clean.


I topped it off with clear enamel lacquer made by Japlac. I've had good results with this before as a top coat for brake callipers. The final result is below:

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