'The Sprocket Change Adventure'

Should be easy? I have a workshop, bike bench, and good tools, even so it was a chore. I had quite a time getting the rear spindle out, it really was hard and I ended up drifting it out over about 15 minutes of hard hammering it was just so tight. God knows how it would have been at the side of a road!

At last it popped out, I cleaned up the spindle removing the surface pitting, and the 37 year old grease that had set like hard wax.

I removed the black paint, and then polished the spindle, first in my lathe chuck with fine wet and dry to remove the pitting that was at each end, then on my spindle with a fine mop.

I also cleaned up the 2 spacers that were black with dirt and old grease.

I removed the old 45 tooth sprocket (below) that is not bad but crappy with chain lube etc..

The greased up m8 flanged nuts I put into some thinners to wash. When I re-fitted these I used a little Loctite on the threads.

and nipped them up.


Whilst it was available I offered up/ loose fitted the black 41 tooth sprocket above just to check the fit, it was a bit tight but did fit ....I am not going to fit it just yet, I want to ride the 42 first.

Although I had cleaned up the spacers (which were pitted inside) and the shaft, I couldn't tell how much of the original zinc plating was still there so I decided to give them a coat of a zinc rich paint called Galva Zinc 99, above right.

which dries a similar colour to the original zinc finish. I greased the shaft with my favorite high temp grease Pro RG2 made by Silkolene,

which was long ago recommended to me by Pete Scott of Two Wheel Motorcycles then reassembled ( the shiny clean shaft pushed in by hand pressure) and tightened it all up.

new sprocket fitted......and the other side.....

I hope you agree it looks better. I expect that it will be a bit more fuel frugal too!

I could have taken a link out of the chain, because it had no wear on it I decided to keep the new one in its box and refit the old, something I wouldn't normally do. I didn't shorten it as it fitted with some adjustment still left. I can shorten it later if I feel like it. I had fitted a new front sprocket 15 tooth only 100 miles before. So still wearing my shorts at 10.30pm and a bit nippy last night I took the bike around the block. What a difference! The revs are lower and although I only took it up to 50 (4800 revs) the bike pulled really well in all gears including first, with my weight on it. It reminded me of riding my Royal Oilfield 250 Crusader Sport when I was 17. There is a real feel of the engine and back wheel working together, what I would call feedback, and no longer having to spin at 6000 revs to go anywhere.

4000 revs was about 45 mph. It really is a different bike. If you are using your bike on the road rather than off, I cannot recommend it enough. Gone are the days of getting into top at 20 mph and staying there even round corners. It's like having overdrive.

Before turning out the light I also fitted a new shiny sidestand spring from a shop in St. Paul Minnesota which is coincidentally/oddly the same town where my wife stays at her friend Linda's in the USA.

April 30th 2020: Here is a little update for you, Hubert read the site (a few times whether or nor with a cold beer is not known) and decided to do the 42 tooth sprocket change on his K4. This is what he reported back:

And here is a picture of the bike he has. I only use my bike on the road, and don't know how it would be on a forest trail, but I'm pleased he agrees with me it transforms the bike.