Dr Joe Ehrlich Motobecane D52 body, wheel building and ignition timing

Published on 7 September 2023 at 12:52
rebuilding a motobecane d52 nmoped wheel

The rear wheel is now made up and will get it's tyre and inner tube fitted soon. The front one is a repeat so hopefully won't take as long.


trueing a motobecane d52 moped wheel

I never imagined I would need to use my bandsaw for trueing a wheel, but here we are.


I have only been at it a few days but it feels like forever, it's a simple little bike but when you have it in bits you realise there are an awful lot of them. It is progressing though, I have now done all the major components and have made a start on the headlight shell. These things are really hard to find so I am glad mine was in pretty good order. Sadly the chrome light surround is in less good order and really need to be replaced - I shall be scouring auction sites and autojumbles, one will turn up some time.

While waiting for paint to dry I thought I would have a go at making up one of the wheels - II had ordered 2 rims but due to a cock up at the warehouse only one arrived. It is a very nice quality Takasago one, I certainly wasn't expecting that for the price. I had already purchased 72 spokes and 72 nipples, the hub was already cleaned so it made sense to get on with it.

I haven't done it before so youtube became my intimate friend for a while and the first thing I learnt is that putting spokes in to a wheel is called lacing. The second thing I learnt is that it's not that difficult, except if you get interrupted and your concentration gets broken, as happened a few times to me. I found that once I had my rhythm broken it was hard to get back in to it, my eyes were playing tricks on me and it became a bit frustrating. I put it down to my inexperience, I hope the second one will be much easier. It is looking good though, not quite finished yet and I know today will be full of interruptions so I may not even get started again until the diary is a bit clearer. I still have to earn money sadly and when jobs come my way I have to take them and my long term projects go on the back burner. Today I have a go kart to fix, tomorrow a war time BMW and sidecar that decided to stop functioning and is now dead needs nursing back to life. That should be interesting as I have never laid hands nor spanner on one before, still it's only a bike, they all kind of work the same.


It's now the day after writing the bit above, the wheel is finished and ready to have the inner tube and tyre fitted. i suspect this is the only time in history that a bandsaw has been used to assist in the building of a wheel. I shall explain - when putting a spoked wheel together it is important to make sure everything is straight and that the rim and hub are concentric. To achieve that objective you need to be able to spin the wheel while using a reference point, you then adjust the spokes until everything is perfect. I found it every bit as frustrating as doing the lacing, it's still not quite where I want it to be, i think I may have run out of adjustment on one or two of the spokes. I will have a better look later when I have calmed down a bit.


In the mean time I now have the data needed to enable me to set up the ignition timing, it's the same procedure as for a Raleigh Runabout, which also used the same Motobecane engine. It may well be the case that Dr Joe determined a different timing value but this should at least give me the starting point to get the thing running. What you have to do is to find top dead center, wind the engine backwards a bit then set the piston to 1.5mm before tdc. I used a vernier caliper for this purpose - I found tdc was exactly 17mm below the height of the spark plug seat so I set my vernier to 18.5mm and used it as a depth gauge. I locked it up, held it so the tang was down the bore and the shoulder of the gauge was resting on the plug seat and then would the crank round in the normal running direction until the piston contacted the end of the vernier's tang. I then used the timing cam to open the points to their max, they were at about 0.3mm, they needed to be 0.45, which is about 18 thou. On this engine the timing cam is a taper fit on the crank, there is no locking key or other device so you have to be very careful and accurate when setting it. I was going to do a video but there are already loads on youtube so I didn't bother. One thing I would advise is to use a meter so you can see the exact point at which the points open - it's very hard to do accurately enough otherwise and the timing makes a huge difference to the performance of the engine.

I am thinking of making a degree wheel so I can play with ignition timing settings but that will be much later. I am also intrigued that the other 50cc barrel I have seems to show more carbon than the one on there, as if it has been run for longer. I am wondering if that was the final one that got used when the bike set it's speed record and then went on the road. The letter from Ted Snook says they got the power up to about 6.2 BHP at 8500rpm but that the engine would over rev freely to about 10k, the bike would do 65 mph and that it would wheely in both first and second gear. That gives me something to aim for when I actually get the thing going.  

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