Motobecane 5 speed gearbox Strip Down

Published on 30 August 2023 at 18:00
motobecane 5 speed gearbox as found
Bristol Siddelly parts label for motobecane 50cc piston rings

Confession time - I hate gearboxes. I love what they do, I just hate having to work on them, I consider them to be witchcraft and always prefer the replace rather than repair route. Such an option does not exist where the D52 is concerned as these boxes are rarer than hen's teeth, as are most of the parts. Mine was absolutely mullered -- a bit like me after 15 yoghurts. I had been able to force it in to gear but the bearings were all either disintegrated or seized, the selector mechanism didn't really work as that was all gummed up, i had run some oil through it that came out looking like something pretty horrible and worthy of a phone call to the environmental health people.

There was no option, it had to come apart, something that was far easier said than done. The two casings started to loosen but then decided that as they had been together for 50 something years they did not want to separate. I had to proceed with caution as if I broke or damaged one it would be game over. Eventually they parted far enough for me to see the full horror of the situation, it was nasty in there. Weirdly the gears and shafts were actually in surprisingly good order, there were however several washers that had disintegrated and the mild steel drum surrounding the starter mechanism is now less than half the thickness it used to be. That would explain the mess in the bottom of the box then.


It all cleaned up surprisingly well, a combination of petrol for the worst of it and then a session in the ultrasonic tank and many more parts than I thought suddenly looked usable again. I'm not saying they are perfect but they are certainly adequate and fine for a bike that is never going to do very many miles. The bearings are all shot but they are standard sizes so that's no big deal. I have them on order, total cost of less than 20 quid so that's a bonus.

My parts manual gives all the sizes for all the bearings, washers and shims etc, which is a massive help, I may have to make some of the washers though, their thickness is critical and I doubt they are available off the shelf.

I did a bit on the engine today as well, I put a new ring in it, I was lucky enough to find a bag full of piston rings in my spares box, I was rather pleased to find another great piece of provenance too - a label from the British Siddeley Stores declaring them to be for Ehrlich Engineering and for the Motobecane engine. I love finding stuff like that, the rings themselves are like gold dust too. The engine now feels great, I have a high degree of confidence that I will get it running, once I can work out how to set ignition timing.


Rather than dozens of photos I thought a video would be a good idea so I have put one up on Youtube - .

Add comment


There are no comments yet.