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CB400F CB250G5 Original Style Rear Sprocket Renovation

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AshimotoK0:
I found on my 400 renovated in 1986 that I had used a new rear sprocket (pattern but with wrong cutout holes) and drilled and tapped it M6 to fit the sprocket chain guard ring with domed cap screws. I had painted the ring in black 'PJ1' style paint.

Fast forward to last week I found that  I had a spare original rear sprocket guard ring, which I had attempted to have plated in the original finish (Zinc plated with a really dark green zinc passivate) but it had somehow got splashed with something during 'storage' and the finish was ruined  :( .  I remember having it re-plated by Allenchrome in Pocklington but they no longer do small-batch plating for bikes etc.

I dug out an original but all over slightly corroded, original compete 400/4 rear sprocket, that I got with a batch of stuff from the estate of an elderly Chinese gentleman down 'sarf' . Story was that he had bought the remains of a 400/4 from 'The House of Wheels' in Leytonstone'  (anyone remember them in the '70s  :D)  that had been crashed with only 600 miles on the clock (Kettle738 got the engine and sold it to a guy in Lincolnshire .. no not Trigger or Julie!). So I set about renovating this '600 mile only' sprocket to use on my 400F.

I decided not to de-rivet the guard from the sprocket. I de-greased it and  masked the exposed parts of the alloy rivets with thick paint and then dunked it in acid to remove the old plating (i.e BZP on the sprocket and the olive drab passivate on the the guard ring. After cleaning all of the remaining corrosion and a dip in 'acid salts' as used in home plating kits, I bright zinc plated the whole assembly and it turned out surprisingly nice as it's a beefy old bit of kit to home electroplate (about 7 amps plating current). I usually restrict home electroplating to much smaller items and send the big stuff out. However, this is a prime example where a commercial plater typically  wouldn't plate anything riveted together with aluminium and where DIY plating comes into it's own.

Next step it to mask off the sprocket so I can finish the guard ring. I mixed up some dark grey etch primer pigmented with green to match the original olive drab colour of the Honda part and I will spray the ring with it. Next I will apply a really thin layer of the Mipa clear-coat I used on my alloy hubs with some matting agent / reducer in it. Will report back show pic's when it's done.

This style of sprocket , .. i.e. with riveted on guard ring .... was used on the CB250/360G5 as well. Not sure about the later model CB550/750's

Just wondering what others on here do as there are some pretty picky 400F members on here?  I know DS sells repro's but they are around £120  described as 'one for the purist' .. well the purist here says that the ring finish on the DS one looks mighty like black colour (paint?) to me, not dark olive-drab like the original.

https://www.davidsilverspares.co.uk/CB400F-SUPER-SPORT-FOUR/part_346752/

Athame57:
I wonder why Honda chose such an odd colour for this part. Where they army surplus?  ;D

Laverda Dave:
It will be interesting to see how it turns out Ash. I need to refinish the same ring on the Honda 400/4 'Rat' bike I recently purchased for restoration.
Going through the spares stash I had for my Honda CB250RSA (now sadly sold to make room for the 'Rat' 400/4) I found a spare sprocket ring and compared it next to the 400/4, nothing like it, you would think that Honda would keep something like a sprocket ring a uniform size if the number of teeth on the sprocket are the same!

AshimotoK0:

--- Quote from: Athame57 on September 11, 2023, 08:45:44 AM ---I wonder why Honda chose such an odd colour for this part. Where they army surplus?  ;D

--- End quote ---

A lot of parts became olive drab passivate finish.. like the solid pipe on the 400F caliper. Maybe better weather protection of to give a colour contrast. Not sure really.

K2-K6:
Interesting product Ash  https://nordicaviation.eu/en/product/1421002acp/ that could be of use.

Says UK made too, so should be obtainable.

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